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Thread: Solar thermal panels to heat garage floor

  1. #1
    jabber@midrivers.com Guest

    Default Solar thermal panels to heat garage floor

    New to the board so I may be in the wrong pew. I have built a 620 sq. ft. garage with 220 feet of 1/2 inch pex pipe at the bottom of a 4 inch concrete floor. I would like to use about 40 square feet of solar panels to heat antifreeze and pump it through the pex tubing. I'm puzzled about the pump size and also whether it would be possible to just cascade the fluid over the metal plate absorber without using tubing? If tubing is necessary what size and how much is about right per square foot of collector? Any comments or suggestions would be appreciated or point me to a book which has some detailed guidance. Thanks, jabber.

  2. #2
    Join Date
    Jul 2007
    Location
    Quetico, Ontario
    Posts
    5,025

    Default Re: Solar thermal panels to heat garage floor

    Couple of questions

    Where are you located and do you have an estimate of the heating load in BTUs required to heat the building. Only then can you figure out, in your climate if your collector sizing is enough (or too much)

    I have no idea about cascading the coolant, my own intuition (and I am no expert) is that I would rather see it in tubing.

    As for pumps, go to WWW.Grainger.com and look for low flow circ pumps, (or NAWS) for that matter. Be cautious however, some cast iron impeller pumps don't like pex tubing, or more correctly, the pex tubing doesn't like the cast iron. Some thing is in the iron that has a detrimental effect on the pex. There are pumps available for pex, and there is hydronic pex that is Ok with cast iron. (I think!)


    Other than that it is pretty simple to do. You might want consider adding a storage tank of some sort to collect during the day, and give back at night. In that case you might need two pumps and two sets of aquastats.

    Tony
    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

  3. #3
    jabber@midrivers.com Guest

    Default Re: Solar thermal panels to heat garage floor

    Thanks for the quick reply. I am in northeastern Montana. My hope is that a solar system would ease the heat bill and add almost comfort at 30 degrees. When it is 20 below I'll almost certainly stay in the house. The 40 feet of collector is based on the excess thermopane windows I have and the fact that I want to tuck them a bit under the eave to keep them away from the June-August sun.

  4. #4

    Default Re: Solar thermal panels to heat garage floor

    You want to keep it in tubing - in fact, you're probably better off to buy absorber plates with tubing, which will also have the fancy coatings that make them work better.

    How many loops is your 1/2" pex in? if it's just one loop, that is a fair amount of dynamic head, IIRC - I went with larger diameter tubing, but if the floor is cast, you work with what you have.

    While I understand the desire to recycle the leftover thermopane, polycarbonate greenhouse glazing makes a better covering for home-made panels. Commercial panels will work better than home-made panels, on the whole. Given the cost of the circulator they might make sense. But anything is better than nothing.

    Basic idea would be to connect your tubing to collector tubing, with a solar circulating pump run by a solar panel when the sun shines (simplest) or a 110VAC circulator which then requires a brain (controller) to know when to run. There also needs to be an expansion tank, a T&P relief valve, and an air removal valve. That's the basics. Something to keep it from cooking in the summer would be the next (a valved loop that ran to fin-tube in the cupola on top of the garage would be a good one - increase ventilation with the heat - you can also shade the panels for the summer). Or perhaps it runs to a hottub built out of a spare watering trough for the summer?

    The folks at http://www.radiantcompany.com/ Should be able to help you sort out an appropriate circulator. They will also be able to advise you on a good ratio of collector area to floor, though that depends hugely on insulation amount and placement - I hope you used some...

    Cheesiest (that's not good, but it's easy-cheesy) home-built collector - build a hot air panel and run fintube though the top of it. By the time you've built a good homebuilt one, you would usually have done better to buy one, IME.

  5. #5
    Join Date
    Jul 2007
    Location
    Quetico, Ontario
    Posts
    5,025

    Default Re: Solar thermal panels to heat garage floor

    Patio door glass comes in standard tempered sizes of 28x76" or 34x76" These can be had free or almost free from almost any glass shop. A single glazing of tempered patio door glass would allow you to build modules of almost any size. I agree that premade absorber plates would be the easiest, but a simple manifold or loop of copper tubing, placed on top of a piece of scrap steel, on top of 2" of thermax insulation enclosed in a wooden box covered with a number of patio door glazing units would be a pretty easy DIY project. A simple Grunfos pump and a simple aqua stat, T&P valve, air bleed valve and away you go.

    I built a domestic hot water system much like that, but with no glycol,, cost ~300 when all was said and done,,, had the copper and the steel however.

    As for over heating in the summer,,, make some simple summer shades. If it doesn't get sun,, it won't get warm. You can also consider the over hang of the roof to shade it in the summer, as well as plantings etc.

    Tony
    Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

  6. #6
    Join Date
    Sep 2006
    Location
    Willits, CA
    Posts
    5,648

    Default Re: Solar thermal panels to heat garage floor

    See an example here:
    Solar Shed
    500 gal storage @ 180F
    http://www.builditsolar.com/Projects.../solarshed.htm
    http://tinyurl.com/6hypyt
    http://tinyurl.com/LMR-Solar
    http://tinyurl.com/LMR-BigLug
    http://tinyurl.com/LMR-NiFe

    Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
    Powerfab poletop PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe battery | 15, Evergreen 205w "12V" PV | Midnight ePanel || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT

  7. #7
    Join Date
    Nov 2007
    Location
    Nova Scotia
    Posts
    27

    Default Re: Solar thermal panels to heat garage floor

    . Be cautious however, some cast iron impeller pumps don't like pex tubing, or more correctly, the pex tubing doesn't like the cast iron. Some thing is in the iron that has a detrimental effect on the pex. There are pumps available for pex, and there is hydronic pex that is Ok with cast iron. (I think!)

    Just make sure the pex has the oxogen barrier then you can use any pump and for the summer a brazed plate heater could help you get domestic hot water.
    Ken

  8. #8

    Default Re: Solar thermal panels to heat garage floor

    There is pex with oxygen barrier, which can be used with cast iron pumps and other components. There is pex without oxygen barrier, which should only be used with bronze, plastic or stainless pumps. It's a rust issue. Whatever he's got in the floor, the rest of the system will have to match.

    Personally, having seen the inside of a number of "sealed" cast iron systems after a few years of operation, I try to avoid cast iron pumps, pipe, etc. anyway. The "in theory limited" rust is often enough to eventually cause problems, but that's practice & experience rather than theory speaking. Cast iron is certainly cheaper, at the start. In the long run bronze & copper may be cheaper, in practice.
    Offgrid non-system consisting of Kohler and Northern Lights generators plus years of fiddling with what panels - inverters - batteries to buy when I finally pry my wallet open and get going on that. Likewise a radiant floor which has air in the tubes, waiting for me to sort out the solar and connection to the cooling systems of the Kohler and Nothern Lights (which might as well provide heat while they are burning fuel to make electricity). In progress, very slowly in progress - but not in debt.

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