Using my pool as a heatsink...or not?

Discussion in 'General Discussions' started by GEK, Jun 13, 2008.

  1. GEK

    GEK New Member

    Feedback on a proposed retrofit system

    I'm working on a retrofit residential geothermal heat pump system and would appreciate feedback from those with more experience.

    The house is large, about 5500 sq feet, currently with two furnaces (oil - forced hot air). It is a 1978 wood frame construction. We're located in New Hampshire.

    The main furnace services about 4500 sq feet, with a second unit servicing a large room over a garage. The main furnace also has central air conditioning. Air conditioning is a low priority, we only need it for a few weeks every summer.

    The property has had several well shafts drilled because of low water flow. The proposed well to be used is a 1000ft shaft that was abandoned because of low flow. I pulled the cap and the current static is at 16'

    Design proposal is to replace the AC unit in the main furnace with a 5 ton system. We'll tackle the secondary furnace in the future as funds allow. Oil will remain as a supplementary heat source in the main furnace. Proposal for the well is to place a pump at 100ft with a return at 980 feet (Standing Column) with zero bleed.

    I realize that a 5 ton system can't meet the total heat load in winter. We currently use 6.5 tons of pellets and 1250 gallons of oil overall. I hope that it will substantially reduce the oil usage. I also plan to increase insulation, seal air ducts etc and we are in the process of replacing windows to reduce the heat load demands.

    The option of a desuperheater has also been discussed. I wonder if it would be worthwhile with our low AC usage and a somewhat undersized system?

    Any thoughts, ideas would be greatly appreciated!

    - Gary
  2. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Sounds like an interesting project. How is your hotwater heated now?
  3. GEK

    GEK New Member

    Hot water is a stand alone oil system.
  4. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    You could add the desuperheater and then turn it off if the unit was not keeping up with the heat load. Just be sure and add a preheat tank for the desuperheater.
  5. 700West

    700West New Member

    I have a 5000sqft home in the Coachella Valley with two 3 or 4ton AC units. As of now it's getting down to 45f, summers reach 110f. My central HVAC units need to be replaced..I just dont know with what yet!

    I don’t want to pay for running my AC units to cool the place, I have a big pool (goes down to about 10ft) with a Jacuzzi that flows over into the pool and a fountain (about 8ft x 8ft) that flows into the Jacuzzi.

    One idea I had was to run lines from the drain of the pool to the heat pump where both the ACs were (just using the pool water). Now would this give me a good year round cooling/heating?

    Idea two is to go the traditional method of a horizontal or vertical closed loop.

    What are the gurus of heat pumps opinions?

    How much do these bad boys cost to run vs. an AC/Heater?

  6. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    This has been discussed - do some searching here and at greenbuildingtalk
  7. 700West

    700West New Member

    sorry didn't see anything that related to a desert multi AC unit equipped house question related to using the pool vs horizontal vs vertical pump topic

    Do you have a link?
  8. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    No link known to me

    A site-specific old school analysis of load and psychrometry of the pool will be needed to assess the viability of a pool-based water source solution.
  9. 700West

    700West New Member


    In your experience am I just being sadistic here lol Would it be easier/better to put a vertical closed loop system?

    Any input on how these systems (vertical closed loop) would preform in the desert?

  10. gabby

    gabby Member Industry Professional Forum Leader

    The last recorded soil survey of that area was in 1928.
    The Orange county and western Riverside pdf can be found here for geological information.

    Since a large portion of that county is used for commercial irrigation, I will guess your "Desert" is really a sandy top soil with rock formations within easy drilling. The cost of drilling and the depth of hole will depend on the geology and ground water depth, which may or may not rule out vertical wells for a 5000 sqft home. If memory serves me, most of Ca is composed of porous rock which may be a good thing for you. I didn't download the pdf...I will leave that to you since it is more of an interest to you.
    Note the soil type, depth, depth to ground water, and bedrock distance.
  11. 700West

    700West New Member


    So what am I ideally looking for when I download this sheet?

    Can I just use any drilling company and do most of the install work/supervision myself (I know you might be a little biased on that one eh lol). I like to get my hands dirty when I work on anything (I've restored some cars, built a few fences, etc.) so is this something I can do/supervise the majority of the work on?

  12. gabby

    gabby Member Industry Professional Forum Leader

    You want to know the soil conditions and type of rock drilling you will be into to give you an idea of what your driller will face. As far as helping...well unless you have experience with electronics/electrical/HVAC systems I would advise you to watch and learn, but don't help...there may be more charges for you helping...LOL.

    The cost of this system commands you get a designer involved to size the loads correctly, and determine the number of wells need for that load. The variables for a manual J will put you all the way to a 12 ton unit unless done correctly with specific data about your home. Depending on orientation to the south, windows, shading,and specific insulation values you may be able to reduce that and lower the well count.
    A well is good for 1 ton or more depending on depth, and that varies from 150'-350' across the country.
    Your local well driller and loop experts should be able to give you ballpark numbers for systems near you, but the specifics of your home will determine the real loads (heating/cooling). Once you know the loads then you have to determine zones and whether multiple units will need installed. This will determine the electrical requirements and whether you have what it takes, or an upgrade is needed. Your house design will tell you whether you can handle everything in a mechanical room or whether a split system is called for, or multiple splits. The designer will also look at your duct system for modifications or enhancements to accommodate the new install, zone dampers, or an increase/decrease in size of drops or trunk lines. It isn't just removing and replacing units and punching a few holes in the ground...getting it right the first time is the goal.
  13. tkestler

    tkestler New Member

    Gabby is right, loads calcs are number one. Don't assume the units you have now are the right size. As for electrical requirements, geothermal units draw about half the power of conventional ac, whether heating or cooling, and the breakers are usually one size smaller. Therefore, upgrading power to the home is not likely necessary.

    I can answer your question about weather a pool can be used as a heatsink. The answer is definitely, yes. The amount of heat you will get in the pool will depend on many factors, but the main point is that the heat rejected by the ac system from the house is FREE, while the heat from a fuel-fired pool heater is expensive.

    The easy way for a retrofit is to use geothermal splits, with the compressor cabinets near the pool filter system and a shell-and-tube heat exchanger sized to reject all the heat to the pool. This could be set up in a mechanical room, vault, or a shed. The indoor units will be matching air handlers connected to your ductwork, with refrigerant lines to the geothermal units.

    For the heating season, you would switch the geothermal units over to a closed loop or else your pool will become a big frozen slushy.

    You can do much of the system yourself, but will want a technician to braze, charge and test.

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