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  1. #1
    Join Date
    Mar 2010
    Posts
    16

    using a domestic water well

    I'm a homeowner, and have been reading about ground source heat pumps. Can an existing domestic water well be used to supply an open loop system? Here's the results of our well test last year, at the end of a dry summer when water tables are presumably lowest:

    Well depth: 450 ft
    Water level at start: 16ft
    Sustained pumping level: 108 ft
    Drawdown: 92 ft
    Test pumping duration: 120 minutes
    Average yield for pumping duration: 8 gallons / minute
    Storage tank: 5000 gallons

    Don't have a load calculation for the house yet, but the existing (oversized) propane furnace produces 120k btus. The site is in Northern California. Does this sound promising? Assuming I return the water with an injection well, are open loop systems considered environmentally friendly?

  2. #2
    Join Date
    Dec 2005
    Location
    Indiana
    Posts
    277
    ya, no problem. but you'll have a lot of on/off and will need a well pump sooner. what everyone around here has been doing is with a new geo, have a well contractor install a new var speed well. if done at the same time as the geo you can file it as part of the job and you get 30% back (tax credit). If you go that route, go with the grundfos well pump. Dont get one of those knockoffs.
    Work sucks, lets go skydive

  3. #3
    Join Date
    Mar 2010
    Posts
    16
    Thanks freefall. I'm happy to hear this sounds not totally crazy. It would be great to put the existing well infrastructure to double duty. The current well pump motor is 1 hp feeding the 5000 gallon storage tank. A separate motor provides pressure to two smaller pressurizing tanks.

    A few more questions for anyone that finds this fun. I found the specs for the Waterfurnace Envision, and their very smallest unit (26k btuh) requires 8 gallons a minute which is exactly what was measured at the well. Is that asking for trouble? Or does the storage tank save the day provided the heat pump is not run 24 hours a day? Can I get away with a 9 gpm heat pump? Also, I'm not sure which water temperature to calculate with. Maps suggest the groundwater is supposed to be ~62 degrees, but I just measured 48F coming out of the tap. Maybe the water has cooled down sitting in the tanks. Do people usually put insulation on holding tanks?

    Finally, what's the right way to find a good geothermal heat pump professional? There isn't a single geo exchange designer in California in the IGHPSA database. Should I call the closest listed installers and ask if anyone has done an open loop system? Somewhere in the back of my head, I'm worried that there's some good (non-technical?) reason I'm having a challenging time finding local examples.

  4. #4
    Join Date
    Feb 2006
    Posts
    468
    Shouldn't need anywhere near 8 GPM for an 026. For an open loop you can go as low as 1.5 GPM per ton so long as source water is 50 deg F or above. At 48 you should need no more than 4 GPM or so.

    You might be able to configure the system to use a bit less water at low stage, which is 2/3 of the capacity of full stage, so water flow could be reduced by 1/3

  5. #5
    Join Date
    Apr 2008
    Location
    Pa.
    Posts
    1,038
    Also consider where you will dump. You could end up moving upwards of a million gallons of water a year.

  6. #6
    Join Date
    Feb 2004
    Location
    Pacific NW
    Posts
    564
    Be sure to check your water rights and state law.

    Here in WA home water rights are limited to about 2 acre ft a year (driven by the drought side of the state, may be similar in CA.

    Of course, what they dont know......??

  7. #7
    Join Date
    Mar 2010
    Posts
    16
    @farbeondriven: I presume I'd need to drill another well to the same 450 ft depth to dump the water back into the same aquifer. That's a pretty deep new well to drill. Also, pumping water from that depth probably takes a lot of power. If it really takes a horsepower as suggested by the existing 1 hp Franklin well pump, then I'm probably spending a kilowatt of electricity just on water pumping. If my math is right, that turns a COP 5 into a COP 3 for a two ton heating load. For a 3 ton load, COP 5 would drop to COP 3.5.

    Does this defeat the purpose?

  8. #8
    Join Date
    Apr 2008
    Location
    Pa.
    Posts
    1,038
    [QUOTE=jbreiden;6186012]@farbeondriven: I presume I'd need to drill another well to the same 450 ft depth to dump the water back into the same aquifer. That's a pretty deep new well to drill. Also, pumping water from that depth probably takes a lot of power. If it really takes a horsepower as suggested by the existing 1 hp Franklin well pump, then I'm probably spending a kilowatt of electricity just on water pumping. If my math is right, that turns a COP 5 into a COP 3 for a two ton heating load. For a 3 ton load, COP 5 would drop to COP 3.5.

    Does this defeat the purpose?[/QUOTE



    Well around here we do somewere around 200' per ton for a closed loop. You will end up drilling and trenching either way so I recommend the closed loop. A closed loop pump will draw .5-1 amps so use this calculation to see run cost for pumps (just an estimate but good comparison). I always use 10 hours to figure ave run time. Also compare to the Grundfos Variable Speed submersable system at your gpm for heat and well head presure (your looking for the ave. amp draw at actuall voltage)

    Formula: Watts x ave run time (hrs.) / 1000 x days x cost per. kilowatt


    Ex. Closed loop 2 pumps likely you'l only need one. anyhow
    246volts x .9 amps = 221.4 Wattts
    221.4 x 10 = 2214 / 1000 = 2.214 x 30 = 66.42 x .14 = $9.29

    Ex. Open loop submersable pump (this is a total guess on amp draw!)
    246 volts x 5 amps = 1230 Watts
    1230 x 10 = 12300 / 1000 = 12.3 x 30 = 369 x .14 = $51.66

  9. #9
    Join Date
    Mar 2010
    Posts
    16
    Reading a "rules of thumb" document at the IGSHPA website, a standing column well needs to be 80-120 feet deep per ton of load. Should I be thinking about converting the 450ft domestic water well into a standing column well? Is that even possible? Is it common practice?

    http://www.igshpa.okstate.edu/pdf_fi...h_vol1_no1.pdf

  10. #10
    Join Date
    Apr 2008
    Location
    Pa.
    Posts
    1,038
    See if you can dump into a city storm drain and use a variable speed pump for open loop orr just do closed loop. Sounds like your well is not standing or artesian which you cannot convert to. I dont like the idea of having above ground storage tanks exposed to ambient conditions. You have the tools to figure your payback and operating cost.

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