Heat Pump Operation

There are many different types and applications, but the those which are commonly used in building applications are presented here.

The heat pump is a mechanical device which transfers energy from one medium to another. The device can provide heating or cooling upon demand. A refrigerator is a good example of a one stage device as it removes heat from the food in the refrigerator and delivers it to outside the refrigerator.

There are four heat pump requirements:

In buildings it is usual that low temperature boilers act as the heat source and roof mounted dry coolers provide the heat removal for heat pump operation.

Circulating pumps, circulate the heating or cooling water.

The main components of a heat pump are:

Cooling Cycle

Evaporator:

The evaporator removes heat from the supply air, that the supply fan is moving through it. The combination of liquid and vaporwhich enters the coil, is converted to a vapor on the leaving side of the coil.

Compressor:

The compressor compresses the low pressure vapor into a higher pressure higher temperature vapor and delivers it to the condenser.

Condenser:

The condenser removes heat from the high pressure high temperature vapor and delivers a liquid to the inlet of the expansion valve.

Expansion valve:

The expansion valve allows the condenser liquid to change to a liquid plus vapor before entering the evaporator coil.

Supply air fan:

The heat pump operation is such that a supply air fan blows warm air across the evaporator coil and supplies cool air to the conditioned space.

Filters:

The filters clean the return air and protect the evaporator coil from dirt buildup.

Heating Cycle

Reversing valve:

The reversing valve allows for the direction of flow of the refrigerant to be changed or reversed upon demand, allowing heat to moved in either direction of the 2 stage heat pump.

Evaporator:

The evaporator in effect becomes the condenser coil and adds heat to the air that the supply fan is moving through it.

Condenser:

The condenser in effect becomes the evaporator coil.

Supply air fan:

The supply air fan blows cold air across the evaporator coil which is now effectively the condenser coil and supplies warm air to the conditioned space.

Both Cycles

Filters:

Filters clean the return air and protect the evaporator coil from dirt build up.

Wall Mounted Programmable Thermostat:

The thermostat will have a fan operation selection capability.

When ON is selected the supply fan will operate continuously providing constant air flow and constant air filtering.

When AUTO is selected the supply fan will operate only on a demand for heating or on a demand for cooling.

The thermostat will have a heat pump AUTO,HEAT,COOL temperature control selection switch.

When AUTO is selected the heat pump will provide heating or cooling on demand.

When HEAT is selected only the heating cycle can be operated on demand.

When COOL is selected only the cooling cycle can be operated on demand.

Perfect-home-hvac-design.com can be an invaluable information source if considering a Heat pump.

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