SUBMISSION TO STANDARDS AUSTRALIA - AFICA · 2019. 11. 25. · INDICATIVE COMMENTS BY HARKNESS ON AS/NZS 4859.2 and AS/NZS 4859.1:2002 11th NOVEMBER 2018 5 pages only 1 [email protected]

Corresponding author: Dr Edward (Ted) Harkness [email protected]

SUBMISSION TO STANDARDS AUSTRALIA For the attention of [email protected] 11th November 2018 PROJECT MANAGER, STANDARDS AUSTRALIA

COMMENTS ON

AS/NZS 4859.1 and AS/NZS 4859.2

Prepared by

DR EDWARD LEO HARKNESS

#

AND DR RICHARD AYNSLEY

+

# Dr Edward Leo Harkness Consultant Architect Formerly Associate Professor of Architectural Engineering KFUPM Kingdom of Saudi Arabia [email protected] Corresponding author

+ Dr Richard Aynsley Consultant Architect Formerly UNESCO Professor of Tropical Architecture, James Cook University

[email protected]

Corresponding author: Dr Edward (Ted) Harkness [email protected]

SUBMISSION TO STANDARDS AUSTRALIA

[email protected] 11th November 2018 PROJECT MANAGER, STANDARDS AUSTRALIA Dear Mr Buchel, We respectfully suggest that the proposed AS/NZS 4859.1 and AS/NZS 4859.2 be subjected to a scientific review before publication or adoption for the NCC 2019. Examples only of matters for review in AS/NZS 4859.2 include: Typographical errors: For example in 8 Air Films Line 1 of (a): “surface son” should read “surface on”; in Table 13, should d - 0.44 read d - 0.44 ? Definition of terms For the lay reader: Define Ug and Ux

XPS could be defined as expanded polystyrene and PU as polyurethane.

In 5.2, To is defined as mean operating temperature as given in Eq 9.3(4) however, Eq 9.3(4) shows Cave, not To.

This is unnecessary fog and shows lack of care. Maybe different sections of the Standard were cut and pasted from different sources. Consistency in the definition of symbols is necessary. The only persons who should be allowed to vote on the adoption of these Standards are those who sit for and pass an examination on their contents. AS/NZS 4859.2 ignores solar radiation in 5.1 “Standard Assumptions” of temperature and temperature difference through the building envelope. The significance of this omission is described in the attachments. Excluding the effect of solar radiation on the exterior surfaces of the building envelope from calculations could lead to inability of installed insulation to enable a cooling system to provide thermal comfort; and lead to higher energy consumption than estimated. In 5.2 NOTES is written “Conversion coefficients [in Tables 1-11] are suitable for temperatures from 0 to 36oC”. However, Sol air temperatures on roofs could reach 90oC. What then is the relevance of Tables 1-11; and of the Fig A1 Spreadsheet?

AS/NZS 4859.2 could include a cautionary note about minimising interstitial condensation opportunities and associated potential health problems. Indicative comments on AS/NZS 4859.1 are included in the attachments. AS/NZS 4859.1 and AS/NZS 4859.2 could be combined as one document which would avoid the need for users to purchase two Standards, would minimise duplication and provide related information more efficiently. PROPOSED ACTION In the context that the above and attachments are only a few examples of matters that should be addressed, we would be willing to put together a team of informed and experienced professionals with knowledge of building physics to advise on AS/NZS 4859.1 and AS/NZS 4859.2, based on current scientific knowledge; before their ratification and adoption into the NCC 2019. In due course there could be a review of related Standards to ensure compatibility and symbol consistency. Please respond to this letter to make arrangements for preparation of scientific advice

Dr Edward Leo Harkness BArch(Hons) MBdgSc PhD ARBNSW 2602 ABSA 20494 MAAS 819 ABN 77 894 687 842 0403 239 858

CONTENTS

Cover

Letter

Indicative comments on AS/NZS 4859.2 and AS/NZS 4859.1

AS/NZS 4859.2

5. Standard Assumptions

8. Air Films

Table 15

9.3 Methodology

Related comments on modelling AccuRate to meet heating target

Flammability of insulation products

AS/NZS 4859.1

Comment on Appendix K

ATTACHMENTS

Insulation of roofs in Warm Climates

Radiator-air heat exchanger incorporated in building design for passive and low energy cooling in the tropics.

Principal Differences – Foil and Bulk Insulations

REFLECT3 & ASTM

Condensation in Residential Buildings

Report on Inquiry into Biotoxin MOULD related illnesses in Australia excerpts

Desensitisation of the building envelope

Measured effects of shading

CV of Dr Harkness

Dr Edward L Harkness Architect and Building Scientist

INDICATIVE COMMENTS BY HARKNESS ON AS/NZS 4859.2 and AS/NZS 4859.1:2002 11th NOVEMBER 2018 5 pages only

1 [email protected]

5 STANDARD ASSUMPTIONS 1

5.1 Temperature differences. 2

Comment: 3

These assumptions may be reconsidered. 4

The external surface temperature is a function of air temperature, solar radiation intensity, 5 solar absorptance of the external surface; and the surface conductance (which is a function of 6 wind speed). 7

The external surface temperate is referred to as the Sol air temperature Tsa and is expressed 8 as follows: 9

Tsa = To + (I x a)/h0 # 10

Where To is the outside air temperature 11

I is the solar radiation intensity including the direct (D) and diffuse (d) components 12

a is the solar absorptance 13

h0 is the external surface conductance W/m2.K 14

In Sydney in January 2018 air temperatures exceeded 40 degrees. 15

On a clear day the Sol air temperatures on a dark tiled roof could be 16

Where To is 40 17

I Direct (D) is 950 W/m2; and diffuse (d) component is 105 W/m2 18

I total is 1055 W/m2 19

a solar absorptance is 0.9 20

h0 external surface conductance is 1/(surface air film resistance of 0.04m2.K/W) 21

h0 = 25 W/m2.K for a wind speed of 3.0 m/s 22

23

Tsa = 40 + (1055 x .9) / 25 24

40 + 38 25

= 78 0C 26

The temperature difference between outside and inside would be 27

78 – 24 28

= 54K (not 12K) and the mean would be 510C, not 30 0C 29

# Richard Aynsley & Bin Su use a more sophisticated formula that accounts for reradiated heat and shows that roof 30 temperatures under still conditions can exceed 900C. Please see attachment: Richard Aynsley and Bin Su, Insulation of Roofs 31 in Warm Climates 2005 CIM W92/W107 International Symposium on Procurement Systems Las Vegas, NV USA 32


2 [email protected]

33

34

5.2 Conversion coefficients for operating temperatures different to declared mean 35

temperature 36

Comment: 37

Do these calculations inform trade literature published by manufacturers of thermal insulating 38 materials? 39

Why are these calculations not done for summer and winter? 40

Are these calculations done for categories of climates? 41

Why use and annual average temperature that would approximate the benign seasons of 42 spring and autumn? 43

44

In the NOTES: 45

1. 46

2. The data for XPS and PU are valid for all blowing agents. 47

Comment: It might help some readers to define XPS as expanded polystyrene and PU as 48 polyurethane 49

50

51

52

8 AIR FILMS 53

8.1 General 54

55

Comment: 56

Consider Clarifying that Table 14 refers to still air. 57

There is a NOTE to that effect but, “in still air” could be in the descriptor of TABLE 14. 58

There is a typo on line 1 of (a): “ . .surface son . . “should read “. . . surface on . . . “ 59

Consider including the resistance of surface films at higher wind speeds, e.g., thermal 60

resistance of air films with wind at 6.0m/s would be approximately 0.03 m2.K/W 61

62

63


3 [email protected]

8.2 Thermal resistance of floors 64

NOTES 65

1. 66

2. 67

3. 68

4. Rgx equals 1/Ug + Ux (see ISO 13370) 69

70

Comment: 71

Consider defining Ug and Ux (overall air to air thermal transmittance) 72

and include its units W/m2.K 73

One may deduce that Ug refers to the thermal transmittance of the ground and 74

Ux refers to the thermal transmittance through sub floor walls and ventilation of the 75

underfloor space 76

77

78

79

80

81

TABLE 15 82

Comment: 83

In the subscript is it intended to be understood that – 84

“thermal transmittance 2.7 W/m2.K “ is Ux? 85

and 86

Ug would be calculated assuming ground temperature at a known depth and that 87

assumption used in calculating the value of Rgx in TABLE 15 was that the ground 88

conductivity was 1.5 W/m.K ? 89

It may be appropriate to state that the overall air to air thermal transmittance (U) includes 90 surface air films; 91

and that U = 1 / Total R 92


4 [email protected]

9.3 Methodology 93

The methodology ignores the contribution of solar radiation to the external building envelope 94 surface temperature. 95

The external surface temperature is a function of air temperature, solar radiation intensity, 96 solar absorptance of the external surface and the surface conductance. 97

The external surface temperate is referred to as the Sol air temperature Tsa and is expressed 98 as follows: 99

Tsa = To + (I x a)/h0 100

Where To is the outside air temperature 101

I is the solar radiation including the direct and diffuse components 102

a is the solar absorptance 103

h0 is the external surface conductance W/m2.K 104

h0 = 25 W/m2.K for a wind speed of 3.0 m/s 105

106

Substituting some reasonable summer values for a wall in Sydney: 107

Tsa = 28 + (600 x 0.7) / 25 108

= 28 + 17 109

= 450C 110

If a house is air-conditioned say to 24 0C, the temperature difference in summer 111 would be 45 – 24 = 21 K NOT 12 K as stated at the end of 9.3 Methodology. 112

Under still air h0 would approximate 10 W/m2 . K, and the Sol air temperature would be 113 70 0C 114

If a house is air-conditioned say to 24 0C, the temperature difference in summer 115 would be 70 – 24 = 46 K NOT 12 K as stated at the end of 9.3 Methodology. 116

117

RELATED COMMENT ON MODELLING USING ACCURATE TO MEET HEATING TARGET 118

The permitted energy requirements for comfort heating are now difficult to achieve for some 119 climate zones. 120

The target can be achieved in some instances only by using a dark roof; which is 121 counterintuitive. 122

FLAMABILITY OF INSULATION PRODUCTS 123

There could be a cautionary note: 124

Foil clad polypropylene sandwich should be questioned regarding flammability. 125


5 [email protected]

126

The following is a comment on APPENDIX K of AS/NZS 4859.1:2002 127

K3.1 128

129

Comment: 130

ROOFS 131

Given that the temperature of a roof could be 800C and higher, the following comparison is 132 made of effective R values for the difference of 80 – 23 = 57K. 133

Effective R values of 134

insulation labelled 135

Decrease R2.5 R4 136

Glass wool / polyester / sheep’s wool 0.65% x 57K = 37% 1.5 2.5 137

Rockwool 0.39% x 57K = 22% 2.0 3.1 138

Cellular 0.52% x 57K = 30% 1.7 2.8 139

This raises a question as to whether or not insulation products should be labelled with 140 effective R values for (a) climate zones and (b) where in a building the insulation is intended 141 to be used. 142

NOTE: The comments in this brief document are indicative of the need for these 143 Standards to be reviewed scientifically. 144

2005 CIB W92/W107 International Symposium on Procurement Systems The Impact of Cultural Differences and Systems on Construction Performance February 7th – 10th; 2005 – Las Vegas, NV USA

INSULATION OF ROOFS IN WARM CLIMATES

Richard Aynsley1 and Bin Su2

11Delta T Corporation, PO Box 11307, Lexington, KY 40575, USA 2School of Architecture and Landscape Architecture, UNITEC Institute of Technology, Private Bag 92025,

Auckland, New Zealand ABSTRACT

There is currently no guideline for builders or home owners to indicate what would be appropriate thermal insulation in roofs to control summer heat gain through roofs in naturally ventilated houses in regions with little or no winter heating requirement. Australian Standard AS 2627.1-1993 indicates recommended values of thermal insulation for roofs and walls at numerous locations around Australia. These recommended values are based on an economic analysis balancing the lifetime cost of installing the insulation during construction against the heating and cooling energy cost over that lifetime. These levels of thermal insulation assume that the house has a closed envelope and is heated or cooled to maintain indoor thermal comfort. In warm, humid climatic regions, houses are often designed with open envelopes to benefit from natural ventilation. Two objectives are proposed for thermal insulation in roofs of houses with efficient cross-ventilation in regions with little or no winter heating requirement. The first is to limit the daytime surface temperatures of the ceiling to prevent infrared radiant heat gains to occupants. The second objective is to design roof insulation that promotes rapid cooling of the house after sundown. A field study to investigate the thermal conditions in houses in a warm humid climate region, and the resulting indoor thermal conditions, was based on a survey of 92 houses in Townsville, Queensland, Australia. A procedure for evaluating roof insulation alternatives is provided.

Keywords: energy efficient, houses, warm climates, natural ventilation, roof insulation.

INTRODUCTION There is currently no guideline for builders or home owners to indicate what would be appropriate thermal insulation in roofs to control summer heat gain through roofs in naturally ventilated houses in regions with little or no winter heating requirement. Australian Standard AS 2627.1-1993 indicates recommended values of thermal insulation for roofs and walls at numerous locations around Australia. These recommended values are based on an economic analysis balancing the lifetime cost of installing the insulation during construction against the heating and cooling energy cost over that lifetime. These levels of thermal insulation assume that the house has a closed envelope and is heated or cooled to maintain indoor thermal comfort. In warm climates, with little or no winter heating requirement, houses are often designed with open envelopes to benefit from natural ventilation. From field, computational fluid dynamics and boundary layer wind tunnel studies, it has been shown that air change rates in well designed, cross-ventilated

1 [email protected] 2 [email protected]

2

houses are extremely high, often hundreds of air changes per hour. Computer modelling has shown that when the air change rate exceeds 30 air changes per hour, indoor air temperature can be assumed to be the same as outdoor shade air temperature (Willrath, 1998). A RATIONALE Two objectives are proposed for thermal insulation in roofs of houses with efficient cross-ventilation in regions with little or no winter heating requirement. The first is to limit the daytime surface temperatures of the ceiling to prevent infrared radiant heat gains to occupants. The second objective is to design roof insulation that promotes rapid cooling of metal roofs of house after sundown by radiation to the night sky. A FIELD STUDY During February and March of 1996, a field study of ceiling temperatures in 92 non-air conditioned houses was conducted by graduate research students and faculty from the Australian Institute of Tropical Architecture, James Cook University, in Townsville, Australia. Of the 92 houses, data from 21 buildings were rejected for comparative purposes due to building type. Some were schools, some data records were incomplete, or data had been incorrectly entered in the survey forms. Data included; outdoor air temperature, indoor air temperature, ceiling temperature, indoor globe temperature, indoor WBGT index, roof colour, roof material, ceiling insulation, eaves overhang, wall construction, and time of observations. All data was collected between 11:00 AM and 1:00 PM while walls were shaded and the sun was overhead. Detailed analysis of the data from the survey can be found in Sariman (1998). The main purpose of the study was to determine the degree to which infrared radiation from hot ceilings was a significant influence on indoor thermal comfort in houses. This study extended work in Africa by Koenigberger and Lynn (1965). This publication suggests that surface temperatures of ceilings should not exceed ambient indoor dry bulb air temperature by more the 4K. Based on the adaptive indoor thermal comfort zone established by Auliciems and Szokolay (1997) and adopted by ASHRAE for naturally conditioned buildings, 79% of the houses surveyed had indoor dry bulb air temperatures exceeding 24°C to 29°C, the comfort zone to satisfy 90% of occupants for the three hottest months. Thermal neutrality dry bulb air temperature for this comfort zone was 26.1°C. Poor thermal design of the roof contributed to about 50% of the houses. Of the houses surveyed, 49% of the roofs were unpainted metal. Ten percent of the houses surveyed had metal roofing with a coloured paint finish. A further 10% of the houses surveyed had white or off-white painted metal roofing. The colour of the remaining 41% of the houses surveyed ranged from beige, green, dark green, yellow, and brown. In summary, 90% of the houses surveyed had roof colours that were not white or off-white colour. As the Townsville region is, on occasions, subjected to tropical cyclone winds it was not surprising to observe that 86% of the roofs on the houses surveyed had ribbed metal roofing. Field measurements have shown these roofs reach temperatures of up to 8K

3

below ambient air temperature by radiating to the night sky (use 5K for design purposes) (Dan and Aynsley, 1998). The remainder of the houses had tile roofs, except for one with corrugated asbestos cement roofing. Of the 71 houses surveyed, 56% had no insulation under the roof or above the ceiling. The remainder of the houses had varied types of insulation. In two of the houses, ceiling insulation was provided over ceilings in only some rooms. Four of the houses had cellulose fibre above the ceilings. Four houses had reflective foil insulation. Three houses had fiberglass or rockwool insulation. One house had expanded polystyrene insulation, and one house owner could not remember the type of insulation installed. In the 71 houses used from the survey, 38% had bedrooms with ceiling temperatures more than 4K above indoor air temperature. In 39% of living rooms, ceiling temperatures were more than 4K above indoor air temperature. In 44% of kitchens, ceiling temperatures were more than 4K above indoor air temperature. ADAPTIVE THERMAL COMFORT In ventilated buildings without air conditioning using the new adaptive comfort criteria in ANSI/ASHRAE Standard 55-2004, thermal neutrality for operative comfort, toc, based on mean monthly outdoor air temperature, tout, can be calculated using the following equation (ASHRAE, 2001). toc = 18.9 + 0.255 tout °C Equation 1 With a mean daily air temperature of (31.3 + 23.8)/2 = 27.6°C in Townsville, QLD during January, toc = 18.9 + 0.255(27.6) = 25.9°C There is significant individual variation in human thermal response. This variation in thermal response can be accommodated by defining a thermal comfort zone, CZ. CZ80 satisfies 80%, or CZ90 ,90% of a population (Auliciems and Szokolay, 1997). CZ80 = 18.9 + 0.255 tout +/- 3.5 °C Equation 2 CZ90 = 18.9 + 0.255 tout +/- 2.5 °C Equation 3 ANSI/ASHRAE Standard 55-2004 suggests the 80% satisfaction level for normal design. For example the 80% thermal comfort zone for January (toc =25.9°C for July) in Townsville, based on the adaptive thermal comfort model, is 25.9 +/- 3.5 = 22.4°C to 29.4°C. AIR FLOW FOR SUMMER COMFORT Air movement is highly effective in creating a cooling sensation on exposed skin, This moderates hot summer conditions. Air movement does not cool the air. This is why air movement is so energy-efficient in restoring indoor thermal comfort. This cooling sensation is effective in warm climates where the air temperature is less than 96°F (35.6°C), about 2°F below core body temperature. An equation for estimating the cooling sensation of airflow over exposed skin was suggested by Szokolay (1998).

