Heat pumps can be operated in a couple of basic ways – they can either remove heat from the atmosphere outdoors (although it might not feel warm out there!), and deposit it inside your house, or they can remove heat from the earth and heat your house with it.
Geothermal heat pumps come in two basic modes – they can either take heat from the air outside the house (even though it may not seem very warm outdoors!), and put it inside to heat your home, or they can be a geothermal type, which takes heat from the earth and does the same thing. The great thing about heat pumps is that they can be reversed, taking heat out of your house and depositing either in the outside air, or into the ground.
The economics of the system make a great case for a heat pump vs air conditioner, or equally, heat pump vs gas furnace. Just 1.5 meters underground the temperature is around 13C (approx. 55F) and doesn’t vary wildly between the seasons.
The pipes outside the heat pump itself, called the collector system, can either be quite near to the surface of the ground and spread over a big area, or lowered a hole drilled straight down into the ground, just like a well. Less pipe is required for the well type, because the temperature fluctuations are and more stable with increasing depth.
A low depth collector system of up to 100 meters long is generally installed at less than a meter in depth, and consists of a grid of a single flexible pipe looped back on itself in the form of an extended “W”. Each loop must be far enough from it’s neighbor such that heat is not passed between the two, but that the heat transfer occurs between the pipes and the surrounding earth.
Naturally, the the diameter and length of the pipe will be determined by the heat pump power rating, and the area of the collector grid needed will be determined by other parameters, like the soil thermal characteristics. The fabrication of such a collector pipe grid is easily within the reach of the practical person. Another option is to contract a specialist company to bore a hole down to one hundred meters deep – the precise depth will depend on your calculations and the nature of the ground in your location. A U-shaped pipe is dropped into the bore-hole, and then hooked up to the geothermal heat pump.
The variation in temperature between the earth 100 meters below and just 1.5 meters underground will only be approximately 1 degree, but it is more steady, hardly changing at all from winter to summer – this is why the collector pipe needn’t be as long as for the shallow grid. After being put into operation, the heat pump is comparatively free of maintenance, excluding regular annual checks. Such a system will have a marked effect on your utility bills, because a big part of the heat for your home comes from the earth and not from the Earth’s valuable and scarce resources. A photovoltaic geothermal heat pump uses only solar energy for it’s electrical supply and it costs nothing to run.