Need info on using a cistern for open loop water source

Discussion in 'HVAC Heating & Cooling' started by CWinAZ, Apr 6, 2008.

  1. CWinAZ

    CWinAZ New Member

    Messages:
    2
    Greetings! I am new to this forum, my first post. I have a question and have been searching for an answer. I live in Metro Phoenix, AZ and want to install an open loop GSHP system using a cistern for water source and return. My home is a 2 story and currently has 2-3 ton air to air HP's. Reading from several sources I would need about 18 gpm of water. How many gallon capacity buried fiberglass cistern would I need? I plan to use the water to irrigate a small area in the back yard and collect water from the roof to add to the cistern when available. Not allowed to drill a well in the neighborhood and am on city water and sewer.
  2. BigLou

    BigLou New Member

    Messages:
    138
    Not so sure in the desert that an open loop is your best option. They waste a lot of water if you don't have a well to dump it down. Why not install a closed loop system ? you could drill a well to install the closed loop tube in to.

    I have no idea about cooling loads in the desert but 18 GPM is 1080GPH. so I would think you need a several thousand gallon tank to make this worth while how would you refill thousands of gallons a day for an open loop system ?

    Lou
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,242
    Location:
    Cave Creek, Arizona
    open loop

    It sure won't be from "rainfall", so the only other option would be expensive city water, and since the rate paid varies with the amount used, dumping that much water would probably increase the cost per gallon significantly. But he might have the greenest yard in the valley with that much water on a small plot of sod.
  4. get the big one

    if you are really looking to do this you
    be wise to get the biggest you can find..

    especially if their is little rainfall to capture...


    are you going to use this to run your swamp cooler
    and water your lawn too??


    why not just cut the top off of it and call it a
    swimming pool...??
  5. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    Are you planning to use this for heat or A/C or both?

    You should first find out what others do for GSHPs in the area. Without a well your only way to get heat from the ground is to use some kind of heat exchange system. Some people use deep "wells" (often more than one) where the well is really a tube that gives access to the ground. Others bury tubes in the ground nearer the surface and pump heat transfer fluid through them. The heat transfer fluid can be liquid such as water or a mixture of water and glycol; or a phase-change fluid such as a refrigerant.

    http://www.ornl.gov/sci/femp/pdfs/gshp-pro-chal.pdf

    http://www.mass.gov/dcr/waterSupply/welldril/heat pumps060706.pdf

    http://www.igshpa.okstate.edu/geothermal/residential.htm

    http://www.igshpa.okstate.edu/geothermal/geothermal.htm

    Without a water source such as a well you will need a closed-loop system. With a closed loop system you will not (should not) lose the heat transfer fluid. In the Phoenix area the heat transfer fluid can be water without antifreeze. You should not need a cistern and a cistern will not be a suitable source of water for a GSHP. There is no way to get heat into the water in the cistern and it would soon be a block of ice if you kept trying to extract heat from it.

    You can also use the ground as a heat sink to improve the efficiency of the A/C.
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