4

CS = 6(V-0.25) – (V- 0.25)2 °C Equation 4 where V is the mean air speed in meters per second (Figure 1). Note 1 m/s is equivalent to 196.9 feet/minute or 2.2 miles per hour. The 0.25 m/s value in Equation 4, represents minimum perceptible airflow in early versions of ANSI/ASHRAE Standard 55. The current ANSI/ASHRAE Standard 55-2004 indicate the minimum perceptible airflow as 0.2 m/s or 40 fpm. For this reason the writer suggests revising Equation 4 to reflect this lower value. Equation 5, has a peak cooling sensation of 8.99°C at 3.3 m/s.

CS = 6(V-0.2) – (V- 0.2)2 °C Equation 5

Figure 1. Plot of Cooling Sensation of Air Flow Using Equation 5. If the outdoor air temperature in Townsville, Australia on a January day reaches 34°C, what airflow is needed to restore thermal comfort to the toc for January? 34°C – 25.9°C = 8.1°C. It would require airflow of 2.25 m/s (or 443 fpm or 5.0 mph or 4.4 knots) to give a cooling sensation of 8.1°C. The typical sea breeze in Townsville at 3 pm in January exceeds 7.7 m/s. (Aynsley, 1996). Indoor air velocities near wall openings of cross-ventilated houses in Townsville exposed to the sea breeze is typically around 0.25 of the external wind speed at a height of 10m in airport terrain roughness (Aynsley and Su, 2003). ROOF INSULATION Alternative techniques of thermal control include use of bulk insulation and reflective air spaces. Use of bulk insulation in the form of various fibre materials, such as fiberglass, mineral wool, cellulose, or expanded polystyrene, have the same thermal insulation value regardless of the direction of heat flow up or down. In contrast, the thermal insulation value of reflective air spaces provided in HVAC industry handbooks is up to 3 times greater when heat flow is downward than when heat flow is upward (AIRAH Handbook,

Cooling Sensation of Airflow °C

0.00

2.00

4.00

6.00

8.00

10.00

0 0.5 1 1.5 2 2.5 3 3.5

Airflow m/s

Co

olin

g S

en

sa

tio

n

de

g. C

5

2000). This means that bulk insulation will slow the dissipation at night of heat which accumulates inside a building during the day more than reflective air spaces in roofs. Another consideration is the adverse effect of moisture on fibrous insulation. This results in reduced insulation value due to dampness, and damage to building fabric from damp insulation. The moisture involved typically comes from condensation on the underside of metal roofs or by air conditioned cooling of building surfaces as a result of temperatures below ambient dew-point. Temperatures of metal roofs can fall by up to 8K below ambient air temperature due to radiant cooling to the night sky. This cooling often brings metal roofing temperatures below the dew-point of ambient air (Dan and Aynsley, 1998). To avoid condensation on the underside of metal roofs in warm humid climates, fibrous insulation is placed as a blanket hard against the underside of the metal roofing using the roofing metal as a vapour barrier with another vapour barrier on the underside of the insulation. Edges of such blanket insulation should be tape sealed to prevent moisture entry. Condensation can occur on reflective foil surfaces during nocturnal cooling. This has the advantage of increasing the emissivity of the surface which in turn increases nocturnal heat loss through roofs. With the solar heating of the roof after sunrise, the moisture on the reflective foil evaporates generally without damage to the surface of the reflective foil. A study in Florida (Beal and Chandra, 1995) noted very little corrosion on the surface of reflective foil. It was limited to a narrow strip along the eaves line in a saltwater, waterfront location. How Much Insulation? Australian Standard AS 2627.1-1993 indicates recommended values of thermal insulation for roofs an walls at numerous locations around Australia. Values recommended for Townsville are R3.5 (3.5 W/m2.K ) in the roof/ceiling. These recommended values are based on an economic analysis balancing the lifetime cost of installing the insulation during construction against the heating and cooling energy costs over that lifetime assuming common indoor thermal comfort criteria. These levels of thermal insulation are appropriate in fully air conditioned buildings. In warm humid climate regions, where buildings are often designed with open envelopes to benefit from cooling airflow, the role of thermal insulation is to limit the surface temperatures of indoor surfaces to prevent heat gains to building occupants from infrared radiation on occupants. Typically the day-time air change rate, through well designed naturally ventilated houses, is from 100 to 600 air changes per hour. At these rates the air passes through the building in a few seconds and its temperature and humidity remain the same as ambient outdoor air. During evenings when breezes die away, ceiling fans are typically used to provide indoor air movement. Sol-air Temperature Control Sol-air temperature Te is that outdoor air temperature that would cause the same amount of heat entry into a surface as the combined effects of air temperature and solar radiation exchanges. ASHRAE (1997) gives the following equation for estimating sol-air temperature. Te = To + It / ho - R / ho C

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where: To = outdoor dry bulb air temperature C; = absorptance of surface solar radiation; It = total solar radiation incident on surface W/m2 ; ho = coefficient of heat transfer by long-wave radiation and convection at outer surface W/m2.K; = hemispherical emittance of surface; R = difference between long-wave radiation incident on surface from sky and surroundings and radiation emitted by blackbody at outdoor air temperature W/m2 For example, what would the sol-air temperature of zinc/aluminium coated corrugated steel roofing with a slope of 20 at noon in Townsville under a partly cloudy sky with a good breeze 7 m/s in January when the outdoor air temperature is 32C ? Table 1. Surface Conductances & Solar & Infrared Radiation Exchange Properties

Surface Conductance ho W/m2.K Radiation Properties Surface Air Flow

Exposure Low Normal

Material Solar

and

Solar Reflect-

ance

Infrared

(50C) Roofs sheltered 11.1 14.3 red tiles 0.65 0.35 0.85

normal 20.0 25.0 white tiles 0.40 0.60 0.50 exposed 50.0 50.0 metal 0.4 0.60 0.40

Walls sheltered 12.5 9.1 brick light 0.40 0.60 0.90 normal 14.3 16.7 brick dark 0.80 0.20 0.90 exposed 33.3 33.3 paint (white) 0.30 0.70 0.95 paint (black) 0.96 0.04 0.96

Absorptance of surface solar radiation by weathered zinc/aluminium is approximately 0.60. Total solar radiation incident on a horizontal roof surface on a sunny day in Townsville during January is typically 1,400W/m2. With a slope of 20 this radiation intensity is reduced according to the cosine rule to COS 20 x 1400 = 1316 W/m2 and R is approximately 105 W/m2 for clear skies, 59 W/m2 for partly cloudy skies, and 24 W/m2 for overcast skies. The for weathered zinc/aluminium is approximately 0.4. The coefficient of heat transfer ho for a low surface with a breeze of less than 4 m/s (sheltered) is 11.1 W/m2.K from the Table 1.For design purposes use sheltered exposure and partly cloudy sky. For a dark green painted metal roof under a partly cloudy sky in sheltered exposure, the sol-air temperature would be: Te = To + It / ho - R / ho C = 32 +( 0.8 x 1316 / 11.1) – (0.95 x 59 / 11.1) = 97.7 C This temperature is similar to field measurements of temperatures of metal roofing with dark coloured paint finishes in Townsville.

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Roof Insulation Required to Limit Ceiling Temperature to 38C When roofs consist of lightweight materials such as metal cladding, the temperature differences across each element in multi-layer construction is proportional to the thermal resistance of each element. When the sol-air temperature on the upper surface Te is high, the total thermal resistance Rt of the roof construction to limit the ceiling temperature to 4K above indoor air temperature can be written in terms of the thermal resistance of the indoor air film at the ceiling Riaf : Rt = Riaf (Te - To)/4 m2.K/W For example consider a timber framed roof with a plasterboard ceiling roofed with zinc/aluminium surface steel roofing in sheltered conditions 3 m/s breeze under a partly cloudy sky which, from the calculation above, has a sol-air temperature of 101C. Based on the proportionality between thermal resistance and temperature difference across the resistive element in a construction, the total thermal resistance of the roof required to limit the temperature across the indoor air film under the ceiling to 4K is: Rt = Riaf (Te - To)/ 4 m2.K/W = 0.16 (101 - 32) / 4 = 2.76 m2.K/W Thermal resistance of the roof without added insulation is: Outdoor air film 0.04 Metal roofing 0.00 Roof space 0.46 (high є surfaces, ventilated, heat flow down) Plasterboard 13mm 0.08 Indoor air film 0.16 Total 0.74 m2.K/W (< 2.76 unsatisfactory) The increase in thermal resistance to reach 2.76 m2.K/W is 2.76 – 0.74 = 2.02 m2.K/W. Material Thermal Resistance Temperature Drop Temperature Profile m2.K/W K 101C (Sol-air T) Outdoor air film 0.04 69 x 0.04/2.76=1.00K 100.0C Metal roofing 0.00 69 x 0.0/2.76=0.00K 100.0C Added R 2.02 69 x 2.02/2.76=50.5K 49.50C Roof space 0.46 69 x 0.46/2.76=11.5K 38.00C Plasterboard 13mm 0.08 69 x 0.08/2.76=2.00K 36.00C Indoor air film 0.16 69 x 0.16/2.76=4.00K 32,00C Total 2.76 m2.K/W Also note that that the surface temperature on the underside of the ceiling of 36C is 4K more than 32C the indoor air temperature. Comparison will now be made of bulk and reflective insulation solutions to the added thermal resistance using data from the AIRAH Handbook (2000). 163mm of fiberglass (density 6.25kg/m3) has a thermal resistance of 2.84 m2K/W. For mid-day heat flow down, the resistance to heat gain is:

8

Material Thermal Resistance Temperature Drop Temperature Profile m2.K/W K 101C (Sol-air T) Outdoor air film 0.04 69 x .04/3.58 =0.77K 100.23C Metal roofing 0.00 69 x 0.0/3.58 =0.00K 100.23C Roof space 0.46 69 x 0.46/3.58=8.87K 91.36C 163mm fiberglass 2.84 69 x 2.84/3.58=54.74K 36.62C Plasterboard 13mm 0.08 69 x 0.08/3.58=1.54K 35.08C Indoor air film 0.16 69 x 0.16/3.58=3.08K 32.00C Total 3.58 m2.K/W (similar to the AS2627.1-1993 standard value of 3.5) For heat flow up assuming an indoor air temperature of 34C due to increased occupancy and lower ventilation, and temperature of metal roofing is outdoor air -5K due to radiant nocturnal cooling through the roof to the night sky (Dan and Aynsley, 1998), the resistance to heat flow up is: Material Thermal Resistance Temperature Drop Temperature Profile m2.K/W K Metal roofing 0.00 7 x 0.00/3.03=0.00K 26.89C Roof space vented 0.00 7 x 0.00/3.03=0.00K 26.89C 163mm fibreglass 2.84 (6.25kg/m3) 7 x 2.84/3.03=6.56K 33.45C Plasterboard 13mm 0.08 7 x 0.08/3.03=0.18K 33.63C Indoor air film 0.11 7 x 0.16/3.03=0.37K 34.00C Total 3.03 m2.K/W Note small rounding errors tend to occur in temperature profile calculations such as the 26.89C versus the actual value of 27C. Single sided reflective sarking with the reflective surface facing down, fixed under roofing battens, creates a 30mm air space with a thermal resistance for downward heat flow of 0.15 m2.K/W and a reflective ventilated roof space with a resistance to heat flow down of 1.36 m2.K/W. Reflective foil fixed 100mm over the bottom chord of roof trusses above the ceiling provides a single sided reflective air space with a resistance to heat flow down of 1.42 m2.K/W. Material Thermal Resistance Temperature Drop Temperature Profile m2.K/W K 100.99C (Sol-air T) Outdoor air film 0.04 69 x 0.04/3.21=0.86K 100.13C Metal roofing 0.00 69 x 0.00/3.21=0.00K 100.13C 30mm air space 0.15 69 x 0.15/3.21=3.22K 96.91C Roof space vented 1.36 (reflective) 69 x 1.36/3.21=29.23K 67.68C 100 mm air space 1.42 (1 side refl.) 69 x 1.42/3.21=30.52K 37.16C Plasterboard 13mm 0.08 69 x 0.08/3.21=1.72K 35.44C Indoor air film 0.16 69 x 0.16/3.21=3.44K 32.00C Total 3.21 m2.K/W

9

For heat flow up (nocturnal radiant cooling) increased indoor load and less ventilation is: Material Thermal Resistance Temperature Drop Temperature Profile m2.K/W K Metal roofing 0.00 7 x 0.00/0.67=0.00K 26.48C 30 mm air space 0.00 (vented) 7 x 0.00/0.67=0.00K 26.48C Roof space 0.00 (vented) 7 x 0.00/0.67=0.00K 26.48C 100 mm air space 0.48 (1 side refl.) 7 x 0.48/0.67=5.01K 31.49C Plasterboard 13mm 0.08 7 x 0.08/0.67=0.84K 32.33C Indoor air film 0.11 7 x 0.16/0.67=1.67K 34.00C Total 0.67 m2.K/W CONCLUSIONS Evening hours are the most critical for indoor thermal comfort in naturally conditioned houses in Townsville as the occupancy tends to increase and the sea breezes tend to die away by 9:00PM when many people are trying to go to sleep. Ceiling fans can provide useful air flow during this critical period. Two objectives have been proposed for thermal insulation in roofs of houses with efficient cross-ventilation in regions with little or no winter heating requirement. The first is to limit the daytime surface temperatures of the ceiling to less than 4K above indoor air temperature to prevent infrared radiant heat gains to occupants. The second objective is to design reflective roof insulation with a low thermal resistance to upward heat flow to promote rapid cooling of the house after sundown. It can be seen from the above calculations that the reflective foil insulation works like a one way thermal valve. Thermal resistance to downward daytime heat flow to limit ceiling temperature is 3.21 m2.K/W. The same reflective insulation has a much reduced thermal resistance of 0.67 m2.K/W to upward heat flow due to radiant cooling to the night sky. In comparison, bulk insulation such as fiberglass that has a thermal resistance to downward daytime heat flow of 3.58 m2.K/W, has a thermal resistance to upward heat flow due to radiant cooling to the night sky of 3.03 m2.K/W. REFERENCES AIRAH (2000) AIRAH Handbook,3rd edition, Australian Institute of Refrigeration Air

Conditioning and Heating Inc., Melbourne, pp.226. Auliciems, A. and Szokolay, S. (1997) ‘Thermal comfort’, PLEA Note 3, Passive and

Low Energy Architecture in association with the University of Queensland Dept. of Architecture, Brisbane, Australia.

Aynsley, R.M. (1996) Estimating Potential for Indoor Thermal Comfort from Natural Ventilation, Proceedings of ROOMVENT'96 the 5th International Conference on Air Distribution in Rooms, , July 17-19, Yokohama, Japan. Vol. 3, 291-298.

Aynsley, R. and Su, B. (2003) A Field Study of Indoor Wind Speed, in L.N. Lowes and G. Miller (Eds), CD of Proceedings of the 2003 ASCE Structures Congress & Exposition, May 29-31, Seattle.

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Beal, David and Chandra, Subrato, (1995) “Side by Side Testing of Four Residential Roofing and Attic Ventilation Systems”, prepared for the Dept of Energy, by Florida Solar Energy Center, FSEC-CR-822-95. 34pp.

Dan, P.D. and Aynsley, R. (1998) Nocturnal cooling of an exposed radiator surface, In Baird, G. and Osterhaus, W.,(eds) Proceedings of the 32nd Annual Conference of the Australian and New Zealand Architectural Science Association, July 15-17, 1998, School of Architecture, Victoria University of Wellington, Wellington , New Zealand. pp.185-191.

Koenigsberger, O. H. and Lynn, R (1965). Roofs in the warm humid tropics. Lund Humphries, London.

Sariman, Andrew (1998) Architectural design procedures for thermal performance of roofs in the warm humid tropics. James Cook University, Townsville, Australia.

