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What is a Heat Pump



Refrigerant is a fluid that has a very low boiling point that can be manipulated by increasing or decreasing the pressure to absorb heat through phase transition. When these refrigerants change from a liquid to a gas it absorbs a lot of energy or heat. All air conditioning systems have heat pumps that use refrigerant. Air conditioning systems use relationship between pressure and temperature to transfer heat. As stated earlier when the refrigerant changes from a liquid state to a gas state it absorbs heat at a high quantity.  Refrigerants have a low boiling point and they are used because they will boil at room temperature. The boiling point can be altered by adjusting the pressure of the refrigerant allow the system to control the evaporation of the refrigerant.


Cooling Mode

When an air conditioning system is in cooling mode the heat pump, located outside, collects cool low pressure refrigerant, from inside the home.  With the refrigerant in a gaseous state, the heat pump then compresses this gaseous refrigerant and pumps into the high pressure side of the system. Because pressure forces the molecules of the refrigerant to get closer together it also causes the temperature of the refrigerant to increase. The hot, high pressure refrigerant gas then travels through a valve known as the reversing valve.  From the reversing valve the hot, high pressure gas travels to the outside coil which functions as a condenser. A fan blows air over the condenser coils cooling the hot high pressure refrigerant. As the gaseous refrigerant cools it condenses back into the liquid state.  Now in the liquid state the refrigerant bypasses the outside expansion valve by means of a one direction valve called a check valve.  The now cooler high pressure liquid refrigerant travels along the liquid line to the indoor unit where it is forced through the second expansion valve. The expansion valve slowly releases the refrigerant through the coils in the air handler.  As the refrigerant is released it decrease in pressure and allows the refrigerant to start evaporating.  As stated earlier as refrigerant evaporates and changes from a liquid to a gas it absorbs heat at a high rate. As the air blows over the coils in the air handler the heat in the air is absorbed by the refrigerant boiling and changing from a liquid to a gas. As air get colder it has to release moisture.  Because of this the air passing over the cold evaporator collects moister which is discarded and provides dehumidification for the home.  The now gaseous refrigerant is then transported back through the lines to the compressor where the process is repeated over and over.


Heating Mode

When the heat pump system is in the heating mode, the reversing valve reverses the direction the refrigerant in the system. Now the coils in the outside portion of the system function as the evaporator and the indoor coil function as the condenser. The cool gaseous refrigerant travels from inside the home and absorbs heat from the air outside air through same coils that were used to condense the refrigerant in the cooling cycle.  The refrigerant is then brought inside as a gas.  The air handler blows are over the coils containing the gaseous refrigerant.  The gaseous refrigerant releases its heat and cools condenses back into a liquid. This release of heat to the air passing over the coils heats the home.  This process continues as long as possible until the evaporator coils outside ice over.  When the heating mode is in use the outside temperatures are typically very low and because the temperature outside is very low the refrigerant must function at much lower temperatures in order to absorb heat. Because the system operates at a low temperature ice begins to build up on the outside of the evaporator coils. In order to combat this heat pumps have a defrost cycle. When the defrost cycle is turned on the heat pump systems functions like it is in cooling mode.  The reversing valve switches the refrigerant path to that of the cooling mode and the indoor heat is picked up by the refrigerant and used to defrost the outside coils on the evaporator.  When defrost mode is activated the outside fan turns off to help melt the ice on the coils. Because heat is now being transferred from inside to outside, a supplementary heat strip in the air handler turns on to supply the house with heat. Within a few minutes the ice melts and the system continues to operate as normal repeating this cycle over and over.



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