MAhoney Table

Thermal comfort and the Mahoney tables in Shanghai building bioclimatic design

1 Bo Xia

1College of Architecture, Chang’An University, China, [email protected]

Abstract In order to research the Shanghai building bioclimatic design strategy, the paper studies the

Shanghai building with the method of Mahoney tables that are a set of reference tables used in architecture as a guide to climate-appropriate design combined with Shanghai meteorological data, and puts forward a series of building bioclimatic design strategies for Shanghai climate characteristics. Finally, according to the climatic characteristics of Shanghai and the residents’ living characteristics, the limitations of strategies proposed by the Mahoney tables were analyzed.

Keywords: Mahoney Tables; Shanghai; Bioclimatic Design

1. Introduction

The Department of Development and Tropical Studies of the Architectural Association in London

developed a methodology for building design in accordance to climate [1]. The proposed methodology is based on three stages of design, the sketch design stage, the plan development stage and the element design stage [2]. For the purpose of systematic analysis during the three stages, they introduced the Mahoney Tables, which research on the thermal comfort using the standard effective temperature (SET). The tables are used to analyze the climate characteristics, from which design indicators are obtained. From these indicators a preliminary picture of the layout, orientation, shape and structure of the climatic responsive design can be obtained.

Shanghai sits on the Yangtze River Delta on China's eastern coast. The municipality as a whole consists of a peninsula between the Yangtze and Hangzhou Bay, mainland China's second-largest island Chongming, and a number of smaller islands. It is bordered on the north and west by Jiangsu Province, on the south by Zhejiang Province, and on the east by the East China Sea. The city proper is bisected by the Huangpu River, a tributary of the Yangtze(shown in Fig.1). The vast majority of Shanghai's 6,340.5 km2 land area is flat, apart from a few hills in the southwest corner, with an average elevation of 4 m. The city has many rivers, canals, streams and lakes and is known for its rich water resources as part of the Taihu drainage area.

Fig. 1 Geography of Shanghai

Thermal comfort and the Mahoney tables in Shanghai building bioclimatic design Bo Xia

Advances in information Sciences and Service Sciences(AISS) Volume5, Number9, May 2013 doi:10.4156/AISS.vol5.issue9.4

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In order to research the relationship between the Shanghai climate and building energy efficiency design and determine the most appropriate building energy efficiency design strategies in Shanghai, the paper adopts the Mahoney tables to Shanghai analyzing the design strategies according to the Shanghai meteorological data [3] [4].

2 Climatic data

2.1 Shanghai's Climate Overview

Shanghai has a humid subtropical climate and experiences four distinct seasons. Winters are chilly

and damp, and cold northwesterly winds from Siberia can cause nighttime temperatures to drop below freezing, although most years there are only one or two days of snowfall. Summers are hot and humid, with an average of 8.7 days exceeding 35 °C annually; occasional downpours or freak thunderstorms can be expected. The city is also susceptible to typhoons in summer and the beginning of autumn. The city averages 4.2 °C in the coldest month January and 27.9 °C in the hottest month July, for an annual mean of 16.1 °C (shown in Fig.2). Shanghai experiences on average 1,878 hours of sunshine and 132 rain days per year. The seasonal distribution of rainfall is more uniform in Shanghai and it accounts for about 40.1% in summer, 13.0% in winter, and about 70% of the rainfall is concentrated in the April- September. The rain intensity is more moderate rain and drizzle.

Fig.2 Shanghai Day dry bulb temperature statistics

2.2 Shanghai's Climate data

The Mahoney tables analyze the meteorological parameters including the monthly mean minimum

temperature, monthly mean maximum temperature, monthly mean range, relative humidity and precipitation. Using the meteorological data provided by the Shanghai Municipal Meteorological Observatory, the paper completed the analysis of the Shanghai outdoor climatic conditions described in Table 1-2.

