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  1. #1
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    DX GSHP problems



    Hi, i am a beginner when it comes to refrigeration, but i have a question about my Heliotherm GSHP.

    It is running on R410a, and at the moment the evaporation temperature is -6 C.

    i would like to raise that temperature to at least -3 C,

    Anyone has an idea what causes this problem?



  2. #2
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    Re: DX GSHP problems

    Who says that -6°C is a problem?

    What is the ground temperature, only if you have any temperature sensors fitted of course?
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    Re: DX GSHP problems

    Its not a problem, besides that it affects the COP.
    I havent fitted any sensors in the ground, but the outside temperature is -2 C, so i guess that the ground temperature should be higher.

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    Re: DX GSHP problems

    I am jus posting the values that i have, from the heat pump.

    Outside temperature -1 C

    Water from Heatpump 47,9 C

    Water to Heatpump 43,4 C

    Heat gas 73,1 C

    Evaporation temperature -6 C

    Evaporation pressure 5,6 bar

    Condensation temperature 47,2 C

    Condensation pressure 28 bar

    Subcooling 37,8 C

    I hope this will help, diagnosing my low evaporation temperature

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    Re: DX GSHP problems

    When did you last have the refrigerant mass checked?

    Is ice forming on the 2-phase line between TXV & evaporator suction?

    What are the water-glycol temperatures in/out of the evaporator?
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    Re: DX GSHP problems

    The refrigerant mass was checked a few weeks ago, but i am not sure that it was done properly, by the tecnician.

    there is is on the evaporator suction, but not at the TXV.

    There is no glycol/water since it is DX

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    Re: DX GSHP problems

    Quote Originally Posted by Larslk View Post
    Subcooling 37,8 C
    How did you calculate the subcooling?... or is this in fact your liquid line temperature?

    Quote Originally Posted by Larslk View Post

    I hope this will help, diagnosing my low evaporation temperature
    You keep saying the evaporation temperature is low, but in fact you don't know if it is low or not.

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    Re: DX GSHP problems

    Quote Originally Posted by Gary View Post
    How did you calculate the subcooling?... or is this in fact your liquid line temperature?

    I didnt calculat the subcooling, its from the display on the heat pump.

    You keep saying the evaporation temperature is low, but in fact you don't know if it is low or not.
    I didnt calculat the subcooling, its from the display on the heat pump.

    Its true that i dont if ifs low or not, but acording to the heatpump factory, i will a higher COP, if the evaporation temperature -3 C rather than -6 C.

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    Re: DX GSHP problems

    I presume that this new?
    The evap being DX, should be deep in the ground where the temp is normally above 10C. The evap SST should be higher than this.
    Posibble Problems.
    Pipes are not deep enough.
    Pipes are to close together
    Not Enough Pipe
    Wrong soil type
    The unit has run a long time and caused locallised freezing around the pipes (reducing heat transfer)
    Lack of refrigerant (I do not think so, from what you have decription)

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    Re: DX GSHP problems

    Quote Originally Posted by Larslk View Post
    I didnt calculat the subcooling, its from the display on the heat pump.

    Its true that i dont if ifs low or not, but acording to the heatpump factory, i will a higher COP, if the evaporation temperature -3 C rather than -6 C.
    When the ground temp goes up, the evap temp goes up and the COP goes up. When the ground temp goes down, the evap temp goes down and the COP goes down. What you need is global warming.

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    Re: DX GSHP problems

    The pipes is at around 1 meter, and with 0,5 a meter between each pipe, there is about 630 meters of 10 mm pipe.

    The soil is wet clay.

    I have noticed, that before the system starts, i can see that the evap temperature is around -2,5 C, when the injection starts, the temperature rises to -1,5 C, and then when the compressor start it drops to -6 and sometimes lower.

    The heatpump i have is a Heliothem HP10E-WEB with 9 kg of R410a (i hope)

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    Re: DX GSHP problems

    I know about the COP, i had just hpoed for another answer, it is not that cold here in Denmark.

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    Re: DX GSHP problems

    Quote Originally Posted by Larslk View Post
    The refrigerant mass was checked a few weeks ago, but i am not sure that it was done properly, by the tecnician.
    Did he add refrigerant?

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    Re: DX GSHP problems

    How many circuits of copper pipe in the ground

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    Re: DX GSHP problems

    Quote Originally Posted by Gary View Post
    Did he add refrigerant?
    He did add refrigerant, but how much i dont know, i just have a suspicion that something isnt as it should, thats why i am trying this forum.

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    Re: DX GSHP problems

    Quote Originally Posted by Larslk View Post
    I didnt calculate the subcooling, its from the display on the heat pump.
    That subcooling is very high, which means overcharge or air in the system.

