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  1. #1
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    Nov 2007
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    23

    Geothermal loop temps help

    i have had some advice here before on a install at my cabin in Canada .iwas having problems with comp head frosting on a brand new install,i was told to chq water temp on return and supply .Outside temp last week when i was there was -15f during the day ,the loop is 11/4 manifold and 4 500 ft loops of 1 in total length is apx 2800 ft with manifold ,45ft rise to cabin in 11/4 lake is 8ft deep at loop.unit is a 4 ton , both return and supply pipes are insulated with 3/8 wall armorflex ,it is not buried runs along rock up to cabin ,i will try bury it in spring! ,intake water temp was 35f return water temp was 28f,loop does have methonal 20%.my supply air temp was 75f and return air was 60f,i know those water temps are low but i beleive it is loosing temp from the cold temps out side as it runs 370 ft apx over land until cabin ,i am using 2 grunfoss 26-116 pumps 1 on intake and 1 on return lines ,so is this poss why comp head frosting as temps to low,thanks for all your help

  2. #2
    Join Date
    Apr 2002
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    11,808
    If your lake was deeper, I would say the water at the bottom of it would be 39F. I do not think you are losing that much temperature, however the lines could freeze to slush if you turned the pumps off.

    A five degree drop of the anitfreeze mixture is about normal, 7 is not overly excessive.

    As a guess, I would say the refrigerant probably evaporates about 20F cooler than what the entering anitfreeze temperature is. so probably as cold as 15F.

    Maybe there is only about 9F superheat, puts the gas temperature at about 24F. Dome will not be much warmer than that.

    So if your place is 60F and any more humid than about 25% RH, the dome will frost.

    What sounds off, is the air temperature rise of the unit. It should be a little bit higher, have a pro check your unit out.

  3. #3
    Join Date
    Dec 2007
    Location
    oregon
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    885
    Quote Originally Posted by cbprov View Post
    i have had some advice here before on a install at my cabin in Canada .iwas having problems with comp head frosting on a brand new install,i was told to chq water temp on return and supply .Outside temp last week when i was there was -15f during the day ,the loop is 11/4 manifold and 4 500 ft loops of 1 in total length is apx 2800 ft with manifold ,45ft rise to cabin in 11/4 lake is 8ft deep at loop.unit is a 4 ton , both return and supply pipes are insulated with 3/8 wall armorflex ,it is not buried runs along rock up to cabin ,i will try bury it in spring! ,intake water temp was 35f return water temp was 28f,loop does have methonal 20%.my supply air temp was 75f and return air was 60f,i know those water temps are low but i beleive it is loosing temp from the cold temps out side as it runs 370 ft apx over land until cabin ,i am using 2 grunfoss 26-116 pumps 1 on intake and 1 on return lines ,so is this poss why comp head frosting as temps to low,thanks for all your help
    Is the 370 feet of header pipe total length or is that one direction? Better put at least three feet of soil on the header pipes, five feet would be ideal. You may also have laminar flow occurring in the loop(low reynolds number) which will also contribute to low thermal transfer. Your split does sound a bit low on the air side, but pretty good on the water side.
    Genius = The guy who can do anything...except make a living!

  4. #4
    Join Date
    Nov 2007
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    23
    each leg of the manifold on land is apx 370ft each ,why would the air side have a low temp thanks

  5. #5
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    Dec 2007
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    oregon
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    Quote Originally Posted by Carnak View Post
    If your lake was deeper, I would say the water at the bottom of it would be 39F. I do not think you are losing that much temperature, however the lines could freeze to slush if you turned the pumps off.

    A five degree drop of the anitfreeze mixture is about normal, 7 is not overly excessive.

    As a guess, I would say the refrigerant probably evaporates about 20F cooler than what the entering anitfreeze temperature is. so probably as cold as 15F.

    Maybe there is only about 9F superheat, puts the gas temperature at about 24F. Dome will not be much warmer than that.

    So if your place is 60F and any more humid than about 25% RH, the dome will frost.

    What sounds off, is the air temperature rise of the unit. It should be a little bit higher, have a pro check your unit out.
    Your header pipe lengths are long, real long for 1.25 piping. what is the delta p at the water in and out at the unit? you have the probable answer right here. ( above) as to the reason for some frost. is the frost just on the head of the compressor? or is it creeping along the piping ? If it is just ambient humidity frosting on the head, it is normal with the long run times you are experiancing. what is the air speed set on in the airhandler?
    Genius = The guy who can do anything...except make a living!

  6. #6
    Join Date
    Apr 2002
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    Quote Originally Posted by geodude View Post
    Your header pipe lengths are long, real long for 1.25 piping. what is the delta p at the water in and out at the unit? you have the probable answer right here. ( above) as to the reason for some frost. is the frost just on the head of the compressor? or is it creeping along the piping ? If it is just ambient humidity frosting on the head, it is normal with the long run times you are experiancing. what is the air speed set on in the airhandler?

    He needs a pro to come out and take a look.

    Pressure readings on the anti-freeze will determine the flow.

    Perhaps if the charge was adjusted, there will be more than 7F drop, especially if the flow is lower due to long headers. But for some reason being able to pick up a net 7 degrees on the loop means it is most likely not laminar. Those pumps have a bit of head.

