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Solar combination question.

Kestrel
Kestrel Member Posts: 102
Hi Gang - and Happy Thanksgiving - quick question



I'm about to start the install of the Lochinvar Knight WHN-085 (wall hung fire-tube) and Lochinvar SDT-065 (65 gal indirect with 2 coils)

Plan is for using second coil for solar hot water input to be installed next year.



The question is, in Seattle, with one or two evacuated tube arrays, will I be able to harvest enough solar BTUs to worry about plumbing for the solar to supplement space heating as well as heating DHW?



That is, plumbing for boiler->tank and boiler->house is straightforward, but tank->house makes things much more complicated, both the piping/valves and the logic.  Is it worth the trouble to do this, or will the solar input only realistically be able to provide for some of the DHW demand?



House is 2100 sq ft, heat loss about 55000-60000 BTUH at 20 degree design, emitters are panel rads on second floor and basement, and joist space tube/extruded plates on first floor.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 24,397
    Probably not...

    Unless you have a very large collector assembly.  On a bright sunny day, as a rough rule of thumb, you can get about 50 watts (max)  -- 150 BTU -- per square foot of collector if it is oriented directly perpendicular to the sun, or if it can really focus.



    And my recollection of Seattle area is that you folks don't tan, you rust...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Ironman
    Ironman Member Posts: 7,501
    Agreed

    Jamie hit it dead on. Two panels is only enough to contribute to your domestic demand. You would probably need 6 - 8 panels to make a dent in your space heating. I would recommend flat panels over evacuated tube. Slightly less output, but better longevity (some may dis-agree).



    Something else you may want to consider: If you do your boiler as one project with the solar, then the entire system (boiler, tanks, piping, solar, labor, etc.) qualifies for the 30% tax credit.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    What will the heat emmitter be?

    If you are supplementing a radiant floor you might be able to get some heat out of it depending on available sunlight. A radiant floor doesnt need hot water, only warm water,(depending on what type of radiant floor you have) I have 90 evac tubes running to a 120 gallon storage tank and I get all my shower water and some of my radiant floor heating capacity. The best part of the investment is the entertainment value of sitting in my lawn chair in the mechanical room watching it work.  
  • ColoradoDave
    ColoradoDave Member Posts: 54
    Old School

    That's so old school Wayne..... you need a Lazy Boy recliner to really appreciate your mechanical room. LOL.



    But I agree with Wayne on the solar output.  With staple up radiant running somewhere between 100-120, you could get some benefit from the solar.  My humble opinion is.... if you're going through the plumbing and labor of mounting 2 collectors on the roof... what's the real difference of mounting 4 or 5 up there anyway?

    I'm not familiar with the weather patterns (solar gain) in Seattle.... but a couple of extra panels probably wouldn't hurt.  The thing is, and this is just my opinion... if you tie it (solar) into space heat, you probably wouldn't want to be drawing the heat from the DHW storage, instead having a seperate 120g storage tank.

    Just an aside.... I'm currently installing a continuous flow system with staple up radiant in my own home and intend on using a differential controller on the return to transfer solar storage to my space heat.  Another (simpler) way to do it for you would be an Set Point control to turn on solar heat OR boiler heat.
  • Kestrel
    Kestrel Member Posts: 102
    Thanks

    That's what I suspected - this makes my plumbing simpler.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,559
    Ironman

    I think you are wrong about the tax credit applying to the fossil fuel portion.

    http://www.dsireusa.org/incentives/index.cfm?state=us&re=1&EE=1



    I'd love to be proven wrong on this
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Gordy
    Gordy Member Posts: 9,546
    Federal energy tax credit

    150.00 on gas boilers>= to 95%

    300.00 on waterheaters >= .82 energy factor

    solar  domestic hot water, and PV 30% no cap.



    State of Illinois funds exhausted.



    Nicor 450.00 for gas boilers >= 95%  350.00 >= 90%.  Storage waterheaters energy factor .67 or greater 200.00.
  • VictoriaEnergy
    VictoriaEnergy Member Posts: 126
    Realistic use of solar

    I'm from Victoria just north of you (as my handle implies). 



    My observation is; we get very nice Septembers, almost a second August, but in mid to late October we say goodbye to the sun for all but the odd day here and there until about March.  When it's overcast enough you can't see the sun through the clouds, the actual solar energy the best vacuum tubes out there still get nearly zero output.  The odd hour of intermittent sunlight we get does very little (except get your hopes up that March has finally come)



    On the other hand, I think solar works great in the summer and shoulder seasons. A properly sized and set up system can do the lions share of your domestic hot water needs.  I also recommend good quality flat plate collectors over tubes.  Tube systems have self destructive issues if they sit in full sun stagnating (ie up to temp and no flow through them, or pump not functioning)  Most homes can get an honest and reasonable return on their investment with a 2 panel flat plate system serving the DHW only.



    I also recommend you configure the setup with a solar preheat tank feeding into your boilers indirect tank to get the most out of the shoulder seasons.

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