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How does a Heat Pump work?

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The most familiar form of heat pump is the domestic refrigerator. Here heat is extracted from the cabinet to keep food fresh and the extracted heat is expelled through the radiator grill at the back of the unit. In this case the heat is merely a waste product. In the heat pump, we utilise this heat, and put the "cold part" outside. To make this more understandable, imagine that the "ice box" of your refrigerator is immersed in a small garden stream and the hot grid from the back is placed inside a house. The "ice box" will attempt to freeze the stream and, if we stopped the stream from flowing, freezing of the water would actually occur. But the passing water will constantly warm up the very cold "ice box". The temperature of the stream will be reduced immeasurably. So we are extracting heat from the stream which ends up as heat in the radiator grill, available to warm the house.


In every case, the useful heat output will be greater than the energy required to drive the heat pump itself. So we have extracted "free" heat from the stream.


diagram.gif ... Photos


Another way to think of it is this:- If an electric kettle element was immersed in the stream, then any warmth would be rapidly absorbed by the water. This would be a one-way loss of energy to the stream. If, conversely, the element was colder than the stream, then the stream would be warming it up, we are therefore absorbing , hence gaining energy.


(thanks to): http://www.heatpumps.co.uk/whatis.htm

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