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  1. #1

    Water source heat pump high head pressure

    Hey there,
    I was working on a water source heat pump Trane serial number# W04C11546 MN# GEVB02411J0110TL. The unit is an upflow with the compressor compartment being on the bottom and the fan and coil on top.

    The problem is that the unit will run for about one minute in cooling mode then goes off on high head (400 psi r-22). Unit runs fine in heat. I replaced the txv to no avail. Believe the problem is the reversing valve at this time, but was wondering what else could possibly be the cause as I normally work on standard split systems and package units.

    I am only working on this for my friend who has a loft in downtown LA. I run my business in the 'burbs, and water source heat pumps are rarely seen here.

  2. #2
    Join Date
    Jul 2005
    Posts
    5,365
    This is mostly due to low or no water circulation. Sometimes it's due to a bad pressure switch, overcharge, or excessive inlet water temp. A bad (bypassing) RV causes low head. HTH.

  3. #3
    Join Date
    Apr 2011
    Location
    Memphis, TN
    Posts
    8
    Is there a strainer in the cond water line that could be stoped up?

  4. #4
    Join Date
    Jul 2010
    Location
    Denver, CO
    Posts
    435
    I agree with the other two that a lack of water flow is the most likely culprit. Is there a circuit setter in the system that is to set correctly, or a restriction somewhere in your piping. Check your inlet and outlet water tempature. You should have a resonable delta t, a very low delta might tell you have to much flow, a very high delta might tell you don't have enough flow.

  5. #5
    Join Date
    Sep 2009
    Location
    PLATTSBURGH, NY 12901
    Posts
    42
    To be sure that the lack of water flow is causing your problem there is more information needed. Think about it...the tube in tube or what ever the exchanger is would also be used in heat. If the strainer or flow was reduced then the unit would most likely also fail in heat due to low temperature cutout. If for some reason it did not fail you would notice that your suction pressure was being effected by the decreased flow. Are you seeing the a low suction pressure in heat? Are you seeing 400 psi on your gauges during cooling or is this the cutout point of the switch? Let's start there first and go from there.

  6. #6
    Join Date
    Dec 2009
    Location
    Southern US
    Posts
    504
    I have seen many of these units that after multiple loss of water flow for whatever reason the high discarge pressure causes the inner tube of the condensor to completely flatten not allowing any water flow. You can check your entering and leaving water for flow and pressure drop.
    I'm good at making things cold...You can ask my first two wives!

  7. #7
    Join Date
    Dec 2009
    Location
    Fort Worth, Texas
    Posts
    151
    good way to get a lot of guessing is to ask a question and give no info.
    what is your entering and leaving water temp, superheat ,subcool,suction and discharge pressure, do you have a condenser water regulating valve of some sort. without info all your going to do is change a bunch of parts.

  8. #8
    When in heating, the outlet water line gets nice and cold. - didn't take the temp of it, but it seems as though the water is flowing correctly. In cooling the opposite it true, outley water line gets very warm.

    I have seen reversing valves on standard heat pumps be functional, but not open all the way.. What troubles me is that when I've run into that in the past,the suction pressure was through the roof. On this unit my low side is at the standard 65 psi. I don't have instrumentation for superheat/subcooling numbers, which I know would really help.


    My temperature splits are right where they should be in heat and cool. 21 degrees in cooling , and 32 degrees in heat. I will also add thatwhen I was recharging the unit after replacing the txv, it would have high head pressure but not go all the way up to 400. I ran it undercharged for about 15 mins and the suction was at 40 psi with the head pressure hovering around 290- 310.


    I did purge the water lines in my initial diagnosis. There was a significant amount of small debris in the bucktet afterwards. Is there a strainer or filter in the water line?

  9. #9
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,702
    Quote Originally Posted by PolarBearAir View Post
    When in heating, the outlet water line gets nice and cold. - didn't take the temp of it, but it seems as though the water is flowing correctly. In cooling the opposite it true, outley water line gets very warm.

    I have seen reversing valves on standard heat pumps be functional, but not open all the way.. What troubles me is that when I've run into that in the past,the suction pressure was through the roof. On this unit my low side is at the standard 65 psi. I don't have instrumentation for superheat/subcooling numbers, which I know would really help.


    My temperature splits are right where they should be in heat and cool. 21 degrees in cooling , and 32 degrees in heat. I will also add thatwhen I was recharging the unit after replacing the txv, it would have high head pressure but not go all the way up to 400. I ran it undercharged for about 15 mins and the suction was at 40 psi with the head pressure hovering around 290- 310.


    I did purge the water lines in my initial diagnosis. There was a significant amount of small debris in the bucktet afterwards. Is there a strainer or filter in the water line?
    In a perfect world there should be a strainer on the inlet of the unit. I think your condenser water side of the unit is where your problem is.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  10. #10
    Join Date
    Oct 2010
    Location
    Baton Rouge, LA
    Posts
    1,110
    If your reversing valve was bad both pressure would be overly high. Something like 350/120 or it would not be changing from heat to cool.

