isolated gain system
In the isolated -gain passive solar concept, solar collection and storage are thermally isolated from the occupies areas of the building. This concept is contrasted with the direct-gain passive solar concept where the collection and storage are integral with the occupies spaces, and with the indirect-gain concept, where collection and storage are separate from the occupied spaces but directly linked thermally. The isolated gain concept thus allows collector and storage to function independently of the building. 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. 

Requirements of Isolated Gain System : The requirements for a sunspace passive solar building type center on the glazed collector space, which must be both attached yet distinct from the occupied space. Provided with a strong exposure, the collector space must be thermally linked to a solar storage mass for heat retention and later distribution.
 

SUNROOMS
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 means of 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 mechanical means (fans), or by conduction if the storage is built into the house.

DAY AND NIGHT OPERATION OF A SUNROOM SYSTEM
The sunroom has some advantages as an isolated gain approach in that it can provide additional usable space to the house and plants can be grown in it quite effectively.The convective air collector by comparison becomes more complex in trying to achieve additional functions from the system. This is a drawback in this area where space heating is less of a concern than in colder regions where the system would be used longer. It is best to use a system that provides more than one function if the system is not an integral part of the building. The sunroom approach will be emphasized in this information since it can provide multiple functions.

The thickness of the thermal wall should be 8-12 inches for adobe or earth materials, 10-14 inches for brick, 12-18 inches for (dense) concrete.Withdraw excess heat in the sunroom (if not used for warm weather plants) until the room reaches 45 degrees and put the excess heat into thermal mass materials in other parts of the house. For a sunroom with a masonry thermal wall, use 0.30 square feet of south glazing for each square foot of living space floor area. If a water wall is used between the sunroom and living space instead of masonry, use 0.20 square feet of south facing glass for each square foot of living area.Have a ventilation system for summer months. If overhead glass is used in a sunroom, use heat reflecting glass and or shading systems in the overhead areas. More elaborate uses of the heated air generated in the sunspace can be designed into this system, such as transferring the hot air into thermal mass located in another part of the house.

Advantages /Disadvantages

  • Temperature variation in the occupied space are small Design is relatively complex and must be carefully integrated to achieve optimum thermal and architectural effect
  • It provides a relatively inexpensive living space that is usable most of the year Thermal control is required to reduce overheating in the summer.
  • The sunspace acts as a buffer zone between the outside and the primary space.
Isolated Gain rules of thumb for sunrooms:
  • Use a dark color for the thermal wall in a sunspace.
  • The thickness of the thermal wall should be 8-12 inches for adobe or earth materials, 10-14 inches for brick, 12-18 inches for (dense) concrete.
  • Withdraw excess heat in the sunroom (if not used for warm weather plants) until the room reaches 45 degrees and put the excess heat into thermal mass materials in other parts of the house.
  • For a sunroom with a masonry thermal wall, use 0.30 square feet of south glazing for each square foot of living space floor area. If a water wall is used between the sunroom and living space instead of masonry, use 0.20 square feet of south facing glass for each square foot of living area.
  • Have a ventilation system for summer months.
  • If overhead glass is used in a sunroom, use heat reflecting glass and or shading systems in the overhead areas.