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  1. #1
    Join Date
    Nov 2010
    Location
    Minnesota
    Posts
    16

    Water to water heat pump going out on high pressure lockout

    5 Ton water to water heat pump with buffer tank. Open loop. 12 GPM on source side. Been in operation for 2 years before any issues. Unit will run for about 25 minutes with high side pressure slowly creeping up until it hits 530 psi and trips the high limit switch. Low side pressure stays steady at 100 psi throughout the entire run time. Temp difference on source side of 7 degrees. Temp difference on hydronic side of 10 degrees. All radiant zones come off of buffer tank, buffer tank set at 100 set point, so temp going back into Geo is 90 degrees. Flow meter on source side shows no signs of scaling whatsoever as it is as clear as the day it was put in. Im not a refrigerant tech, but shouldnt that low side pressure climb along with the high side? Anybody have any thoughts?

  2. #2
    Join Date
    Feb 2009
    Location
    Portland OR
    Posts
    2,029
    Any more information such as what your EWT temps are from the well? What brand equipment is this incase there are known issues with a certain brand. I can't answer this question for you since I don't do refrigerant and all my techs are getting ready for the weekend, but the more info you post the more likely you are to get an answer.
    Check out my YouTube channel - http://www.youtube.com/user/skyheating1 We have customer testimonials, product reviews and more!
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  3. #3
    Join Date
    Nov 2010
    Location
    Minnesota
    Posts
    16
    EWT temp is 50 degrees, leaving water temps 43. Checked low and high side temps today high side temp. at 500 psi was right around 185 degrees. Low side temps were around 41 degrees at 100 psi. On the phone with the engineer i know he was quite concerned with the superheat and subcool calculations, but was unable to come up with an answer for what might be causing the issue. As high side pressure climbs so too does the amp draw on the unit obviously near cutout it is drawing a tad over 25 amps. Im just baffled and I do believe they (manufacturer engineers) are as well. Anybody see anything that we could be missing?

  4. #4
    Join Date
    Nov 2010
    Location
    Missouri
    Posts
    371
    Have you checked your Pump on hydronic side to make sure of circulation. It would be like a restriction in air coil with dirt build up
    causing head pressure to do Like what you said. Also Can you name this Geo? I am assuming you are heating going by your temps

  5. #5
    Join Date
    Nov 2010
    Location
    Minnesota
    Posts
    16
    Thanks for your reply. The main hydronic pump was my first thought even though my delta t tells me the pump is indeed moving water. I did replace pump with a new one I had on the truck and the issue remained the same. Id rather not name brand as ive really had nothing but great equipment and service in the past. Would bad compressor bearings or something cause high head like that.while maintaining low suction pressure? Officially stumped. Thanks guys.

  6. #6
    Join Date
    Nov 2010
    Location
    Minnesota
    Posts
    16
    Yes in heating mode sorry I am in Minnesota. Tank temp is derived through outdoor sensor to improve efficiency.

  7. #7
    Join Date
    Feb 2005
    Location
    L.I. NY
    Posts
    129
    Quote Originally Posted by Vikingsguy View Post
    EWT temp is 50 degrees, leaving water temps 43. Checked low and high side temps today high side temp. at 500 psi was right around 185 degrees. Low side temps were around 41 degrees at 100 psi.
    If you are saying the leaving water temp on the hydronic side is 185 you either have low circulation or the water is short circuiting the buffer tank and being returned directly to the inlet. 185 leaving is way to hot it's no wonder it trips the HP

    What is the hydronic inlet temp when the outlet is 185, also what is the buffer tank temp under the same conditions

  8. #8
    Join Date
    Nov 2010
    Location
    Minnesota
    Posts
    16
    185 is the temp of the high side liquid line in the refrigeration cycle. Inlet water on hydronic side is 90 leaves Geo at 100.

  9. #9
    Join Date
    Jan 2013
    Location
    Champaign Illinois
    Posts
    97
    Assuming this is 410a system 100 psi on low side is slightly lower than what it should be. Probably should be around 120 psi or so. You may want to investigate TXV by placing bulb in hot and cold water to see if you get a change in pressures you may have a stuck TXV. If its stuck Part way open it would raise discharge pressures and lower suction. If you see littlle to no change in pressures as you have bulb in hot and cold water there's your problem.

  10. #10
    Join Date
    Jan 2013
    Location
    Champaign Illinois
    Posts
    97
    After re reading posts I have a ?
    The 500 psi is that beeing found at discharge from compressor or is that liquid pressure?
    I'm assuming it's discharge because of the 35 degrees of super heat it would help to see what the liquid pressure is and the amount of sub cooling is been obtained from the buffer tank coax. Just thinking out loud maybe some thing will help I noticed you said that the open loop was flowing at 12 GPM if the water is flowing through to quickly ( think it should be 1.5 to 2 GPM/ ton) the evap coax can not absorb enough heat causing low super heat causing TXV to try to slam shut which would increase liquid pressure and increases sub cooling intern increasing discharge pressure sort of like running over charged. The last thought would be just beeing overcharged this seams like a far fetched idea seeing how system is only 2 years old and you seem to be the only one to work on it. However it may not be a bad idea to recover the refrigerant check weight with unit info and at that time I would replace with fresh refrigerant ( contaminated refrigerant can do some weird stuff. Maybee thies thoughts are out there and not helpfull but I do hope they can ster some other thoughts to lead to an answer. Can't wait to find out what hapens, good luck.

  11. #11
    Join Date
    Mar 2007
    Location
    Cedar Rapids, Iowa
    Posts
    122
    What's the flow rate on the LOAD side? You need to know if the load side is absorbing the proper amount of Btu's.

    Bergy

  12. #12
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    2,483
    According to what you posted, you are only picking up 42000 btu on the open loop. IF that is correct you would only have about 9 GPM on the load side. On a 5 ton unit you should be running closer to 15 GPM on both sides. 3 gpm/ ton is normal water flow for the open loop side, not sure if they run the same on the load side or if they slow it down to raise the temp. All the Geo systems I have done have been water to air, no water-water. If the flow has not changed, I don't know why you would be having hte issue now. But it looks to me like low water flow on both sides.

  13. #13
    Join Date
    Jan 2014
    Posts
    20
    Quote Originally Posted by Vikingsguy View Post
    Thanks for your reply. The main hydronic pump was my first thought even though my delta t tells me the pump is indeed moving water. I did replace pump with a new one I had on the truck and the issue remained the same. Id rather not name brand as ive really had nothing but great equipment and service in the past. Would bad compressor bearings or something cause high head like that.while maintaining low suction pressure? Officially stumped. Thanks guys.
    i would love to help you out but i really need to know what brand and what model.

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