Geothermal Heat Pumps, are they worth the effort (and expense)?
First some terminology: Geothermal is better termed “Ground Source”. Why? Few of us actually have a Geothermal feature such as a Geyser or Hot Springs to take advantage of. But we do have ground or in some cases maybe a lake or a pond from which heat can be extracted.
Properly designed a Ground Source heatpump can be very efficient, particularly when coupled with a low temperature heating system such as hydronics. Possibly a Coefficient of Performance (COP) of 5:1 (5 units of heat energy for every unit of electrical energy to run the heatpump compressor). To compare, an air to water heatpump might have a COP of 3:1 and air to air maybe a COP of 2:1.
The COP for the air units are Overall Estimates as “Heating” must be supplemented by Restive Heat. In the Air to Water this would be an Electrical Element in the water buffer thank. This is essentially the same as the electrical element in your electric hot water tank. This supplemental heating is necessary because the air-source heatpump’s heat output drops with decreasing air temperature, just as the heating load for the building increases. But this does drive down the efficiency or overall COP of the air source heat pump.
The familiar Air to Air heat pumps operate on the same backup principle. In this case there are electrical surface elements within the blower housing that cut-in to maintain temperature as the heatpump output drops due to lowering outside temperature.
Of the two styles of heat pumps, the Air/Water heat pump will have the better COP because the heating temperature required will be lower than the Air/Air. An in-floor radiant water system may only require 90F water to heat the house. While for a Forced Air system it is not uncommon to require 120-130F at the heat pump heat exchanger.
The answer to the original question? It depends!
Properly Designed can be a very big question for the ground-source heatpump. While I claim no expertise on designing these systems, there have been enough failures to use caution here. In particular, the ground loops might be undersized to minimize construction costs but at the expense of the system. The water to earth heat transfer through the relative thick HDPE piping is not a great heat transfer mechanism at best. Or another issue, the hydraulics of the pumping loops have not been properly evaluated. Here I do claim some expertise. Pumping horsepower directly offsets against system efficiency and should be fractional horsepower requirements.
Heating Load is always an issue. Minimizing heating load goes a long ways toward decreasing the need for extraordinary solutions. Ground-source heatpumps being one of those. Note: See other discussions on minimizing heat loads.
Equipment Availability is the final issue. There are a number of manufacturers of Water-Water heatpumps and many-many that manufacture Air-Air heatpumps but very few that offer the air-water heatpump which might be the best option in terms of return on investment.
What a discussion, right?
First some terminology: Geothermal is better termed “Ground Source”. Why? Few of us actually have a Geothermal feature such as a Geyser or Hot Springs to take advantage of. But we do have ground or in some cases maybe a lake or a pond from which heat can be extracted.
Properly designed a Ground Source heatpump can be very efficient, particularly when coupled with a low temperature heating system such as hydronics. Possibly a Coefficient of Performance (COP) of 5:1 (5 units of heat energy for every unit of electrical energy to run the heatpump compressor). To compare, an air to water heatpump might have a COP of 3:1 and air to air maybe a COP of 2:1.
The COP for the air units are Overall Estimates as “Heating” must be supplemented by Restive Heat. In the Air to Water this would be an Electrical Element in the water buffer thank. This is essentially the same as the electrical element in your electric hot water tank. This supplemental heating is necessary because the air-source heatpump’s heat output drops with decreasing air temperature, just as the heating load for the building increases. But this does drive down the efficiency or overall COP of the air source heat pump.
The familiar Air to Air heat pumps operate on the same backup principle. In this case there are electrical surface elements within the blower housing that cut-in to maintain temperature as the heatpump output drops due to lowering outside temperature.
Of the two styles of heat pumps, the Air/Water heat pump will have the better COP because the heating temperature required will be lower than the Air/Air. An in-floor radiant water system may only require 90F water to heat the house. While for a Forced Air system it is not uncommon to require 120-130F at the heat pump heat exchanger.
The answer to the original question? It depends!
Properly Designed can be a very big question for the ground-source heatpump. While I claim no expertise on designing these systems, there have been enough failures to use caution here. In particular, the ground loops might be undersized to minimize construction costs but at the expense of the system. The water to earth heat transfer through the relative thick HDPE piping is not a great heat transfer mechanism at best. Or another issue, the hydraulics of the pumping loops have not been properly evaluated. Here I do claim some expertise. Pumping horsepower directly offsets against system efficiency and should be fractional horsepower requirements.
Heating Load is always an issue. Minimizing heating load goes a long ways toward decreasing the need for extraordinary solutions. Ground-source heatpumps being one of those. Note: See other discussions on minimizing heat loads.
Equipment Availability is the final issue. There are a number of manufacturers of Water-Water heatpumps and many-many that manufacture Air-Air heatpumps but very few that offer the air-water heatpump which might be the best option in terms of return on investment.
What a discussion, right?