    Ask the factory what the subcooling should be, then have your tech remove refrigerant until the subcooling is within specs.

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    Re: DX GSHP problems

    Quote Originally Posted by mad fridgie View Post
    How many circuits of copper pipe in the ground
    There are 9 circuits in the ground each is about 70 meters.

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    Re: DX GSHP problems

    I do not know the product, is this a nominal 10Kw machine

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    Re: DX GSHP problems

    Quote Originally Posted by mad fridgie View Post
    I do not know the product, is this a nominal 10Kw machine
    Yes it is.

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    Re: DX GSHP problems

    Evap pressure drop is Ok about 3.5C.
    Do you know the temp of the gas coming out of the circuits, does it have ice on it?

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    Re: DX GSHP problems

    Quote Originally Posted by mad fridgie View Post
    Evap pressure drop is Ok about 3.5C.
    Do you know the temp of the gas coming out of the circuits, does it have ice on it?
    Yes it has.

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    Re: DX GSHP problems

    Is working as good as it can. I suspect that either the ground is cold, or you have ice insulation on your ground pipework, or simply not he best heat transfer.

  24. #24
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    Re: DX GSHP problems

    Quote Originally Posted by Larslk View Post
    The soil is wet clay.
    Soil is now possibly frozen clay around the pipes.
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    Re: DX GSHP problems

    Quote Originally Posted by Larslk View Post
    The refrigerant mass was checked a few weeks ago, but i am not sure that it was done properly, by the tecnician.

    there is is on the evaporator suction, but not at the TXV.

    There is no glycol/water since it is DX
    Again, please.

    GSHP = ground-source heat-pump, no? So you're going DX directly implanted in the ground, not the conventional circulating loop system.

    There should be temp sensor somewhere - in the ground, otherwise you'll not be able to work out what is going on.

    Could your ground temp have really dropped so low? I'd wonder about that.
    Last edited by desA; 18-01-2010 at 01:34 AM.
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    Re: DX GSHP problems

    How many seasons has this heat-pump run for?
    Was the same effect obvious in previous years?

    If this is the first season of operation, then I'd suspect, judging from numerous comments here, that you may have some level of icing on your DX ground coil, reducing the effective heat-transfer from ground to DX coil.

    Interesting...

    If I may ask - why did you select a DX ground coil, instead of using a water-glycol loop onto DX PHE?
    Last edited by desA; 18-01-2010 at 01:46 AM.
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    Re: DX GSHP problems

    Quote Originally Posted by desA View Post
    How many seasons has this heat-pump run for?
    Was the same effect obvious in previous years?

    If this is the first season of operation, then I'd suspect, judging from numerous comments here, that you may have some level of icing on your DX ground coil, reducing the effective heat-transfer from ground to DX coil.

    Interesting...

    If I may ask - why did you select a DX ground coil, instead of using a water-glycol loop onto DX PHE?
    This is the first season, the heatpump was installed at the beginning om september, so icing might be the reason.

    I selected a DX because it will have a higher COP, than the conventional water-glycol loop.

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    Re: DX GSHP problems

    Ok, then this makes sense.

    What I'd suggest is that you dig up a sample section, if possible, & investigate the icing issue in your soil type. You may want to have the installer involved in this as well.

    He may have to provide additional surface area in the DX to compensate for the icing issues, or he may have re-think completely.

    I'm sure that others will have a lot to contribute here. Let's see what their advice is.
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    Re: DX GSHP problems

    Quote Originally Posted by desA View Post
    Ok, then this makes sense.

    What I'd suggest is that you dig up a sample section, if possible, & investigate the icing issue in your soil type. You may want to have the installer involved in this as well.

    He may have to provide additional surface area in the DX to compensate for the icing issues, or he may have re-think completely.

    I'm sure that others will have a lot to contribute here. Let's see what their advice is.
    Thanks for the advice.

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    Re: DX GSHP problems

    ^ It is an absolute pleasure.

    There are some really top guys on this site. I'm sure between all our heads, we can point you in the right direction.

    From what I'm seeing, you are short of heat-transfer area under icing conditions. Now the thing your contractor will have to work out is if he adds more surface area, that it too does not ice up. Then you will be back to where you started.

    Let him check further down to see what the temperatures look like - this may help. You may also need to find a way to get below the clay, if this is possible (not sure, as it may be deep).

    If you & your installer really get stuck, & he runs out of ideas - if he gives me details on the thermal conductivity & density of your soil type, together with some idea of your coil positioning - this could even be checked using a Finite Element Analysis simulation. The actual predicted heat-transfer coefficient could then be estimated.
    Last edited by desA; 18-01-2010 at 01:42 PM.
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