The Energy Chronicles

Absorption Heat Pumps


Familiar forms of refrigeration include household refrigerators, dehumidifiers, and central air conditioners that use vapor-compression refrigeration cycles.  These function by raising the pressure of a refrigerant (using a compressor) with a proportional increase in temperature that facilitates heat transfer from (or to) the air depending on the desired direction of heat flow.  A different, but not new, technology is absorption refrigeration.  Absorption refrigeration accomplishes the movement of heat differently by using a heat source (natural gas, propane, waste heat recovery) and a pump.  There is no use of a compressor.  What is new is the development of a unitary absorption heat pump.

What are the benefits?  A primary benefit is a reduction in the required electric capacity.  Other benefits include modular scalability, and a reduction in overall energy cost.

A 5-ton air conditioner (60,000 Btu/hour) with an Energy Efficiency Rating(EER) of 11.7 (Btu/Watt-hour) (~14 SEER) would have an input power requirement of about 5.1 kW with most of that energy being consumed by the compressor.  For an equal amount of cooling, an absorption heat pump would consume only about 1.0 kW (not 5!) of electric energy plus about 95,000 Btu/hour (roughly 1 Therm/hour) of heat energy.  It could provide heating, cooling, simultaneous heating and cooling, and domestic hot water depending on the model.

Heating efficiency is between 88% and 146%.  Cooling efficiencies with absorption refrigeration are not as impressive, but the economics of using gas versus electricity are still worth investigation.

Rising electric rates, and low natural gas prices could make an absorption heat pump an ideal solution, especially where an electric service size is limited (such as a retrofit).

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