Table 1. Mean relative humidity and Humidity group

Mean relative humidity Humidity group Below 30% 1 30-50% 2 50-70% 3 Above 70% 4


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Table 2. Shanghai climatic data

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.Aug.

Sep.

Oct.

Nov.

Dec.

Total

Monthly mean max. (℃)

7.7 9.7 13.7 19.0 24.5 27.430.7*

29.8 27.2 22.4 17.0 11.0

Monthly mean min. (℃)

1.6† 3.7 6.6 12 17.4 21.7 25.3 24.6 21.9 15.9 10.5 4.3

Monthly mean range (℃)

6.1 6 7.1 7 7.1 5.7 5.4 5.2 5.3 6.5 6.5 6.7

RH 76 71 78 73 76 82 81 82 76 73 67 66 HG 4 4 4 4 4 4 4 4 4 4 3 3 Rainfall (mm)

75 44 118 63 85 212 142 230 76 64 43 34 1186

* Highest monthly mean; †Lowest monthly mean; AMR=Annual mean range=Highest - Lowest=16.9; AMT=Annual mean temperature= (Highest + Lowest)/2=29.1; RH: relative humidity; HG: humidity group

3 The Comfort limits

The Mahoney tables take into account the climatic adaptability of people in different climatic

zones in determining the thermal comfort limits, and divide the comfort zone into three temperature ranges in accordance with the level of the annual mean temperature (AMT): ≥ 20℃, 15 ~ 20℃ and <15℃ . Furthermore the Mahoney tables take into account people difference dressing habits and activities in the day and night, and limit difference thermal comfort range on the day and night the two time periods, which is shown in Table 3.

Table3. Comfort limits

Average RH HG AMT over 20℃ AMT 15-20℃ AMT under 15℃

Day Night Day Night Day Night

0-30% 1 26-34 27-34 23-32 14-23 21-30 12-21

30-50% 2 25-31 17-24 22-30 14-22 20-27 12-20

50-70% 3 23-29 17-23 21-28 14-21 19-26 12-19

>70% 4 22-27 17-21 20-25 14-20 18-24 12-18

RH: relative humidity; HG: humidity group; AMT: annual mean temperature.

4 The analysis of each month comfort limit

Similarly the monthly mean maxima and minima of the site in question are compared to the day and night comfort limits for each individual month, according to the annual mean ranges given in Table 3 respectively (i.e., maxima with the day comfort limit and minima with the night comfort limits). The classification is established as follows:

Above comfort limit H Within comfort limit N Below comfort limit C The humidity and comfort classifications are compared for each month to establish humidity and

arid indicators.


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4.1 Humidity indicators

H1 Indicates that air movement is essential. It applies when high temperature (day thermal stress=H) is combined with high humidity (HG=4) or when the high temperature (day thermal stress=H) is

combined with moderate humidity (HG=2 or 3) and a small diurnal range (＜10℃). H2 Indicates that air movement is desirable. It applies when temperature within the comfort limit (day

thermal stress=N) are combined with high humidity (HG=4). H3 indicates that precautions against rain penetration are needed. Problems may arise with even low

precipitation, but will be inevitable when rainfall exceeds 200mm per month.

4.2 Arid indicators

A1 Need for thermal storage. This applies when a large diurnal range (10℃ or more) coincides with moderate or low humidity (HG=1,2or3).

A2 Indicates the desirability of outdoor sleeping space. It is needed when the night temperature is high (night thermal stress=H) and the humidity is low (HG=1 or2). It may be needed also when nights are comfortable outdoors but hot indoors as a result of heavy thermal storage (day=H, night=N,

HG=1or2) and when the diurnal range is above 10℃. A3 Indicates winter or cold-season problem. These occur when day thermal stress=C. The climatic data of Shanghai is tabulated in Mahoney’s Tables4-5.

Table 4. Diagnosis of Shanghai climatic data

Jan. Feb. Mar.

Apr.

May

Jun. Jul.Aug.

Sep. Oct. Nov.

Dec.