Standards Australia (1993) Thermal insulation of dwellings: Part 1: Thermal insulation of roof/ceilings and walls in dwellings, AS 2627.1-1993, Standards Association of Australia, Sydney.

Willrath, H. (1998) Comparison of the thermal performance of free running and conditioned houses in the Brisbane climate, In Baird, G. and Osterhaus, W.,(eds) Proceedings of the 32nd Annual Conference of the Australian and New Zealand Architectural Science Association, July 15-17, 1998, School of Architecture, Victoria University of Wellington, Wellington , New Zealand.

RADIATOR-AIR HEAT EXCHANGER INCORPORATED IN BUILDINGDESIGN FOR PASSIVE AND LOW ENERGY COOLING IN THE

TROPICS

P.D. Dan and R.M. AynsleyAustralian Institute of Tropical Architecture, James Cook University

[email protected]

SUMMARY

Investigation of nocturnal cooling on both exposed and wind-screen metallic radiators, with andwithout air as working fluid, has been experimentally conducted at James Cook University ofAustralia. A warm and humid tropical region, summer nights in the region are typically calm and with ahigh level of humidity. Experimental results indicate that night-time cooling is possible in the tropics,provided that the sky is not overcast. Considering the radiators acting as the roof of the building,passing air underneath insulated roofs would be a way to transfer the cool energy from the sky intothe building during summer nights. In this paper, based on the experimental results, mathematicalmodels for the exposed and wind-screen radiators are presented, with and without air passingunderneath as working fluid. In humid climates, the formation of dew on radiator surfaces at nightsignificantly affects cooling performance. Dew formation is taken into account in these models, andthis is what makes the modelling in this paper different from those in drier climates. From the models,prediction of radiator surface temperature and exit air conditions may be made for other similarclimates, using data available from the local Bureau of Meteorology.

INTRODUCTION

In warm and humid regions, ventilative cooling methods such as natural ventilation and fan-inducedventilation are usually considered effective and simple to incorporate in buildings. However, wind isoften non-existent during summer nights, causing stress to building occupants.

At night, the “atmospheric window” promotes long-wave radiation from surfaces to the sky in theinfrared spectrum between 8 and 13 µm. As water and water vapour also radiate heat, this radiativecooling effect diminishes under an overcast sky. This often happens before the rain comes, restoringthermal comfort. Provided the sky is not overcast, surfaces such as painted metallic surfaces emitlong-wave radiation to the sky as soon as there is no incident radiation from the sun. Without short-wave radiation from the sun, surfaces exposed to the night sky act as natural coolers, bringing theirsurface temperature down below ambient air. The level of cooling effect is then determined by theamount of heat absorbed from the surrounding warmer air.

A wind-shielding film may be used to suppress the counter effect of the surrounding warm air. It is tobe transparent to infrared radiation in order to retain the long-wave surface emission at the sametime. Thus wind-screen radiators consisting of a natural polyethylene thin film placed above aninsulated radiator surface, are for the purpose of enhancing the cooling performance.

The simplest way to transfer the cooling energy into buildings is by passing air through gapsunderneath the insulated radiator. The airflow increases the total heat absorbed by the radiator,raising radiator surface temperature. Simultaneously, the radiator emits a higher level of radiation tothe sky at higher surface temperature. As a result, the radiator attains a temperature that balances allheat components acting on it.

On calm nights, especially when the sky is either reasonably clear or having predominantly highclouds, the radiator surface temperature drops below the dew point of ambient air. A layer of dewforms on the surfaces, growing thicker as long as there is no wind. The large latent heat of waterreleased from this condensation counteracts the cooling process the way the warm ambient air doesto it.

On wind-screen radiators, it is not just the latent heat of water that affects the cooling rate, it is alsothat the covering film now becomes a radiation shield to the radiator below. Despite the fact that thewater on the cover radiates heat to the sky at high emissivity, the radiator is now radiating heat to thewater instead of the sky. Thus the radiator temperature gradually increases until its temperaturereaches that of an equivalent exposed metallic radiator surface.

It is the effect of dew formation on exposed and wind-screen radiator surfaces that makes themodelling in this paper different from ones that are for drier climates [1,3,5,6,9]. Once the modelshave been established and validated, prediction of radiator cooling performance may be made forother warm and humid climates, using the climate data available from the local Bureau ofMeteorology.

EXPERIMENTAL SETUP

The radiators

Five zincalume steel colorbond roofing sheets, 0.42 mm in thickness, different in shapes and sizesare mounted on a horizontal roof. Their upper surfaces are exposed to the sky, and the under-sidesare insulated. An additional one is mounted at an angle on the same roof, for comparison..

A wind-screen radiator of the same material is placed on the same roof. Air gaps between the under-side insulation and the radiator form the radiator-air heat exchanger for the experiment. A fan withadjustable speed settings is connected to the radiator assembly to draw air through the air channels.Heat is thus extracted from the warm air and rejected to the night sky through radiation occurring atthe radiator surface. The polyethylene film is removable, so that the surface of the heat exchangermay be made a directly exposed surface or a wind-screen surface with respect to the surrounding airand the sky.

Instrumentation and data logging

Wind-screen cover surface temperature of both sides, and surface temperatures at various positionson each radiator, both on the upper surface and the under-side, are measured using type-Tthermocouples. The thermocouples are connected to a multi-channel multiplexor before being fed to aCampbell Scientific CR10X data logger. Dry-bulb and wet-bulb temperatures of ambient air arelogged every thirty seconds by a self-logging Q15-QuestTemp device. Wind speed is measured by astandard three-cup anemometer mounted on a roof adjacent to the radiators. The anemometer isapproximately 2 metres from the base of the radiators, standing in free air. Offset margin for theanemometer is 0.2 m/s. Signals from the anemometer are logged by a separate CR10 logger. Theloggers sample the input signals every five seconds and log one-minute averages during the nightfrom 6 PM to 6 AM the following day. Cloud covers are estimated from the data obtained from thelocal Bureau of Meteorology.

GENERAL EQUATIONS and GENERAL APPROACH TO MODELLING

Figure 1: The radiator for modelling, Figure 2: The wind-screen radiator for a 0.86 m x 1.4 m commercial zincalume modelling, cross-sectional view. steel colorbond roofing sheet, Material and dimension exactly the 0.42 mm in thickness, insulated under-side. same as the exposed radiator.

General equations used in modelling

SI units are used otherwise stated.

gap forairflow

coverradiatorinsulation

Net radiative heat transfer on any horizontal surface exposed to the night sky:QRnet = QRsurface – εsurface (QRsky + QRground) (1)where: QRsurface = εsurface σ Tsurface

4

and using the concept of effective sky emissivity for clear sky [2]:QRsky = Cn εsky σ Tdb

4

Cn=1 + 0.0224 n - 0.0035 n2 + 0.00028 n3

εsky=0.787 + 0.764 ln((Tdp+273)/273)for radiation from the ground, all near-by objects emitting radiation to the radiator surface areincluded. An estimated view factor Fg of 0.003 is applied:QRground = Fg εg σ Tg

4

Convective heat transfer from surrounding airQC = hc (Tdb - Tsurface) (2)where convective heat transfer coefficient hc is from the dimensionless Nu = hc L / kair (3)L is the characteristic length of the radiator, and is equal to area/perimeter [7].for free convection: Nu = C (GrPr)1/4 (4)for forced convection: Nu = C Re4/5 Pr1/3 (5)

General approach to modelling

- Case 1: No dew formation:

To calculate the convective heat transfer, the coefficient C in the expression for the Nusselt number,Nu, (Eqs. 4,5) is to be determined.

Based on the collected data, the nights with no dew formation are selected for this purpose ofestimating C. For each time interval, the net overall heat rate is readily calculated from the measuredradiator surface temperature and the temperature of the wind-screen cover. The radiator QRn is alsoreadily calculated. As a result, the convective heat transfer QC is calculated, hence hc, Nu, and finallyC. From the calculated C values for each time interval, a single C value for the cooling process is theresult of the best-fit method. The experimental radiator surface temperature is the determining factorin the curve-fitting procedure.

Critical wind speeds, though only an approximation, have been identified. These are the wind speedsabove which convective heat transfer corresponds to a different level of effect.

- Case 2: Dew forming on the surface

Instead of calculating the amount of dew formed on the surface, the method of using C described inthe above section for no-dew formation is extended for the case with dew.

The C value in this case represents the combined effect of dew formation translated to convectionequivalence. The procedure of calculating C for the case of dew formation is thus identical to that ofno dew. However, in this case, the variation of C is noted as it represents the pattern and amount ofdew forming as time progresses.

MODELLING EXPOSED RADIATOR

No airflow

A mathematical model has previously been presented for exposed radiators with no air flowingunderneath [4]:QC-QRnet+QM = [Mrcpr(dTr)/A + δρlcpl(dTl)] / dt (6)-when there is no dew: δ=0, QM=0, Tsurface=Tr, εsurface=εr=0.9-when dew is present: δ#0, QM#0, Tsurface=Tl, εsurface=εcondensate=0.95

QM is the heat released by the condensation of moisture in the surrounding air.

Mr, A are the mass and surface area of the radiator material.δ is the thickness of the dew layer, and cpl is heat capacity of the water, ε is emissivity in general.

With airflow – An exposed radiator-air heat exchanger

Air flows underneath the radiator exchanges heat with the radiator in the form of forced convection byinternal fluid flow in tubes, ducts and conduits. Due to the fact that the air channels are not regular, anequivalent diameter, Deq = 4.cross-sectional area / wetted perimeter, is used as the characteristiclength for the convection process [7].

The convective heat transfer from airflow is: QCaf = hc,af (Taf – Tsurface) (7)where hc,af is from relationship: Nu = 0.02 Re4/5 Pr1/3

Incorporating QCaf into the model for exposed radiator without airflow [Eq.6], the exposed radiator-airheat exchanger model is as follows:QC+QCaf-QRnet+QM = [Mrcpr(dTr)/A + δρlcpl(dTl)] / dt (8)

QCaf is the heat extracted from the cooling air, rejected to the radiator and subsequently to the sky.Assuming that whether or not there is condensation of moisture from the cooling air, the temperaturedrop dTaf of the air may be calculated from: QCaf = Mafcp,af dTaf (9)

The calculated temperature drop dTaf indicates if condensation takes place in the air channels. In thesimulation of the model, the exit air temperature is adjusted for the condensation, based on themoisture content and dew-point temperature of the inlet air.

MODELLING WIND-SCREEN RADIATOR

Modelling a wind-screen radiator is an analysis of the interaction between the radiator and the cover,and the interaction of the radiator and the cover with the surroundings. It is similar to modelling a solarcollector, the heat exchange between the cover glass and the surfaces below it [1,8]. Figure 3 showsthe interaction of the radiating surfaces to radiation emitted from the sky, when there is no dewpresent on the cover surface.

In the modelling, subscripts l, r, c, s, g, af are for the dewairflow for the cooling air respectively.

No airflow

In terms of radiation, the radiator and the under-side of from the following sources: the radiator, the cover, the sfor these radiative heat transfer components below, sub

cover

radiatorinsulation

1 2 3 4

a

b

c

d

e

f

gap forairflow

5

Figure 3: Wind-screen radiator- Radiatingsurfaces react to incoming radiation from thesky. No dew on the cover surface.

“a” represents τcCnσεsTdb4

“b” - ρr τcCnσεsTdb4

“c” ρcρr τcCnσεsTdb4

“d” - ρcρr2 τcCnσεsTdb

4

“e” ρc2ρr

2 τcCnσεsTdb4

“f” - ρc2ρr

3 τcCnσεsTdb4

“1” represents - CnσεsTdb4

“2” ρc CnσεsTdb4

“3” ρr τc2CnσεsTdb

4

“4” ρcρr2 τc

2CnσεsTdb4

“5” ρc2 ρr

3 τc2CnσεsTdb

4

“6” ρc3 ρr

4 τc2CnσεsTdb

4

τc is transmissivity of the polyethylene film.ρc,ρr,εc,εr are reflectivity and emissivity of thecover and the radiator respectively.

sky

, radiator, cover, sky, near-by objects, and

the cover react to each other due to emissionky, and all near-by objects. In the expressionsscript “rc” is used. Similarly, reaction between

the upper-side of the cover and the sky and near-by objects is due to the same radiation sourceslisted above. Subscript “cs” is used to refer to these radiative heat transfer components

In general, the heat balance around the radiator and the heat balance around the radiator and thecover describe the behaviour of the wind-screen radiator, with or without dew on the cover:QCrc – QRnet,rc = Mrcpr(dTr)/A (10)QCcs – QRnet,cs + QM = [ Mrcpr(dTr)/A + Mccpc(dTc)/A + δρlcpl(dTl) ] / dt (11)

QCrc is the natural convective heat transfer from the under-side of the cover to the radiator surface,thus: QCrc = -kair (Tc – Tr) / d (12)QCcs is the convective heat transfer from ambient air to the upper-side of the cover, as generallydescribed in the section “General equations used in modelling” above. d = 5 mm, the distance fromthe radiator surface and the polyethylene cover.

- No dew

Radiation exchange between the radiator and the under-side of the cover:

. Due to emission from the sky, referring to Fig. 3 above:QRrc,s = - τcCnσεsTdb

4 + ρr τcCnσεsTdb4 - ρc ρr τcCnσεsTdb

4 + ρc ρr2 τcCnσεsTdb

4 - ρc2ρr

2 τcCnσεsTdb4

+ ρc2ρr

3 τcCnσεsTdb4

= τcCnσεsTdb4 (ρr -1) ∑( ρcρr)

n n = 0 to ∞ (13)

. Due to emission from the radiator:QRrc,r = σεrTr

4 (1-ρc) ∑( ρcρr) n n = 0 to ∞ (14)

. Due to emission from the cover:QRrc,c = σεcTc

4 (ρr -1) ∑( ρcρr) n, n = 0 to ∞ (15)

. Due to emission from near-by objects:QRrc,g = Fg τcσεgTg

4 (ρr -1) ∑( ρcρr) n n = 0 to ∞ (16)

The net radiation exchange between the radiator and the cover, QRrc, is the sum of all above. Notethat the infinite series ∑( ρcρr)

n converges to 1/(1-ρcρr) :QRnet,rc = QRrc,s+ QRrc,r+ QRrc,c+ QRrc,g (17)

Radiation exchange between the upper-side of the cover and the surroundings

. Due to emission from the sky, referring to Fig. 3 above:QRcs,s = - CnσεsTdb

4 + ρc CnσεsTdb4 + ρr τc

2CnσεsTdb4 + ρcρr

2 τc2CnσεsTdb

4 + ρc2 ρr

3 τc2CnσεsTdb

4 +ρc

3 ρr4 τc

2CnσεsTdb4

= CnσεsTdb4 [ –1+ρc+ ρrτc

2 ∑( ρcρr) n ] n = 0 to ∞ (18)

. Due to emission from the radiator:QRcs,r = τcσεrTr

4 ∑( ρcρr) n n = 0 to ∞ (19)

. Due to emission from the cover:QRcs,c = σεcTc

4 (1+ρrτc) ∑( ρcρr) n n = 0 to ∞ (20)

. Due to emission from near-by objects:QRcs,g = Fg σεgTg

4 [ -1+ρc + ρrτc2 ∑( ρcρr)

n ] n = 0 to ∞ (21)

The net radiation exchange between the radiator and the cover, QRcs, is the sum of all above:QRnet,cs = QRcs,s+ QRcs,r+ QRcs,c+ QRcs,g (22)

- With dew on the cover surface

When there is dew present on the cover surface, there is no radiation exchange from the radiator tothe sky. Instead it is now to the water layer on the cover. As the water on the cover radiates heat to

the sky at much higher emissivity than the cover, it is primarily responsible for the cooling process inthis case.

The mathematical model for the wind-screen radiator with dew is still the same as that by the generalEqs. 10 and 11. However, the components of radiation exchange are as follows:QRrc,s = τc σεwTw

4 (ρr -1) / (1-ρcρr) (23)QRrc,g = 0, expressions for QRrc,g and QRrc,g are still the same as Eqs.14 and 15, QRcs,s + QRcs,g = QRnetas in Eq.1, and QRcs,r = 0, QRcs,s = 0

With airflow – A wind-screen radiator - air heat exchanger

With air flowing beneath the wind-screen radiator, an additional convection term QCaf is included inthe model, as in the case of exposed radiator with airflow described above. Thus Eqs. 10 and 11become:QCrc + QCaf – QRnet,rc = Mrcpr(dTr)/A (24)QCcs + QCaf – QRnet,cs + QM = [ Mrcpr(dTr)/A + Mccpc(dTc)/A + δρlcpl(dTl) ] / dt (25)

SIMULATION AND EXPERIMENTAL C VALUES

Data for the radiator experiments are over three summers, 1999 to 2001. Simulation is for every one-minute interval of the night.Critical wind speeds for exposed and wind-screen radiators are 0.6 m/s and 2.5 m/s.For exposed radiators, the experimental C values found are as follows:- No dew: C=0.27 for free convection, C=0.04 for 0<=v<0.6m/s, C=0.028 for 0.6<=v<2.5m/s,

C=0.025 for v>=2.5m/s.- With dew: C=0.27 to 1.4 for free convection, C=0.04 to 0.08 for 0<=v<0.6m/s, C=0.037 for

0.6m/s<=v<2.5m/s, C=0.03 for v>=2.5m/s.For wind-screen radiators, the efficiency of the removable cover is about 0.5, due to rippling effectand air leakages and diffusion throughout the night.- No dew: C=0.4 for free convection, C=0.012 for all wind speeds > 0 recordable.- With dew: C=0.4 to 2 for free convection, C=0.012 to 0.065 for 0<=v<0.6m/s, C=0.008 to 0.05 for

0.6<=v<2.5m/s, C=0.004 to 0.04 for C>=2.5m/s.Alternatively, the wind-screen radiator under dew-forming condition may be modelled as if therehad been no dew and there had been convection directly on the radiator surface instead. It hasbeen found experimentally that this is equivalent to 0.5 to 2 times the convection by thesurrounding air. The simulation results are identical to those derived from using progressive Cvalues. No variation of C values with time is applied in this case.It is not unusual that dew starts forming on the wind-screen cover surface prior to the start of theexperiment at 6 PM. On those nights, there is no wind and humidity rapidly reaches 90% or overeven before midnight. A maximum C value of 2.4 and a maximum convection equivalence of 2.2are used instead.

