I am a new kid on the block although I have known about- and helped install- a very sophisticated system about 6 years ago. I live in Santa Fe, NM and have been a long time custom home builder here. We have a house (I did not build) that is an older adobe and not well insulated- there for high gas bills. I think I might have found a way to use a 3 ton water to water geothermal heat pump to offset a good part of our gas bill..... using our existing well as a the heat source- that will not break the bank on parts and installation. We use hot water radiant floors here for heat in the winter in probably 3/4 of the homes built. Most homes do not have air conditioning, but there are times when the ability to cool the house somewhat would be nice..... and geothermal gives us that option. We can use the heat pump in conduction with our existing gas boiler so that those times when 3 tons is not enough (December, January) the boiler can make up the difference needed.

This all seems great- but here is my problem:

We have natural gas here, which last winter cost about $.84 per therm- or per 100,000 btu's.
Electricity here costs about 10.4 cents per Kw-hr. Using the conversion factor of 3,413 btu's per Kw-hr, I calculate the cost of electricity about 3.5 times higher than natural gas for equivalent energy use. So if my system (closed loop) can achieve 3.5 times the heat energy out as electricity energy in, I don't really save anything- I just trade a gas bill for an electric bill. Beyond that, most of the electricity here is generated by burning coal in the 4 corners region- which is far dirtier than natural gas in terms of just about everything.

If I could use solar or wind to run the heat pump, then it would make sense- but given what seems to me to be the case it would not make sense to go this route.

I hope I have missed something here....... I usually do.... so I hope someone can tell me what it is.

Thanks to anyone who can shed some light on this, Chris in Santa Fe

No, unfortunately your analysis is spot-on. You're just running to the fact that if you have cheap natural gas available geo rarely makes sense form a cost or environemntal standpoint if you don't have much of an AC load.

If "green" considerations take precedence over cost, you could get a more detailed idea of where your power cones from at the EIA website (or your utility company might send this out ocassionally). Maybe the generation mix isn't as bad as you think.

I'm not a fan of coupling PV systems to geothermal - similar to what you said you're generating electricity at maybe 15% efficiency on a good day and getting 3-4 units of heat from that, so most of the time a much simpler solar HW system would be a better bet. I guess one exception would be if you were net-metered and could essentially use the power grid to shift the bulk of your heating load to the summer months.

That seems like an almost unbelievably low price for NG per therm. Does it include transmission, distribution and other costs?

If so your math is essentially correct and your points about the CO2 impacts of NG vs coal are well taken and were the essence of a recent editorial in FineHomebuilding.

Geo works best in area where NG is more expensive or completely unavailable. Propane and oil are generally much more expensive per btu than NG, and air source heat pumps rely heavily upon high cost aux strips anywhere outside the deep south.

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Curt Kinder

www.hoviscustombuilders.com

Without data, you have but an opinion.
No thing done well is as simple as it seems

Thanks, Engineer, for your reply

Hi... I double checked the cost per therm and over the heating season last year it was fairly volatile, however it ran between 80 cents and 92 cents per therm. I know that the rule of thumb here is propane is double NG and electricity is triple..... so that works out about right with my calcs. There are a lot of people who do use propane, so my application might work for them and others.

Anyway, thanks for replying and helping to confirm my thoughts. I still may go forward with this as I think it has some merit. If you are interested I would love to share me idea with you.

Thanks, Chris

Thank you CNYGEO2

I am still figuring out how to use this website, so I did not see your message until just now. Thank you very much for confirming my thoughts..... I was actually looking at devising a relatively low cost (for equipment and installation) in this area. We have some unique circumstances that might lend itself to having this type of installation make sense here- however it looks it will only be truly cost effective for those here who do not have access to cheap natural gas. There are a lot of people in that boat.......

I appreciate your feed back very much. All the best, Chris

Santa Fe, NM has very high solar insolation rates, so PV may be more feasible there

__________________
Curt Kinder

www.hoviscustombuilders.com

Without data, you have but an opinion.
No thing done well is as simple as it seems