Illinois Typical well pressure fluctuations on a closed loop system

Discussion in 'Maintenance and Troubleshooting' started by wssix99, Jul 22, 2016.

  1. wssix99

    wssix99 New Member

    My first thread - this site has helped me over the past few years in leading the design and install of the Geo system on my new ICF home. Diagnosis of maintenance issues is now in my lap... (We have very few Geothermal experts here within the city limits of Chicago. As to not offend - we'll just say you can count them on one hand... and you don't need close to all the fingers on that hand to do the job.)

    Can someone assist me with what I should expect to see for a typical pressure fluctuation on a closed loop system (with proper functioning expansion tank) when in operation?

    I'm pretty sure I have an expansion tank issue. I have a two stage Carrier (Climatemaster) Water-to-Air system (with built-in expansion tank for the well) that has been getting high pressure lock-outs periods of during high cooling demand since it was installed 2 years ago. (Since the pressure sensors for the refrigerant and well pressures are hooked up in series and throw the same code - that was a fun one to diagnose and narrow down...)

    Within a given summer day, (like we are experiencing now) my pressures are fluctuating by 120+ psi. After the system has rested for a while, it may start cooling in the morning at a well pressure of 40 psi and then it will shoot up to 160 psi where we get the lockout. In the cooler spring season, the pressures never get high enough to trigger the lockout.

    My HVAC company has limited experience with Geo systems and swears that they followed the commissioning instructions at the install. They are hesitant to load up their geo tools and make the trip out to us (to depress the system, check the expansion tank, and re-press the system) so any advice you all can provide will help me expedite this next step.
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Yeh, something is off. Especially with an expansion tank in place.

    Are you measuring pressure drop directly across the heat pump or somewhere else?

    You should be looking at pressures fluctuating between 30 to 50psi seasonally. Not a delta of 30-50. The pressures themselves on a static loop varying between 30 and 50 all year round.

    To get the huge 100+ psi's you're measuring, your loopfield has been way overpressurized or your pumps are deadheading against something.
  3. wssix99

    wssix99 New Member

    Thanks. I'm measuring static pressure just before the well water enters the unit. (I have a drain valve there, next to my air separator, which is really easy to hook a gauge up to.)

    I have also measured pressures moving across the heat exchanger and only see a few psi of difference. BTW - This is a bit of a PITA due to the Schroeder valves for this, but I have some fittings for filling airplane nitrogen shocks that make it a little easier. (I didn't want to invest in a purpose built tool just for this one task.)

    My seasonal fluctuation has only been around 30 psi.

    My 120+ psi fluctuation isn't from the pump. I'm measuring static pressure with the unit off. This is 100% from expansion as the fluid in the well heats up.

    ^ My HVAC guys are wondering if this is normal for a geo well, or not. I just need some expertise/evidence to say "No, this is not normal. We need to depress the well and find out why the expansion tank isn't doing its job."
  4. arkie6

    arkie6 Active Member Forum Leader

    Do you have the valve open on the built-in expansion tank? I'm pretty sure the unit is supplied with the expansion tank outlet valve closed and then needs to be opened once the loop is pressurized. It would be easy for the installer to forget to open that valve.
  5. wssix99

    wssix99 New Member

    I recall checking that with them last fall. I am going to check that again this evening. I'm thinking someone may have turned that valve before the system was pressurized, possibly throwing things off.

    ^ The one thing I could not find is what the initial pressure of the bladder on the tank was supposed to be. Any ideas how one would find that out?
  6. wssix99

    wssix99 New Member

    It shouldn't matter here, but the well is a single 400' deep Rygan well. It's kind of like the house's third leg, but underground:

  7. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Doesn't factor in at all, unless you're somehow measuring pressure at the bottom of the borehole.
  8. arkie6

    arkie6 Active Member Forum Leader

    Those expansion tanks usually have a Schrader valve (like a tire valve stem) on the end opposite the water connection for checking and adding air pressure. If you can find it, just put a tire pressure gauge on it and check the pressure. You typically want to maintain the air bladder pressure a few psi higher than your expected water pressure.

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