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A heat pump is designed to extract heat from outdoor or indoor air, giving it the capacity to both heat and cool. Through the process of evaporation, heat extracted from cold outdoor air is used to warm indoor air. When the mode is switched from heating to cooling through the use of a reversing valve, the reverse takes place and air cooled through the process of condensation replaces warm air, which is exhausted outdoors. Since heat flows from a higher temperature to a lower one toward a balance, an observation explained in the second law of thermodynamics, warmth can be extracted from cold air molecules even when the temperature outdoors is below freezing. As a heat pump’s system of various indispensable parts work together, each contributes to the process of using evaporation and condensation for heating and cooling.


In the heating mode, the drawing force of a motor driven fan, mounted on top of the outdoor unit, causes heat laden air molecules, to come into contact with a series of heat conducting, tiny aluminum fins designed to direct air onto inlaying rows of copper tubing. The fin encased 3/8 inch tubing extends the width of the sides of the unit it wraps around, and then makes a 180 degree curve to form the next of approximately twenty evenly spaced rows, to complete the evaporator coil. A metal frame protects the coil and internal parts. In the cooling mode, an evaporator coil can be referred to as a condensing coil because its function changes when the reversing valve is turned. The coil is filled with refrigerant, a liquid chemical compound that responds predictably to heat and pressure. By being drawn across the evaporator coil, higher temperature molecules are  brought into contact with the refrigerant’s lower temperature molecules causing them to surrender heat.


The compressor starts the process by pumping refrigerant through the tubing, which flows into the compressor in a gaseous state. The refrigerant becomes pressurized through the force of motion applied by the mechanics of the compressor, which turns low pressure gas into high pressure super heated gas and then pumps it from the outside coil into the inside coil. Copper tubing is fed through holes drilled into an exterior wall to make one system of the outdoor and an indoor coils.

Tempstar heat pump brochure illustration