Presented by

Emma ÖzsenSustainability Consultant

M.Sc. Environmental Design and Engineering

Energy Efficiency Building Code2nd Consultative Workshop - 27 January 2011

Passive Design Strategies

• Building envelope design is a very important part of the passive solar design process.

• It is essential to adapt the envelope design to the climate where the building is located.

• Important factors to consider:Orientation, Shading, Building material, Colour…

Comments on passive design strategies

The project does not consider the thermal capacity of walls and night cooling

The passive design strategies aspect would rather be moved to a specific guide

Alternative 1Single dwellings

& small non-residential buildings

Total floor area: < 500m2

Prescriptive

Alternative 2

Maximum annual energy consumption

OTTV < max table values

Alternative 3Overall Energy Performance

Energy simulation software

Compared with a “reference”

building

INCREASING CALCULATION COMPLEXITY

INCREASING DESIGN FLEXIBILITY

Prescriptive requirements for building envelope

• Maximum Solar Factor (S) specified for walls, roof and windows.

• Similar to U-value but with additional coefficients of shading and absorption.

whereR : thermal resistance of the element, based on the thermalconductivity of the material and its thicknessCm : coefficient of reduction, based on shading of elementα : absorption coefficient, based on the colour of element

Prescriptive requirements for building envelope

Other requirements/recommendations of the building envelope

Restriction of skylights (depending on exposure to direct sunlight)To minimise solar heat gains through the roof.

Transparent / translucent skylights in roofs not allowed unless skylight is not exposed to direct solar gains (i.e. oriented South or adequately shaded) and has a purpose towards passive cooling, such as to enhance stack ventilation.

Overall Thermal Transfer Value (OTTV)OTTV = measure of the energy consumption of a building due to its envelope, i.e. rate of heat transfer from the outdoor environment into a building, through walls and roof.

Comments on OTTV

Values of OTTV for Mauritius have to be provided by the Consultant

CountriesMaximum OTTV criteria (W/m2)

Wall RoofThailand 45 45

Singapore 45 45Malaysia 45 25

Comparison of OTTV values for some Asian countries

• Limiting OTTV usually is based on the latitude. • Will consider other countries with similar latitudes

and climate as Mauritius.

THANK YOUFOR YOUR ATTENTION!

Prescriptive requirements - building envelope• Values for α and Cm to be chosen from tables provided

Cm value for walls

Orientation Withoutshading

With ventilatedvertical shading Wall with horizontal shading

d/h ≥ 0.25 d/h ≥ 0.50 d/h ≥ 0.75 d/h = 1.0North 1.0 0.25 0.70 0.45 0.3 0.25

West 1.0 0.25 0.80 0.50 0.4 0.35

South 0.3 0.25 0.25 0.25 0.25 0.25

East 0.5 0.25 0.80 0.50 0.4 0.35

Examples of Cm and α values for walls

Colour White, Yellow, Orange, pale red

Dark red, light green, light

blue, light grey

Brown, darkgreen, blue,

grey

Black, dark brown, dark

blue, dark greyDescription Light Medium Dark Very dark

AbsorptionCoefficient

α

Horizontalsurface α = 0.6 α = 0.6 α = 0.8 α = 1.0

Verticalsurface α = 0.4 α = 0.6 α = 0.8 α = 1.0

Example calculation of S factor for wallsIDEAL CASE FOR A NORTH-FACING WALLAssuming:Colour = white Optimal shading, i.e., shaded by a horizontal overhang of depth (d), which is equal to the height of the wall (h)Cm = 0.25 and α = 0.4Therefore,S = (0.074 x 0.25 x 0.4) / (0.228 + 0.20) = 1.73%

WORST CASE Unprotected north-facing wall Colour = Very darkCm = 1 and α = 1S = (0.074 x 1x 1) / (0.228 + 0.20) = 17.3%

Solar Heat LoadAll buildings should be designed and constructed such that:• Naturally ventilated spaces do not overheat; and• Spaces subject to mechanical ventilation or cooling do

not require excessive cooling plant capacity.

Compliance Method 1: meeting the prescriptive requirements for the Solar Factor of building envelope.

Compliance Method 2: meeting the OTTV limit.

Compliance Method 3: showing that the solar heat load per unit floor area would not exceed the maximum load specified in the EEBC.

Compliance with solar heat load requirement