Direct-gain system
From Swikipedia
Introduction
Direct Gain System is a type of passive solar heating system in which south-facing windows provide heat gain during the daytime and high-mass thermal-storage materials absorb and store that heat. At night, the stored heat radiates back out, warming the space. This is the simplest type of passive solar heating system, but careful design is required to prevent overheating.
Brief Description
Direct-gain system is the most common, simple and effective approach generally used in cold climates.
The main considerations for a direct-gain system include:
• Surface Colour: Light coloured surfaces will reflect light around within the space, distributing it over a greater number of surfaces, whereas dark coloured materials will absorb most of the incident energy as soon as it strikes. Thus, the amount of heat storage is affected by the surface colour.
• Thermal Conductivity: Highly conducting materials will quickly transfer any heat build away from the surface deeper into the material resulting in less instantaneous re-radiation back into the space. In a poorly conductive material, however, the surface will heat up more and will quickly re-radiate most of the heat back into the space.
• Thermal Capacity: When the surface of a material with a high thermal mass heats up, a significant proportion of the thermal energy is quickly conducted deep into the material. This means that, instead of the first couple of millimetres heating up 5-10 degrees, the entire wall heats up only 1-2 degrees. When the internal temperature of the space falls at night, there is then more energy stored within the walls to be re-radiated back out.
Various controls such as roof overhangs, shutters and reflectors can be used for decreasing or increasing solar heat gain. Exhausts and vents can be used to cool the interior spaces through ventilation when summer temperature rises. Direct gain can be achieved by various forms of openings like clerestories, skylights, green houses or glass curtain walls designed for the required heating.
References:
http://www.greenbuildingadvisor.com/glossary
