As an additional feature, ventilation windows between the Trombe wall and the building can be opened to allow circulation of the preheated air, thus increasing the heating performance of the Trombe Wall. At night, or on cold days, these small windows can be closed to prevent the loss of heat energy from the building. In practice, a Tombe Wall can exist in many forms, particularly in retrofit situations, where modifications are being made to the building after construction has been completed, often by many years. The most common and easiest method of solar thermal space heating is the direct gain of heat energy through north facing windows and glass doors. Incoming solar radiation is transmitted through the transparent glazing and is absorbed by objects, including walls and floor, inside the building.
Direct gain is the same principle which results in a warm car interior on a cold, but sunny day.
In adsorption cooling systems, heat collected from a solar thermal collector is used to evaporate a prepressurized refridgerant in a vapour generator. Dessiccant Cooling Dessiccant cooling systems use a dessiccant, such as a water absorbing wheel, to remove the most of the moisture content from the air, making it feel cooler, particularly in humid, tropical climates. The heated air then passes through a heat exchanger which is then exhausted from the system which passes the water absorbing wheel, drying it out for use again. The dessiccated, cooler air passes through an evaporative cooler to chill the air further before existing the system. This heated working fluid is then used to power a Rankine cycle heat engine.