In the simulation for the wind-screen, the transmissivity, reflectivity, and emissivity of the polyethylenefilm are 0.7, 0.15, and 0.15 respectively. Cooling air flow rates in the experiments are 0.7m/s, 0.9m/s,0.95m/s, by adjusting the fan speed setting and by using orifice fitting at the end of the exhaust airpipe. In the simulation, the term ��lcpl(dTl) representing the change in sensible heat of the dew layeris assumed to be negligible.

Figures 4, 5, 6 show the experimental variation of radiator and air temperatures over a period oftwelve hours on the day indicated. Calculated curves for radiator and exit air temperatures are also onthese graphs. Fig. 6 highlights the difference in the experimental temperature of the wind-screenradiator and the corresponding calculated value if no dew was assumed, for comparison.

CONCLUSIONS

Night-time cooling in summer is possible in the tropics, provided that the sky is not overcast. Insulatedmetallic roof of the building may be built in such a way that it acts as an air cooler, rejecting heat fromthe air to the sky via the painted roof surface. On calm and clear nights, dew deposits on the roof

surface, reducing cooling performance. The effect of dew is especially obvious on the wind-screensurface. Dew formation has been taken into account in the modelling the radiators. Results from thesimulation of these models indicate a good fit for both calm and windy conditions.

Figure 4: Exposed radiator – air heat exchanger, 16-January-2001

Figure 5: Wind-screen radiator – air heat exchanger, 30-March-2000

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a: Ambient air dry-bulb temperature(deg.C)

b: Ambient air dew-point temperature(deg.C)

c: Radiatortemperature(deg.C)

d: Exit airtemperature(deg.C)

e: Calculatedradiatortemperature(deg.C)f: Calculated exit airtemperature(deg.C)

g: Ambient airrelative humidity(0.1%)

h: Wind speed(m/s)

i: Cloud cover(tenths)

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abc

d

e

f

g

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i

Figure 6: Wind-screen radiator – air heat exchanger, 01-March-2001.Dew on the cover after 10 PM.The lower radiator temperature curve calculation assumes no dew on the cover surface.

Under windy condition, the wind-screen radiator performs significantly better than an exposedradiator. However, under calm and humid condition, there is no real difference in performancebetween the two. The wind-screen radiator would be more practical to have a solid cover on it insteadof a thin film, so that there is no need for constant re-stretching and fixing. An ideal wind-screenradiator would be one that eliminates all convection effect, at the same time being free ofmaintenance over its life. Research on such an ideal wind-screen would be beneficial for the future.

REFERENCES

1. Blampied, M., 1980, “A Model of Nocturnal Radiative Cooling Through Infrared TransparentWindscreens”, Masters Thesis, Trinity University.

2. Clark, E., and Allen, C., 1978, “Estimation of Atmospheric Radiation for Clear and Cloudy Skies”,Proceedings, The 2nd National Passive Solar Conf., Vol.2. Ed. Don Prowler, Philadelphia,Pennsylvania, AS/ISES, pp. 675-678.

3. Clark, G. and Blampied, M., 1979, “The Effect of I.R. Transparent Windscreens on Net NocturnalCooling from Horizontal Surfaces”, Procs. 4th National Passive Solar Conf., Kansas City, pp. 509-513.

4. Dan, P.D., and Aynsley, R., 1998, “Nocturnal Cooling of an Exposed Radiator Surface”, Refereedpaper, Proceedings, 32nd ANZAScA Annual Conference, Wellington, New Zealand, pp. 185-190.

5. Givoni, B., 1994, Passive and Low-Energy Cooling of Buildings, Van Nostrand Reinhold, NewYork, pp. 92-93.

6. Givoni, B., 1982, “Cooling by Longwave Radiation”, Passive Solar Journal, Vol 1, No. 3, pp. 131-150.

7. Incropera, F.P., and De Witt, D.P., 1990, Fundamentals of Heat and Mass Transfer, 3rd edition.John Wiley & Sons, New York, pp. 501, 546-548, 610-615.

8. Kreith, F., and Kreider, J., 1978, Principles of Solar Engineering, McGraw-Hill, New York, pp. 156-159.

9. Mostrel M. and Givoni, B., 1982, “Windscreens in Radiant Cooling”, Passive Solar Journal, Vol 1,No. 4, pp. 229-238 Givoni, B., 1982, “Cooling by Longwave Radiation”, Passive Solar Journal, Vol1, No. 3, pp. 131-150.

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c: Radiatortemperature (deg.C)

d: Calculated radiatortemperature,ASSUMING no dew(deg.C)e: Calculated radiatortemperature (deg.C)

f: Exit air temperature(deg.C)

g: Calculated exit airtemperature (deg.C)

h: Ambient air relativehumidity (0.1%)

i: Wind speed (m/s)

j: Cloud cover (tenths)

a

b

c

d

gf

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INSULATION MATERIAL THERMAL TESTING: PRINCIPAL DIFFERENCES BETWEEN ALUMINIUM FOIL AND BULK INSULATIONS June 2002 Federal regulatory thermal performance measures for buildings should be based on products that have proven in-situ performance. Under Australia's summer sunshine, the temperature of building envelopes rise as they absorb solar radiation, particularly metal roofing which can reach temperatures from 60°C to over 90°C during calm conditions, depending on their surface colour. Heat transfer from hot external surfaces, across airspaces to the interior of buildings, is principally by infrared radiation. As the principal source of heat gain into buildings, in warm climates, radiant heat gain creates the need for indoor cooling, by airflow from breezes or fans, evaporative coolers or refrigerative airconditioning. The latter, consumes significant amounts of electrical energy. Greenhouse gas emission reduction is focussed on reducing the burning of fossil fuel to generate electricity. As proven, in the past, by international studies, and known by all authorities, the low emissivity of aluminium foil materials (typically 0.03) facing an airspace, reduces radiant heat transfer by around 97%. In warm climates, these radiant barriers significantly reduce the costs of cooling building interiors. Established testing of resistive bulk insulation materials using a Heat Flow Meter, involves moderate temperatures up to 33°C, but does not address radiant heat transfer. Authorities should be pro-actively constructing energy codes that require testing of all insulation materials to be used in Australian buildings take account of radiant heat transfer. Richard Aynsley, B.Arch(Hons I), MS(Arch Eng), PhD. Member : AIRAH & ASHRAE Former UNESCO Professor of Tropical Architecture, James Cook University, QLD Dean, College of Technology, Southern Polytechnic State University, Marietta GA, USA

SUMMARY OF REFLECT3 AND ASTM C 1340-1999

Dick Aynsley

Dean, Engineering Technology & Management, Southern Polytechnic State University, GA, USA

February 2, 2003 REFLECT3 is for calculation of R-values, up and down, in plane air cavities, reflective, non reflective and multiple, at 0, 45 and 90 degrees inclined orientations, for a range of temperature differences and materials, based on Robinson & Powlitch heat transfer methods, with conduction/convection corrections and curve fitting by Yarbrough, and validated up to 60 deg C with VERY close correlation to physical measurements. [Reference: “Assessment of Reflective Insulation for Residential and Commercial Applications” David Yarbrough, ORNL, TN, 1983] ASTM C 1340 standard, with software, is for calculation of heat transfer through ceilings under reflective roof spaces (attics). This is important software because it is the only program handling heat transfer through complicated roof space geometries, with a wide range of ventilation rates through the attic space, validated up to 60 deg C for typical US construction materials. Software results closely correlate with physical measurements taken in attics without radiant barriers, and less so for those with radiant barriers, due to the complication of the emissivity of the timber rafters. Richard (Dick) Aynsley has been granted permission to make modifications to ASTM C 1340 to suit Australian needs. [Reference: “Standard Practice for Estimation of Heat Gain or Loss through Ceilings under Attics Containing Radiant Barriers by the use of a Computer Program.” ASTM C 1340 – 1999) developed by Ken Wilkes, ORNL)] REFLECT 3 REFLECT 3 is a user-friendly, state-of-the-art, PC software tool for computing R-values (both up and down) for reflective and non-reflective plane air cavities in horizontal, vertical and 45 degree inclined orientations. The term plane refers to cavities with parallel surfaces. SI or IP units of measurement can be used in this software that runs under Windows operating systems. The original FORTRAN program, developed by the Oak Ridge National Laboratory in USA, was called REFLECT. This program used the procedure developed by Robinson and Powlitch. Computations in a revised program REFLECT 2 incorporated Yarbrough’s improvements in modeling of conductive/convective heat transfer. This program was rewritten by Richard Aynsley and Glenn Allen from Southern Polytechnic State University with ORNL's permission in Visual Basic as REFLECT 3. The basis for REFLECT was published in 1983 in an ORNL report by D.W. Yarbrough titled "Assessment of Reflective Insulations for Residential and Commercial Applications. It was reviewed by experts in the field as well as industry and government representatives. Their names are listed in the publication. REFLECT 2 formed the basis for later work on the ASTM C1340 computer model for heat transfer through attic spaces, by Kenneth Wilkes. ASHRAE also adopted the REFLECT 2 computation method for its R-value tables for reflective cavities. The problem with ASHRAE is that it is limited in print form and does not include sufficient values, particularly for high temperature conditions associated with metal roofing. There are a few obvious errors in the tables. REFLECT3 allows the user to input data relevant to the installation

location. Dr. David Yarbrough who was given a copy of REFLECT 3 and he emailed the following reply on Feb.2, 2003: “Thank you for sending the CD with the reflect program. The package arrived several days ago. I ran the program and did a calculation to observe the result. It is a very useful program.” Dr Ken Wilkes also has a copy of the program and he said he is happy with the output. Important Extracts: "Approximately 94% of the 309 of the calculated hc(50) are within +/- 2% of the input values and 98% are within +/- 3%." (p.37) [Reflect2] "would have the effect of reducing the calculated R values [of Robinson & Powlitch] and bring calculated and experimental results into better agreement." (p.31) ASTM C 1340 – 1999. “Standard Practice for Estimation of Heat Gain or Loss through Ceilings under Attics Containing Radiant Barriers by the Use of a Computer Program.” My strong support for the use of ASTM C 1340 – 1999, is that it is the only standard with software capable of predicting heat flow through attics that has been validated against physical measurements both in the ORNL Large Scale Simulator and in field studies. These validations have shown the standard to be capable of predicting the insulation effects provided by both reflective and resistive insulation products separately and in combination. The standard also accommodates a wide range of ventilation rates through the attic space. The current version of the standard is in US units and requires a specific format for the hour by hour climatic data but Angelo has had plenty of experience in coping with these issues. There is an ASTM committee of experts who are responsible for reviewing and updating this standard from time to time. Important extract: “Calculated cumulative heat flows under summer conditions were accurate to 5-10% for attics without radiant barriers and were accurate to about 15% for attics with radiant barriers. A significant source of uncertainty in the calculations for a radiant barrier attached near the roof was in the effective emittance of the combination of radiant barrier and exposed wood surfaces.” P.11

eColI BR I u M • n oVe M Be R 2012 32

F O R U M

CONDENSATION IN RESIDENTIAL BUILDINGS Part 2: Hygrothermal analysis

By Richard Aynsley, f.AIRAH Building energetics Pty ltd

IntRoduCtIonAustralia, with relatively warm climates compared to Europe, has experienced fewer problems of mould in houses resulting from condensation in winter. Over recent decades a common form of wall construction, brick veneer, has undergone changes in timber sizes and use of insulation for increased energy efficiency. With a history of little risk of condensation and mould in brick veneer walls in the past, builders and designers paid little attention to hygrothermal analysis. In hindsight, the changes in brick veneer wall construction over a few decades certainly influenced the risk of condensation.

HYGRotHeRMAl AnAlYsIsThe following examples of steady-state hygrothermal analysis follow procedures described in UK Building Research Station Digest 110 (BRS, 1969) for heated and ventilated houses, and are based on the Glaser method (Glaser, 1958).

Melbourne and western Sydney, BCA climate zone 6, was chosen as representing major suburban areas where brick veneer walls were used in the 1970s. The Bureau of Meteorology’s Melbourne mean monthly climate data indicates the lowest mean minimum monthly air temperature as 6°C in July. No coincident relative humidity is provided for this temperature in the data set. However, coincident mean monthly air temperature and relative humidity of 8.7°C at 79% RH is provided at 9am in July.

Assuming that there is no sudden change in moisture content of the air, between say 5am and 9am, the water vapour pressure at 9am can be used to calculate the equivalent relative humidity at the mean monthly air temperature of 6°C at 95% RH, with a water vapour pressure calculated as 0.89kPa.

The method used in UK Building Research Station Digest 110 (BRS, 1969) for estimating indoor condition in heated and ventilated houses, at normal ventilation rates, is to take the outdoor condition of air and use a psychrometric chart

to determine what the water vapour pressure and mixing ratio of the air is after it has been raised to the indoor air temperature proposed for thermal comfort, say 20°C. To this condition, 0.0034kg/kg is added to the mixing ratio to allow for indoor sources of moisture such as washing, bathing, breathing, and the like, to estimate the indoor mixing ratio and water vapour pressure.

In the example, hygrothermal analyses below-water vapour pressures were calculated using psychrometric equations. The resulting indoor condition for Melbourne in July was 20°C at 62% RH or water vapour pressure of 1.43kPa. The typical ventilation rate at the time the Building Research Station Digest 110 (BRS, 1969) was written was one air change per hour.

WInteR HYGRotHeRMAl AnAlYsIs of BRICk VeneeR WAlls In WesteRn sYdneY And MelBouRneIn the 1970s brick veneer walls typically consisted of an external skin of 110mm brickwork (density≈ 1690 kg/m3), a 50mm cavity, reflective foil sarking with an antiglare surface (≈ 0.3) and reflective surface (ԑ≈ 0.03), 100mm timber stud frame, and 10mm gypsum plasterboard. At that time additional thermal insulation was rare. No widespread mould problems were experienced with these brick veneer walls over a few decades in Melbourne or western Sydney, BCA Climate Zone 6.

It can be seen, from the graph in Table 1, that indoor vapour pressure is higher than outdoor vapour pressure, so vapour flow is from indoors to outdoors. The temperatures through the 1970s brick veneer wall do not fall to, or below, dew point anywhere through the construction when indoor air is heated to 20°C. This suggests that under these conditions there is only slight risk of condensation from indoor or outdoor mean minimum monthly air temperature or relative humidity conditions in July in the 1970s brick veneer wall.

ABstRACtCondensation in buildings becomes more of a concern as thermal insulation is increased to improve energy efficiency. Examples of steady-state hygrothermal analysis of Australian brick veneer wall construction in temperate winter conditions are provided, as are reinforced concrete masonry in the tropics. A standard is needed for assessing condensation risk in buildings to establish a consensus on appropriate input data and analysis, and assessment procedures for conducting hygrothermal analysis of Australian construction in all climate zones.

keywords: houses, condensation, hygrothermal, insulation, ventilation, standards.

33n oVe M Be R 2012 • eColI B R I u M

F O R U M

If condensation did occur intermittently on the interior side of the foil sarking, construction element 4, under extreme conditions, the timber framing had sufficient moisture storage that it could store intermittent condensate and release it during warmer, drier periods. This is reflected by the absence of mould problems observed in this type of wall construction over many years.

Melbourne 1970 style Brick Veneer Wall, Winter Heated & Ventilated space with Reflective sarking

Energy-efficiency requirements in the Building Code of Australia were introduced in the 1990s. A number of changes occurred in brick veneer walls in Melbourne and western Sydney between 1970 and 2011. A typical 2011 brick veneer wall had 90mm stud framing, housewrap over the studs and a 90mm R2.5 fibreglass batt insulation. But few builders or designers bothered to analyse the implications of these changes on the risk of condensation.

In hindsight, a hygrothermal analysis in Table 2 suggests condensation will occur behind the sarking within the fibreglass batt insulation where air temperature in the graph has fallen below dew-point. This is a serious condition because damp fibreglass loses much of its insulation values and compounds the condensation problem.

