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Adding Geothermal source to a Heat pump with gas backup system

Here's a creative question. I have a heat pump with a gas backup system in my house. It is an older system, so it is good only to the 40s (if I remember correctly). I have explored modernization of my system, but my local trustworthy heating guy has said not to do anything until there is evidence the system is in need of replacement.

Where I live, the temperatures used to go as low as -30 on the coldest days...those days may be gone. Mini-splits are only good to -13ish, and when I ask the sales people in the big box stores, I get some odd answers. One guy said, "Wait until it warms up outside."

Has anyone come across a workable scheme to use a geothermal ground water heat source added to the existing outdoor unit that could provide the energy in the extreme cold situations?

Comments

  • hot_rod
    hot_rod Member Posts: 15,037
    Certainly any earth connected heat pump is going to provide the best source. Cost and ability to drill or trench them can make it a big ticket item.

    The A2WHP air to water heat pumps technology is advancing rapidly. Cold climate versions ccA2WHP are being installed and working down in those 0 and below conditions. Obviously COP drops at extremes but what % of the heating season are you at those cold conditions? Kick on the fossil fuel when COP drops to the $$ viable condition.

    It's possible to provide heating, cooling and also DHW from some of the new units.

    In a few month we will have a journal out showing how to accurately select, design and determine if HP technology makes sense.

    Pull the weather data for your area, graph a heat duration curve in the mean time.

    A heat load calculation on your home will be helpful also.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    @hot_rod Thanks.

    Interestingly, one of the local TV stations showed a list of the 5 most recent winters with no temperatures below 0 degrees F. 4 of the 5 were within the last about 10 years.

    Several years ago, I found some technology development going on to create a really low temperature heat pump. I think it was going on in Vermont, but can't be 100% sure.

    I toyed with using my inground pool, but came up with some astronomical numbers for how many gallons of water I would need in the pool to provide heat and I had no clue as to how to estimate a recovery time for the pool in my climate in upstate New York.
  • hot_rod
    hot_rod Member Posts: 15,037
    Here is a case study on a system in Vermont.

    One key to HP is low temperature heat emitters to keep the operating temperatures friendly to the HP.

    https://www.greenbuildingadvisor.com/article/air-to-water-heat-pump-retrofit

    I have slides from another day long seminar on HP applications that a friend presented in MA recently, let me get permission to link that here.

    My friend lives up above Utica, NY and has a A2WHP on his office, two winters worth of data. A second install on his daughters home that he is datalogging.

    Some actual installed data helps wade through all the performance claims.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Pughie1
    Pughie1 Member Posts: 130
    I had an opportunity recently to visit the job in upstate NY Hot Rod is referring to, there have been several articles written about it. However, I compare it to going to the Masters golf tournament in person as opposed to watching it on TV. seeing it in person makes all the difference in the world. The quality of the design and workmanship of this job are unbeatable!
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    @hot_rod That link is full of amazing information. It'll take time to digest it all, even though it's quite different from my situation.
  • hot_rod
    hot_rod Member Posts: 15,037
    The GEO would be a system of its own, I don’t think a loop field could connect to the outdoor condenser that you have, if that is the question. The GEO would size to the load and replace most of the components you have. Duct work if properly sized could be reused
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    What I am suggesting is pretty simple, although it may not be very efficient. The existing system has the external heat exchanger and fan (plus other things like the compressor, etc.). The interface with the geothermal system could be another heat exchanger such that the "heat or cooling" source would be transferred from the GEO heat exchanger to the HP heat exchanger simply by using the fan to flow air across both heat exchangers, thus transferring the energy from the GEO to the HP systems. See the very simple sketch for the idea, realizing the shape of the HP heat exchanger is usually not a simple single flat unit. Three of the four sides of mine are heat exchanger panels.
  • hot_rod
    hot_rod Member Posts: 15,037
    You would be running two compressors and all the components in both units, plus the circulators for the loop field, essentially more than doubling the electricity used. Plus a substantial cost for then loop field. For what end result?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    SuperTech
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    Why couldn't the GEO heat exchanger be like a car radiator and circulate the groundwater? The air flowing across it would pick receive heating or cooling and then deposit it on the HP heat exchanger. The only additional energy would be the GEO pumping power and whatever upsizing the fan would need to handle the extra flow restrictions of the second heat exchanger.

    I realize this is Rube Goldberg-ish, but that's how some our mankinds best inventions have developed. Plus it's fun to wildly speculate.
    Brewbeer
  • psb75
    psb75 Member Posts: 474
    Just have the existing heat-pump/gas unit and the proposed Geo-therm. able to send fluid to a buffer tank inside the house. House draws from buffer tank for heat. Buffer tank as hydraulic separator.
  • hot_rod
    hot_rod Member Posts: 15,037

    Why couldn't the GEO heat exchanger be like a car radiator and circulate the groundwater? The air flowing across it would pick receive heating or cooling and then deposit it on the HP heat exchanger. The only additional energy would be the GEO pumping power and whatever upsizing the fan would need to handle the extra flow restrictions of the second heat exchanger.

    I realize this is Rube Goldberg-ish, but that's how some our mankinds best inventions have developed. Plus it's fun to wildly speculate.

    So basically 55°or whatever ground loop water thru a coil without the actual heat pump?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    I haven't thought about it very much, but if the air flow across the heat exchangers was a closed loop, it might improve the efficiency. In those circumstances where the GEO loop isn't needed, the add-on system could be designed to use atmospheric air instead of GEO loop energy
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    Yes, but you use the term, "coil", which I have to ****-u-me that refers to the ground loop(s), not the actual heat transfer interface with the HP heat exchanger panels. I could have added more to the sketch as follows:

    To the left of the GEO heat exchanger would be the tubing/pipe holding the liquid, a circulating pump and whatever valves, if any, for isolating loops to allow for recovery.

