One low pressure fault after 6 hour rest

Discussion in 'Maintenance and Troubleshooting' started by Paul Bruneau, Feb 22, 2014.

  1. Paul Bruneau

    Paul Bruneau New Member

    Hi All-

    I have a self-installed 3 ton water to air unit from Ingram's. My only issue with it is that it will often throw a low-pressure fault after it has been resting for 5-6 hours or so. I don't care about the fault itself--the compressor always starts back up without issue after the one fault--I just want to make sure the fault isn't a sign of a bigger or growing problem.

    I have a 500' deep 1.5 inch closed loop that becomes 1" at the foundation entry point. The flow center is also 1" lines which then goes to 3/4" at the heat pump. (I supply these sizes in case there is some pressure gain/drop issue that someone might spot).

    The flow center is non-pressurized. I filtered the ground loop before hooking it up to the heat pump, and let it flush itself.

    In these screen shots you can see my data system showing one of the low-pressure fault events. I do set back the thermostat at night which is why I have these longer "rest periods" on my system. During the day, it has a more typical cycle pattern of 30 minutes on, 1 hour or more off (based on outside temp of course). It NEVER faults except after this prolonged rest period, and then ONLY one time.

    The left screen shot is the watt meter of the system showing the loop pump and the compressor running at 3kw, then the fault occurs and the fan runs by itself during the 5 minute fault at about 250 watts. The right screen shot is the flowmeter.

    Any ideas? Thank you!

    Screen Shot 2014-02-22 at 2.17.44 PM.png Screen Shot 2014-02-22 at 2.20.14 PM.png
  2. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Ingram made the money. What do they say?

    You are clogging your heat ex-changer and the pump goes out on internal thermal over load, therefore your unit stops.

    What did you buy?

    How much did you save?

    Even though you thought the loop was clear, did you install strainers?

  3. Paul Bruneau

    Paul Bruneau New Member

    I haven't asked them yet, but I'll let you know.

    You think the compressor is getting overheated due to no heat exchange because of a clogged heat exchanger if I am understanding you. That seems strange to me because you can see good 10gpm flow right from the start, no? Also, how would a clogged heat exchanger present as one and only one low pressure fault on the first cycle of the morning, followed by all day fine performance? Not trying to argue, just trying to understand.

    I bought this guy:

    I saved enough to replace it every year for 5 years plus about $10,000 after that plus I had the satisfaction of learning and doing it myself, thanks for asking.

    No, I didn't install strainers. What is the size of the line through the typical heat exchanger? I filtered the loop through t-shirt material for an hour and only caught some sand-size dirt and some little plastic chips from the drill crew honing and welding the loop pipe. I would think it would have to be like 1/16 or so tube to clog up on that stuff.

    You seem kind of angry at me for installing my own heat pump? Sorry about that but I couldn't have justified the cost that the local contractors wanted. I would have kept my fuel oil. I live in an area with lots of wealthy people, and I think they price their quotes for those people who keep them busy even with those prices. If it is wrong to install my own system and then ask a question here, then I won't bother you any more.

    Thanks for your reply
  4. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    How cold are you letting it get? Unit refrigerant is exposed to that ambient air and it is expected to be in a conditioned space.​

    Mark is more likely frustrated with Ingram's. The service and enquiries being downloaded to us - the volunteers.
  5. Paul Bruneau

    Paul Bruneau New Member

    Thanks Chris. The unit is in what I would refer to as a semi-conditioned space. It's in a mechanical room that is exposed to my finished basement office (also semi-conditioned). It could get down to 50 or so. Does the refrigerant get weird at that temperature? If so, I could see how that could be the cause. I could make it more of a fully-conditioned space by adding a register to the hot air plenum (it currently just get leaked/conducted heat from the plenum and the ductwork in there)

    Ingram's didn't send me here. I just found it online. I see lots and lots of posts by people who had their systems professionally installed and I assume the people answering them typically aren't the same people who installed those systems so I think those enquiries are no different than mine, but I might not be seeing some aspect.

    I am happy to do my part to volunteer help where I can and I plan to.

    Thanks again!
  6. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader


    Let us start over.

    I did not intend to be harsh. I am sorry if I sounded that way. It was after a long day of fixing errors of others for 6 hours and 2 hour drive each way from the problem geothermal system.

    We internet volunteers learned what we know the hard and expensive way, OJT. We work to elevate our industry away from the hack and whack guys who are in geothermal for the buck that the prevailing tax credits make possible. My list of FAQs still holds, but I am sorry about my attitude.

    Your link to what you bought is half of what I pay for like sized equipment from my manufacturers of choice, so when the mail order guys fail in their approach to a well designed system at half my cost it hurts.

    Ask Joe Hardin what he thinks about Ingram.

    Thanks Chris.

    warm regards,

  7. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    Yes. That sounds like your problem. The temps being likely on the edge of operating conditions.
  8. RgEngr

    RgEngr New Member

    I don't have an answer for you (sorry), but questions of my own. I am in the process of selecting and ordering heat pumps for my own system (ground loop is in and ready to go). I had concluded that a flow-meter would be a good idea. What kind of flow-meter and instrumentation do you use and what generated the plots?
  9. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I use flow meters when ever I can. Like isolation ball valves it is impossible to have too many.