By carefully choosing a low-vapour resistance house wrap and adding a higher vapour resistance vapour retarder behind the plasterboard, the condensation on the warm side of the sarking can be controlled. It can be seen, from the graph in Table 3 that with these modifications, the dew-point has been lowered by increasing resistance to vapour flow with the vapour retarder behind the plasterboard and decreasing the dew-point within the fibreglass insulation.

suMMeR HYGRotHeRMAl AnAlYsIs of A ConCRete MAsonRY VeneeR WAll In dARWIn’s HuMId tRoPICsThe hygrothermal analysis of an insulated concrete masonry wall of an air conditioned house in Darwin in summer was conducted using the Glaser method set out in the BRS Digest 110 (BRS, 1969) Table 4. The outdoor conditions were taken as 30°C at 72% RH, vapour pressure 3.03kPa being mean monthly conditions in Darwin during the most humid month of February. Indoor conditions were taken as 22°C at 50% RH, vapour pressure 1.31kPa provided by the air conditioning system.

The construction consisted of 20mm of cement render over 190mm concrete masonry cored limestone aggregate blocks (density ≈ 2200 kg/m3 and vapour resistance of 3.64MN.s/g). Thermal insulation and vapour resistance data for these blocks was found in the ASHRAE Handbook of Fundamentals (ASHRAE, 2009).

Weather-side Room-side

Material Thickness m

Thermal resistance

m2.K/W

Temperature difference

K

Surface temperature

°C

Surface temperature

°C

Vapour resistance

MN.s/g

Vapour press ∆

kPa

Vapour press kPa

Dew Point Temperature

°C

Construction Elements 6 0.89

1 External air film 0.01 0.040 0.31 6.00 6.31 0.00 0.00 0.89 5.30

2 Brickwork 110 mm 0.110 0.170 1.31 6.31 7.61 5.50 0.01 0.90 5.42

3 Semi-reflective cavity 0.050 0.720 5.53 7.61 13.15 0.00 0.00 0.90 5.42

4 Alum. foil sarking 0.001 0.000 0.00 13.15 13.15 400.00 0.53 1.43 12.32

5 Semi-reflective cavity 0.100 0.712 5.47 13.15 18.62 0.00 0.00 1.43 12.32

6 Plasterboard 10mm 0.010 0.060 0.46 18.62 19.08 0.45 0.00 1.43 12.33

7 Internal air film 0.01 0.120 0.92 19.08 20.00 0.00 0.00 1.43 12.33

Total resistance 1.822 14.0 20 405.95 0.54 1.43

(Heat flow horizontal in winter)

Outdoors: 6°C at 95% RH (0.89 kPA) Indoors: 20°C at 62% RH (1.43 kPa) Melbourne, July

table 1: Winter Hygrothermal Analysis of a 1970 Brick Veneer Wall for July in Melbourne.

RSElement 1

19

17

15

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9

7

5RS

Element 2

T°C Tdp

Tem

pera

ture

°C

RSElement 3

Position through wall

RSElement 4

RSElement 5

RSElement 6

Figure 1


F O R U M

On the interior side a 90.5mm light-gauge cold-formed steel stud wall is bolted to the concrete floor slab and is set 20mm away from the interior face of the block wall. This 20mm space creates a drainage cavity between the concrete block wall and a waterproof but highly permeable building wrap is screwed to the steel studs before the block wall is laid. Fibreglass batts R2.7 90mm thick, between the 90.5mm steel studs, provide further thermal insulation. Material properties for the plasterboard, wall wrap, and fibreglass were obtained from manufacturers’ data sheets and the ABCB Condensation Handbook (ABCB, 2011). Thermal insulation building materials used in Australia must comply with AS/NZS 4859.1 (Standards Australia, 2002).

It can be seen, from the graph in Table 4, that indoor vapour pressure is lower than outdoor vapour pressure so vapour flow is from outdoors to indoors. There is a separation of at least 5.44°C between the temperature profile and the dew-point profile throughout the wall, so there is little risk of condensation.

However, the dew-point of outdoor air, 24.3°C, is above indoor air temperature 22°C. In total the dewpoint of outdoor air in Darwin is above 24°C for approximately 1,613 hours per year based on Wooldridge data (Wooldridge, 1979). Given recent global warming it is probably time to update the Wooldridge data.

It should be noted that these temperatures are not contemplated in the BRS Digest 110 because the psychrometric chart provided has a maximum air temperature of 20°C. A detailed discussion of the problem of air conditioning in humid tropical regions is provided in AIRAH’s DA20 publication (AIRAH, 2002).

The insulated concrete masonry wall, in Table 4, may appear to be satisfactory in terms of condensation risk, as temperatures through the wall are well above dew-point; however, further analysis may be necessary. Additional considerations that are applicable to all construction methods and climate zones include thermal bridging through metal studs, sealing penetrations in vapour barriers for electrical and plumbing services, particularly in cold-climate regions where vapour control membranes are close to the internal linings.

The Australian house-building industry also has difficulty achieving tight building envelopes and installing effective vapour barriers and vapour retarders. Vapour barriers or retarders in walls need to be connected to vapour barriers or retarders in floors and ceilings. Indoor pressurisation offers a possible solution for air leaks but can be difficult and expensive.

ConClusIonA couple of decades ago mould on interior surfaces due to condensation in buildings was rare. Recent increases in thermal insulation for energy efficiency and utilisation of air conditioning in Australian houses, has resulted in increased risk of condensation in winter in temperate climate regions and summer in humid tropical regions if hygrothermal analysis is ignored.



Thermal resistance

m2.K/W


K

Surface temperature

°C

Surface temperature

°C

Vapour resistance

MN.s/g

Vapour press ∆

kPa

Vapour press kPa


°C

Construction Elements 6 6 0.89


2 Brickwork 110 mm 0.110 0.170 0.74 6.17 6.91 5.50 0.46 1.35 11.40

3 Non-reflective cavity 0.030 0.170 0.74 6.91 7.65 0.00 0.00 1.35 11.40

4 Building wrap 0.001 0.000 0.00 7.65 7.65 0.12 0.01 1.36 11.52

5 Fibreglass R2.5 batt 0.090 2.655 11.56 7.65 19.22 0.45 0.04 1.39 11.93

6 Plasterboard 10mm 0.010 0.060 0.26 19.22 19.48 0.45 0.04 1.43 12.33


Total resistance 3.215 14.0 14 20 6.52 0.54 1.43



Melbourne 2011 style Brick Veneer Wall, Winter Heated and Ventilated space with Wall Wrap and fG Insulation

RSElement 1

19

17

15

13

11

9

7

5RS

Element 2

T°C Tdp

Tem

pera

ture

°C

RSElement 3


RSElement 4

RSElement 5

RSElement 6

table 2: Winter Hygrothermal Analysis of a 2011 Brick Veneer Wall for July in Melbourne.

Figure 2

35n oVe M Be R 2012 • eColI B R I u M

F O R U M



Thermal resistance

m2.K/W


K

Surface temperature

°C

Surface temperature

°C

Vapour resistance

MN.s/g

Vapour press ∆

kPa

Vapour press kPa


°C



2 Brickwork 110 mm 0.110 0.170 0.74 6.2 6.9 5.50 0.03 0.92 5.84


4 Building wrap 0.001 0.000 0.00 7.7 7.7 2.00 0.01 0.94 6.03

5 Fibreglass R2.5 batt 0.090 2.655 11.56 7.7 19.2 0.50 0.00 0.94 6.07

6 Vapour Retarder 0.001 0.000 0.00 19.2 19.2 80.00 0.49 1.43 12.30

7 Plasterboard 10mm 0.010 0.060 0.26 19.2 19.5 0.45 0.00 1.43 12.33





table 3: Hygrothermal Analysis of a Brick Veneer Wall with Moisture Control for July in Melbourne.

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Obtaining vapour-resistance properties of materials used in Australian house construction can be problematic. Much of the existing vapour resistance data are from Europe, measured at temperatures well below most Australian in-service conditions. Reliable water vapour resistance data at in-service conditions are needed from Australian building material manufacturers.

Australia needs a standard on moisture control in buildings that reflects the huge span of latitude of the country. ASHRAE Standard 160 (ASHRAE, 2009) offers some useful indications on how to deal with condensation risk in cold, temperate and tropical climate regions. Without an Australian standard for assessing condensation risk, there is no consensus on what are appropriate input data, hygrothermal analysis methods, or evaluation of results. Without such a standard, assessment of condensation risk is a matter of opinion. ❚

Melbourne 2011 style Brick Veneer Wall, Winter Heated and Ventilated space with Wall Wrap and fG Insulation

darwin Concrete Masonry Veneer Wall, summer Conditioned space with Wall Wrap and fG Insulation



Thermal resistance

m2.K/W


K

Surface temperature

°C

Surface temperature

°C

Vapour resistance

MN.s/g

Vapour press ∆

kPa

Vapour press kPa


°C



2 Cement render 0.020 0.040 0.14 32.86 32.73 2.00 0.45 3.19 25.17

3 Conc. Masonry 190 mm 0.190 0.200 0.68 32.73 32.05 5.48 1.24 1.95 17.13


5 Building Wrap 0.001 0.000 0.00 31.48 31.48 1.92 0.43 1.51 13.20

6 Fibreglass Batts R2.7 0.050 2.622 8.87 31.48 22.61 0.45 0.10 1.41 12.13

7 Plasterboard 10mm 0.010 0.060 0.20 22.61 22.41 0.45 0.10 1.31 11.00




Outdoors: 33°C at 73% RH (3.64 kPA) Indoors: 22°C at 50% RH (1.31 kPa) Darwin, February

RSElement 1

19

17

15

13

11

9

7

5RS

Element 2

T°C Tdp

Tem

pera

ture

°C

RSElement 3


RSElement 4

RSElement 5

RSElement 7

RSElement 6

RSElement 1

35

30

25

20

15

10RS

Element 2

T°C Tdp

Tem

pera

ture

°C

RSElement 3


RSElement 4

RSElement 5

RSElement 7

RSElement 6

RefeRenCesABCB (2011) Condensation in Buildings Information Handbook. Australian Building Codes Board, Canberra, ACT, 91 pages.

AIRAH (2000) Tropical Air Conditioning, Design Application Manual DA 20. Australian Institute of Refrigeration, Air-Conditioning & Heating Incorporated, Melbourne.

ASHRAE (2009) ASHRAE Handbook Fundamentals, SI edition, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Atlanta, GA. Chapter 26.

ASHRAE (2009) ASHRAE Standard 160, Criteria for Moisture-Control Design Analysis in Buildings. ASHRAE, Atlanta, 16 pages.

BRS (1969) Condensation. Building Research Station Digest 110, Oct., 8 pages.

Glaser, H. (1958) Vereinfachte Berechnung der Dampfdiffusion durch geschichtete Wände bei Ausscheidung von Wasser und Eis (Simplified calculation of vapour diffusion through layered walls involving the formation of water and ice). Kälttetechnik 10, H 11, S. 358-364 und H 12, S. 386-390.

Standards Australia (2002) AS/NZS 4859.1/Amendment 1:2006, Materials for the thermal insulation of buildings – General criteria and technical provisions. Standards Australia, Sydney, NSW.Figure 3

Figure 4

table 4: Insulated and Vapour Controlled Concrete Masonry Veneer Wall in darwin in february.

Page 1 of 4

THREE PAGES OF SELECTED QUOTATIONS FROM

Report on the Inquiry into Biotoxin‐related Illnesses in Australia

House of Representatives Standing Committee on

Health, Aged Care and Sport Members

building research [is recommended] into structural requirements, building

techniques and materials to avoid growth of moulds and development of

biotoxins, the best methods to treat mould in commercial and domestic situations

(including methods to avoid spreading fungal spores), and . . . .

Design or construction flaws and inadequate maintenance, which the TMSA stated

was ‘the leading cause of water damage’;

Natural events such as floods, storms, hail and/or cyclones; and

Occupant behaviour, such as keeping windows shut at all times or flooding of sinks

and baths.1

Building and Construction Practices

2.1 Building Biology Sydney stated that there is a ‘lack of understanding’ that dampness

and mould in houses may have health effects. Building Biology Sydney stated that

this lack of awareness has ‘resulted in the continuance of poor building practices,

poor building design [and] insufficient building maintenance’.2

2.2 Building practices that were put forward as potentially increasing dampness and/or

mould levels included: exposing building materials to moisture during

construction;3 inadequate ventilation (such as buildings that are air‐conditioned at

all times);4 practices that enable a build‐up of condensation (such as the use of foil to

wrap buildings);5 the use of timber framing and/or gypsum board which may

encourage mould growth;6 or inadequate and/or incorrectly installed

waterproofing.7 The ASBB also put forward concerns that the uncovering of ‘hidden

mould’ in wall cavities during renovation works could expose occupants to

biotoxins.8

1 TMSA, Submission 105, p. 10.

2 Mrs Jeanette Williams, Building Biologist, Building Biology Sydney, Official Committee Hansard, Canberra, 9

August 2018, p. 3.

3 ASBB, Submission 45, p. 9.

4 Dr Tim Law, Private Capacity, Official Committee Hansard, Canberra, 9 August 2018, p. 25.




8 Mrs Nicole Bijlsma, ASBB, Official Committee Hansard, Canberra, 9 August 2018, p. 5.

Page 2 of 4

2.3 Dr Law was of the view that the creation of highly energy‐efficient and fireproof

homes over recent years may have had the unintended consequence of increasing

the incidence of condensation, and consequently increasing the risk of dampness

and mould build‐up. DrLaw further stated that ‘the persistent damp from

condensation has led to other problems with mould and its deleterious effects on

human health.’9

2.4 The TMSA pointed to the Australian Building Codes Board’s (ABCB)

non‐mandatory guide for condensation in buildings and an ABCB scoping study

regarding condensation, and recommended both these items be incorporated into

Australia’s Building Code. The TMSA also recommended ‘a remediation program

be instigated for buildings already built to the current building code to mitigate

condensation issues.’10

2.5 Dr Law stated that Australia’s codes ‘are decades behind international best practices in managing and responding to condensation problems’.11 Countries Dr Law

considered to be best practice included Canada and Ireland, while the United

Kingdom of Great Britain, the USA and New Zealand are also ‘way ahead’ of

Australia.12

Air Conditioning Systems

2.6 Ducted Air Solutions (DAS) stated that in recent decades ‘buildings have become

“sealed”, relying on mechanical air processes to provide breathable air over natural

ventilation.’13

2.7 HydroKleen advised that air conditioning systems that are not properly maintained

can become clogged with mould and dust, and can subsequently spread airborne

mould spores throughout a building.14 The DAS similarly stated that mould spores

within air conditioning systems that are then dispersed become ‘a

majorcontaminant of indoor air.’15 The ASBB added that ‘heating, ventilation

9 Dr Tim Law, Submission 75, p. 10.


11 Dr Tim Law, Submission 75, p. 7.


13 Ducted Air Solutions (DAS), Submission 70, p. 2.

14 HydroKleen, Submission 31, p. 3.

15 DAS, Submission 70, p. 2.

Page 3 of 4

andairconditioning systems that are not properly maintained are frequently a source

of biotoxins, especially in commercial buildings’.16

16 Mrs Nicole Bijlsma, ASBB, Official Committee Hansard, Canberra, 9 August 2018,

p. 25

Further Research

2.1 A range of recommendations for further research were put forward in order to create

a stronger evidence base and consensus regarding mould, its effects, and testing and

remediation methods.

2.2 The REINSW was of the view that a scientific study on mould and its potential effects

is needed to determine at what levels mould may become a danger to human health.

The REINSW stated:

We encourage a scientific study on mould—its levels of toxicity and what level is

dangerous. We find that, whilst mould might exist in properties, more often than not it is

not dangerous. The tests used to determine the extent of toxicity are not scientifically

proven. A lot of the inspectors donʹt have qualifications. They use a lot of common sense

and the experience theyʹve had in the industry … we need to work out the problems we

actually have before we start solving issues.16

2.3 Mr Stamkos called for ‘research to better understand the mechanisms causing illness

resultant from water‐damaged buildings and how to better identify the risks’.16

2.4 Tenants Victoria recommended a research centre be established to undertake:

‘building standards research into the precursors for and conditions to

promote mould, and those that prevent mould and biotoxin formation

(with a view to revision of the [National Construction Code]),

building research into structural requirements, building techniques and

materials to avoid growth of moulds and development of biotoxins, the

best methods to treat mould in commercial and domestic situations

(including methods to avoid spreading fungal spores), and

medical research into respiratory and other conditions caused by

biotoxins.’16


16 Mrs Jeanette Williams, Building Biologist, Building Biology Sydney, Official Committee Hansard, Canberra, 9

August 2018, p. 3.






16 Mrs Nicole Bijlsma, ASBB, Official Committee Hansard, Canberra, 9 August 2018, p. 5.

As part of our modernisation andenhancement of the Association’s imageI am proud to present to you, our latestedition of the National Precaster, whichhas undergone a complete facelift.

Perhaps more importantly is the content detail, whichhighlights the sophisticated, innovative, and quality basedindustry that we are. Our focus is now on the cutting edgeissues that are community and socially related to modernAustralia. Precast is responding to the demands of modernconstruction in addressing issues such as energy efficiency,sound transmission, quality of construction and affordability.

The use of precast in residential construction is being rapidlyembraced throughout Australia, for all the above reasons.This issue includes the first of a series of articles prepared by Dr. Edward Harkness which deals with the social andeconomic benefits precast provides in construction. Dr. Harkness provides an in-depth review of the benefitsprecast affords in energy efficiency in multi-storey structures.

