I'm startting to question the Goethermal idea.

[awegrzyn]

First, I was all hyped up when I discovered geo thermal energy, but now I question the concept all together.

From what I understand, so far is that the whole “earth loop” concept is nothing else but a condenser. Since the earth cools or heats the refrigerant (direct exchange), there is no need for the condenser. This leads to efficiency, because the need for electricity that powers the condenser is eliminated. If my reasoning is true, I have the following questions:

1. Is the elimination of power for the condenser the only efficiency in geothermal systems? I see no others.

2. Is electrical power for the condenser that “big” that it provides those “big” savings everyone is talking about?

3. If I am able to provide free electricity to a Heat Pump condenser would the system be as efficient as a geothermal system? (Here I omit other advantages of the geothermal system).

The only think that a standard heat pump cannot do is operate as quite as a geothermal unit. Therefore, it cannot be located inside. Other than that, I do not see the big deal here.
Maybe you guys shine some light on this topic.

In addition, I am not going to hide the fact that I am more interested in my own electric power for my heat pump (solar, dams, other ideas) as oppose to this geothermal idea.

 

[DickRussell]

When talking about efficiency in a refrigeration cycle, it all comes down to the temperatures of heat source and destination. The refrigerant must be evaporated at some temperature colder than the source, and it must reject the heat absorbed at a temperature higher than the destination. The greater the temperature difference between rejection and absorption temperatures, the more work that must be done to lift a given amount of heat to the destination temperature, and thus the lower the efficiency. Geothermal (I am assuming we are talking about ground source heat pumps) provides a fairly constant-temperature heat source that, for a cold heating climate, is on average warmer than ambient air, and above the freezing point. The efficiency of pumping heat out of ambient air gets progressively lower as the air temperature drops. Also, the air source heat pumps must ultimately deal with frosting of the outside coils. Finally, since the air source heat pump must operate over a much wider range of source temperatures, it must be designed for the lowest air temperature that must be seen in service. This inherently results in a lower efficiency when the heat is needed most, in contrast to the more even source temperature of the ground-based heat pump.

There is a gain in efficiency obtained by DX (direct exchange of heat between ground and refrigerant), relative to that when the refrigerant exchanges heat with a circulating medium. This comes from the introduction of a second temperature difference: the refrigerant must absorb heat at a temperature lower than that of the circulating medium, which in turn must absorb heat from the ground at a temperature lower than that of the ground. Just how big these temperature differences are is a matter of surface area, equipment cost, volume of refrigerant required, and ground area (or well depth and number).