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BEAM PLUS FOR NEW B UILDINGS APPENDICES
V ERSION 1.2 8.8 PASSIVE DESIGN ASSESSMENT METHODOLOGY
Copyright © 2012 BEAM Society Limited. All rights reserved.
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 Hong Kong weather data from the U.S. Department of Energy – Energy
Efficiency & Renewable Energy - Hong Kong SAR 450070 (CityUHK) [3].
 Computational model has the same orientation and massing as the design.
 Glazing shall not be included in the model and replaced by an opaque
surface.
 Surrounding buildings and a reasonable approximation to topography can
be included.
 The average solar irradiation across the all external facades shall be
calculated.
 The effect of roofs shall not be included in the results.
8.8.1.3 Building
Envelope
Building envelopes in Hong Kong shall be designed to minimise solar heat gain.
This reduces summer cooling loads and associated energy consumption.
There is no current measure for residential envelope heat transfer in Hong
Kong, as such reference is made to the Overall Thermal Transfer Value
(OTTV)[4]. As this does not directly apply to residential developments, it shall
be used only as a method to quantify envelope parameters, not to calculate
actual heat transfer.
The OTTV calculation methodology was published in 1995 by Hong Kong’s
Buildings Department for commercial buildings, and is an indicator of the
thermal performance of building envelopes. It considers the following factors:
1. Orientation;
2. Window to wall ratio;
3. Glazing specification (shading coefficient);
4. Solar shading;
5. Wall configuration (overall u-value, thermal mass and outer absorptivity);
and
6. Roof configuration (overall u-value, thermal mass and outer absorptivity).
For this assessment the OTTV is calculated only for external walls which
connect to habited spaces and not the roofs. Roofs are excluded to eliminate
the risk that a high specification roof could enable a lower specification facade.
In the case of residential developments this would be detrimental to the majority
of occupants.
In order to undertake an assessment based on OTTV, a maximum permissible
OTTV (baseline) is required. As there is no current baseline for residential
buildings reference is made to the National Standard of the People’s Republic
of China – JGJ 75-2003 - “Design Standard for Energy Efficiency of Residential
Buildings in Hot Summer and Warm Winter Zone”[5] .
3
ina
4 Buildings Department -Code of Practice for Overall Thermal Transfer Value in Buildings, 1995.
5 National Standard of the People’s Republic of China – JGJ 75-2003 “Design Standard for Energy Efficiency of Residential
Buildings in Hot Summer and Warm Winter Zone”