Geothermal vs boiler using well water
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What is the difference between heating with a geothermal furnace vs a regular boiler that pulls from a deep well?
More specifically if the spirit of a geothermal furnace is to use the near constant temps of water from a deeply drilled well to aid in getting your medium(I think most geothermal units heat with hot air) up to the temp needed to heat the house, than shouldn’t a normal boiler on the house’s drilled water well basically be doing the same thing?
Just curious.
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Replies
Brent,
What some people call a "geothermal" system is more properly called a ground-source heat pump. It is basically a heat pump that resembles the one in your refrigerator or air conditioner. A ground-source heat pump with an open loop takes well water and circulates the well water through a heat pump. The heat pump extracts some heat from the well water, lowering its temperature. It then returns the water, now cooled, to the well.
The water in a hydronic heating system with a boiler is part of a sealed system. Unless there is a leak, the water never needs to be replenished. The water is heated by burning a fuel like natural gas or oil.
Heat pumps can generate 95F heating air (or water) out of 45F well water, returning 35F water back to the well, which is a really neat trick, involving multiple heat exchangers, pumps exploiting the heat-of-vaporization characteristics of the working fluid (R410A refrigerant, in most systems these days.)
It's the same basic principle that allows you to make 10F ice in your refrigerators freezer by extracting heat from inside the freezer, dumping that heat into a 75F room. It's moving the heat out of the freezer compartment at a dramatically lower temperature that it's delivering the heat to the 75F room, but it takes liquifying the gaseous working fluid with a compressor on one side of the pump raising it's temperature with one heat exchanger (called the condensing coil), and evaporating that liquid on the other end of the loop in another heat exchanger (called the evaporator coil). It's the act of compressing that raises the temperature of the gas to above room temp, and the temperature drop from evaporation that takes it well below freezing on the other end.
In a geothermal system there is another all-liquid heat exchanger between the evaporator coil that exchanges heat with the soil or well-water, and in hydronic geo you have the all-liquid water radiator loop as heat exchanger between the condensing coil and the room air.
But there's no way to do that with a boiler - all it can do is add heat to the water in the last heat exchanger- the radiators or baseboards, etc., The radiators return the water to the boiler maybe 15-25F cooler than the boiler delivers to the system well above room temperature, and not at well-water temperature.