Another initiative approved by the NPCAA Board is a formalprocedure for Member Certification. This sets a minimumcriteria that must be met before a precast concretemanufacturer can be admitted to the Association as aCorporate Member. This initiative has been introduced toraise the standing of the Association and its Members and toprovide the construction industry with assurance that, bychoosing to deal with our members they can be assured thatthey are dealing with a competent manufacturer, capable ofproviding quality products and service.

Contractors will be able to confirm a manufacturer’s credentialsby a Certificate of Membership, signed by the President andissued to Corporate Members on an annual basis.

Another highlight since our previous edition of NationalPrecaster is the Concrete Institute of Australia “2003 Awardfor Excellence in Concrete – Technology” for our PrecastConcrete Handbook. We were delighted to be presented withthis prestigious Award at the Institute’s Biennial ConferenceAwards Night held on the 19th July 2003 in Brisbane. Thecomments made by the presenter confirmed the quality of thepublication and the extensive material it contains for allaspects of the Australian precast concrete industry.

The Handbook content accurately reflects the state-of-the-artpractices in the precast concrete industry. It is a fantasticpublication and is a must-have document in every engineer’s,architect’s and designer’s technical library.

Matt Perrella, President

The recently completed Moorebank Interchange hasremoved the last remaining set of traffic lights on the mainhighway link between Sydney and Albury. Motorists cannow travel from the north side of Sydney Harbour via theSydney Harbour Tunnel, the Eastern Distributor, the M5East and M5 motorways and the Hume Highwayunimpeded to Canberra and the Victorian border.

The grade separation interchange with onloading andoffloading ramps in all directions was constructed over anintersection with an operating motorway that carries90,000 vehicles each day. The site was small andconstricted and the design solution demanded that safetyof motorists and construction personnel and continuoustraffic movement be uncompromised.

The interchange bridge consists of two 18m long simplysupported spans, two abutments and a central pierlocated in the motorway median. The bridge is variable inwidth ranging from 50m over the central pier to 64m atthe abutments.

Initial design considerations favoured steel because of itsapparent ease of construction. Maintenance requirements,however, over-ruled this material. Concrete was thematerial of choice.

A further consideration for the designers was speed ofconstruction. A short construction period would reduce theexposure of traffic to construction conditions while similarlyreducing risk to construction personnel. Nor did the obviouscost savings achievable through a shorter constructionperiod pass un-noticed by the Construction and DesignManagement team of Kellogg Brown and Root (KBR).

Precast concrete construction appeared a naturaloutcome to the designers combining both the ease andspeed of construction with the durability and lowmaintenance requirements inherent in high-class, high-strength precast concrete.

By consulting early in the design process with industryspecialist, Structural Concrete Industries (Aust) Pty Ltd

NATIONAL

PRECASTERNUMBER 32 • OCTOBER 2003

NATIONAL PRECAST CONCRETE ASSOCIATION AUSTRALIA WEB ADDRESS: www.npcaa.com.au EMAIL: [email protected]

ACN 051 987 181 • ISSN 1037-9908

Precast headstocks being erected on Y-shape pier columns

MOOREBANK Ave Interchange –A Tribute to the Versatility of Precast Concrete in Fast Track Infrastructure Construction

PRESIDENT’SMessage

(SCI), an elegant solution evolved which allowed all ofthe bridge structure above pile cap level to be entirelyprecast (with the single exception of the insitu deckpavement), thus providing the option for stagedconstruction of the overpass without impeding trafficflow. This solution for the two-span bridge comprised thefollowing principal precast concrete elements:

550 mm square Abutment Columns

Abutment Headstocks with integrated backwall

Y-shaped Pier Columns

W-shaped Pier Headstocks and

Type 2 Open-Top Super-T’s

In using precast, the two span portal structure wasdesigned with fixity at the base of the abutment and piercolumns so as to be totally freestanding and withoutreliance on the adjacent civil works. This independence ofstructure allowed significant construction planningfreedom, particularly in respect of efficient use ofresources.

This independent fully precast structure solution alsoovercame many of the safety and resourcing aspects sooften inherent in construction adjacent to, within and overa very busy operating motorway.

Through the efficiency of off-site precasting, the bridgesubstructure was erected in just days using night-timepossession periods when traffic flows were low. Thisallowed other concurrent work activities involvingreinforced earth walls and earth embankmentconstruction to proceed with minimal interface orinterference to the bridgeworks construction.

To achieve fixity at the bottom of the abutment columns,four 80mm dia vertical ducts were cast into their bases.These ducts mated with accurately located reinforcingbars projecting from the pile caps and on erection were

grouted with high strength grout. The precast abutmentswere similarly fixed to these columns through ducts inthe abutment elements mating with bars projecting fromthe column heads.

Due to the restriction of space within the column baseand the congestion of reinforcement, fixity of the Y-columns with the pile caps was achieved usingproprietary cast steel grout sleeves. The beneficial featureof these devices is their relative shortness in lengthcompared with a grouted duct requiring full bar bondlength to provide the same anchorage force.

Immediately after erection, the abutment and pierheadstock segments were structurally joined to providecontinuously reinforced headstocks over the full width ofthe bridge. These connections were achieved throughlarge complex bar joining recesses in the internal ends ofeach precast segment and the use of specialisedmechanical reinforcing bar couplers. Once the couplerconnections were in place, the recesses were filled withconcrete with the same strength characteristics as theprecast elements.

The abutment headstocks are of reinforced concrete andsit on the closely spaces abutment columns. The pierheadstocks are of prestressed concrete and span ascantilevers some 5 m between tops of each Y arm.

Because the abutment columns sit behind an architecturalfeature precast, reinforced earth wall they are not visible inthe completed bridge structure. On the other hand, the Y-columns and pier headstocks are highly visible toapproaching and passing traffic. For this reason, greatattention to detail has been employed to ensure that theresultant pier structure presents as form expressingfunction in a most aesthetic way.

Minimum section size, tapered edges and fluted faceshave been incorporated with a very high class finish intothe Y-columns with striking effect. Together with theirtapered W-shaped headstocks, the Y-columns present asuperb structural image, particularly at night where

judicious floodlighting has been used to great effect.

The overall visual effect is further enhanced by the vaultedsoffit provided by the Super T superstructure establishingthis interchange overall as a fine piece of highwayarchitecture.

Several factors combined to make this project anoutstanding success. The first factor is the earlyrecognition of the benefit of consulting with the specialistprecaster at concept stage to establish achievable limits.The second was that the client selected carefully thosecontractors which they considered should be on theirtender list. The successful contractor then brought onboard their specialist precast concrete supplier so thattogether, with the designers, the fine detail and buildabilityissues of the project design could be properly resolved.This attention to detail plus the achievement of the finetolerances necessarily achieved in the manufacture of thecomponents ensured that the whole bridge was assembledfaultlessly in just days.

The interchange has received wide acclaim for itsaesthetics, the minimal disruption to motorway activitiesand the fact that construction took only 9 months. TheMoorebank Interchange represents a genuine successstory which champions the benefits of precast concrete ininfrastructure.

PrecastC O N C R E T E H A N D B O O K

tel: 1300 65 46 46 fax: 1300 65 49 49email: [email protected] post: Customer Service Centre

Reply Paid 5420 SYDNEY NSW 2001

NATIONAL PRECASTER NUMBER 32 • OCTOBER 2003

Erection of abutment headstocks.

Precast substructure - ready for girders

To find our more about the design of the precast elements featured in the Moorebank Project, refer toSection 2 of the award-winning “Precast Concrete Handbook”.

The completed interchange.

CIA Z48—2002 Precast ConcreteHandbook can be purchased fromSTANDARDS AUSTRALIA's Customer Service Centre:

www.standards.com.au

Dr Harkness has joined National PRECASTER as anoccasional author of technical articles. An architect andengineer, he has 20 years experience as an energyconsultant and presently lectures at UNSW and theUniversity of Sydney. His books were published in theUK and Russia. Experience includes practice in Australia,South East Asia and the Middle East.

In 2002 he completed a three-month study in the FarEast, Europe, UK and USA meeting with key players inthe international trading of carbon credits. He hasformulated a proposal for the abatement of greenhousegas emissions by shading buildings.

Introduction

This article is a conceptual assertion that shadingexisting buildings would be an effective approach toachieving significant greenhouse gas abatement. Spacelimitations have led to a decision to mention onlybuildings in Sydney and the development of shading inthe work of only one architect: Harry Seidler. Moredetailed quantification of greenhouse gas abatementachievable from shading will be presented in asubsequent article in National PRECASTER.

1. Imminent action

The time has come to desensitise the facades of existingbuildings that have thermally sensitive facades and toensure that future buildings are built with facades of lowsensitivity. See Fig.1.

Currently, international legislation is being directedtowards minimising greenhouse gas emissions that aresaid to cause climate change.

This in turn is said to raise the level of the seas. [1], [2]Holland, that lowest of low-lying countries, much of whichis below sea level, is at the forefront of encouraging co-inhabitants of this planet to take action to minimise therate at which waters in the world's oceans may rise. [3]

The Commonwealth Government of Australia has initiatedRound 3 of its Greenhouse Gas Abatement Program withproposals submitted on the 21st August 2003.

Although not a signatory to the Kyoto Protocol, Australiaappears to be intent on meeting the expectations of thatProtocol. [4]

The NSW Government has initiated a system of saleablecredits for reducing greenhouse gas emissions. This isthe NSW Greenhouse Gas Abatement Scheme, whichissues NSW Greenhouse Abatement Certificates(NGACs). Electricity Retailers are involved in purchasingand surrendering NSW Greenhouse AbatementCertificates (NGACs) to the Scheme Administrator. Thisprocess encourages retailers to reduce their averageemissions to the approved Greenhouse Benchmark Level.Users can reduce the impact by undertaking energyefficiency projects that produce NGACs (for the user) andthen sell them back to the Retailer. [5]

On international, national and state government levelsthere are currently actions aimed at reducing greenhousegas emissions.

2. Emission factors

The Australian Greenhouse Office (AGO) providesemission factors for electricity usage in all States(conversion equivalent of tonnes CO2 per MWh). [6] SeeTable 1.TABLE 1

Greenhouse Gas Emission Equivalents in the States and Territories of Australia

VIC: 1.444kg CO2 per kWh

SA: 1.197kg CO2 per kWh

WA: 1.114kg CO2 per kWh

QLD: 1.079kg CO2 per kWh

ACT: 1.012kg CO2 per kWh

NSW: 1.012kg CO2 per kWh

NT: 0.654kg CO2 per kWh

TAS: 0.002kg CO2 per kWh

Reduction in electricity consumption would achieve moregreenhouse gas abatement in Victoria than in NSW. Verylittle abatement would accrue from reducing electricityconsumption in Tasmania. Abatement in the NorthernTerritory would be only about 65% of that in NSW.


DESENSITISATION of the building facadeBy Dr Edward L Harkness FRAIA FIEAust CPEng

Figure 1. Sydney building facades have various thermal sensitivities. The least sensitive have concrete or GRC facades with shaded windows. Some of the moresensitive unshaded fully glazed facades have low energy star ratings and could become unleasable if a minimum energy rating of 3 stars were required by prospectivetenants. Photographs by E. L. Harkness

3. Some benefits ofshading

Described in Rewards for Shading [7] are ways inwhich the cooling loads on chillers may bereduced. These include, in descending order ofeffectiveness: (a) reducing the area of glass (b)shading that reduced area of glass and (c) double-glazing.

Whereas so-called "high performance glass" wasused on new buildings in the closing decades of the20th Century, it is now known that shading whichglass would achieve further greenhouse gasabatement. A significant glass tower of that period is50 Bridge Street, Sydney, which is the black glasstower second from the left in Fig.1 and in Fig.2.

This building is the poorest performing buildingin energy terms in the AMP Henderson GlobalInvestors' portfolio. It has a voluntary self-ratedSEDA rating of 1.5 stars.

Shading the glass on the northern and westernfacades of 50 Bridge Street would reduce coolingloads on chillers in one hour commencing at 3 pmEastern Summer Time in February by approximately1 megawatt.

Applying a coefficient of performance of 4 forchillers, this equates to reducing greenhouse gasabatement by about 0.25 tonnes equivalent of CO2in one hour.

In the facade of the Renaissance Hotel, Sydney,windows occupy less than 50% of the length of thefacade, admitting less that 50% of instantaneousradiation compared to a facade in which windowsoccupy the full length of the facade. See Fig. 3.

Grosvenor Place has shaded windows in a GRCfacade making it less sensitive than 50 Bridge Stand the Renaissance Hotel. See Fig. 4.

5. CommonwealthGreenhouse GasAbatement Program

A proposal for which the author of this paper is aconsultant, is a bid for a grant under theCommonwealth Greenhouse Gas AbatementProgram Round 3 to shade sufficient windows inbuildings throughout Australia to achieve anabatement of 250,000 tonnes equivalent of CO2.

There will be other proposals. The receivers ofgrants will be those who can demonstrate costeffective achievement of abatement and a high levelof expectation of achieving greenhouse gasabatement.

There is absolute certainty in any air-conditionedbuilding that greenhouse gas abatement would beachieved by shading any type of glass whether itbe clear or the best of so-called "highperformance glass."

6. Thermally sensitivebuilding facades unlikely to be shaded

The heritage-listed first of the AMP buildings atCircular Quay is the concave curved facadebuilding second from the left on the waterfront inFig. 1. In a post occupancy evaluation of thatbuilding carried out by the author of this paper in1963 some of its occupants considered it to bethermally uncomfortable. They were instructed bythe building managers to keep internal venetianblinds set at a standard angle in the expectationthat would eliminate thermal discomfort from solarradiation. It didn't. Internal blinds cannot be aseffective as external shades.

Also heritage-listed, Seidler's cylindrical AustraliaSquare Tower is unlikely to have its shadingincreased. The radial projecting columns provideonly partial shading.


Fig. 2. 50 Bridge Street, Sydney: a highlysensitive facade.

Fig 3. Rennaissance Hotel, Sydney: a sensitivefacade.

Fig. 5. Precast wall with shaded windows: lowsensitivity.

Fig. 6. Cast-in fixings for on-site attachment oflight -weight shades.

Fig 4. Grosvenor Place, Sydney: a facade of lowsensitivity.


7. Thermally less sensitivefacades

The MLC octagonal planned building, also bySeidler, which is in front of Centre Point Tower inFig. 1, has windows set deeply back from thefacade. Seidler used shades on his GrosvenorPlace, which is the tallest convex curved buildingthird from the right in Fig.1. See also Fig. 4.

8. Lightweight shades onprecast walls

Fig. 5 shows lightweight shades fitted to precastconcrete wall panels. Fixings can be cast into theprecast wall panels in preparation for on siteplacement of lightweight shades. Fig.6 shows howfixings can be accurately located prior to casting inthe factory. Concrete can also be self-shading withcast-in shading forms.

9. Glass box buildings willbe shaded

So-called "high performance glass" does admit,instantaneously, radiation from the sun.

It is now known in the 21st Century, thatgreenhouse gas abatement has a higher prioritythan building owners' preparedness to pay forenergy use. That higher priority is a responsibilityto the international community to reduce the rate ofclimate change.

Glass box buildings will be retrofitted with shading.

10. Forms of shade

Shades on the IBM Building, Darling Harbour,Sydney appear as large-scale forms withchanging shadow patterns throughout the day.See Fig. 7.

Horizon Apartments, by Seidler, show the use ofconcrete to self-shade the building. The facade hasinteresting forms. See Fig. 8.

The geometry of shade has evoked a newawareness among architects and engineers becauseof its benefits in reducing the size of air-conditioning plant and its creative potential.

11. Existing buildings

Given that at 3pm Eastern Summer time, the directcomponent of solar radiation is 600 watts/sqm andthe diffuse radiation is 144 watts/sqm, a window ofarea 2000mm high x 4000mm wide of heatabsorbent glass of 50% transmittance would admitinstantaneously, about 3000 watts.

This quantity of heat gain could be reduced byapproximately half by fitting insulated panels to halfof the window area. These panels could be fittedvertically to occupy half of the horizontal length ofthe window. Alternatively, half of the height of thefull width of the window could be covered withinsulated panels so as to leave unobstructed viewshorizontally.

Both configurations would reduce the instantaneousheat gain to 1500 watts. Leaving the entire glazedarea and simply shading it would reduce the heatgain to 345 watts. That is, an 88% reduction.

12. New Buildings

Opportunities are available in the design of newbuildings to minimise the consumption of electricalenergy by shading glass; and optimising the designof air-conditioning equipment to peak cooling loadsthat would be significantly less than if the glasswere not shaded. Shading the glass would extendthe hours during which up to 100% outside air maybe sufficient for cooling and therefore reduce thehours of operation of chillers and extend the life ofthose chillers.

13. Summaryrecommendations

Existing buildings with highly sensitive facadesshould have the first priority for being fitted withshades to abate greenhouse gas emissions.

GRC is ideal for retrofitting shading.

Existing buildings with less sensitive facadesshould have the second priority for being fitted withshades to abate greenhouse gas emissions.

Existing buildings that are exemplars of design atthe time they were designed, should be exemptedfrom this proposed program.

In new buildings precast concrete wall systems canincorporate forms for shading.

Research and development should be undertaken toproduce shading systems at low cost and with lowembodied energy.

