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Thread: Adding solar hot water, plus other issues..

  1. #1
    DIY Junior Member asolarheat's Avatar
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    Default Adding solar hot water, plus other issues..

    Hi, I am not sure which forum this should go in so if this is not correct I apologize in advance, and would not object to a moderator moving it to the correct forum if this is not the right one. This is a long post as I tried to give as much nfo as I could think might be needed.

    I am looking for design ideas. I have an out building I am calling my power building that needs heat of a minimum of 68 degrees. Currently, it drops down to about 44 degrees, even though it ids buried on 3 sides, with only the doors exposed / open to the environment.. Additionally, there is a storage building that would be nice to have heated also. I cannot put any kind of flame / fire in the power room due to fumes.

    I am looking to do the manual labor: digging trenches, laying pipe, etc., and then hiring the licensed plumber to come make the connections, install any specialized valving, etc. IN other words, I want to come up with the plan, do the labor intensive / manual labor aspect, and then have the professional do the expertise-required tasks.

    The power building is approximately 10x 12’ and is buried on 3 sides. The roof is on the same grade level as the 1st floor of the house. The storage building is approximately 6’ x 8’.

    The original idea, idea #1, was to add a zone to the house’s radiant floor system, running it to the power building, and return it via the storage building. This would give the storage building some heat, although it would not be a lot. The power building would have a wall-mounted radiator type heating unit. The new zone pipes would run through the 1st floor ceiling of the house, down approximately 9’, enter the ground, and run over to the power building. The return line would leave the power building, be routed thru the storage building and then return to the house, going up the side of the wall and back to the boiler system.

    The radiant pipe is Ύ” Kitec - the newer stuff, not the stuff lawsuits are made of.  The Kitec pipes would be set inside 3” PVC pipe, and the 3” pipe would be filled with expandable foam, encasing the Kitec pipe. The 3” PVC, wrapped in fiberglass insulation, will be placed in a double 2” rigid foam box. Additionally, 2” rigid foam will be placed on top of the ground and then covered in concrete. I think that should be sufficient insulating qualities.

    The 2nd idea is to run a ½” PVC cold water pipe from the house to the power building. This line would feed a gas-fired tankless water heater that would then heat the water for the wall-mounted radiant radiator. There would be a Kitec line run from the power building to the storage building, and the return line would go back to the power building.

    The 2nd idea seems better for the following reasons: There is a plan to build a nice insulated building on top of the power building. The propane gas line regulator is right next to the power building. There is no need to add to the existing radiant system of the house and run a long line from the house to the power building.

    Other considerations: we would like to add domestic solar hot water to our house. I could install the hot water storage tank to the nice building being planned for on top of the power building. I could then run the hot water line from the storage tank to the house, up the wall, and across the 1st floor ceiling to the mechanical room, where it could be tied into the existing radiant & domestic hot water system. The current radiant boiler supplies both domestic hot water & water to the radiant floor. The ouse is a 2-story house approximately 3,150 sq. ft. in size.

    What is better: idea #1 or #2?

    Is a ½” cold water PVC line sufficient for a small gas –fired tankless water heater? I saw a Powerstar model at Home Depot tonight that looked like it would fit the bill. There is a ½” copper line coming out of the house currently that supplies a hose bib that could be tapped into to feed the cold water line to the power building.

    What size line from the domestic solar hot water panels to the storage tank is required ? ½”, Ύ”, or 1”?

    What size line from the hot water storage tank to the existing radiant & domestic hot water system is required? ½”, Ύ”, or 1”?

    Thanks for the thoughts. The drawing attached is not to scale, although the dimensions are very clse, give or take 1‘.
    Attached Files Attached Files

  2. #2
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by asolarheat View Post
    Other considerations: we would like to add domestic solar hot water to our house.
    60 >enter water temp rise in F
    100 >enter gals per day usage
    2075 =calc'd avg. BTU/hr

    5 >enter 24 hr U.S. avg. insolation energy in kwh per sq. meter
    701 =calc'd avg. BTU/hr per sq. meter
    3 =calc'd solar panel area in sq. meters.

    In NM you'll do better than 5.
    Last edited by Thatguy; 11-29-2010 at 12:16 PM.

  3. #3
    In the trades Dana's Avatar
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    Any gas fired tankless would likely be 10x oversized for these spaces, but only a heat loss calc will tell. Buried hydronic loops have to be very well insulated, which could add a lot to the expense of running separate zones off the house boiler.

    A PowerStar electric tankless is a dubious hydronic boiler, and purpose-specific electrioc boilers are available for similar cash. But...

    ...if you're going electric, radiant cove heaters or oil-filled baseboards have about the same comfort level as low-temp panel radiators at a fraction of the cost of a hydronic solution.

    What's your zip code? (for weather and subsoil temp data)

    Is these rooms/buildings insulated all 6 sides? With what, and to what R-value?

    Insulated doors?

    Any windows? (size & type?)
    Last edited by Dana; 11-30-2010 at 02:35 PM.

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