This is a ground-source heat-pump system I have been working on for several years. I have been rather distracted by gasifiers and wood-chip burners but now my attention is coming back to this project. The science is very simple - put 1kWh of electricity in and get at least 3kWh of heat out. This doesn't violate any laws of physics because the pipes under-ground lower the temperature of the earth to allow the water on the other side of the heat-pump to rise in temperature. Its a bit like someone pulling a piano up the side of a tall building on a rope, although the person is much lower down, what they are doing is having an effect on something much higher up. The important thing to know about taking heat from under ground is that the system can be used anytime no matter what the weather is like outside. (Click on picture to enlarge)
These are the pipes going into the ground for the heat-pump pictured above (I'm sure I have a better picture somewhere, I'll replace this one when I find it). In my system I have 400 metres of pipe at a depth of 2 metres (the pipes must be well below the frost line). The longer the pipes, the more heat you can take from the ground. There are 6 loops in total, 2 in each of 3 trenches. Each loop is joined onto the next so the water must travel the full length of pipe before in returns to the heat-pump. (Click on picture to enlarge)
This is the other common type of heat-pump. In this case the heat comes from the air. The large fan cuts in to keep the unit at working temperature. The hot refrigerant is pumped along a pipe through the wall to a unit inside that dumps the heat into the room, then the refrigerant retuns through a second pipe to be heated again and so on. Often, as in this case, a heat-pump is designed so that it can provide heat in the winter and air-conditioning in the summer. Its exactly the same system except a valve simply reverses the flow of refrigerant as required. There is one big drawback with air-coupled heat-pumps, if it is below about 10 degrees C outside and there is any rain or the air is humid, the fins on the pipes of the outside unit clog with ice and the unit must be switched off. The unit can still extract heat at that temerature but there is no way of getting the heat into the unit from the air no matter how fast the fan goes round. Some units (not this) auto-defrost to avoid this problem. (Click on picture to enlarge)
Here is the inside unit corresponding to the air-coupled heat-pump above. Again it is an arrangement of fins on pipes with a fan to blow air over them, however, the compressor for the refrigerant is only in the outside unit. O yes, that's another drawback, because the outdoor unit has to be quite close to where the heat or cooling is going, the noise of the compressor cutting in and out might annoy some people. Personally, it does not bother me at all. I installed this system in 2006 and since then it has been easy to use and very reliable. It produces around 6kWh of heat for 2kWh of electricity. It is very useful in spring and autumn to lift the temperature of the house when it is not worth starting the central-heating. (Click on picture to enlarge)
