The two basic types of "traditional" space heating systems are:
o Water (hydronic).
In forced air heating systems, the air entering the heating system (the return air) is
at room temperature. When the solar heated water is warmer than this return air,
solar heat is introduced. A duct coil is used to transfer the solar heat into the return
air before it enters the heating system.
If solar energy alone is sufficient to maintain the room at the thermostat setpoint, the
auxiliary system remains off. If the room temperature continues to drop, the
auxiliary system boosts the air up to a higher temperature. The auxiliary system can
be a gas or oil burner, or electric coils.
Even when the auxiliary system is on, the solar coil can still preheat the return air,
as long as the water temperature is higher than the return air temperature.
A two-stage thermostat usually controls the two heat sources. Stage one (the pump
delivering solar-heated water) is usually allowed to stay on when stage two (the
back-up heater) comes on (Figure 2-6).
A Forced Air Heating
2.1 BASIC SYSTEM CONFIGURATION