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  1. #1
    Join Date
    May 2005
    Posts
    71

    Ground-source heat pump question

    I live in Michigan and the heat output of ground source heat pumps is inadequate if I size the units for AC. I am considering the 2 stage WaterFurnace Envision series heat pumps. I plan on adding a modulating condensing boiler for other purposes and think that it would be ideal for a supplemental heat source for the ground source heat pump by adding a hydro coil to the air handler. I would be interested in hearing opinions on adding a hydro coil as a supplemental heat source to this heat pump and how to set up the controls. Also, I assume it is not a good idea to oversize the heat pump for cooling to get greater heat output because it will lead to short cycling and inadequate humidity removal but I would like confirmation of that.

  2. #2
    Join Date
    Jan 2007
    Location
    N.E. KS
    Posts
    723
    Quote Originally Posted by rumn8r View Post
    I live in Michigan and the heat output of ground source heat pumps is inadequate if I size the units for AC. I am considering the 2 stage WaterFurnace Envision series heat pumps. I plan on adding a modulating condensing boiler for other purposes and think that it would be ideal for a supplemental heat source for the ground source heat pump by adding a hydro coil to the air handler. I would be interested in hearing opinions on adding a hydro coil as a supplemental heat source to this heat pump and how to set up the controls. Also, I assume it is not a good idea to oversize the heat pump for cooling to get greater heat output because it will lead to short cycling and inadequate humidity removal but I would like confirmation of that.
    Is your cooling load smaller than half of your heat load? I guess that would be the deciding factor in your sizing choice. I am not sure of the capacity between first and second stage on these GSHP's but with a two stage variable speed and some dehumidifiing contol work, I would think they would have one that would suit both your cooling and heating needs without the added hydrocoil. I am from N.E. KS though and you obviously have higher heat loads and lower cooling loads. Have your dealer do a good heat load calc on your house, you might be suprised what you find out. My 2 cents
    Some people know the cost of everything but the value of nothing.

  3. #3
    Join Date
    Jan 2007
    Posts
    115
    Also, I assume it is not a good idea to oversize the heat pump for cooling to get greater heat output because it will lead to short cycling and inadequate humidity removal but I would like confirmation of that.
    Yeah, I recall going through all that w/my dealer. If I recall correctly the answer is:

    You can size to heating, to a degree, based on the second stage and assume the cooling can be handled by the first stage. That, and todays "cool to dehumidify" setting (which I believe slows fan speed down to better support dehumidification) can by and large eliminate short cycle and related. But you still may (and I did) need some aux heating if the cooling load is substantially different. (lower)

    but I'm a home owner, so take that wa/grain of salt.

  4. #4
    Join Date
    Jan 2007
    Posts
    1,359
    If you go with a DX system they can be 100% over the cooling load without a problem. I'm not sure what Water Furnace recommends. DX is better all the way around for residentital applications in my opinion.

  5. #5
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    Quote Originally Posted by EarthLoop View Post
    DX is better all the way around for residentital applications in my opinion.
    Just another opinion.

    All of the DX systems that I have seen have had problems. Insufficient heat transfer and "permafrost" have been the most common issues. If you look at the relatively poor heatflow of earth, it is understandable why a large transfer area is needed for efficiency. Add to that the occasional corrosion or damage to the buried copper lines and the large amount of freon in the loop, you can understand why there are only a couple of companies making DX systems. Quite a few others have fallen by the wayside.

    paul

  6. #6
    Join Date
    Jan 2007
    Posts
    1,359
    Quote Originally Posted by tecman View Post
    Just another opinionTrue.

    All of the DX systems that I have seen have had problems How many have you seen or installed. Insufficient heat transfer and "permafrost" have been the most common issues.possibly installation problem... .If you look at the relatively poor heatflow of earth, it is understandable why a large transfer area is needed for efficiencywhy are glycol systems even bigger. Add to that the occasional corrosion or damage to the buried copper linesdon't plastic lines ever get dug up or wear out.. i like oil filled copper very heavy duty. and the large amount of freon in the loopa lennox 19 seer 5ton has 16.5 poounds, a 4 ton DX has approx. 28lbs. wow big deal it's not like there 100ton chillers, and everybody knows there is no comparison between air to air and geo. you can understand why there are only a couple of companies making DX systemspeople are really starting to jump on board....don't get left behind!!! lots of lies floating around about DX mainly from the glyocol guys that don't like competition. Quite a few others have fallen by the waysideyes even more glycol companies have especially in the beginning.

    paul
    peace

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