ABSTRACT
Passive systems are defined, quite generally, as systems in which the thermal energy flow is by natural means: by conduction, radiation, and natural convection. Passive features increase the use of solar energy, ambient conditions, and earth and deep space to meet the heating, cooling, and lighting loads of buildings. For example, window placement can enhance solar gains to meet winter heating loads, provide daylighting, or do both. Using a solar chimney to draw air through a building directly or via an earth air tunnel is an example of passive cooling. A passive solar heating system is one in which the sun’s radiant energy is converted to heat upon absorption by the building. The absorbed heat can be transferred to thermal storage by natural means or used to directly heat the building. Passive cooling systems use natural energy flows to transfer heat to the environmental sinks: the ground, air, and sky (space). A distinction is made between energy conservation techniques and passive solar measures. Energy conservation features are designed to reduce the heating and cooling energies required to thermally condition a building, for example, the use of insulation to reduce either heating or cooling loads or the use of window shading or window placement to reduce solar gains, reducing summer cooling loads. If one of the major heat transfer paths uses a pump or fan to force the flow of a heat transfer fluid, then the system is referred to as having an active component or subsystem. Hybrid systems use both passive and active energy flows. The use of the sun’s radiant energy for the natural illumination of a building’s interior spaces is called daylighting.
