Virginia Optimizing well pump usage for open loop system

Discussion in 'General Discussions' started by optimist, Jul 8, 2018.

  1. optimist

    optimist New Member

    First time caller... I'm replacing a very old Bard 5 ton with a Miami HP 5 ton...current system is regulated to 8 gpm on a 12 gpm well pump. But the MiampHP system is nominally rated at 15 gpm, though I'm told that that will be more like 10-11 gpm here due to groundwater temps (65). The "extra" gpm of the current system goes to house water. I don't have the well log (haven't yet gotten it from the county), so I don't know what the well is rated at. Assuming it has enough flow, I could get a 15 gpm pump and regulate the HP at 12 to provide 3 to the house, or leave the 12 gpm pump and regulate at 10 with 2 for the house. The latter is less $ up-front but might starve the HP so seems short-sighted. The former could be problematic if the well isn't rated high enough and will $ for a new pump. So, while studying about this, I stumbled upon a thread in another forum that suggested that the most-efficient design for this case is instead of splitting the water supply to house water and HP, run all water through the HP and tee to the house between the HP and the shutoff solenoid so that the 12 gpm well pump would provide both. The thread I mentioned mentioned plumbing components I have no experience with (cycle stop valve, modulating pressure sustain valve, booster pump) and the diagram showed a pressure tank (with the cycle stop valve) both before the HP and one (without cycle stop valve) on the house water supply after the HP...a little overwhelming to me. I've no idea which of these are absolutely necessary.

    Does anyone have experience with running house water through your HP to reduce well pump flow requirements?
     
  2. geoxne

    geoxne Active Member Forum Leader

    The general rule of thumb for open loop flow rate is 1.5 GPM per nominal ton for entering water above 50F. Anything over that you are wasting your money pumping water. Do yourself a favor and get a Hays or Dole flow control to limit flow to what the HP needs and leave everything else alone.
     
  3. optimist

    optimist New Member

    Reply appreciated! I've read that (the 1.5 rule of thumb) and if I can apply it here it definitely suits my situation - but am I at risk of under-flowing this specific pump (Miami 5 ton) in this specific situation? I know, it's hard to get specific. I just don't know enough to be confident that I can safely apply the rule-of-thumb without paying for it in decreased efficiency. Heck, in theory at 1.5 per ton I could leave everything alone (8 gpm Dole restrictor)...though I feel like at least upping that to a 10 gpm restrictor gives me a little more chance of supplying enough to the hp. I tried to read the Miami spec sheet...all I got was a headache.
     
  4. geoxne

    geoxne Active Member Forum Leader

    I can NOT address the efficiency of a Miami HP. I have no experience with them. I do know cheap HP's (Miami's description) have small heat exchangers. The efficiency of a HP is most directly related to the size of the HX's (air coil and coax). An decrease in flow will not get you a proportional proportional decrease in efficiency.

    Miami HP does not publish its performance at different flow rates. Other manufacturers do. When you look at those other performance charts comparing 3 GPM per ton to 1.5 GPM the heating capacity drops fractionally 6% to 8%. Cooling capacity drops around 2%. When you consider the total efficiency of the system including the pumping, increasing the flow rate does NOT get you a more efficient open loop system. The cost to pump an open loop system is often overlooked and it varies due to many factors (depth to water, size of pipe, pressure, efficiency of motor, etc). Even in a well designed system the cost to pump can approach 30% of the total cost to run the HP open loop system.
     
  5. nc73

    nc73 Member

    I have experience with Miami HP. It's barebones but rule of thumb of 1.5 gpm per ton does apply here. I have run it open loop and closed. It's runs like crap in closed. This thing is made for open loop. You are reading their instructions incorrectly, it is not 15gpm. It is more like 7.5 gpm for the 5 ton. I've run it in open loop before for a 3 ton at 4.5gpm. 15gpm is for closed loop.
     
  6. optimist

    optimist New Member

    Thanks for the input. That gives me the confidence to not throw more money at a non-existant problem.
     

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