How Does a Gas Heat Pump Work?

    Air Conditioning in Reverse
 

Heat pumps are an alternative form of home heating to the traditional furnace. Instead of warming the air by direct application of heat (by the use of electricity, natural gas or oil) and then forcing the warmed air through a duct with a blower, a heat pump takes heat from natural sources in the air, water or ground and transfers it to areas of cooler air, using a refrigerant gas that runs through pipes between two sets of coils. A heat pump works like an air conditioner in reverse. In fact, heat pumps can be switched over to act as air conditioners during the summer months.

    Heat Pump Operation
 

Gas-fired heat pumps (also called absorption heat pumps) use a controlled natural gas or propane flame to heat a refrigerant solution, typically ammonia and water, which is sealed in a closed chamber. As the refrigerant boils out of the pot, its pressure rises. Heat is extracted from the condensing vaporized refrigerant, which is pulled by low pressure into an evaporator where it then removes heat from the outdoor atmosphere just as a refrigerator does from its interior. This process re-vaporizes the refrigerant. It is combined again with leftover water from the original flame-heating chamber (which has flown through a separate pipe) in an "absorber," a low-pressure heat exchanger. As the water mixes in solution again with the ammonia, a chemical reaction generates heat, which is transferred to the unit's heating output. The solution returns to the first chamber, where it is ready to be re-heated to start the cycle all over again. At this point, absorption heat pumps are considered to be cost-efficient primarily for large buildings and homes of more than 4,000 square feet.

    Advantages of Absorption Heat Pumps

 Gas-fired heat pumps are environmentally friendly on two counts. First, they use clean-burning natural gas rather than requiring electricity generated by coal-burning power plants. Secondly, unlike electric heat pumps, they require no freon-type refrigerants. Gas-fired heat pumps also offer the possibility of reversing their operation for summer to serve as a reasonably efficient air conditioner for northern climates, eliminating the need to purchase a separate air conditioning unit.

 While the air-conditioning function of heat pumps has been limited, technology for absorption heat pumps is rapidly advancing. A new "high cool" standard of efficiency is intended to increase air conditioning efficiency by 30 percent over current standards, while also making absorption heat pumps cost-effective for small homes. A cutting-edge technology currently being developed by the HVAC industry in partnership with the U.S. Department of Energy is the "triple-effect chiller," which promises another 50 percent gain in efficiency.