Building owners and users should be educatedregarding the environmental and financial benefitsthat could result from well-designed shading.

Architects and consultants may be engaged todesign shading to enhance the appearance ofbuildings.

Acknowledgements

Appreciation is expressed to Frank Lowe, Editor of TAS &Archizine and President of the Francis Greenway Society;Bruce Forwood of the University of Sydney and Steve Kingof UNSW for reading this paper and making suggestions.

References

[1] The Marrakesh Accord.http://envfor.nic.in/news/octdec01/accord.html

[2] Kasting J. F., The carbon cycle, climate, and the longterm effects of fossil fuel burning.http://www.gerio.org/CONSEQUENCES/vol4no1/carbcycle.html

[3] Rose H., Changing the market for emissions trading.http://www.weathervane.rff.org/features/feature045.htm

[4] Greenhouse Gas Abatement Program Guidelines May2003, http://www.greenhouse.gov.au/ggap/

[5] http://www.greenhousegas.nsw.gov.au/scheme_overview.htm

[6] AGO Factors and Methods Workbook:http://www.greenhouse.gov.au/challenge/tools/workbook/index.html (Greenhouse emissions factors for fuels)

[7] Harkness E. L., Rewards for Shading. ArchitectureBulletin. July, 2003.

Photographs by Dr E L Harkness

The next issue of National Precaster will featured the secondarticle in Dr Harkness’s series entitled “Effect on Chiller Sizeof Various Proportions of Precast, Glazing and Shading”.

Fig 7. Shades on IBM Building

Fig 8. Horizon Apartments.

It has not been too fashionable within the constructionindustry to look for building techniques that minimisethe use of raw materials and energy. Concepts suchas sustainable development, intergenerational equityand the precautionary principal have had scantexposure. Instead, the construction industry has beenfocussed pretty exclusively on making money.Adversarial contracts too often dictate that the onlyimportant criteria is finishing on schedule and to hellwith the collateral damage to the quality of the buildingor to the future environment.

In far too many cases the initial cost of a building isthe governing factor. When the developer intends tosell a building immediately after construction profit ismaximised by maximising floor area and minimisingthe cost of construction. The result is too often abuilding which is expensive to maintain and to heatand cool and which will be difficult to demolish.

Making money will continue to be the prime driverfor business but the legal and regulatory environmentwill change to reflect changing community concernsand sustainability imperatives.

Change can come about in several ways. Increases inthe cost of fuel of all types will automatically lead thecost minimisers to design so as to reduce usage.More discriminating purchasers and tenants ofbuildings will demand better standards of sunshading and energy use and laws enacted bygovernment will force change upon the industry.When it becomes necessary to change in order tomaximise profits, then change will occur.

In recent years we have been given no choice aboutinstalling better QA and OH&S systems and there ison doubt that compliance with the AS/NZS ISO 14000International environmental standards will follow.

The Australian precast concrete industry is in a uniqueposition to assist the construction industry in thereduction in waste, the best use of resources, thereduction of the release of pollutants into theenvironment and in the provision of products whichminimise their environmental impact in production, useand disposal. One of the world’s largest precasters,Addtek whose headquarters are in Finland points outthat in Europe, with the use of precast concrete incomparison with in-situ construction, one can obtain:

Reduced use of materials of up to 45%

Reduced use of energy of up to 30%

Reduced waste at demolition of up to 40%”

There is no reason to doubt that similar figures couldbe achieved in Australia.

Precast concrete has many natural environmentaladvantages, some of them are:

Production in factories with controlled emissionsand recycling of waste water and solids

Optimum use of resources possible with plannedfactory manufacture

Shorter on site construction time, no dust or noiseon site, no on site waste

Excellent acoustic, fire resistance and thermalproperties

Durability derived from production under factoryconditions

Ease of design for simple demolition at the end of astructure’s life

The National Precaster will bring more news on thissubject as it becomes available.

National Precast ConcreteAssociation Australia

Asurco Contracting ■ [08] 8240 0999

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Constress ■ [08] 8262 2321

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Georgiou Group Precast ■ [08] 92099200

Girotto Precast ■ [03] 9794 5185 or [02] 96085100

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Icon Industries ■ [02] 9612 5800

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Baseline Constructions ■ [02] 9080 2222

Blue Circle Southern Cement ■ [02] 9033 4000

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Cathay Pigments Australasia ■ [02] 8788 9088

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Hallweld Bennett ■ [08] 8437 0800

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N P C A A

CORPORATE MEMBERS

ASSOCIATE MEMBERS

OVERSEAS MEMBERS

The information provided in this publication is of a general natureand should not be regarded as specific advice. Readers are cautionedto seek appropriate professional advice pertinent to the specificnature of their interest.

Published by National Precast Concrete Association Australia8–10 Palmer Street North Parramatta NSW 2151 Australia

Tel [02] 9890 8853

FOR FURTHER INFORMATIONabout the New Zealand precast industryincluding Member details, list of pub-lications, visit Precast NZ Inc at:

PRECASTN E W Z E A L A N D I N C .

www.precastnz.org.nz

TOWARDS MORE efficiency& sustainability in construction

Hollowcore planks deliver strength and fire rating with up to 45% less material plus savings instructure dead load and transport costs.

Measured Effects of Shading a North-facing Wall with External Horizontal Slats of Different Reflectances at Latitude 33’53”South

Flavio GerboliniMr University of Sydney Australia [email protected]

Edward HarknessDr University of Sydney Australia tedharkness@ edwardleoharkness.com

Keywords: Shading walls, direct solar radiation, effectiveness of reflectances of shades.

Abstract

The shading of walls relates to the sustainability of building materials in the context that shading has been shown to reduce the temperature of the face of a wall during the day and reduce heat loss at night. As such this may be equated to a quantity of thermal insulating material being either low emissive (e.g. reflective foil insulation) or bulk thermal insulating material. Most thermal insulating materials have a high embodied energy. Thus, achieving the effect of thermal insulation by using, for example, a low embodied energy shading system may be seen to be sustainable because the quantity of high embodied energy thermal insulating material may be reduced.

Three separate experiments were carried out. All experiments were performed with the same configuration, consisting of two identical reinforced concrete panels 500mm high x 500mm wide x 50mm thick. These panels were physically linked to a table using thin metal fixtures, so as to minimize thermal conduction.

Both test panels were installed inside a protective wooden box custom-built; in order to protect the edges and back surfaces of the panels from rain, wind and solar radiation. Both concrete panels were arrayed in the vertical plane exposed to solar radiation on the front face and shaded on the back. The orientation of the front surfaces was north at latitude 33’53”South and longitude 151°11”East. The back surfaces of both panels were exposed to outdoor air temperature. Horizontal slats were positioned to shade one of the test panels. The other test panel remained unshaded for all experiments. The horizontal slats were in turn painted white, grey and black.

The test panels were fitted with 7 thermocouples each: two on the front surface, four on the back surface and one suspended in the shaded box behind each panel but not in contact with the test panel or the box. Each of the two groups of 7 thermocouples was connected to a 7-channel data logger that recorded temperatures every 10 minutes for 144hrs.

Data collected from the three experiments showed that during daytime darker coloured slats were more effective in preventing the shaded panel from gaining heat than lighter coloured slats.

Regardless of colour, the ability of the slats to reduce heat gain on the shaded panel during cloudy days was dramatically reduced. On cloudy days the temperature difference between the shaded and unshaded panels was less than 1°C at any time.

Paper presented at the SB13 Oulu Conference, May 21-25 2013 in Oulu, Finland.

Attachment 3.2.3b.i

On the four hottest days, temperature differences (∆t) between the front surfaces of the shaded and unshaded panels during a 24hr period of clear skies, reached an average peak difference of 11°C on the front surface and 8°C on the back surface using black slats.

When using Grey slats the ∆t between the front surfaces of the shaded and unshaded panels was 10°C; and between the back surfaces the ∆t was 7.5°C.

When using White slats the ∆t between the front surfaces of the shaded and unshaded panels was 9°C; and between the back surfaces the ∆t was 6°C.

During nighttime the shaded panel remained slightly warmer than the unshaded panel for all experiments. The ∆t between the wall and the slats, being less than between the wall and the heat sink of the sky at night, would result in less long wave radiation being emitted from the wall protected by the slats. The shading slats may have reduced wind speed on the panel’s front surface, reducing the amount of heat lost through convection.

The presence of slats on the exterior face of a wall reduces the external surface temperature of the wall during the daytime as a function of the reflectance of horizontal shading slats; and reduces the rate of loss of heat at night.

White horizontal slats were less effective than grey and black slats because the white slats reflected more shortwave radiation onto the surface of the wall. The presence of the slats reduced the area of wall that could emit long wave radiation directly to the heat sink of the night sky.

This makes a case for using dark coloured low mass shading systems for shading walls, particularly in hot climates with clear skies.

Slats are much less effective on cloudy days, when a larger percentage of the total solar irradiance is indirect. Slats enable the wall to be significantly cooler on sunny days by blocking direct radiation more effectively rather than diffused solar radiation.

Measured Effects of Shading a North-facing Wall with External Horizontal Slats of different reflectances at Latitude 33’53”South

Flavio GerboliniMr University of Sydney Australia [email protected]

Edward HarknessDr University of Sydney Australia tedharkness@ edwardleoharkness.com

Keywords: Shading walls, direct solar radiation, effectiveness of reflectances of shades.

1. Introduction

The shading of walls relates to the sustainability of building materials in the context that shading has been shown to reduce the temperature of the face of a wall during the day and reduce heat loss at night. As such this may be equated to a quantity of thermal insulating material being either low emissive (e.g. reflective foil insulation) or bulk thermal insulating material. Most thermal insulating materials have a high embodied energy. Thus, achieving the effect of thermal insulation by using, for example, a low embodied energy shading system may be seen to be sustainable because the quantity of high embodied energy thermal insulating material may be reduced.

Interest in shading walls as an energy conserving measure is shown in the literature. Cook [1] states: “In modern construction the various means of heat avoidance are by far the most economical energy conservation methods in spite of the availability of many technical or mechanical solutions”. Papadakis et al [2] found shading from plants to be efficient for solar control by comparing surface temperatures of a shaded and an unshaded wall. Sandifer [3] took readings from walls shaded with vines in an effort to quantify the amount of heat gain avoided by different thicknesses and varieties of vines, in comparison to an unshaded wall. Okba [4] presented a checklist for building envelope design options that included shading walls. Abou-El-Fadl [5] combined the effects of shading and night ventilation to reduce summer thermal load. Parker [6], Heisler [7] and others published on the benefits of shading walls to reduce heat gain.

Throughout history architects have used vegetation, external colonnades and roof overhangs to shade walls in an effort to avoid excessive heat gain. Although most papers mentioned in the preparation for the present research involve the use of trees, for taller buildings it would be difficult to shade with any kind of vegetation. Also, buildings located in arid regions where vegetation does not thrive would benefit from passive shading devices. There is a case to investigate more thoroughly the performance of external shading devices for walls for which plants are not suitable.

The series of experiments presented in this paper report on the effect of shading a north-facing wall in a southern hemisphere location with horizontal slats of different reflectances compared to an unshaded wall. Data recorded at 10 minute intervals were analysed to indicate which reflectances were more effective in shading the wall panels.

Experiments 1.1 Test panel array The experiments were carried out at latitude 33°53’South and longitude 151°11”East, on the roof of the Wilkinson Building at the University of Sydney, in an effort to avoid external objects casting shadows on the panels. The sun’s altitude at noon in this latitude is 81° at the summer solstice (December 21st); 57° at both of the equinox days (March 21st and September 22nd); and 33° at the winter solstice (June 21st). Three separate experiments were made. All were performed with the same setup, consisting of two identical reinforced concrete panels 500mm high x 500mm wide x 50mm thick. These panels were physically linked to a table using thin metal fixtures, so as to minimize thermal conduction with the table. Both panels were installed inside a protective wooden box custom-built for the purpose of the experiments, in order to protect the edges and back surfaces of the panels from direct and diffuse solar radiation, as well as rain and wind (Fig. 1). The front surfaces of both panels were placed vertically facing the northern sun.

Fig. 1 Diagram of the test panel array

Each of the two panels was fitted with 7 thermocouples: two on the front surface, four on the back surface and one suspended in the shaded box behind each panel but not in contact with the test panel or the box (Fig. 2). Each of the two groups of 7 thermocouples was connected to a 7-channel high resolution data logger that recorded temperatures every 10min for 144hrs. Calibration, setup, and data recording were done according to the manufacturer’s specifications.

2.2 Data Logger Calibration

Both 7 channel data loggers were identical: Smart Reader Plus 6 by ACR Systems Inc., with a 128kB memory. The thermocouple cables used were Type J (Range: -50°C – 600°C, Resolution: 0.3°C). The calibration was done by fixing equal lengths of cable to each of the channels and submerging the ends of the coupled cables in icy water with a known temperature. The loggers were then connected to a computer using TrendReader (software bundled with the data loggers). All channels were re-calibrated in real time using the low reference temperature while the ends of the cables were still submerged. Once calibrated, the thermocouple cables were fixed to the panels (Fig. 2) and the calibrated loggers were reset. An initial test was performed on both panels unshaded, in order to verify their physical similarity by confirming that their respective back and front surface temperatures were similar: results were satisfactory with mean deviations of no more than 0.3°C indicating that the loggers were adequately calibrated and that all 14 coupled wires were firmly connected.

1.3 Thermocouple fixing method

Ø1.5mm x 8mm perpendicular holes were drilled into the panels at the locations shown in Figure 2. The coupled wires, of an approximate diameter of 1.6mm, were cut 5mm long and fitted inside the holes. Silicon was then applied around the hole to prevent the coupled wires from sliding out and to protect them from wind and humidity (Fig. 3).

Fig. 2 Thermocouple locations Fig. 3 Thermocouple fixing method

2.4 Experiment #1 – White Slats

In the first experiment, an external shading device with horizontal slats painted white (approximately 70% reflectance) was installed in front of one of the concrete panels. The shading device was fixed to the wooden box to eliminate physical connection to the panel, avoiding thermal conductance. The loggers were set to record temperatures every 10min for a period of 144hrs of predominantly clear skies. The dates recorded were Feb26/2009 through Mar02/2009. The sun’s average altitude at noon during these dates was approximately 68°.

2.5 Experiment #2 – Grey slats

In the second experiment, the external shading device was painted medium gray (approximately 50% reflectance) and temperatures were recorded every 10min for a period of 144hrs of predominantly clear skies. The dates recorded were Mar02/2009 through Mar08/2009. The sun’s average altitude at noon during these dates was approximately 62°.

2.6 Experiment #3 – Black slats

In the third experiment, the external shading device was painted black (approximately less than 5% reflectance) and temperatures were recorded every 10min for a period of 144hrs of predominantly clear skies. The dates recorded were Mar24/2009 through Mar30/2009. The sun’s average altitude at noon during these dates was approximately 55°. 2. Results 3.1 Front Surface Readings

Figures 4, 5 and 6 show the temperature difference (∆t) between the front surface of the unshaded panel and the front surface of the shaded panel. Table 1 summarizes the results.

Table 1 Front surface temperature differences (∆t) between the shaded and the unshaded panels

Experiment

Panel

24h average

temp. (°C)

24h average ∆t

(°C)

Daytime ∆t At the highest point

in the graph

Nighttime ∆t At the lowest point

in the graph (°C) Date (°C) Date

#1: White slats

Shaded 24.6 1.2 (shaded is

cooler)

9.0 (shaded is cooler)

02Mar 13:20

-0.9 (shaded is warmer)

27Feb 05:20 Non

shaded 25.8

#2: Grey slats


cooler)


05Mar 13:40


05Mar 05:40 Non

shaded 25.5

#3: Black slats


cooler)


28Mar 13:30


28Mar 01:20 Non

shaded 26.6

3.1.1 Maximum daytime temperature differences between front surfaces:

On March 2nd at 1:20PM the white slats produced a temperature on the shaded panel that was 8.8°C cooler than the unshaded panel. On March 5th at 1:40PM the grey slats produced a temperature on the shaded panel that was 10.0°C cooler than the unshaded panel. On March 28th at 1:30PM the black slats produced a temperature on the shaded panel that was 11.1°C cooler than the unshaded panel.

3.1.2 Maximum nighttime temperature differences between front surfaces:

On February 27th at 5:20AM the white slats produced a temperature on the shaded panel that was 0.9°C warmer than the unshaded panel. On March 5th at 5:40AM the grey slats produced a temperature on the shaded panel that was 1.2°C warmer than the unshaded panel. On March 28th at 1:20AM the black slats produced a temperature on the shaded panel that was 0.8°C warmer than the unshaded panel.

3.1.3 Average temperature difference over a 24hr period between front surfaces:

Over a 24hr period (daytime and nighttime readings combined), the front surface of the panel shaded with white slats was on average 1.2°C cooler than the unshaded one; with grey slats 1.5°C cooler than the unshaded one; and with black slats 2.0°C cooler than the unshaded one.

Fig. 4 White slats: Front surface ∆t between the shaded and the unshaded panels

Fig. 5 Grey slats: Front surface ∆t between the shaded and the unshaded panels

Fig. 6 Black slats: Front surface ∆t between the shaded and the unshaded panels

3.2 Back Surface Readings

Figures 7, 8 and 9 show the temperature difference (∆t) between the back surface of the unshaded panel and the back surface of the shaded panel. Table 2 summarizes the results.

