Method and apparatus for solar heating air in a forced draft heating system

Abstract

A solar heating system for use in combination with a forced draft heating system for heating ventilation air of a building. The solar heating system includes a solar collector assembly for heating a liquid circulated through the assembly. The heated liquid is stored in an insulated storage tank where it can be circulated through a heat exchanger positioned in an air duct of the forced draft heating system as need to heat air flow through the duct. The use of a liquid as the heat transfer fluid and providing a storage facility for heated liquid permits the heating system to operate for a period of time after the sun sets or becomes ineffective in providing solar radiation until the heat stored in the liquid becomes exhausted. To increase the heat storage capacity of the liquid, one or more heat sinks can be utilized to absorb excess heat from the liquid and then transfer the absorbed heat back to the liquid when an opposite thermal gradient exists. Additionally, the heating system can recover waste heat from hot combustion gases exhausted from a fuel-fired forced draft heating system.

1 . A solar heating system for use with a forced draft heating system for heating ventilation air of a building, where the forced draft heating system includes an air handler, a heat source, a return air duct, an air discharge duct and a thermostat that controls the operation or the forced heating system, the solar heating system comprising:
 a solar collector assembly which heats a liquid as it is circulated therethrough by solar radiation;   a fluid storage tank for containing a quantity of heat transfer fluid;   a first heat exchanger positionable in an air duct of the forced draft heating system such that air flowing through the duct is caused to flow across said first heat exchanger;   said solar collector assembly is in fluidic communication with said fluid storage tank such that heat transfer fluid contained therewithin can be circulated through said solar collector assembly and returned to said storage tank;   said first heat exchanger is in fluidic communication with said fluid storage tank such that heat transfer fluid contained therewithin can be circulated through said first heat exchanger and returned to said storage tank;   a controller;
 said controller operative to effect the circulation of the heat transfer fluid through said solar collector assembly as a function of a temperature differential between the heat transfer liquid in said solar collector assembly and the heat transfer liquid in said fluid storage tank; and 
 said controller operative to effect the circulation of the heat transfer fluid through said first heat exchanger as a function of the temperature of the heat transfer fluid in said fluid storage tank, the temperature of the air to be heated, and the desired temperature of the air to be heated. 
   
     
     
         2 . The solar heating system of  claim 1 , wherein the duct of the forced draft heating system is the return air duct. 
     
     
         3 . The solar heating system of  claim 1 , further comprising:
 one or more heat sinks positioned to be in heat transfer communication with the heat transfer liquid contained within said fluid storage tank.   
     
     
         4 . The solar heating system of  claim 3 , wherein said one or more heat sinks is positioned within said fluid storage tank. 
     
     
         5 . The solar heating system of  claim 1 , further comprising:
 a second heat exchanger positionable in the flow of hot combustion gases exhausted by the heat source of the forced draft heating system, wherein said second heat exchanger is in fluidic communication with said fluid storage tank such that the heat transfer fluid contained within said fluid storage tank can be caused to circulate through said second heat exchanger and returned to said fluid storage tank; and   said controller operative to effect the circulation of the heat transfer fluid through said second heat exchanger as a function of the temperature of the heat transfer fluid in said fluid storage tank.   
     
     
         6 . The solar heating system of  claim 1 , wherein
 said solar collector assembly is in fluidic communication with said fluid storage tank in a first closed loop flow path; and wherein   said first heat exchanger is in fluidic communication with said fluid storage tank in a second closed loop flow path.   
     
     
         7 . The solar heating system of  claim 6 , wherein said first and second closed loop flow paths are separate from each other. 
     
     
         8 . The solar heating system of  claim 7 , further comprising:
 a first pump in said first closed loop flow path for circulating the heat transfer liquid through said solar collector assembly;   a second pump in said second closed loop flow path for circulating the heat transfer liquid through said first heat exchanger; and   said controller operatively connected to said first pump to effect the circulation of the heat transfer fluid through said collector assembly and operatively connected to said second pump to effect the circulation of the heat transfer fluid through said first heat exchanger.