Correct Closed Loop material & static pressure

Discussion in 'Geothermal Loops' started by FHPx3, Jan 25, 2011.

  1. FHPx3

    FHPx3 New Member

    I just recently had my 3rd FHP ES035 installed with a new loop field.
    This time I used a new contractor. To my surprise he used white PVC pipe between flowcenter and the the FHP unit (20 ft to HP). This was "glued" with the purple type compound.

    Originally when he had pressurized the system the first time he had to replace about 5ft of white PVC with the black HDPE GEOLink pipe that had been installed in front of the flow center. When I asked him why not use the HDPE all the way to the rubber hose connection (HP) he said it was not necessary: The operating pressure is only 15PSI and the white PVC is rated 200PSI...

    What is the correct static loop pressure? My other systems have always between 35PSI (lowest) to 60 PSI (highest) pressure. Is it ok to use the materials he used?

    BTW: My current static loop pressure is 12PSI (Jan 2011). The system was initially started in Nov 2010 and pressurized from/to the water line pressure of 40PSI.

    The only literature I found about this was @ waterfurnace and said: "...pressurize the loop to a static pressure of 40-50 PSI (summer) or 50-75 PSI (winter) ... "
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Yes that is low

    That is a low pressure, but are you using a non-pressurized flow centre such as this -

    Flow Centers
  3. FHPx3

    FHPx3 New Member

  4. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    The problem with the schedule 40 pvc pipe is temprature. Depending on your loop field design parameters your low could go below freezing and your high could easily exceed the 73 degree high rating for the pipe. The other consideration is that the solvent welded joints were not designed for repeated expansion and contraction. We allways use hdpe from the field to the flow center and use the "100 psi rated rubber hose from the flowcenter to the unit. I would question why the flow center is 20' away from the unit? Although this is not really wrong, it does not make for a clean install imho.
  5. FHPx3

    FHPx3 New Member

    This is a second floor HP installation. We put the flowcenter in the 1st floor because there we have a concrete foundation kneewall to attach to with the intent to minimize the sound from vibration and the ground loop pipe comes out through the concrete floor.

    I agree with the problem of the repeated expansion and contraction of that pipe and joints as weel as the delta T between heating and cooling. That was one of my concerns.
    When I asked the contarctor he said he " does that all the time."

    With the the correct static pressure (is it anywhere between 35 to 70 PSI?) the problem with the white PVC pipe would only get worse and/or fail sooner. He gave me a 1 year warranty. Maybe I should ask for 5 years, 8, 10 Years??

    My question still remains: What would be the correct static loop pressure and should be HDPE GeoLink installed all the way to the rubber hose connection?
    Is it good practice to have ball valves installed right before connecting to the rubber hose?
  6. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Operating PSI

    We aim for a static pressure of 50psi. Seems about what we can achieve with our existing purge cart, so that is what we aim for. One could top this up with domestic through the PT ports if domestic pressure is higher.

    So, that being said, I like my lowest pressure in the ground loop to be 20psi. Winter time when the water is cold is when you'll usually see lowest pressures.

    That is just our company policy really. But 12psi starts causing some issues as you will have a pressure drop across the unit that will start reducing this down to single digits. That is too close to pump cavitation numbers.

    As to PVC, we do not use it at all due to the temperature swings Eric mentioned. My first purge cart had some PVC on it that blew glycol all over me - that was the end of that experiment.
  7. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    The pressure in the loop field is really not important. What is important is the flow rate. without the correct flow rate the unit will not operate correctly. flow and pressure are related but not directly.
    One of the golden rules we wrote down years ago was to never pipe fluid out of mechanical space. If it were open loop you run the risk of water damage should there be an incident. If it is closed loop you run the risk of air entrapment, poor circulation, multiple call backs. We state in our contracts that we will not plumb to multiple package units on different floors. Your situation would have been better addressed by a "split" for the second floor with the compressor in mechanical space next to circulator pump, then this piping issue would never have come up. imho
  8. FHPx3

    FHPx3 New Member

    Thank you urthbuoy and waterpirate for your replies.
    The system is a 3 Ton closed loop system. I was looking into moving the compressor down close to the flowcenter. I was told with the FHP HP design it is possible but requires some finesse. So far have not found the trustworthy contractor to do it.

    The flow rate seems to be excellent. Initially too high, the installer disabled one of the pumps.
    Still left it in the flowcenter though.

    When waterpirate says the static loop pressure does not matter, what would be a good range then? Doesn't the loop pressure have an impact on heat transfer and hence efficiency?
  9. Looby

    Looby Member Forum Leader

    No, static loop pressure has absolutely no effect on heat transfer.

    Closed loops are pressurized mainly to prevent cavitation on the
    suction side of circ pump(s). As a secondary benefit, maintaining
    a positive pressure insures that air (or mud!) will never be sucked
    into the piping as the result of a minor loop leak.

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