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Passive Solar Design
Passive solar energy means that mechanical means are not employed to utilize solar energy.
Passive solar systems rules of thumb:
Two primary elements of passive solar heating are required:
There are three approaches to passive systems - direct gain, indirect gain, and isolated gain. The goal of all passive solar heating systems is to capture the sun's heat within the building's material and release that heat during periods when the sun is not shining. At the same time that the building's material is absorbing heat for later use, solar heat is available for keeping the space comfortable.
With direct gain , the living space is a solar collector, heat absorber and distribution system. South facing glass lets solar energy into the house where it strikes directly and indirectly thermal mass materials in the house such as masonry floors and walls. The direct gain system will utilize 60 - 75% of the sun's energy striking the windows.
Thermal mass in the interior absorbs the sunlight and releases the heat at night
In a direct gain system, the thermal mass floors and walls are functional parts of the house. The thermal mass will regulate the intensity of the heat during the day by absorbing the heat. At night, the thermal mass releases heat into the living space.
Direct gain system rules of thumb:
In an indirect gain system, thermal mass is located between the sun and the living space. The thermal mass absorbs the sunlight that strikes it and transfers it to the living space by conduction. The indirect gain system will utilize 30 - 45% of the sun's energy striking the glass adjoining the thermal mass.
Thermal storage wall systems:
The thermal mass is located immediately behind south facing glass in this system.
Operable vents at the top and bottom of a thermal storage wall permit heat to convect from between the wall and the glass into the living space. When the vents are closed at night radiant heat from the wall heats the living space.
Indirect gain system rules of thumb for thermal storage walls
An isolated gain system has its integral parts separate from the main living area of a house. Examples are a sunroom and a convective loop through an air collector to a storage system in the house. The ability to isolate the system from the primary living areas is the point of distinction for this type of system.
The isolated gain system will utilize 15 - 30% of the sunlight striking the glazing toward heating the adjoining living areas. Solar energy is also retained in the sunroom itself.
Sunrooms employ a combination of direct gain and indirect gain system features. Sunlight entering the sunroom is retained in the thermal mass and air of the room. Sunlight is brought into the house by via conduction through a shared mass wall in the rear of the sunroom, or by vents that permit the air between the sunroom and living space to be exchanged by convection.
The use of a south facing air collector to naturally convect air into a storage area is a variation on the active solar system air collector. These are passive collectors. Convective air collectors are located lower than the storage area so that the heated air generated in the collector naturally rises into the storage area and is replaced by return air from the lower cooler section of the storage area. Heat can be released from the storage area either by opening vents that access the storage by fans, or by conduction if the storage is built into the house.
Isolated Gain rules of thumb for sunrooms:
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