About Heat Pumps

     This page will inform you on the function and efficiency of modern heat pumps. Heat Pumps are more efficient in heating mode than electric resistive heat element heaters. Heat Pumps have more sophisticated parts than a standard air-conditioning unit.

Components of a Heat Pump

Indoor Coil - The coil that usually functions as an evaporator in a normal air-conditioning unit.

Outdoor Coil - The coil that usually functions as a condenser in a normal air-conditioning unit.

Reversing Valve - The valve that directs the flow of refrigerant to the appropriate coil based on which mode the heat pump is in, Heating or Cooling.

Defrost Board - An electronic control board that controls the operation of the Defrost Mode. Normally de-energizes the outdoor fan motor, energizes or de-energizes the reversing valve depending on the manufacturers specifications to direct hot-gas into the outdoor coil to remove the formation of ice on the outdoor coil. Normally energizes the auxiliary heat to offset the coil effects of the indoor coil acting as an evaporator.

Compressor - The component that pumps the refrigerant throught the system.

Indoor Fan Motor - The Fan Motor that circulates air through the indoor coil and supply side of the duct system.

Outdoor Fan Motor - The Fan Motor that pulls air through the outdoor coil to cool the refrigerant or condense the refrigerant and remove heat from the refrigerant.

Crankcase Heater - A electric resistive heater installed on the compressor to keep the compressor warm during the cold seasons to keep the liquid refrigerant from migrating to the coldest part of the system and possibly slugging the compressor.

Accumulator - The part of the refrigerant system that is usually placed before the compressor to prevent liquid refrigerant from entering the compressor.

Bi-directional Expansion Valve - A metering device that is capable of metering refrigerant or bypassing the metering section depending on the direction the refrigerant is flowing.

Check-Valve - Restricts or allows flow of refrigerant depending on which way the refrigerant is flowing.

Efficiency of a Heat Pump

The Heat Pumps efficiency depends on the temperature of the outside ambient air. A Heat Pump can absorb heat from the outside ambient air down to a temperature of absolute zero, -460 degrees Fahrenheit. Heat Pumps are really efficient based on the fact that the Heat Pump uses the mechanical refrigeration system to remove heat from the outside ambient air. Electric resistive heaters use a vast amount of electricity compared to a Heat Pump in order to heat a home. Gas Units are efficient but the recent rise of gas and fuel prices make these units just as much or more expensive to operate than a Heat Pump.

ENERGY STAR - Products/Homes/Buildings that earn the ENERGY STAR prevent greenhouse gas emissions by meeting strict energy efficiency guidelines set by the U.S. Environmental Protection Agency and the U.S. Department of Energy. To learn more, please visit www.energystar.gov.

EER - The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures. SEER rating more accurately reflects overall system efficiency on a seasonal basis and EER reflects the system’s energy efficiency at peak day operations.

SEER - This is a measurement of the efficiency of cooling products. The U.S. Government's minimum efficiency level is 13 SEER for split systems and packaged units. The higher the SEER, the more efficient the cooling product. SEER stands for Seasonal Energy Efficiency Rating.

HSPF - This is a measurement of a heat pump's heating efficiency. There is no governmental minimum rating. The higher the HSPF, the more efficient the heat pump's heating performance. HSPF stands for Heating Seasonal Performance Factor.

COP - Coefficient Of Performance. A ratio that compares a heat pump system's heating efficiency to that of electric resistance heat. For example, a heat pump system with a COP of 3.0 provides heat at 3 times the efficiency of electric resistance heat. A heat pump's system COP will decrease as outdoor temperatures drop, eventually providing little or no efficiency advantage over electric resistance heat - and that's when your auxiliary heat strips start to heat your home.

A Note About Efficiencies: When you're getting ready to replace an older heating or cooling system, it's very important for you to get a Load Calculation done by your dealer/contractor. The greater the difference between the efficiency of your old system to the new system, the more likelihood that the dealer will recommend a smaller sized unit. This should not cause alarm, as the dealer, by running a Load Calculation, will be able to accurately size the system to the load in your home. It can be quite detrimental to equipment if the units are too large for the load in your home - they can start to "short cycle" (they run often but for very short periods of time, because they are pumping out too much heat/cooling and reach the thermostat's setting too quickly), which can shorten the life of the unit dramatically.

Operation of a Heat Pump in Cooling Mode

The Heat Pump operates normally in Cooling Mode as a normal air-conditioner. The Heat Pump uses the indoor coil as an evaporator and the outdoor coil as a condenser in the Cooling Mode. The reversing valve is energized or de-energized based on the manufacturers specification to direct the flow of refrigerant to the appropriate coils.

Operation of a Heat Pump in Cooling Mode

Operation of a Heat Pump in Heating Mode

The Heat Pump operates in a reverse cycle in the Heating Mode. The Heat Pump uses the indoor coil as an condenser and the outdoor coil as an evaporator in the Heating Mode. The reversing valve is energized or de-energized based on the manufacturers specification to direct the flow of refrigerant to the appropriate coils. Whenever the outdoor coil, or evaporator section in the Heating Mode, detects ice formed on the coil, blockage of air through the coil, or senses a temperature usually around 42 degrees Fahrenheit or below - the Heat Pump will switch into Defrost Mode every 30, 60, or 90 minutes based on the settings on the Defrost Board. In the Defrost Mode - the Heat Pump will reverse cycle which will allow hot gas to enter the outdoor coil and defrost the coil. This will also make the indoor coil become cold and in turn to offset this temperature - the electric heat strips or auxiliary heat will come on. Also, the outdoor fan motor will stop during the Defrost Mode. A Heat Pump can absorb heat from ambient air down to absolute zero, -460 degrees Fahrenheit. The lower the ambient temperature - the lower the efficiency of the unit.

Operation of a Heat Pump in Heating Mode