Discussion in 'General Discussions' started by DickRussell, Apr 21, 2008.

  1. DickRussell

    DickRussell New Member

    Pump head for domestic water and GSHP

    For a NH location, where groundwater is plentiful and a well must be drilled for domestic water anyway, a GSHP (standing column well, SCW) makes a lot of sense for a very well insulated house. That's the plan. The well will be drilled to the depth that provides sufficient water supply for the house or sufficient water column for heat transfer from rock to water for the heat pump, whichever is deepest.

    Obviously, minimum pump circulation power will be for just enough head to move the water through the heat exchanger and back to the well. However, domestic water supply normally calls for pump on at 25-30 psig, off at 45-50. I have seen very limited info on how the plumbing is set up to minimize the pump power most of the time and boost the pressure when house use of water calls for it. It would seem a waste of power to have the pump always deliver water at a pressure just above maximum needed in the house plumbing.

    So, what is typically done in this situation? One approach, from a GSHP design company, is to have a jet pump take water from downstream of the heat exchanger and boost the pressure into the pressure tank of the domestic supply. That's a second pump, however, and it would be inside the house, creating a noise problem if not isolated.

    If I were designing this, I would be inclined to use a variable speed pump in the well, with a three-way valve downstream of the heat exchanger. When domestic water supply pressure dropped to cut-in, the valve would close the return to the well and open the flow to the pressure tank. The pump speed would be increased to deliver the pressure needed to deliver water into the pressure tank. At cut-out pressure, the valve would switch back, and a check valve in the line to the pressure tank would close, preventing backflow from the tank.

    I want to know what other solutions are used. I would imagine all of this has been worked out by now, but I have to wonder. Where can I find descriptions of the various schemes used?
  2. bartman

    bartman New Member


    Was wondering if you were able to find answers to your questions above? I too am contemplating a SCW system here in central Virginia. Any resources or answers you have found that you would like to share would be much appreciated.


  3. DickRussell

    DickRussell New Member

    No response at all. I monitored this for a couple of weeks, to no avail. Either no one knows, this site doesn't get much readership, or it got overlooked, then ignored due to age.

    GSHP with SCW also feeding domestic water supply has been done before, and people do care about the pumping costs. So I can't imagine no one knows what is done.

    On looking back at my starting post, and my thought as to what would work well, that three-way valve wouldn't be needed, just a valve on the return to the well. This assumes that the head needed to get the water back to the well is less than the domestic supply tank minimum pressure.
  4. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

  5. DickRussell

    DickRussell New Member

    I did post there, back on April 22. No response there either.
  6. Bobsat99

    Bobsat99 New Member

    Constant pressure pump system

    Hi, I'm in the starting stages of an open loop system, I also was looking for an answer to the water pressure and GPM , The technology has been used in the oil and gas industry for years but in the last 3 has it been available in the home market, Franklin makes a sub drive that can deliver up to 30 GPM at 60 PSI, the one have installed is the 20 GPM, it has a control box inside and converts the 220 V AC to 3 PH AC, the pump is variable speed, it speed's up the motor to meet the demand, If you turn on one tap, it uses very little power, 2 taps, geothermal, it speeds up to meet the demand, It also requires a very little storage tank, I have included the web site,:)
    Franklin Electric SubDrive
  7. dbelisle

    dbelisle New Member

    Standing column

    I'm getting ready to install a 2 ton WaterFurnace heat pump tied to my domestic water system , but I am going to dump the water rather than return it to the well.....

    I service a system that has seven GEO units running off a standing column well , but the well is only used for the GEO units...

    I have seen systems like what your thinking of doing , but I would try open loop instead of standing column if the well has the recovery ....

    There are a couple of things that concern me using standing column with domestic.......

    #1 From April to maybe June and in the fall you could have three or four months the line returning to the well is going to have water sitting in it . When the unit comes on it will dump all that stagnant water back into the drinking water .

    #2 You could heat the water up in the well to the point that bacteria growth gets high....

    #3 Unless the GSHP has to double wall heat exchanger a failure of the exchanger could contaminate the well and send poison into the drinking water and rendering your well unusable for domestic use.....

    Variable speed pumps are becoming popular and work great with heat pumps.....
    Most heat pumps need at least 2 GPM per ton on a open loop.....

    So if your well deliverers the water required and you have a place to dump it .... Think about open loop........

    NH requires permits for water wells and also a discharge permit to dump water ... Welcome - NH Department of Environmental Services
    Neither a big deal.....

    Dave in NH
  8. jrh

    jrh Member

    are there enviormental complications with dumping millions of gallons of ground water?

    what if several of your neighbors did it to?

    could your well dry up?

    i know open loop can be super efficient,how efficient would it be if it stops working in 5 years?
  9. lobr

    lobr New Member

    Our situation doesn't exactly match what your asking but it does offer another idea so I'll throw in my two cents. We're in the middle of an install in NH ourselves. We have town water so we weren't concerned about the domestic supply although we did have plans to tap into the well water for irrigation.

    Our inital plans were for a standing column. While we were drilling though we encountered some geological issues and could not go deep enough for the standing column. We were forced to drill a second well - one for supply and one to dump. Turns out the cost of drilling 2 shorter wells worked out to the same as drilling one really deep one. (Admittedly, we got lucky in that each well produced and each could easily accept water.) So we're going to end up with a pump and dump system.

    What we decided to do though was drop a pump into the return well. For the $2,000 cost, we now have a complete pump setup that we can do anything we want with - and it's independent of the geo system.

    Some have told us that it's overkill - that many use the same standing column for both domestic and geo without issue. But I figure it provides 2 things for us. First, we won't have to tax the same pump that we rely on for heat to simply water our lawn. There will be less wear and tear on it. Second, it gives me some peace of mind in that if anything were to happed to our geo well - let's say in the middle of a blizzard... I have another pump I can switch over to. Not perfect because it's not variable and the column certainly isn't setup for geo, however it would be enough to hold us over...
  10. bartman

    bartman New Member

    Thanks for your concerns/comments. Here is how we plan on addressing the some of these issues:
    1) Our system will have a gravity drain system back into the well when the system is not running (ie "shoulder" seasons). This should eliminate stagnant water in the pipes.

    2)If #2 does happen, my guess is the system won't function very efficiently anyway. There are certainly bacteria that live in 50F water anyway, and we have our well water tested regularly. Coliform bacteria, since they normally reside in the gut, need a temp ~98F. If our well reaches that temp, and cannot be cooled by bleeding off water, then the whole SCW system will be a failure anyway. We will be monitoring EWT's.

    3) We may use a double walled heat exchanger which should eliminate the risk for contamination. OTOH, failure of a single wall HE would be extremely rare (has anyone ever had a failure?). Also, from what I can gather from the R410A MSDS, this refrigerant has little toxicity. It is not appreciably soluble in water (0.09%) so would evaporate quickly. There is a risk that the lubricant could contaminate the well water in the case of a catastrophic failure (though not with a double walled HE), but I think the overall risk is low.

    Thanks again.

  11. ciws14

    ciws14 Member

  12. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Just now looked at it. Looks expensive. The website is woefully short on any details.

    Let us know if you find out any more.

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