Figure 15-12.Space heating system with a closed-loop collector.
solar-heated water in standard baseboard heaters
is impractical. Only modified baseboard heaters of
adequate size or radiant panels are suitable for use
in hydronic systems that use solar-heated water.
One economical means of auxiliary heat
supply and heat distribution for liquid types of
solar systems involves the use of a warm-air
system. A typical system is shown in figure 15-15.
In this system, the warm-air furnace is located
downstream from a liquid-to-air heat exchanger
supplied with solar-heated water. The furnace can
then serve to boost air temperature when
insufficient heat is available from the solar-heated
water, or it can meet the full heat load when no
heat is available in solar storage. Auxiliary heat
can be supplied by a gas, oil, or electric furnace, or
by the condenser of an air-to-air heat pump.
Another method of heat distribution is to use
a water-to-air heat pump that draws heat from the
solar storage tank and pumps it to a condenser coil
placed in a central air duct. The advantage of this
system is that it can effectively use heat from solar
storage at temperatures down to 45°F; thus more
of the stored heat is available. Also, average
storage temperatures are lower, resulting in
significantly increased collector efficiency. Some
manufacturers are combining solar systems with
heat pumps to reduce auxiliary energy costs.
When a heat pump and solar system are combined
Figure 15-13.Space heating and domestic hot-water systems.