    He is in a cold area, -15F, probably a closed loop horizontal would have loop temperatures a few degrees cooler hovering around freezing right now.

    He is also keeping an unoccupied space cool. With a low return air temperature, I would expect more heat transfer to the air than what he is getting, over 20F even, maybe dropping to say 19 to 20F once the place was up to temperature. Not sure on his fan speed settings, so this is something for a pro to look at.

    He can't do much about the exposed headers right now, but going out from the house it will drop off cooler than 28F before it is in the lake. The bottom of the lake is 39F maximum, so he can only pick up so much heat, then he loses some heat going back to the house.

    Probably if he lived there full time, he would be freezing a block of ice on the bottom of the lake and have an enetering loop temperature stuck at the freezing point of water.

  7. #7
    Join Date
    Dec 2007
    Location
    oregon
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    885
    I remember this guy from a month ago or so, got all bent out of shape when I suggested a pro evaluate the system. The loop was put in before winter if I remember right. It was a diy install on the duct and equipment with a loop contractor doing the loop. THe cabin is reached by airplane. The ho says he is an hvac a/c tech. I told him the three things to look for in this situation were water flow, water flow, water flow. If there was some heat strips in the unit maybe it would raise the incoming air temp faster.
    Genius = The guy who can do anything...except make a living!

  8. #8
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    Nov 2007
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    23
    Hi Geodude you are right on the money ,if you want to pm me i will give you my work # ,i have been doing hvac installs since 1988 ,as i said before i do not service and the co i wk for does not do geo ,i have nothing to hide and i did take your advice and install pt ports to get temp readings with a temp gauge in the water as you posted with the supply and return air temps ,the unit does not have a back up heater i left the electric furnace in that is horiz in ducting and installed geo pump in upflow position with a damper in plenum , if heat pump fails electric will cut in at 50f and close damper and geo will shut off ,i never did get pressure to det flow rate ,i will get it next week thanks again for all your help

  9. #9
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    Apr 2002
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    11,808
    Quote Originally Posted by geodude View Post
    I remember this guy from a month ago or so, got all bent out of shape when I suggested a pro evaluate the system. The loop was put in before winter if I remember right. It was a diy install on the duct and equipment with a loop contractor doing the loop. THe cabin is reached by airplane. The ho says he is an hvac a/c tech. I told him the three things to look for in this situation were water flow, water flow, water flow. If there was some heat strips in the unit maybe it would raise the incoming air temp faster.
    yes the heat strips work better as it works on top of what the heat pump can do.

    If there is no road and it is a fly in place, there are no power lines from a grid.

    He must be a furnace guy then other wise superheat, subcooling etc would have been posted. He needs to fly in a refrigeration mechanic

  10. #10
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    Apr 2002
    Posts
    11,808
    cbprov

    If you are in the field as you claim, you should register as a pro member. You will get more specific answers then with your situation posted in the pro forums.

  11. #11
    Join Date
    Nov 2007
    Posts
    23
    Thanks for all the advice so far ο do app it and i do have yr round power i run a 25kW el in winter thanks

  12. #12
    Join Date
    Dec 2007
    Location
    oregon
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    Quote Originally Posted by cbprov View Post
    Hi Geodude you are right on the money ,if you want to pm me i will give you my work # ,i have been doing hvac installs since 1988 ,as i said before i do not service and the co i wk for does not do geo ,i have nothing to hide and i did take your advice and install pt ports to get temp readings with a temp gauge in the water as you posted with the supply and return air temps ,the unit does not have a back up heater i left the electric furnace in that is horiz in ducting and installed geo pump in upflow position with a damper in plenum , if heat pump fails electric will cut in at 50f and close damper and geo will shut off ,i never did get pressure to det flow rate ,i will get it next week thanks again for all your help
    Relax man !, no one is questioning your experiance, when the suggestion to call a pro was made, it was to call a geothermal application professional. There are situations in a geo install that you will not encounter on an air source install. We can only do so much from this side of the screen. your low air temps are more then likely due to the low entering air temp at the air coil. You may also want to check your duct to be sure it is sealed absolutely air tight if any of it is in unconditioned space. As carnack stated, with that much loop exsposed (740') to the ambient conditions, (-15f) your losing capacity. The small amount of pipe insulation on the loop header pipe protects little at -15f. cover the pipes with five feet of soil, keep the indoor temps higher, or run strip heat for an hour when you get to your cabin, then switch to water source, I'll bet the frost may go away. Do not add charge to the system untill you have done these things.
    Genius = The guy who can do anything...except make a living!

  13. #13
    Join Date
    Apr 2002
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    11,808
    It may only get chilled a degree or so going to the lake, maybe 2 degrees coming back. Just guessing

    If he was living there year round, he would be making ice at the bottom of the lake, loop temp will drop, even with the headers buried if he was running it longer to keep the place at 68 to 70F instead of 60.

    Closed loop in Canada, you were supposed to pick out the equipment based on its capacity at an EWT of about 32F.

    Horizontals with 600 ft per ton (non-slinky) will still get down around freezing for february to march, getting your heat by making frost 5 to 6 feet below surface of the ground.

    Verticals ran a bit warmer.

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