Combination heating system including a conventional furnace, heat pump and solar energy subsystem

A system for heating an air stream to condition an enclosure comprising, in combination:

• a heat pump having an inside coil in communication with said air stream and an outside coil;
• a solar energy subsystem operable in a direct heating state to heat said air stream, said solar energy subsystem including storage means for storing heat derived from solar energy, a solar energy collector thermally coupled to said storage means, and coil means in communication with said air stream and in heat transfer relationship with said storage means for transferring heat from said storage means to said air stream;
• enclosure thermostatic means for producing a first enclosure signal, a second enclosure signal and a third enclosure signal whenever the temperature in said enclosure drops below a first predetermined enclosure threshold, a second predetermined enclosure threshold and a third predetermined enclosure threshold, respectively;
• storage thermostatic means for producing a first storage signal whenever the temperature in said storage means drops below a first predetermined storage threshold;
• furnace means for heating said air stream;
• and
• control means responsive to said enclosure thermostatic means and said storage thermostatic means for coordinating operation of said heat pump, said furnace and said solar energy subsystem, said control means activating said solar energy subsystem in response to said first enclosure signal, activating said heat pump in response to said first enclosure signal and said first storage signal, activating said heat pump in response to said second enclosure signal, and activating said furnace means in response to said third enclosure signal.