    The same is true of pressure gauges. Water treatment and filtration is imperative.

    Since I am no longer walking I thought of opening an on-line store until I re-read my post above.

  10. mrrxtech

    mrrxtech Member

    I'm a Do It Yourselfer, not a Pro. But I'm good at seeing issues from an objective point of view.

    I believe your mistake was not flushing the loop with an equivalent of a flush cart.
    The flow on your right hand graph shows flow instability which is a sign of air in the loop.

    For around $150 you can buy a 1.5 hp swimming pool pump and flush the system of air. From what I've read you have to pump your loop contents at a high rate of flow in both directions. I flushed my loop in one direction then used an air removal float valve to remove air at the high point in the system for continuous air removal. At the time I wasn't familiar with the need to reverse the flush flow direction.

    I have pictures of my home made flush cart if you would like some ideas. You are down to the point where you could take suction on a column of 4" PVC pipe around 5 ft tall to see changes in level as the air is displaced. Add loop coolant mixture as needed to bring the level up in the column until the level stabilizes indicating the air remaining in the loop is minimal. I used a Tygon hose on the return so I could see air bubbles.

    To remove foreign material during the flush you can buy a GE lexan/clear body whole house water filter at Home Depot for $50 to catch any dirt, and other material that may have gotten into the loop during loop installation. The filter has a selector for bypass, isolation and full flow.

    I'm not familiar with the Thumb Rule for Well depth required per Ton of Geothermal. Is your loop sized for 3 Tons?

    What size Grundfos pump(s) did you use?

    If you want recommendation on the pump model and where to buy it and other components, like the air removal float valve, let me know and I'll pass that information to you.
  11. mrrxtech

    mrrxtech Member

    If a DIYer didn't make a mistake on his install, he would never learn the details of how his unit works.
    Working through issues is how most people learn on their own.

    Open your on line store. There are more people that need supplies and help than current HVAC companies can deal with.
  12. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The last time Paul was posting here was Feb 23, 2014. Kind of late to get back to him...
  13. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Geo heat pumps need a certain amount of water flow at a certain temperature to keep the happy, not much else.

    You need pressure/temperature ports for thermometer and pressure gauges to be inserted, and you would be able to calculate the flow with good precision.
    Analog pressure gauges have too much variance, it is imperative to use the same instrument in the ports (same for thermometers) to insure accuracy. Accuracy for flow meters is also questionable, I never found one which works well.
    Thus I never put in a permanently installed pressure gauge, nor do I have flow meters anywhere in the system. P/T ports before and after the heat pump where you insert the same needle instruments is all you need.
  14. mrrxtech

    mrrxtech Member

    Did you all help him out? It looks like Mark and I are a bit late.

    So Paul, if you are still out there monitoring this website. What was your problem?
  15. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    I just re-read the entire thread. I think there is air in the loops and it floats back to the high point with the rest time

  16. mrrxtech

    mrrxtech Member

    When Paul said:
    "I filtered the ground loop before hooking it up to the heat pump, and let it flush itself."
    He told us what the problem was, air in the loop.

    With recommended flush flow rates and times, allowing a loop to flush itself could work on a Well loop, but you would need a continuous air removal device, plus make up to the loop as the air vents out.
    To protect the compressor, you would need defeat the compressor start by lifting a lead to the compressor, or power the loop circulator pumps with another source of power.

    Over time the air would be vented out. A 2 gallon bladder tank could provide the loop makeup for the slow flush after most of the air was removed.

    Hooking up the swimming pool Flush Cart would be a quicker fix.
  17. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    No, he did not tell us anything. It depends on what flow center he has on wether he has enough velocity to purge the air out. Non pressurized flow centers are self purging, they have a canister where debris and bubbles get purged out.

    Again, you keep commenting without having the knowledge...

    He obviously had good flow, as indicated by his gpm graph.
  18. mrrxtech

    mrrxtech Member

    Why was the graph of loop flow changing if there was no air in the loop? I would expect the flow rate to be constant unless there was interference like air or large particles causing the pump flow rate to change.
  19. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    The first spike was the flow after the unit shut down. That was stable at 10 gpm. The second much wider curve shows the flow AS INDICATED over roughly 30 minutes, and suggests flow rates between 9 and 11.5 gpm.

    So the unit had a low pressure fault during stable 10 gpm flow. After reseting, the flowmeter indicated flow between 9 and 11.5 gpm, which did not cause an faults!

    Plus the non pressurized flow centers are usually placed before the circulator pump and the heat pump, thus any air in the loop would have been purged out before it hits the pump and the heat pump, unless the canister is empty.

    You fall for the illusion of precision, namely that cheap flow meters deliver precise data. Wether you have 9 or 11 gpm is irrelevant for the issue at hand, a 3 ton heat pump would be happy with it.

    Again, sit back, relax, and learn first!
  20. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    The flow bounces shows me the air. It moves when the system does its I/O thing and runs through the co-ax heat exchanger causing the lock out. Once it is out of the heat pump it goes to find the highest point in the loops. It sits in the high point until the system shuts off, and then goes to the gravitational high point not the pumping high point.

    The Delta P shown does not prove flow, it just show what the flow could be "IF" the piping is full of fluid.

    It is possible an improperly installed open flow center, (backwards) could gulp air, not eliminate air.

    Our guy froze to death, so?

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