Open loop efficiency

Discussion in 'Open Loop' started by nc73, Jan 24, 2015.

  1. nc73

    nc73 Member Forum Leader

    So I ran open loop the first winter last year and my output at the register was 88-90 in first stage, 95-97 in second stage. EWT 56. This winter I converted to closed loop. What a big disappointment. My ewt is 32, lwt 26, even if it was 40 ewt, temperature at the register was still only around 82 in first stage, and 85 in second. I disabled a loop because there's a kink somewhere. It's comparable to a standard heat pump temperature rise. I've read that open loop is high maintenance, etc. That was not the case for me. I have good water, so no scaling problems. The heat pump will not keep up in closed loop, so when the temperature is below freezing at night I switched back to open loop. Sort of a hybrid setup. There is no way I'm going to run heat strips when I can pump and dump to maintain my temperature. What am I missing here? I should have stayed open loop and saved some cash. My electric bill is unchanged.
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Your ewt and lwt is a direct result of feet of pipe in the ground vs. your load. The rules for closed loop design are a lot different than those for open loop. Somewhere in the switch from open to closed, you failed to make that connection, or make your goals clear to your loop installer. If you are happy running a hybrid system, which a lot of people do, than you have solved your own issue.
    urthbuoy likes this.
  3. engineer

    engineer Well-Known Member Industry Professional Forum Leader

    Open loop has the advantage of higher (winter) EWT, but it is all to easy to squander that advantage via high pumping power.
  4. nc73

    nc73 Member Forum Leader

    It wouldn't be so bad if I didn't have to worry about the antifreeze level every time I do the switch over to open loop and back. Can't seem to find anything accurate to test antifreeze percentage. I use the freezer method. Even the hydrometer I ordered from the UK was useless junk. Also I see people using CSV's to prevent the pump from cycling too much. If I adjust the flow for 5 gpm, the pump does not cycle.
  5. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    What happens to your pump when you create artificial head pressure to prevent cycling?
  6. pfer10

    pfer10 Member

    I looked at the CSV when I first moved to this place since it was my first experience with a well and Geo thermal open loop. I purposely installed a valve so I could throttle down the pump when I changed out 1 water logged bladder tank. The house has 2 bladder tanks. On my 1/2hp submersible current draw is about 4.4 amps @238VAC. When I "throttled" it down to just keep up with the Geo flow at 40 psi (tank cycles from 30-50psi to best simulate the CSV) current dropped to 4.1amps. Is this what you typically see Eric? The CSV guy acted like power draw would go way down and I remember he said one pump head does more than others. I wasn't impressed.

    Right now my pump uses around 900 watts and with my current bladder tank setup it is only on 30% of the time the Geo is on so roughly 300 watts average. I know they say you will replace pumps more often without the CSV but I had to replace mine last year and it was 12 years old. Geo is 10 years old so it made it all that time with the Geo. It failed for another reason. I also know larger than 3/4hp you need to rest longer. I am blessed with high water tables so 1/2hp submersible can handle the house and Geo.

    I am looking at ways to reduce my pump power further by using a different type pump in the basement if I can get the flow or by using a combination of 2 pressure tanks running at different pressures. Still working on details of both.
  7. birkie

    birkie Member

    With regard to a CSV and power draw - apparently there are two different impeller architectures that result in very different power/flow characteristics. Read this:

    "Some 2 HP submersibles with floating stack impellers may only reduce from 14 amps to 12 amps at low flow. Others with fixed stack impellers can reduce from 14 amps to 5 amps, and would be considerably more efficient at low flow rates"

    I don't have open loop, but I did buy a house with a way oversized well pump, very low drawdown (~ 20 gal), but supports about 6.5 gpm steady state. To defer well maintenance, I cobbled up my own homemade cycle stop valve using a pressure regulator, and a globe valve for bypass. In the process, I discovered that my pump is a "floating stack", and hardly drops in the amp draw while throttled back to low flow rates.
  8. pfer10

    pfer10 Member

    I guess that shows what type pump I have also. :( Thanks for the additional information Birkie.
  9. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Ok, first EWT of 32 in January is okay for closed loop, but is your heat pump big enough with the reduced out put to heat your house? Leaving air temps mean nothing without EATs. be carful switching back to open loop, you need to change your freeze protection.
    I agree if you were happy with open loop I'd have spent the loop money on a variable well pump instead.

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