Closed horizontal loop pressure

Discussion in 'General Discussions' started by geome, Apr 26, 2010.

  1. geome

    geome Member Forum Leader

    Just had our 12 month system check. We have a closed horizontal loop. At what loop pressure would you consider increasing the pressure, and what would you set it to?

    The tech said that he would not increase the pressure if the reading was 40psi or more (it was in the mid 30's.) Do you agree with this? He raised the pressure up to the mid 50's. Low 60's is probably our max since our pressure tank (for our potable well water) is set to that. Thanks
  2. Palace GeoThermal

    Palace GeoThermal Well-Known Member Industry Professional Forum Leader

    There is nothing wrong with what the tech has done. There is no hard and fast rule on system pressure.

    I have seen them as low as 5 psi and as high as 60 psi.

    They all work.
  3. geome

    geome Member Forum Leader

    Thanks Dewayne!

    The tech had an analog pressure gauge that went into the PT port. It was a Weiss gauge, maybe 4" round. I'd like to pick up a pressure gauge to do more thorough system checks myself since the tech used an IR thermometer to read loop temperature and no water flow (gpm) and heat of extraction/rejection was calculated.

    What pressure gauge (to check loop pressure) would you recommend for a homeowner (accurate, sturdy, but not necessarily the most expensive)? I'd preferably to buy one ready to go into the PT port since I don't need another project right now.
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Keep in mind that the plastic expands slightly because of the pressure, so a fresh installed loop will loose pressure. Even more pressure change comes from temperature changes. Given the fact that we use now widely non-pressurized systems, which work like charm, I am not sure that I would change too much unless I get negative pressure (and who says that even this would not work).

    We use analog 5 inch gauges, they are accurate enough for the purpose of determine performance within specs. Digital ones are not more accurate and significantly more expensive.
  5. Bergy

    Bergy Member Industry Professional Forum Leader


    If a heat of extraction/rejection was not done, the tech has ZERO idea about the system's performance. I would ask the contractor for a complete report to be kept with the Geothermal unit.

    An IR thermometer is not the recommended way to check water temps because a shiny surface will give false temp readings. Any pressure gauge reading up to 100 PSI with single PSI marks will work fine.

  6. geome

    geome Member Forum Leader

    I'll speak to the owner the next time he calls me for a reference. Included in the installation price was one fall and one spring check. Not much of a check without knowing about system performance (and having accurate readings.)

    Thanks for the feedback on gauges. I'll post results as soon as I get readings.
  7. Looby

    Looby Member Forum Leader


    For what it's worth, here's what I did for a P/T port pressure gauge

    Total cost (gauge + snubber + P/T port adapter) was about $140.

    BTW, digital gauges aren't necessarily more accurate than analog,
    but they do have higher resolution than even a large analog gauge.

    IMO, that makes it easier to get good differential readings in the
    presence of a high (and fluctuating) static pressure background --
    especially when delta-P across the coax is as small as it is with
    the WF Envision (only about 3 psi @ 8-9 gpm for my NDV038).

    The ability to select various pressure units is also kinda handy.

  8. WF_Inc

    WF_Inc Member


    The typical operating loop pressure is 40-70psi with no air present in the system. Loop pressure will fluctuate with the seasons; therefore, it is normal for a technician to verify that the loop pressure is above 40psi while on service calls. We would not be concerned until the pressure is below 15psi. Even then the unit will still run; however, it may not be as efficient.
  9. geome

    geome Member Forum Leader

    Thanks for the info. Our system will be 1 year old in a few weeks. It was explained to us that we may need to have pressure added to the loop, possibly several times within the first year or two (more so toward the beginning than the end of this time frame). Our loop pressure was close to the mid 30's if I recall correctly (my notes are on a different floor.)
    Does WF teach it's installers to calculate the heat of extraction/rejection as part of normal service visits and/or at system startup? While I am extremely satisfied with the installation that was done, I am a bit surprised (based on other installers here typically calculating this) that I have never received this information from our installer.