Diurnal mean range (℃)

6.1 6 7.1 7 7.1 5.7 5.4 5.2 5.3 6.5 6.5 6.7

HG 4 4 4 4 4 4 4 4 4 4 3 3

Monthly mean max. (℃)

7.7 9.7 13.7 19.0 24.5 27.4 30.7 29.8 27.2 22.4 17.0 11.0

Day comfort Max. (℃)

25 25 25 25 25 25 25 25 25 25 28 28

Day comfort min. (℃)

20 20 20 20 20 20 20 20 20 20 21 21

Monthly mean min. (℃)

1.6 3.7 6.6 12 17.4 21.7 25.3 24.6 21.9 15.9 10.5 4.3

Night comfort Max. (℃)

20 20 20 20 20 20 20 20 20 20 21 21

Night comfort min. (℃)

14 14 14 14 14 14 14 14 14 14 14 14

Thermal stress: Day

C C C C N H H H H N C C

Thermal stress: Night

C C C C N H H H H N C C

HG: humidity group; H: above comfort limit; N: within comfort limit; C: below comfort limit.


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Table 5. Indicators

Jan.

Feb.

Mar.

Apr.

May

Jun.

Jul.Aug.

Sept.

Oct.

Nov.

Dec.

Total

Humid

H1 Air movement

X X X X 4

H2 Air movement

X X 2

H3 Rain protection

X X 2

Arid

A1 Thermal storage

0

A2 Outdoor sleeping

0

A3 Cold-season

X X X X X X 6

5 Application of Mahoney tables in Shanghai

The Mahoney tables established a relationship between climate indicators and building design. The

relation between the climatic data of Shanghai and recommendations design strategies is tabulated in Mahoney’s Tables 6. And the recommendations of the climatic analysis for Shanghai building design are summarized in Table7.

Table 6. Design recommendations Indicator total from Table(5) Recommendations Humid Arid H1 H2 H3 A1 A2 A3 4 2 2 0 0 6 Layout 0-10

★ 1 Building oriented on east to west axis to reduce exposure to sun

11,12 5-120-4 2 Compact courtyard planning

Spacing 11,12 3 Open spacing for breeze penetration

2-10 ★ 4 As3, but protect from cold/hot wind

0,1 5 Compact planning Air movement 3-12

★ 6 Rooms single banked. Permanent provision for air movement

1,2 0-5 6-12

7 Double banked rooms with temporary provision for air movement[

0 2-12 0,1 8 No air movement required

Openings

0,1 0 9 Large openings, 40-80% of N and S walls

11,12 0,1 10 Very small openings,10-20%

Any other conditions ★ 11 Medium openings,20-40%

Walls

0-2 ★ 12 Light walls; short time lag

3-12 13 Heavy external and internal walls


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Roofs

0-5 ★ 14 Light insulated roofs

6-12 15 Heavy roofs; over 8 hours’ time lag Outdoor sleeping 2-12 16 Space for outdoor sleeping required Rain protection 3-12 17 Protection from heavy rain needed

(★ in the table is appropriate building design strategies for Shanghai)

Table 7. Recommendations for building design in Shanghai

Element Recommendations

Layout Building oriented on east to west axis to reduce exposure to sun

Spacing Open spacing for breeze penetration, but protect from cold/hot wind

Air movement Rooms single banked. Permanent provision for air movement

Openings Medium openings,20-40% Walls and doors Light walls; short time lag Roofs Light insulated roofs

6 Conclusions

1. Through the above analysis, it can be found that the Shanghai natural environment is not very

ideal. The Shanghai climatic (including day and night) within comfort limit is only about 16.7% (shown in Table 3), that is Shanghai throughout the year only 16.7% of the time when building do not need energy to heating or cooling, and the natural environment can meet the comfortable building internal environment. The other time of the Shanghai climatic is out of comfort limit and can't meet the building interior environment comfortable requirement. Building requires either mechanical air conditioning or other passive cooling or heating strategy to meet the building interior environment comfortable. The ratio of above comfort limit is 33.3%, and both day and night are above comfort limit from June to September; the ratio of below comfort limit is 50% there are below comfort limit conditions from November to April (shown in Fig.3).