    To the right would be the copper lines connected to the compressor, indoor heat exchanger in the air handler system and the valves for changing the direction of flow for heating vs. cooling.

    There is no intention to show any electrical equipment or wiring.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    @psb75 I'm not familiar with the function of a buffer tank or where in the schematic of a system it would be located. If the GEO liquid is 55F, how does that interface with the refrigerant lines between the indoor and outdoor heat exchangers? Can you draw a sketch?
  • hot_rod
    hot_rod Member Posts: 15,037
    GEO for me means anything earth connected. A GEO heat pump uses the refrigeration to upgrade the energy, in some cases you can get 3 units of energy out for every 1!unit of energy in

    Are you trying to use the earth loop via a loop field, or adding a heat pump.

    I doubt blowing air across a coil of 55 air at the current condenser would be worth the cost and energy required to run it. It would require a large loop field to provide consistent water temperature

    Might be better to upgrade the system you have to a higher SEER
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    @hot_rod No, the concept does not use a second heat pump. That should be clear from what I have written.

    My existing system is good down to 40ish, so an air supply at 55 would be capable of providing heat. The fundamental question is how efficient it would be compared to how the system works using atmospheric air at 55 degrees. As I said in earlier posts, the only added energy consumption is the circulating pump for the loop and what additional energy would be consumed if the fan had to be upgraded.

    Was I that unclear?
  • SuperTech
    SuperTech Member Posts: 1,689
    So you are talking about operating one compressor that can use an outdoor air to air heat exchanger as typically seen with heat pumps as well as ground source like typically seen with geothermal?
  • hot_rod
    hot_rod Member Posts: 15,037
    edited March 2020
    I think he is talking about blowing cool air from a second coil connected to the loop in the ground against the existing outdoor condenser. trying to lower the ambient around the unit?

    If only it was that easy :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • psb75
    psb75 Member Posts: 474
    This thread is very confusing. Are we talking about heating? Cooling? Both? Mr. "SteamingatMohawk", could you please submit some more detailed drawings of your ideas appropriately labeled. I have a suspicion that people are confused by your verbal descriptions. Schematics are worth a thousand words.
    SuperTech
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    The heat pump used in a house for both heating and cooling operates in two different modes, depending on whether you want cooling (air conditioning) or heating. What makes the diagram complicated and potentially confusing is that to switch from cooling to heating, all that needs to be done within the system is for a couple of valves to be operated. The attached diagram shows the basic system twice. The top sketch is the cooling mode, while the bottom is heating. The only difference you will notice is the position of the red and blue lines in the black circle and the labeling of the heat exchangers as evaporator or condenser.

    In the cooling mode the system takes heat out of the air in the house and transfers the heat to the outside.

    In the heating mode the system does the opposite, it takes heat from the outside and deposits it in the inside.

    Because with the system operating in opposite directions, the terminology of evaporator and condenser for the heat exchangers changes depending on which way it is working.

    It may help if you think of a window air conditioner. When you install it it takes heat out of the house and puts it in the yard. If you turned the entire unit around, it would take heat from the outside and put it in the house.

    Back to the whole house heat pump. It works great both ways until the outside air temperature gets low, because it becomes less efficient as the air is colder.

    All I am speculating on is adding the GEO loop, pump and heat exchanger. There would be no mechanical connection of the GEO fluid with the existing heat pump system. Energy would move between the two GEO part and the house system part by the fan passing air through the two outdoor heat exchangers.

    Admittedly, whether this can be efficient is a challenge, but if it can work, it can save a lot of money by not having to modify or replace the existing system in the house.

    I hope this makes it clearer and doesn't cause too many headaches.
  • pecmsg
    pecmsg Member Posts: 2,335
    If your going thru that much trouble just put in a geo system.

    No valves to play with, you get full efficiency year round.
    psb75
  • psb75
    psb75 Member Posts: 474
    "If your going thru that much trouble just put in a geo system.

    No valves to play with, you get full efficiency year round."

    I like it.
    K.I.S.S.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    I agree with the KISS method, this escapade is merely to see if anyone has done anything similar.

    I wonder what the cost would be to remove the old system, which is working fine so far, and install a new GEO. I have a small backhoe, so horizontal loops are no big deal and it's a fun way to mangle the landscape.

    In starting the discussion, I made a false assumption that how a reversible heat pump system works is well known. Oops.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    @hot_rod I just noticed your sketch. Right on, elegantly simple, but who knows if it saves any money. Sorry I didn't see it sooner.
  • hot_rod
    hot_rod Member Posts: 15,037
    You would want to do some calculations first. Determine how many ton your home actually requires. The equipment and importantly the loop field needs to be sized correctly.

    The ducting in the home needs to be adequate also.

    The type of soil and the depth you can bury to has to be part of the design.

    Installed properly it is one of the the best heat exchange technologies.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • psb75
    psb75 Member Posts: 474
    Good Ol' Mother Earth!
    Respect.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 482
    @hot_rod Agreed on all points.

    A few years ago I did a deep clean and was pleasantly surprised how clean the evaporator/condenser coil (since it works both ways) in the ductwork was. However, for all practical purposes the house for the 31 years we have been in it has had only two non-smoking occupants and one golden retriever for some of the early years.

    We changed the capacitor for the compressor and recharged the freon once. I replaced the fan motor last April and that is only the second replacement.

    Not bad performance in my book.

    To all the other contributors, thanks for your comments.