Monday, April 5, 2010

Heat Pumps

Last time I wrote about the solar hot water panel at the Northfield Ecocentre. This week the blog is about the air source heat pump. The “air source” bit is because it grabs the heat out of the air whereas other heat pumps grab it from the ground.
If ever you have looked behind your household fridge you will see there is a coil. If the fridge is working then the coil will be warm. This is how the heat pump works. In the case of the fridge a pump is taking the heat out of the fridge and getting rid of it through the coil. In the case of an air source heat pump it takes the heat from outside air and heats a coil which we use as a radiator to heat the building. The physics of it means that for every kilowatt of electricity we use to drive the pump then over two kilowatts are put into the radiators to heat the building. It seems like magic to me! Of course one still has to pay for the electric but only half what it would have cost with conventional electric heating. However they do say that if gas is available it is still more economical to use gas for heating. For rural and isolated buildings it is well worth a study.
The graph above shows the electricity used by the Ecocentre heat pump and the heat produced. You will see that the output is about twice the input. Unlike the solar panel the graph is at present reducing as the weather gets warmer. Our peak was at New Year when we had a pipe frozen and had to leave the heat on overnight to thaw it out. We regular update the graph and this is shown here.