Fig.3 The condition of Shanghai year-round comfort limit

2. Through the above analysis, the Shanghai climatic require building not only has a certain

passive cooling strategy [5], such as rooms single banked, light walls and so on; also require


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passive heating strategy [6] [7], such as open spacing but protect from cold/hot wind design strategy[8] indicated by Mahoney Tables (shown in table6).

3. However, the Mahoney tables have some limitations. The Mahoney tables is mainly aimed at tropical climate, so the method used to evaluate the Shanghai climate can more truly reflect the Shanghai summer environmental conditions. But Shanghai climate is hot in summer and cold in winter [9], and Shanghai residents live for so long time in such climate that they not only have a certain degree of adaptation and tolerance of summer heat [10], but also have a greater tolerance in the winter cold environment than people living in the tropics. Therefore there may be some errors for the evaluation of the Shanghai winter environment that the actual below comfort limit situation should be less than 50% [11]. Shanghai residents have a better tolerance to cold environment, but the essence of building is to offer people a comfortable indoor environment, so it is also important to pay attention to the passive heating strategy used in Shanghai building energy efficiency design [12].

7. Acknowledgments

This work was financially supported by the Special Fund for Basic Scientific Research of Central

Colleges, Chang’an University (CHD2012JC081) and the Natural Science Foundation of China (51178050).

8. References

[1] Ali Sayigh, A. Hamid Marafia, “Thermal comfort and the development of bioclimatic concept in

building design”, Renewable and sustainable Energy Reviews, vol.2, no.1-2, pp.3-24, 1998 [2] Baruch Givoni, “Comfort, climate analysis and building design guidelines”, Energy and Buildings,

vol.18, no.1, pp.11-23, 1992 [3] D.A.Mcintyre,” Indoor Climate”, Applied Science, USA, 1980 [4] T. A. Markus, Edwin N. Morris, “Building, Climate and Energy”, Pitman Publishing Ltd,USA,

1980 [5] Lv Aimin, “Climate-Responsive Building”, Tongji University Publications Limited, China, 2011. [6] Xibiao Cai, Xiaoxiang Wang, Dongxia Wang, Dongyu Wang, “Energy-efficient Cooperative

Broadcast Transmission in Clustered Wireless Sensor Networks”, International Journal of Digital Content Technology and its Applications, Advanced Institute of Convergence Information Technology, vol.6, no.7, pp.327-336, 2012.

[7] Ling Tan, Huiqiang Tang, Yujuan Liu, “Energy-Efficient Wireless Sensor Networks: A Novel Dynamic Clustered and Cross-Layer Cooperation Approach”, International Journal of Advancements in Computing Technology, Advanced Institute of Convergence Information Technology, vol.3, no.9, pp.337-346, 2011.

[8] Sophia Behling, Stefan Behling, “Solar power: the evolution of sustainable architecture”, Prestel, USA, 2000.

[9] Bo Xia, " Ecological Architecture “Passive Control” Theory and Technical System ", International Journal of Advances in Information Sciences and Service Sciences, Advanced Institute of Convergence Information Technology, Vol. 4, No. 22, pp. 274-284, 2012.

[10] Baruch Givoni, “Climate Consideration in Building and Urban Design”, A Division of International Thomson Publishing Inc., USA, 1998.

[11] Zhang Jun, Yin Qing, "The Application of Energy-saving Technology for Buildings in Cold Areas", International Journal of Advances in Information Sciences and Service Sciences, Advanced Institute of Convergence Information Technology, Vol. 4, No. 14, pp. 80-88, 2012.

[12] Bo Xia, “Research on the Control System of Ecological Architecture”, In Proceeding of 2nd International Conference on Civil Engineering, Architecture and Building Materials, pp.3196-3201, 2012.


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MAhoney Table