Table 2 Back surface temperatures differences (∆t) between the shaded and the unshaded panels

Experiment

Panel

24h average

temp. (°C)

24h average ∆t

(°C)

Daytime ∆t At the highest point

in the graph

Nighttime ∆t At the lowest point in

the graph (°C) Date (°C) Date

#1: White slats

Shaded 24.2 0.8 (shaded is cooler)


28Feb 14:10


27Feb 05:00 Non

shaded 25.0

#2: Grey slats



07Mar 13:10


05Mar 06:50 Non

shaded 24.8

#3: Black slats



28Mar 13:20


28Mar 02:00 Non

shaded 25.8

3.2.1 Maximum daytime temperature differences between back surfaces:

On February 28th at 2:10PM the white slats produced a temperature on the shaded panel that was 6.1°C cooler than the unshaded panel. On March 7th at 1:10PM the grey slats produced a temperature on the shaded panel that was 7.5°C cooler than the unshaded panel. On March 28th at 1:20PM the black slats produced a temperature on the shaded panel that was 8.2°C cooler than the unshaded panel.

3.2.2 Maximum nighttime temperature differences between back surfaces:

On February 27th at 5:00AM the white slats produced a temperature on the shaded panel that was 1.0°C warmer than the unshaded panel. On March 5th at 6:50AM the grey slats produced a temperature on the shaded panel that was 1.1°C warmer than the unshaded panel. On February 28th at 2:00AM the black slats produced a temperature on the shaded panel that was 0.8°C warmer than the unshaded panel.

3.2.3 Average temperature difference over a 24hr period between back surfaces:

Over a 24h period (daytime and nighttime readings combined), the back surface of the panel shaded with white slats was on average 0.8°C cooler than the unshaded one; with grey slats 1.1°C cooler than the unshaded one; and with black slats 1.5°C cooler than the unshaded one.

Fig. 7 White slats: Back surface ∆t between the shaded and the unshaded panels

Fig. 8 Grey slats: Back surface ∆t between the shaded and the unshaded panels

Fig. 9 Black slats: Back surface ∆t between the shaded and the unshaded panels

3.3 Performance on overcast/cloudy days

Solar irradiance on a completely overcast day would be up to 100% diffuse. Other days may have various proportions of direct and diffuse solar radiation due to passing clouds. This affects the slats’ ability to reduce the surface temperature of the panels.

On March 4th the skies were mostly overcast, except for short periods of clear skies in the morning and afternoon. The temperature difference (∆t) between the shaded and unshaded panels reached a daytime maximum of just 1.0°C on the front surface with grey slats, compared with an average of 10.0°C on a sunny day. On the back surface the ∆t between the shaded and unshaded panels reached only 0.8°C.

On March 27th (Fig. 10) passing clouds resulted in an intermittent exposure of the shaded and unshaded panels to direct solar radiation throughout the day. The daytime maximum difference on this day was 5.5°C, compared to 11.1°C on a sunny day.

Conversely, on both dates the nighttime maximum temperature difference did not vary significantly, although the shaded panel still remained slightly warmer than the unshaded panel.

Fig. 10 Front surface ∆t on a day with partial direct solar radiation

3. Discussion of results

Data collected from the three experiments showed that during the daytime, darker coloured slats were more effective in preventing the shaded panel from gaining heat than lighter coloured slats. Regardless of the colour, the ability of the slats to prevent heat gain on the shaded panel during cloudy days was dramatically reduced. On cloudy days the ∆t between the shaded and unshaded panels was less than 1°C at any time, which indicates the significance of shading against the direct component of solar radiation under clear sky conditions.

Figure 11 shows the ∆t between the front surface of the shaded and unshaded panels over a 24hr period of clear skies. To produce this graph, data from the four hottest clear days was averaged. By avoiding most of the direct solar radiation with the horizontal slats, the ∆t reached an average peak of 10°C on the front surface and almost 8°C on the back surface using black slats.

Fig. 11 Front surface ∆t between shaded and unshaded panels over 24hrs of clear skies.

(This graph averages of the four hottest clear days and compares results of all three experiments: white, grey and black slats)

It was also found that during nighttime the shaded panel remained slightly warmer than the unshaded panel. The temperature difference between the wall and the slats, being less than between the wall and the heat sink of the sky at night, would result in less long wave radiation being emitted from the wall protected by the slats. This may have also reduced wind speed on the panel’s front surface, reducing the amount of heat lost by convection.

The ∆t between the back surfaces of the shaded and unshaded panels was less than the ∆t of the front surfaces; the reason being that the thermal mass of the panels caused the temperature curve of the back surface ∆t to flatten slightly in comparison to the front surface ∆t. Temperature differences were calculated in both cases, as shown in Tables 1 and 2.

4. Conclusions

Shading a wall reduces the external surface temperature of the wall as a function of the reflectance of horizontal shading slats. Shading systems also reduce the rate of loss of heat at night.

White horizontal slats were less effective than grey and black slats because the white slats reflected more shortwave radiation onto the surface of the wall. The presence of the slats reduced the panel’s area that could emit long wave radiation directly to the heat sink of the night sky.

Black slats resulted in a front surface temperature reduction of up to 11°C, while grey slats achieved 10°C and white slats achieved 9°C, compared to an unshaded wall.

This makes a case for using dark coloured low mass shading systems for shading walls, particularly in hot climates with clear skies.

Slats are much less effective on days with clouds. During cloudy days a larger percentage of the total solar irradiance is indirect, being up to 100% on days with overcast skies. During cloudy and overcast days the outside temperature of the wall is lower due to lack of direct radiation.

By being much more effective at blocking direct rather than diffuse solar radiation, slats enable the wall to be significantly cooler on sunny days. Slats can be designed to provide more shade in summer than in winter by modifying the geometry of the shading device (e.g. slats could be designed to allow some direct solar radiation during winter, when the sun’s altitude is considerably lower).

5. Further investigations and experiments

The ability of darker coloured slats to maintain lower temperatures on the exterior surfaces of walls than lighter coloured slats is not yet well understood. Further experiments may produce more precise results, in which thermocouples could include surface temperature readings of the different coloured slats themselves, both on their upper and lower surfaces. This would shed some light on how solar energy is being reflected, transmitted and emitted by slats with different reflectances. Installation of additional monitoring equipment could include:

Installation of thermocouples in several parts of the different coloured slats, in particular the upper and lower surfaces. This which would help explain where and how the energy is being dissipated in each different coloured set of slats.

Wind velocity measurements with anemometers near the surface of the test panels would also help explain how wind influences the overall results.

Include data from nearby meteorological stations (e.g. temperature, relative humidity, wind velocity). This would provide useful information necessary to draw conclusions about how external factors influence on the overall results.

Measurement of global and direct radiation intensity would provide information about how changes in solar irradiation affect the results, as well as providing reliable information about sunny, cloudy and overcast days.

Further work could include developing slat designs for other orientations and latitudes, as well as the development of commercial products that could be retrofitted on existing buildings that suffer from excessive solar gain on windowed or windowless walls exposed to the direct component of solar radiation. Reflectance selection for any shading system could significantly affect cooling loads in buildings.

7. References

[1] COOK J., “Passive Cooling”, U.S.A., M.I.T. Press. 1989 Geoscience Australia: http://www.ga.gov.au/

[2] PAPADAKIS G., TSAMIS P., KYRITSIS S., “An experimental investigation of the effect of shading with plants for solar control of buildings”, Energy and Buildings, Volume 33, Issue 8, October 2001, pp 831-836

[3] SANDIFER S., GIVONI B., “Thermal effects of vines on wall temperatures – comparing laboratory and field collected data”, U.S.A, School of the Arts and Architecture, University of California. 2001

[4] OKBAR E.M., “Building envelope design as a passive cooling technique”, International Conference Passive and Low Energy Cooling for the Built Environment; May 2005, Santorini, Greece

[5] ABOU-EL-FADL S., “Cooling energy saving in residential buildings in UAE by shading and night ventilation”, UAEU Funded Research Publications, Vol. 25, 2006.

[6] PARKER J.H., “Landscaping to Reduce the Energy Used in Cooling Buildings”, Journal of Forestry, Volume 81, Number 2, 1 February 1983, pp. 82-105(24)

[7] HEISLER G.M., “Effects of Trees On Wind and Solar Radiation in Residential Neighborhoods”, Final Report On Site Design and Microclimate Research, Anl No. 058719, Argonne National Laboratory, Argonne, IL. 1989.

CV OF DR EDWARD LEO HARKNESS [email protected]

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QUALIFICATIONS Bachelor of Architecture, University of Sydney 1965 Master of Building Science, University of Sydney 1967 Doctor of Philosophy, University of Sydney 1985 Thesis title: Performer tuning of stage acoustics. Certificate IV Nathers Assessment Wodonga TAFE (Computer modelling of energy) 2017 Certificate IV Strata Management Crows Nest TAFE AFFILIATIONS Architect registered to practise in NSW No 2602 Current 2018 Previously registered to practise architecture in Victoria and Queensland Member of the Australian Building Sustainability Association No 20494 Current 2018 Member of the Australian Acoustical Society No 819 Current 2018 Previously a Fellow of the Royal Australian Institute of Architects Previously a Fellow of the Institution of Engineers Australia ACADEMIC POSITIONS HELD Associate Professor of Architectural Engineering, KFUPM Kingdom of Saudi Arabia 1992-96 Deputy Director the Australian Institute of Tropical Architecture, James Cook University 1996-97 Acting Head of Department to Architecture, University of Newcastle 1978 PART TIME UNIVERSITY TEACHING 1998 – One year contract teaching technical subjects to architectural students at UTS, Sydney. 1998. Leader of design studio electives at UNSW on the design of hospitals, airports and opera houses. Part time teaching Building Construction Technology in the Master of Building Science program at the University of Sydney. Part time teaching of technical subjects to architecture and interior architectural students at UNSW Part time teaching of technical subjects to architecture students at the University of Sydney. SUPERVISION OF THESES At KFUPM I supervised four Research Masters Students who all passed their theses defence. EXAMINER OF THESES I examined theses for the University of Sydney.


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MENTORING OF PHD CANDIDATES A mature music student at the University of Sydney Conservatorium of Music told me his thesis was failed by examiners. I read his thesis, made comments, he rewrote the thesis and I reread it. He subsequently resubmitted and it was passed. The thesis was on the melodies of Sergei Rachmaninov. A former architectural engineering student from Saudi Arabia asked me to go to the University of British Columbia, Canada to coach him in preparation for his thesis on Facilities Management. I rehearsed him in his presentation and he passed the defence. Rabee Reffat, a former student of mine in Saudi Arabia wished to study for a PhD under a friend of mine at the University. Arrangements were made. The thesis was on artificial intelligence which is not my field. Rabee showed me the manuscript of his thesis. It needed serious tidying up to convey his intentions. I worked through the draft with him. In due course the thesis was submitted and passed. One of the examiners remarked on how well it was written. EDITORIAL Presently an associate editor of the Architectural Science Review. Reviewed manuscripts submitted for publication for the past 30 years. BOOKS PUBLISHED Solar Radiation Control in Buildings, with Madan Mehta. Elsevier, London. English language edition 1978. Russian language edition 1984 (Moscow) Chapter 13 “Sun Shading Devices” in Solar Energy Applications in the Design of Buildings. Applied Science, Essex 1980. Energy Cost Effective Precast Facades, Precast Concrete Manufacturers of NSW 1986. Letters From Arabia, Minerva Press London 1998. Building Investment Sustainability: Design for Systems Replaceability, with M A Hassanain, Minerva Press, London 1998. Chapter 27 “Innovations in Building Systems” in Design and Construction: Building in Value editors Rick Best and Gerard De Valence. Butterworth & Heinemann 2002. PAPERS PRESENTED TO CONFERENCES Papers presented to the Acoustical Society of Japan and the Acoustical Society of America in Honolulu and at the Massachusetts Institute of Technology. Papers presented to conferences of the Architectural Science Association of Australia and New Zealand.


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PAPERS PUBLISHED IN REFEREED JOURNALS Papers and letters to the editor published in Acustica (Tri Lingual ; German, French and English), Journal of Sound and Vibration, Applied Acoustics and the Journal of Architectural Engineering (USA), the Architectural Science Review. TRADE LITERATURE Trade literature written for the Precast Concrete Manufacturers Association. EXPERT WITNESS IN COURTS Expert witness on Local Courts on noise nuisance matters. Expert witness in the Supreme Court of NSW in a claim of professional negligence. ACOUSTICS Visited 60 concert halls and opera houses around the World. I have met the following leading lights in Acoustics: My second meeting in London with Professor RWB Stephens, Editor of Acustica, lasted 11 hours on the one day. Professor Stephens was professor of physics at University College London. I met with Professor Manfred Schroeder, Professor of Physics at Gottingen University, Germany; Professor Krokstadt in Trondheim, Norway and Professor de Langer in Utrecht, Netherlands. In London I met with Peter Parkin who walked through the ceiling of the Royal Festival Hall with me; with Tom Summerville and Dr CLS Gilford who were former heads of BBC Acoustics research and Sandy Brown, jazz saxophonist and also formerly of the BBC. In Boston I met Professor Newman of the firm Bolt Beranek and Newman; and with Ted Shultz also of BBN. In New York I met with Russel Johnson, formerly of BBN and ho established himself as a leader in acoustics consulting. Bill Allen, architect for the Royal Festival Hall wrote to me after he saw my paper published in Acustica. CONTINUING PROFESSIONAL DEVELOPMENT PRESENTATIONS I presented continuing professional development workshops on solar geometry to architects and in Hobart, Melbourne, Adelaide, Perth, Darwin, Brisbane, Newcastle, Sydney and Canberra in 2008. In recent years I made CPD presentations to the Inner West Architects Network on aircraft noise control, energy modelling and solar geometry. On behalf of the Institution of Engineer have made CPD presentations on solar geometry.


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PROFESSIONAL As architect in association with a colleague, we won a competition for the design and construction of the then largest marina on the NSW coast at Nelson Bay, Port Stephens. In 1988 we hosted tall ships from other countries in our marina. As consultant to the NSW Government I did all of the computer modelling for John Hunter Hospital. Mechanical engineers used the output from my modelling to design the air conditioning systems. 1987. I was environment consultant to JTCW in a competition for Pacific Powers’ Advanced Technology Centre on the campus of the University of Newcastle I did the energy computer modelling. We won two architectural awards for the project. 1990-2. My early experience as an architect was in the design of military buildings, telephone exchanges and post offices. PROFESSIONAL ACTIVITIES 1999-2015 Consulting for other architects in certifying sustainability; initially under the NatHERS protocol and subsequently under BASIX protocol. BASIX includes designing to limits of energy consumption for heating and cooling to achieve thermal comfort for which computing modelling is used. BASIX also included targets for reducing water use and energy consumed by appliances. Credits are given for the use of solar water heaters and for photo-voltaic generation of electricity. Configuration options include one site batteries and feeding PV generated electricity int0 the grid for credit. Noise control in office buildings. Noise attenuation for residences affected by aircraft using Sydney Airport. Design of residences. PRESENT PROFESSIONAL ACTIVITIES 2016-2018 Consultant to other architects on Aircraft Noise Control Computer modelling of the energy consumption of buildings Solar Geometry Architect for a substantial residence in Berry NSW (2016-18) CURRENT MENTORING 2018 An interior architect known to me is a candidate for examination to become a registered architect. Because the project is to design an Academy for Music and Dance, I have been asked to provide mentoring services. I have arranged access to the Recital Hall at Angel Place, the Conservatorium of Music and the ABC Eugene Goosens Hall; in each of these halls I described the acoustic attributes.


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STEM I was invited by the CSIRO to teach, as a volunteer, extension courses in a high school on the subject of solar geometry. Over 5 years I made 89 presentations to years 7, 8 and 9 at the Scots College Bellevue Hill, Sydney. RECREATIONAL ACTIVITIES Sailing and swimming. I lived in Port Stephens for 24 years where I had my own yacht. OVERLAND TRAVELLING Crossed the Sarah Desert, swam in the Amazon River, trekked in the Himalayas, walked on a glacier in Southern Argentina Countries through which I have travelled overland include: Morocco, Algeria, Niger, Nigeria, the Congo / Zaire, Chad, The Cameroons, The Central African Republic, Rwanda, Tanzania, Kenya, South Africa, Mexico, Peru, Bolivia, Argentina, Paraguay, Brazil, England, Scotland, Norway, Denmark, Belgium, Holland, France, Spain, Portugal, Italy, Austria, Germany, Thailand, Nepal, India, Pakistan, Afghanistan, Iran, Turkey, Greece. I have visited Tahiti, Curacao, Singapore, Malaysia, Indonesia and New Zealand.

Dr Edward Leo Harkness PO Box 335 PYRMONT NSW AUSTRALIA [email protected] M 0403 239 858 11th November 2018


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Technical books co-authored by Dr Edward L Harkness

Documents

SUBMISSION TO STANDARDS AUSTRALIA - AFICA · 2019. 11. 25. · INDICATIVE COMMENTS BY HARKNESS ON AS/NZS 4859.2 and AS/NZS 4859.1:2002 11th NOVEMBER 2018 5 pages only 1 [email protected]