A solar space-heating system can consist of a passive system, an active system, or a combination of both. Passive systems are typically less costly and less complex than active systems. However, when retrofitting a building, active systems might be the only option for obtaining solar energy.
Passive solar space heating takes advantage of warmth from the sun through
design features, such as large south-facing windows, and materials in
the floors or walls that absorb warmth during the day and release that
warmth at night when it is needed most. A sunspace or greenhouse is a
good example of a passive system for solar space heating.
Passive Solar Space Heating
Direct gain (the simplest system) stores and slowly
releases heat energy collected from the sun shining directly into
the building and warming materials such as tile or concrete. Care
must be taken to avoid overheating the space.
Indirect gain (similar to direct gain) uses materials
that hold, store, and release heat; the material is located between
the sun and living space (typically the wall).
Active solar space-heating systems consist of collectors
that collect and absorb solar radiation combined with electric fans or
pumps to transfer and distribute that solar heat. Active systems also
generally have an energy-storage system to provide heat when the sun
is not shining. The two basic types of active solar space-heating systems
use either liquid or air as the heat-transfer medium in their solar energy
collectors.
Liquid-based systems heat water or an antifreeze solution
in a hydronic collector. Air-based systems heat air in an air
collector.
Air-based solar heating systems usually employ an air-to-water heat
exchanger to supply heat to the domestic hot water system, making
the system useful in the summertime. Both of these systems collect
and absorb solar radiation, then transfer the solar heat directly to
the interior space or to a storage system, from which the heat is
distributed. An auxiliary or backup system provides heat when
storage is discharged. Liquid systems are more often used when
storage is included.