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Heat Pump Discharged Water to Feed Pond

EhvC | Posted in General Questions on

I will be putting a 4 or 5 ton geothermal heat pump in a new house using well water. I am wondering if anyone has ever used the discharged water from the heat pump to supply water to a man made pond? Possibly even put fish in there.

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Replies

  1. Expert Member
    NICK KEENAN | | #1

    Geothermal doesn't get a lot of love here, it doesn't save that much energy and is a lot more expensive than air-source heat pumps. That said, if it's really what you want to do, I see three issues:
    1. Regulatory: will your local jurisdiction even let you do this? Groundwater and surface water are highly regulated in many parts of the country.
    2. Well water tends to be corrosive and have a high mineral content, which can be hard on the equipment. Most geothermal systems use a closed loop, where a treated solution is circulated instead of well water.
    3. You have to keep your water from freezing. You're going to want to cool the outlet water as close to freezing as possible for maximum efficiency. Then you're going to pump it outside, in winter. It's going to hard to prevent freeze-ups which will shut down the whole system.

  2. EhvC | | #2

    I am in the north east (New Brunswick, Canada) so it gets cold in the winter. I figured that geothermal would make more sense than air source heat pumps. Researching the pros and cons.

    1. paul_wiedefeld | | #3

      You’d think, but not always the case. There’s a case study from Canada that compared a GSHP and ASHP and the air source actually outperformed for $20,000 less.

    2. Expert Member
      Akos | | #4

      Here in Toronto, I have no issues heating a house with about $5k of cold climate hyper heat air source heat pumps. About the only "infrastructure" that was needed was a mounting bracket on the wall. Unless you can get the bore holes done for free, geo is not worth it.

      The one that could be made to work if your lake is large and deep enough, is to use a slinky loop in the bottom of the lake as your geo source.

      I would also do a proper heat loss calculation for your place. 4 to 5 tons of heat is for about a reasonably sealed code min 5000sqft house in zone 6.

      Also, like DCC said, open geo is a very bad idea. Asking for a maintenance nightmare.

  3. Expert Member
    BILL WICHERS | | #5

    It sounds like you will be putting in an open loop system. The cost to run that well pump for long periods is likely to cancel out a lot of your otherwise "saved" energy by using the heat pump. You're much better off using a closed loop system, or possibly an open loop just using a circulation pump from the pond. I've actually worked with cooling ponds before setup that way, but we were only cooling, never heating, with the system (this was for a datacenter, which needs cooling all year and never needs any extra heat). Such systems work, and in this case, the customer was able to run their fountain all year with no freeze risk which was kinda neat.

    I would either put in an air source heat pump in the usual way and not worry about the geothermal aspect, put in normal ground source heat pump, or put in an open loop with the pond only, in that order. The reason the open loop with the pond is the last option is because it will need the most maintenance -- gunk in the pond will tend to clog up other parts of the system -- and you may need regulatory approval to do this. Ground source systems can work, but tend to be prohibitively expensive to install. Air source systems are cheapest to install, and that's one of the main reasons they tend to be the most recommended.

    Bill

  4. Expert Member
    PETER G ENGLE PE | | #6

    I also agree that open loop geo HP is a bad idea, for all the reasons covered above. I have had some experience with semi-closed loop groundwater systems for commercial (winery, warehouse) heating/cooling though. The area in question has very high permeability (sand) aquifers and the scheme was to use standard well pumps to raise the water to the HP, then re-inject the water into another well about 200' away from the first. So the water "recirculates," but at an uncontrolled rate. The cost was substantially lower than for a horizontal field system and energy costs for the well pump were not outrageous. Rather elegant solution actually, as their annual inlet water temps showed that the space between the wells was acting as a relatively effective seasonal thermal battery. Note that in many areas, the idea of re-injecting water into a potentially potable aquifer would be frowned upon. Even if legal, it raises significant potential for liability if the aquifer accidentally becomes contaminated.

    1. user-1127834 | | #9

      -Can areciate t. Repping 34 dealers as well, seeing, but since 1980 open loop has been 70% of the installs for 21 counties, of a very great hydrologic state.

  5. user-1127834 | | #7

    Made A couple pond heatexchangers- 26 years ago; AND STILL FINE TODAY. Heating from ~ 420 ft coils for a commercial cold brick-metal warehouse uses 8ton on 10 coils in 11ft to 9ft depth at the pond- because it was first designed saving 84% overall energy and maintenance costs of electrical 30-ton 25hp chiller/ on less than 3 hp... process testing cooling needed.

    The first, also on a rack of 10 x 1" coils in 11.ft deep pond near zone 6 -6600dgdays , 52f ground heat exchange at start - this area, resulted in cooling 28tons -summer/ 33 net usable tons - winter [ you may rem: pull from that heavier 38f water if recirculating from deep-enough pond ].

    Second 12.ft deep pond; 7ton residential; 6700 living sq.ft, saving 60- 62% annually over previous all electric (entire billing, net calculations) because of hotwater for the home is 100% reclaimed in the summer while doing extra staging of de-humidification modes, as well as A/C crispy cool comfort. Then 100% temperature controlled HW heating still occurs as needed, 50% less costly than all electric, as fast as oil HW heaters- recovery: over 70,000 btuh.
    But first stage does that as fast as Gas HW: 30,000 net BTUh

    Wells - open-loop here have proven electrically efficient, all 1.1/4" to 1.1/2" I.D. piping, lifting water 110-120ft, : check with calculations, standards known for decades, vs. electrical KW costs+charges. Likely: Most well, return, open discharge hydro-logic cycles are available to consider locally.

    Well with GTHP oversized water coils (now most have, as AirHP caught up to) yield ~ 1.7 GalPerTon Entering Water 50f, leaving above 37f, Never had open discharge freeze up issues in 3" or 4" draining lines pitched 1:35 or 1:30 a foot above frost line depths.

    Simple test kit will show if iron comes of the water over 1/2.ppm; and 19.grains hardness here is no problem for CuNi HX open well coils. (into 5 decades)

  6. user-1127834 | | #8

    Pond coils for HVAC and HWater heat recovery in A/C ; and good for commercial chilling, saving 84% over regular chillers.

  7. ErikOlson | | #10

    Believe it is more common to put a close loop system in a pond. The high thermal conductivity of the water is beneficial.

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