MIL-HDBK-1003/13A
2.5.2 Heat distribution for air-type solar systems. The pipes and pumps of
the liquid-type system are replaced by air ducts and fans. The warm air
system is obviously the best heat distribution system for use with an air-
type solar system. The ability to circulate building air directly through
the collectors is one of the major advantages of an air-type solar system.
The rock bed storage also works best with a warm air system.
Although warm air as low as 100 deg. F can be used to heat an occupied
building, most existing warm air systems are sized assuming warm air
temperatures of 120 deg. F to 150 deg. F. Typical mid-day collection
temperatures usually range from 130 deg. F to 170 deg. F. Maximum storage
temperatures are typically around 140 deg. F at the end of the collection
period. Thus the heating load can be met by the temperature of the solar
heated air a large portion of the day. When storage temperatures are
insufficient to maintain the desired temperature in the building, heat from
an auxiliary source must be added to supplement the solar heated air. The
auxiliary furnace is located downstream from the rock bed so that the rock
bed serves as a preheater for the furnace. This arrangement allows the rock
bed to deliver useful heat until all of the rocks are at room temperature.
An air handler unit provides the dampers and blowers necessary to direct air
circulation between the solar collectors, rock-bed, and building as needed.
An air handler unit may be more expensive than the combined cost of
individual dampers and blowers, but it will probably be less expensive to
install. It is also more compact.
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