OTTV (Overall Thermal Transfer Value)
In the building regulations, a design criterion for building envelope, known as the overall thermal transfer value (OTTV), has been adopted. The OTTV requirement, which applies only to airconditioned buildings, is aimed at achieving the design of adequately insulated building envelope so as to cut down external heat gain and hence reduce the cooling load of the air-conditioning system.
The OTTV concept takes into consideration the three basic elements of heat gain through the external walls of a building:
(a) heat conduction through opaque walls;
(b) heat conduction through glass windows;
(c) solar radiation through glass windows.
For the purpose of energy conservation, the typical permissible OTTV has been set at 45 W/m2, however this is changing as technology develops and commitments to environmental impact become more enhanced.
Equivalent Temperature Difference (TDeq) is that temperature difference which results in the total heat flow through a structure as caused by the combined effects of solar radiation and outdoor temperature. The TDeq across a structure takes into account the types of construction (mass and density), degree of exposure, time of day, location and orientation of the construction and design condition. By adopting the TDeq concept, the unsteady heat flow through a construction may then be calculated using the steady state heat flow equation:
q = A x U x TDeq
The Solar Factor for vertical surfaces has been experimentally determined for the Singapore climate. From data collected over a period of time for the eight primary orientations, the average Solar Factor for vertical surfaces has been worked out to be 130 W/m². This figure has to be modified by a correction factor when applied to a particular orientation and also if the fenestration component is sloped at an angle skyward. For the purpose of the building regulations, any construction having a slope angle of more than 70º with respect to the horizontal shall be treated as a wall. For a given orientation and angle of slope, the Solar Factor is to be calculated from the following formula:
SF = 130 x CF(W/m²)
The gross area of an exterior wall shall include all opaque wall areas, window areas and door areas, where such surfaces are exposed to outdoor air and enclose an air-conditioned space. The fenestration area shall include glazing, glazing bars, mullions, jambs, transoms, heads and sills of window construction and shall be measured from the extreme surfaces of the window construction.
Preferably, doors and windows should be designed to meet the following criteria when tested under a pressure differential of 75 Pa:
(i) windows: leakage to limit to 2.77m³/h per metre of sash crack
(ii) swinging, revolving or sliding doors: leakage to limit to 61.2m³/h per linear metre of door crack
The OTTV concept takes into consideration the three basic elements of heat gain through the external walls of a building:
(a) heat conduction through opaque walls;
(b) heat conduction through glass windows;
(c) solar radiation through glass windows.
For the purpose of energy conservation, the typical permissible OTTV has been set at 45 W/m2, however this is changing as technology develops and commitments to environmental impact become more enhanced.
Equivalent Temperature Difference (TDeq) is that temperature difference which results in the total heat flow through a structure as caused by the combined effects of solar radiation and outdoor temperature. The TDeq across a structure takes into account the types of construction (mass and density), degree of exposure, time of day, location and orientation of the construction and design condition. By adopting the TDeq concept, the unsteady heat flow through a construction may then be calculated using the steady state heat flow equation:
q = A x U x TDeq
The Solar Factor for vertical surfaces has been experimentally determined for the Singapore climate. From data collected over a period of time for the eight primary orientations, the average Solar Factor for vertical surfaces has been worked out to be 130 W/m². This figure has to be modified by a correction factor when applied to a particular orientation and also if the fenestration component is sloped at an angle skyward. For the purpose of the building regulations, any construction having a slope angle of more than 70º with respect to the horizontal shall be treated as a wall. For a given orientation and angle of slope, the Solar Factor is to be calculated from the following formula:
SF = 130 x CF(W/m²)
The gross area of an exterior wall shall include all opaque wall areas, window areas and door areas, where such surfaces are exposed to outdoor air and enclose an air-conditioned space. The fenestration area shall include glazing, glazing bars, mullions, jambs, transoms, heads and sills of window construction and shall be measured from the extreme surfaces of the window construction.
Preferably, doors and windows should be designed to meet the following criteria when tested under a pressure differential of 75 Pa:
(i) windows: leakage to limit to 2.77m³/h per metre of sash crack
(ii) swinging, revolving or sliding doors: leakage to limit to 61.2m³/h per linear metre of door crack