Page 10

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Experimental Heat Pump

The heat pump, introduced on page 9,  is one  item which can be installed in the home. It transfers - pumps - heat from a large reservoir (stream, lake, garden - which can be thought of as an infinitely large source) into a dwelling room, say, and the quantity of heat is increased over and above the energy used to drive the pump. 

Suitable web sites are:  www.heatpumps.co.uk   www.heatpumpnet.org.uk    www.energysavingtrust.org.uk

The following section is concerned with a small scale experimental unit manufactured by GUNT, Germany, which is used by student to gain an understanding of the thermodynamics of Heat Pumps. It is included here to show what are the main components of any heat pump and  results are included to show what would be a typical heat gain.

An illustration of the apparatus is given below:

The basic operation is that heat is absorbed from the surrounding air to the refrigerant in Exchange 2 . Since air has not a high heat capacity a fan is used to draw in new air all the time. The refrigerant is then passed through another exchange unit 1 where the warm refrigerant heats up circulating water. Thus the main apparatus has all the components of a normal houshold refrigerator with the addition of flow and temperature sensors.

The experiment is carried out in the following manner. A constant flow of water is set on the flow gauge by adjustment of the valve. The fan and compressor are switched on ( red buttons on right hand side of diagram). Inlet and outlet water temperatures are measured with the digital meter (just above the red buttons). The temperatures are recorded when they reach stability and the electrical power is measured. The results are tabulated:

The coefficient of performance (COP) is, simply, the ratio of the two calculated powers:

 In sequence of flow 10, 30 and 50 we have  COP values 2.3   3.0   2.8 and these are typical values to be expected from commercial heat pumps.

The gain for any household is that we have only to pay for 400 or so Watts of electrical power and get over a kilowatt of heat.

Of course, the capital cost of installing the heat pump has to be rewarded by this energy saving over several years.