    Your water flow is not high enough, your water enter is to hot, or you have non-condensables in your refrigerant.

    If you truly blew out the heat exchanger and your not over charged it has to be one of those three problems.

    Make sure you don't have a water actuator with a delay in start and/or your compressor is starting after the actuator is 100% open.

    My money is on the water is too hot. Your friends loft is probably connected to a water tower that is most likely not getting the chemicals it is suppose to be and the tower fins are covered in scale.
    If you're too "open" minded, your brains will fall out.
    Artificial intelligence is no match for natural stupidity.

  11. #11
    Join Date
    Sep 2009
    Location
    PLATTSBURGH, NY 12901
    Posts
    42

    Smile Sounds like you might be getting somewhere!!

    Quote Originally Posted by PolarBearAir View Post
    When in heating, the outlet water line gets nice and cold. - didn't take the temp of it, but it seems as though the water is flowing correctly. In cooling the opposite it true, outley water line gets very warm.

    I have seen reversing valves on standard heat pumps be functional, but not open all the way.. What troubles me is that when I've run into that in the past,the suction pressure was through the roof. On this unit my low side is at the standard 65 psi. I don't have instrumentation for superheat/subcooling numbers, which I know would really help.


    My temperature splits are right where they should be in heat and cool. 21 degrees in cooling , and 32 degrees in heat. I will also add thatwhen I was recharging the unit after replacing the txv, it would have high head pressure but not go all the way up to 400. I ran it undercharged for about 15 mins and the suction was at 40 psi with the head pressure hovering around 290- 310.


    I did purge the water lines in my initial diagnosis. There was a significant amount of small debris in the bucktet afterwards. Is there a strainer or filter in the water line?
    From this post it sounds like there are two water lines connected to the heatpump unit. (Water inlet and water outlet) There should really never be a need to have an actuated valve on the main loop lines due to the fact that the water is only meant to be a stable source of temperature media and it is supposed to be kept clean and pure. On a typical system the entering water temperature is kept between 70-80 degrees at all times of the year. The leaving water temperature should have a temp difference of 6-8 degrees in heat mode and 10-12 degrees in the cooling mode. I am beginning to believe that incoming water and flow may be an issue. If the inlet water was higher temperature than the recommended and the flow was reduced then your suction pressure has the chance to be near normal ranges. The load would still be present, even though the flow is reduced it is at a higher temperature which would make up for the loss of flow. In heating the air coil is your condenser and the water coil is your evap. I believe (without being on site) that you could maintain running without issue during heat mode because of this higher loop temp. But when you switch to cooling and your water coil becomes your condenser the lack of flow and the higher temp is detrimental because you can not remove the heat and lower the pressure from the heat pump and the unit subsequently trips off. I was surprised to read the temp differences of 21 and 32 as this numbers are high to begin with and they should be reversed meaning your outlet main water loop should be higher in cooling not heating. Cooling - water coil - condenser - (hot) removes heat lowering the high side pressure in the heat pump refrigeration cycle.
    Heating - water coil - evaporator- (cold) adds heat and raises low side pressure in the heat pump refrigeration cycle.

    Check your inlet water temps and verify your outlet temps and see where you stand good luck.

  12. #12
    Join Date
    Jul 2011
    Location
    Croatia
    Posts
    51
    you can measure temperature by any kind of wrap-on sensor, and before that you are guessing, and, what is frequent problem in maintenance work, if you stay stick by unproved hypothesis for too long, it can drain your energy.

    are you sure in any way that your heating mode is working properly? i mean if you are in some warm area, and outdoor temperature is very high now, you can hardly check how heating system works with no load imposed on it.

  13. #13
    Quote Originally Posted by marsmech View Post
    I was surprised to read the temp differences of 21 and 32 as this numbers are high to begin with and they should be reversed meaning your outlet main water loop should be higher in cooling not heating. Cooling - water coil - condenser - (hot) removes heat lowering the high side pressure in the heat pump refrigeration cycle.
    Heating - water coil - evaporator- (cold) adds heat and raises low side pressure in the heat pump refrigeration cycle.

    Check your inlet water temps and verify your outlet temps and see where you stand good luck.

    The temperature differentials I was referring to was for the air, not the water.

    Yes there is a big cooling tower on the roof of the building. But wouldn't everyone in the building be experiencing issues as well?

    Is it possible that my supply and return water lines were crossed during installation and im trying to cool with water that has already had a bunch of heat dumped into it from other tenants?

    I guess my starting point should be to get some pressure and temperature readings on the water inlet/outlet. Temperature is easy, but what should i use to get the pressures? There are shutoff valves on both the supply and return water lines that have hose bib attachments. Do they make a pressure gauge that fits?

    Thank you all for your responses, very much appreciated. Wish I had more experience with these things.

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