How A Heat Pump Works

All air-conditioning systems, including heat pumps, rely on the refrigerant’s pressure temperature relationship. When a refrigerant evaporates or boils it absorbs heat at a very high rate, as is the case with all liquified gasses. Since refrigerant has a lower boiling point than most liquids we can easily manipulate it so that the only heat source needed is room temperature air. We can control this boiling point by altering the pressure placed upon the liquid. Now let’s take a look at the operation of a common split system air source heat pump. In the summer the compressor, the heart of the heat pump, receives cool, low pressure refrigerant vapor. It then pumps this vapor into the high pressure side of the system. This hot, high pressure gas now travels through a routing valve, known as the reversing valve, to the outside coil which functions as the condenser. In the condenser the heat is removed from the refrigerant by the outdoor fan, causing the refrigerant to condense into a liquid. The liquid refrigerant now bypasses the first expansion valve by means of a one direction valve, known as a check valve, the refrigerant, now cooler but still under high pressure, travels along the liquid line to the indoor unit where it is forced through the second expansion valve, this valve partially restricts the flow of refrigerant, creating the needed decrease in pressure which allows the refrigerant to start evaporating. As the refrigerant evaporates it absorbs heat from the passing air, in addition the cold evaporator collects moisture which provides dehumidification for the home. The refrigerant then travels back to the compressor where the process is repeated over and over again. 

During the winter mode the reversing valve reroutes the refrigerant path, thereby making the outside coil function as the evaporator and the indoor coil as the condenser. The heat is absorbed from the outside air by the evaporator then brought inside and released by the condenser to heat the home’s air. Also notice the outdoor expansion valve is now active as the indoor expansion valve is bypassed. This is a very efficient and cost effective method for heating the home. There is one inherent problem however, in order for the evaporator, now outside, to absorb heat it must operate at temperatures lower than the outside air. This very low operating temperature allows ice or frost to accumulate on the outside of the evaporator. 

The remedy? The defrost cycle. As the defrost cycle is initiated the reversing valve switches the refrigerant path back to that of the summer mode. This allows indoor heat to be transferred from the inside air stream to the outside coil thereby melting the accumulated frost. To speed this process up, outdoor fan operation is terminated throughout the defrost cycle, also notice that the indoor air stream now being robbed of its heat becomes very cold which is not a desirable condition during winter, to compensate for this condition the auxiliary heat is activated for the duration of the defrost cycle. After a few minutes the outdoor coil is frost free and the defrost cycle is terminated and that’s how a heat pump works. 

Auxiliary heat, or Emergency heat mode, is the back up heat mode within every heat pump, which exists to heat your home when the outdoor temperature is below the temp of the refrigerant, usually 40 degrees or so. Aux heat is usually electric heat strips. They are much more expensive to operate than the heat pump which is why they are just the back up, and only get used when the outdoor temp is too low, or when the heat pump is in defrost cycle. 

For a comparison, the heat pump uses the outdoor compressor to heat your home, which operates on between 8-12 amps of power. The heat strips use 21 amps per strip to heat your home and your home could have anywhere from two to four heat strips. This means you could be using up to 84 amps to heat your home with heat strips. This is why heat pumps are so efficient when compared to heat strips. 

If you would like to have your heat pump serviced or repaired give us a call or check us out online here. Our team are top brand technicians licensed and certified to work on heat pumps in Texas.

Or check out our video on HVAC split systems to learn more.

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Prestige Air proudly serves Northeast Tarrant County and the Fort Worth, Texas area including Hurst, Euless, Bedford, Colleyville, Grapevine, Southlake, Keller, Watauga, Haltom City, and North Richland Hills.

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