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Community and Q&A

Geothermal considering heating and cooling

user-1096787 | Posted in Mechanicals on

so I’ve read a few threads here discussing geothermal (ground source heat pump) but they all seem to focus on the heating only. I have a limited yard and consider the ditching of the AC unit a big win. Is there research looking into the efficiency of geothermal vs AC unit? and comparing the entire HVAC system? Also, since I know that it’s a split at best with a good heating unit, has there been much looking into split unit systems? The one quote I’ve seen so far is for an 80% unit gas backup, but if I could get a 90-92% efficient unit as the “backup” would I be able to use it to do the heating in the winter instead?

Also, how much does brand and fluids in the wells make a difference?

Also, in case it matter, state is Maryland

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, if you haven't gotten a bid yet for your ground-source heat pump, talk to a few contractors. These systems usually cost $18,000 to $30,000.

    If you invest the same amount of money in envelope improvements -- air sealing, more insulation, and better windows -- you can probably get away with a much smaller HVAC system.

    Here in New England, designers of energy-efficient homes are finding that ductless minisplit air-source heat pumps from Asia are always cheaper than ground-source heat pumps -- and almost as efficient.

    For the record: a ground-source heat pump is likely to be very efficient, if it is designed properly, commissioned properly, and if the pumps are properly spec'd. Unfortunately, researchers looking at the performance of installed GSHPs find that many of them haven't been properly commissioned and are operating at a low efficiency because of oversized pumps or bad heat distribution systems.

    The simplicity of a ductless minisplit system avoids all of these commissioning problems.

  2. user-659915 | | #2

    In addition to Martin's comments, if you have a limited yard you may not have the option of a GSHP anyway. Shallow ground loop systems take a lot of yard space, and your local jurisdiction may not permit the deep well option.

  3. user-1096787 | | #3

    I've gotten quotes, they come in at about 30k with an 80% gas backup and vertical wells. I already have ducts run throughout the house so I certainly want to keep a central air system, I just haven't been able to find or talk to these people who have had GSHP installed to see what they're actual before/after costs are.

    Martin: what are things to look for? I saw on an earlier post the mention of ESM fans (I think they were fans), but based on the description it seemed as if they'd be relevant for gas central air too, do you have more information on those? Do you have any links to what is good design for a GSHP? I'll be doing all the air envelope things, we already had the windows replaced, foam sprayed into the wall and I'll be putting 9 inches or so of closed-cell foam between the roof rafters in the near future.

    Also, for all the discussion of how better envelope control results in a smaller HVAC system, the gentleman who gave me the original quote walked the house and counted square footage when he sized the system. How would he take into account the air/insulation envelope?

  4. GBA Editor
    Martin Holladay | | #4

    You wrote, "The gentleman who gave me the original quote walked the house and counted square footage when he sized the system."

    It's time to find another contractor -- one who can perform a Manual J heat loss and heat gain calculation, and who can show you the paperwork to prove the calculations were made.

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