Roof Radiation Trap
From Swikipedia
Introduction
A roof radiation trap is technique in which the incident solar radiation is trapped and is used for heating the air inside the trap. Some amount of energy is also absorbed by the roof and is conducted through it to be radiated into the living space. It can be used for both heating in the winters and cooling in the summers.
In the northern hemisphere, the trap consists of an inclined south-facing glazing and a north sloping insulated surface on the roof. The latter projects over the glazing to shade it during the summer. Between the roof and the insulation, an air-pocket is formed which is heated by solar radiation. A shutter is used to cover the glazing when desired.
In winter, solar radiation penetrates the glazing and is absorbed by the black roof surface designed to minimize heat loss to the ambient. Further, a movable insulation reduces heat loss through the glazed plane during nights. Part of the absorbed energy is conducted and radiated into the living area through the roof, while the rest is transferred to the air-pocket. This hot air can be drawn to a thermal storage unit (rockbed / water mass) to be used on cold nights or cloudy days. The system can also be used for summer cooling. The insulating plane is covered with a white metal sheet to increase its emissivity. On summer nights, the sheet gets cooled by nocturnal radiation exchanges and in turn, cools the air blown under it. This coolness is stored in the storage unit and used for cooling the living space during daytime.
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