Geothermal electrical use

dogsunderfoot2September 14, 2011

Hi all - We're trying to get a feel from actual geothermal users on how well a GT system works in a fairly cold climate. We're in Ohio, zone 5-6, and regularly see winter temps in the 5-15 degree F range (along with summer days 95+, yuck!), and occasionally temps below 0F. We're looking at a two-phase, 4 ton system with 4 vertical wells, plus keeping our existing propane furnace for backup. We have an old house, but newer windows and doors and lots of insulation added, about 1600 square feet plus half basement-half crawlspace.

Does this sound like it would be a cost-effective replacement for a propane forced air furnace? I'm concerned that the supplemental electric heater that's part of the geothermal unit would be running all the time in cold weather, driving our electric bills up, or that the GT wouldn't be able to keep up and we'd end up running the propane backup half the winter. Part of me thinks that anything has to be cheaper than propane, but I feel like some of the geothermal claims are maybe a little overstated. Should I expect a big increase in electric use? Lots of supplemental heat? Or can a GT system really keep up without sending my electric bill through the roof? No sense investing in GT to reduce our propane bills if they're just replace by huge electric bills... Thanks for any advice you have.

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Great question. Iam no expert but I have installed one in a home and live right next to it. No complaints in five years and I hope it stays that way. Also pricing out a very unique system to use the new Bosch Ground source products (formerly Florida Heat Pump).

The system we modeled and am currently pricing is similar to you because we were assuming propane as the other heating source, a very expensive fuel source. I think your electric consumption concerns are understandable based on how normal heat pumps work (backup electric resistance in very cold weather). Ground Source Heat Pumps however rarely rely on this backup resistance. I dare to say never. If the wells and system are designed right, it should provide 99.5% of your heat from the ground.

Your electric bills will certainly increase but you should come out ahead if you will be getting off propane. You will also have the ability to cool and dehumidify with the same equipment and possibly reduce you domestic water heating with the desuperheater option.

The big question of course is will it be cost effective. If you plan on staying in your house for a long time then probably so plus you will be helping the environment and your community. What concerns me is that your ducts are probably not sized correctly and the extra costs and inefficiencies of doing it as a retrofit can be prohibitive.

    Bookmark   September 14, 2011 at 8:02PM
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The cost comparisons should be pretty straightforward using current energy prices. You need the efficiency of the propane system and the proposed replacement. I think that you will find some work sheets at the US DOE web site.

    Bookmark   September 14, 2011 at 8:28PM
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I think the hardest part is how well designed the GT system is. If you get COPs of 3.5 consistently and enough BTUs to maintain temp at an outside temp of 5 degrees, then you can compare. But if you only get 50% of the btus needed at that temp, then you will be in backup a lot.

That has everything to do with an accurate heat loss assessment. Not easy on an older house.

Obviously a well designed GT system will save a lot compared to propane. I'd venture to say 75% depending on your electric rates.

    Bookmark   September 15, 2011 at 6:12AM
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