What should the delta range be?

Discussion in 'Maintenance and Troubleshooting' started by morecode, Nov 1, 2011.

  1. morecode

    morecode New Member

    Ok, things are up and going well, we have just over 30 days of data recorded by the welserver and the system is delivering as designed.

    Equip review:
    Location: Central Michigan
    ClimateMaster TT 27 072 (6 ton)
    Horizontal closed loop (3/4) buried at 8ft, 4800 Ft pipe - 20% Methonal
    QT (non-pressurized) flow center (2 pumps)

    What should the delta be running? I throttled back the return a little and it went from 3-4 to 5-6, now averaging closer to 6 as the EWT water temps drop below 60.

    I'm using the pressure difference to calculate the flow, but I'm thinking I will probably need to get a flow meter soon to get more accurate data and ensure I maintain the flow rate range required.

    As I throttled back the return a little, the pressure went up on both sides, I'm assuming this is normal?

    I've checked those around me and there are welservers showing a delta as low as 3 and as high as 8... I'm assuming that higher is better? Of course their equipment is all different, including their water sources...

    Is there a correlation? Your thoughts?
     
  2. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    We try to get a delta of 5-10. You gain nothing by throttling back the pumps to up the delta. The efficiency of the heat pump does not go up by doing so.


    If you have a two pump system, you can cut the power to one pump as long as you still get enough flow.

    What flow are you calculating? The pressure difference is still the best way to go.
     
  3. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    Remember that the delta will be lower in first stage than second stage.
     
  4. morecode

    morecode New Member

    flow

    D, thanks for the input, perhaps you are right, maybe I was reading stage 1, then throttled back the valve and just happened to read it in stage 2. I will double check that procedure this weekend.

    I thought by restricting the flow, the water was staying in the loop longer because the pressure went up on the return side, and only slightly up on the supply side.

    I'm an amatuer.... but I'm trying to learn! ha ha.

    My gpm (calculated on pressure difference - good to hear this is a perferred method) is about 18 gpm (rounded up). Based upon my 6 ton unit, I'm required to have a min of 15 (2.5 gpm per ton) and the like to see 3 gpm per ton (ClimateMaster).

    I don't think 1 pump can give me that, so I'm kinda thinking I shouldn't consider shutting one down. I did however think of another option.

    My designed callled for 7 - 600 ft loops of 3/4.... I installed 8 - 600 ft loops of 3/4 with the header inside the basement, each having a shut off valve on the supply and return.

    What if I just shut down one loop, what would be the "expected" results?

    your thoughts?
     
  5. Howard Ek

    Howard Ek Member

    "I don't think 1 pump can give me that, so I'm kinda thinking I shouldn't consider shutting one down. I did however think of another option.

    My designed callled for 7 - 600 ft loops of 3/4.... I installed 8 - 600 ft loops of 3/4 with the header inside the basement, each having a shut off valve on the supply and return.

    What if I just shut down one loop, what would be the "expected" results?

    your thoughts?"

    It would decrease your efficiency.
    I would shut one pump off and see what it does. We have been having good results with only one pump running on first stage, then go to two pumps running on second stage.
     
  6. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    btus of extraction are not only determined by delta T but also gpm. higher delta T with lower gpm may not change btu.
     
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Running 7 loops with no outside header means a low pressure drop in the loopfield, achieving high flow rates. Congrats! Let it run without throttles. Heatpumps run slightly more efficient when higher flowrates are used. What pumps are you using to circulate the water through the loopfield. Do they read 26-99 or 26-116?
     
  8. morecode

    morecode New Member

    pumps

    Thanks for the input guys... Yes, the pumps are 26-99's, with the B&D (QT) flow center.

    So if I understand correctly, shutting down 1 loop (would still have the reommended design parameters of 7) would drop the efficiency? I will perform the "no throttling" test this weekend and monitor the results. Still curious if I duped myself with the stage1 - stage2 data results of throttling... So glad you guys are here and make yourself available.... Thank you!

    Anyone use the QT (non-pressurized) systems? I was wondering about the water level in the QT center... It says "top off" after purging... and also noticed a line on the inside of the tank - I assumed indicating water level. I held to that line, as opposed to "topping" it up to the bottom of the plug. Any thoughts on this?? Thought about emailing B&D for a clarification to their instructions.
     
  9. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    We use the QT on pretty much every install. Top it off to about 2 inches below the top. Keep all the loops open, the larger your ground loop, the higher your incoming water temp, the more efficient the heat pump.
     
  10. morecode

    morecode New Member

    top off

    Thanks Doc... I will do that today.
     

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