TABLE OF CONTENTS Heat pumps are mechanical devices that extract low-grade heat from one source and transfer the heat to another. The advantage of a heat pump is that it up-grades the heat and delivers it at a higher temperature than the source from which the heat was extracted.
Heat pumps are usually based on refrigeration cycles. Unlike refrigerators the primary aim of heat pumps is to provide heating, although reverse cycle heat pumps can provide both heating and cooling.
Much of the technology used in heat pumps is identical to that used in refrigeration plant. The bias to heating, however, changes the emphasis of the design of the refrigeration circuit towards the condenser.
Heat pumps are characterized by the mediums between which they transfer heat. There are three primary sources of energy, air, water and the ground. The heat extracted can be transferred to heat air or water, although it would also be possible in a cooling application to reject heat to the ground.
In an air-to-air heat pump energy is extracted usually from ambient air and transferred to heat or cool a second air stream.
Ambient air is the most common energy source used by heat pumps. It should be remembered that air contains energy down to very low temperatures i.e. the point at which its constituents, Nitrogen and Oxygen, become liquids.
The energy in air...
