division of heat flow between conduction through roof and convection to storage through air. External insulation can be used to keep summer radiation out and prevent heat loss on winter nights. 3.3.3
Isolated Gain In isolated gain systems, the solar radiation collection and storage are thermally isolated from the living spaces of the building. This allows in a greater flexibility in the design and operation of the passive concept. The most common example of isolated gain is the natural convective loop. In this system, solar radiation is absorbed to heat air or water. The warm air or water rises and passes through the storage, transferring its heat. The cooler air falls onto the absorber to get heated up again. Thus, a ‘thermosiphoning heat flow’ occurs as shown in Fig 3.22.
Fig. 3.22 Isolated gain
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The basic requirements for this system are: a collector, which absorbs the solar radiation to heat the fluid a storage mass, which absorbs the heat from the fluid, to be stored for distribution into the living space a mechanism to distribute the heat stored in the storage mass
Variations and controls : The collector can be located at any suitable place and oriented independently of the building for maximum solar gain. Thus the building design can be flexible. The slope of the collector is generally equal to the latitude of the place. Its area may range from 20 to 40 % of the floor area of the living space to be heated. The collector consists of an absorber (usually a corrugated metal plate with a black paint that can withstand temperatures upto 120o C) and glazing. Single glazing is the norm except in severely cold climates where more than one is required to be used. The gap between the glazing and the absorber should be about 5 – 6% of the absorber length.