|Design Handbook on Passive Solar Heating and Natural Cooling (HABITAT, 1990, 162 p.)|
|VII. Detail design|
The detail design for passive solar heating and natural cooling involves the careful checking and selection of the various elements of the building. Some design issues are important to both passive solar heating and natural cooling principles such as the control of conductive heat flow (control of heat out in winter and in during summer) whilst the design or selection of shading is important for its summer control and important in its absence in winter to let the sun in.
It has been found in recent studies undertaken for the 5-star design rating system that thermal-storage materials inside a house influence comfort levels in both summer and winter. The mass has little effect however on the heating loads of an intermittently heated house (the more common pattern of heating in most of Australia except in the very cold areas).
1. Passive solar heating
In both the cool-temperate and the hot-arid zones, passive solar heating is necessary in winter. The detailed design procedure should be as follows:
(a) Locate as many habitable rooms as possible with a northerly outlook to receive winter sun and buffer spaces to the south as natural insulation to habitable rooms. Provide adequate air-lock protection to main entrances for draft control;
(b) Determine the desirable glass-mass relationship for specific location and building use;
(c) Select or adapt the desired construction system to achieve the appropriate glass-mass relationship;
(d) Develop construction details to facilitate the economic installation of appropriate insulation levels in all external fabric;
(e) Select and specify glazing and window treatments for optimum daytime solar gains and minimum conductive losses:
(f) Develop construction details to minimize heat loss due to infiltration.
2. Natural cooling and summer comfort
In much of the year overheating inside buildings is the result of excess solar heating and internally generated heat reaching the interior spaces. This is certainly the case where the ambient air temperatures are no greater than about 27C. In such cases it is usually practicable to maintain comfort conditions with appropriate control of those heat gains (such as shading of windows and exhausting internal heat) and good ventilation and air movement patterns.
Where air temperatures are above reasonable comfort levels it is necessary to apply other strategies that will collect or soak up the excess heat for disposal into the cooler earth or to the cooler night air. In these cases the design approach should be as follows:
(a) Reduce solar gains to the interior by correctly designed shading;
(b) Minimize conductive gains by shading wall and other surfaces as appropriate and insulating the external fabric of the building;
(c) Minimize the effects of internal gains (lights and other appliances) by exhausting the heat:
(d) Design night ventilation openings to optimize the cooling of thermal sinks (thermal mass):
(e) Allow for appropriate air movement (ceiling fans and the like) to raise the occupants' comfort threshold;
(f) Design for minimum air infiltration during the day when external air is 3 deg.C greater than the upper comfort limit.
The overall goal is to be warm in winter and cool in summer. The sections that follow will assist the designer to achieve these goals by design, not by accident.