    Thank you for the link and for your thoughts. It looks like you have assembled a very nice unit. I wouldn't mind assembling these parts, but is there any way to get more specific information on the P/T port adapter that I would need to connect to the other parts? Figuring the type of connectors that I would need is not my strong suit.
  10. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Could you tell me why you would loose efficiency at lower loop pressures?
    More and more installs are now non-pressurized systems, including mine at home. I measure 13 psi between flowcenter and heatpump, and 4 psi leaving source pressure after the heatpump, which gives me a bit over 19 gpm flow.
    (one of your Synergy 3D 6 ton units).
    The heat extracted is 40,500 at 32 F degree EWT, which given your COP of 3.6 in the second stage gives me a total capacity with the compressor heat added over the 50000 btu/h which you have published for the 2nd stage. So overall very pleasing, with performance nicely exceeding over factory specs.
    Very pleased with the performance of your unit!
    So are you telling me that the system would run more efficient as a pressurized system? Why?
  11. teetech

    teetech Member Forum Leader


    HE = GPM X water deta T X 485 (brine)

    There are no pressure numbers in that formula.

    Grundfos recommends 2 - 3 lbs pressure at pump inlet which is met by standing water column on a pressure-less flow center.

    I think Dewayne hit this on the head.
  12. Looby

    Looby Member Forum Leader

    Just those three parts, they thread together directly. Nothing else needed
    except some teflon thread-sealing tape -- available in any hardware store.

    Gauge is 1/4" NPT male, P/T probe (gauge adapter) is 1/4" NPT female.
    The (optional) snubber goes between; one end is male, the other female,
    both 1/4" NPT threads. Here are some gauge adaptor part numbers:

    Sisco model# GA-125 or Petesplug model# 520

    Or, ask your installer to get one for you -- he might have it in stock.

    good luck,

  13. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    May be you misunderstood. My point for heat extraction was that the numbers indicate that the system runs very efficient wether you have a pressurized or non-pressurized system, actually above factory specs. Since waterfurnace commented that with lesser loop pressure you loose efficiency, I was doubting that this was the case and questioning why.
  14. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Loop Pressurization

    Loop pressurization is to ensure air has been removed and to prevent pump cavitation on the suction side of the pump.

    I've never been an expert on pump cavitation as it can get pretty complex. Most pump manufacturers report desired minimum pressures (required head pressures). Cavitation can take place at some relatively high pressures in some cases.

    If in doubt, look up the head pressure requirements for your circulating pumps and see if they are adequate.
  15. WF_Inc

    WF_Inc Member


    In WaterFurnace training courses we teach that the heat of extraction/rejection should be calculated during startup and service.
  16. WF_Inc

    WF_Inc Member


    We apologize for not specifying in our original post that the numbers provided were for a pressurized closed loop system. Non-pressurized systems are a little different. When using a non-pressurized flow center in a closed loop system, the minimum water pressure required by the circulating pump is maintained by a column of water in the cylinder above the pump. Pressures that we refer to are suggested operating pressures. Pumps used in these applications, only need 3psi or greater to function normally. Our concern is that the pressure does not drop below the minimum 3psi.
  17. geome

    geome Member Forum Leader

    Looby & WF, thank you again for your replies.
  18. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Thanks for your reply.
    I understood that you meant pressurized systems, however you made a comment that you loose efficiency with lower pressure, which I questioned.
    As long as you do not suffocate the pump, which would reduce flow, efficiency should not be affected. I used the non-pressurized systems as an example. Grundfos 26-99 are used for both pressurized and non-pressurized systems, it would be new for me that they differ.
  19. Looby

    Looby Member Forum Leader

    I agree. I don't see how a heat pump could possibly know/care about
    the static pressure of the brine. GPM is GPM; delta-T is delta-T; and
    static pressure has no effect on heat capacity.

    As long as the loop circ pump isn't cavitating, I see no mechanism
    by which the static pressure of the brine could affect heat extraction,
    pumping losses, compressor load, or any other aspect of efficiency.
  20. WF_Inc

    WF_Inc Member


    You are correct. The efficiency loss and will occur when the pressure is below 3psi. At these pressures we are concerned with air getting in the pump and causing cavitation, which then could result in pump failure. Pressure will change as the temperature changes. Our goal is to have enough pressure on the loop that it can go through the seasonal temperature changes and still maintain a positive pressure.

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