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Thread: What can you tell me about solar heaters?

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    What can you tell me about solar heaters?

    Pool surface area is 800 SF. Current solar heating panels are 600SF. Climate zone 8/9. rainy winters, hot summers, few clouds

    What I would like to know:

    1- is there a formula given
    a- pool surface
    b-solar surface
    c-outside temp
    d-water flow rate
    e-starting water temp
    f- no pool cover
    results in approximate temperature rise
    {looking for better results than, oh 10 to 15 degrees}

    2- one contractor said, adding 200 to 400 SF would not increase the effectiveness of the solar heater

    3- what is the optimal flow rate of water thru the pump: some number, low, medium or high speed?

    Thank you
    36K gal, gunite w/ plaster,[18W x 38L x 8 deep end] 300SF cartridge, 80-100 GPM filter, Sta-rite S7M120 and Polaris 9300 electric robot. Rooftop 6 panel Solar heater, Sacramento Valley, Climate Zone 8

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    Mod Squad jblizzle's Avatar
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    Re: What can you tell me about solar heaters?

    The more panels the more heat .... assuming you can provide enough water. Most panels want around 1 to 1.5 gpm per 10 sqft of panel. The heating is more efficient at these higher flow rates.

    The efficiency of the panels is dependant on the mounting angle and exposure to the sun.

    A cover helps immensely to retain the heat that is lost to evaluation at night. For example, in April I would get 5-6 degree rise each day, but would lose 5+ degrees at night without a cover.
    Jason, TFP Moderator
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    Re: What can you tell me about solar heaters?

    TY. this is on the south roof, peaking east-west, on typical 2 story house. So if you have 500SF solar, and I only have 600 for pool twice the volume, ours is under heated.

    we're seeing about a 4 degree rise during the daytime
    36K gal, gunite w/ plaster,[18W x 38L x 8 deep end] 300SF cartridge, 80-100 GPM filter, Sta-rite S7M120 and Polaris 9300 electric robot. Rooftop 6 panel Solar heater, Sacramento Valley, Climate Zone 8

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    Mod Squad jblizzle's Avatar
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    Re: What can you tell me about solar heaters?

    Some may argue that mine is oversized ... Just depends what you are trying to do. I happened to find a good deal on 11 panels used, but one was damaged and would not fit well on the roof.

    Mine is off now as the pool was too hot. Really more about extending the season than maintaining heat in the summer. Although running them at night can actually cool the pool.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    JasonLion's Avatar
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    Re: What can you tell me about solar heaters?

    Check out the Florida Solar Energy Center, they have lots of information along those lines.

    More panels always means more heat.

    One drastically over-simplified rule of thumb is that panel area equal to pool surface area is a serious amount of heat. Of course that varies dramatically with a number of factors.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: What can you tell me about solar heaters?

    Thank you for the link. It's not so much about heating in the summer, but trying to extend the season.
    36K gal, gunite w/ plaster,[18W x 38L x 8 deep end] 300SF cartridge, 80-100 GPM filter, Sta-rite S7M120 and Polaris 9300 electric robot. Rooftop 6 panel Solar heater, Sacramento Valley, Climate Zone 8

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    Isaac-1's Avatar
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    Re: What can you tell me about solar heaters?

    More is always better, but when it comes to exact performance there are too many hard to predict factors, there are various derating formulas that can be applied based on geographic location, level of pool sun exposure, angle the panels are mounted, etc., but in the end they only get you into the ballpark. At the fringes of the season you tend to find the actual weather patterns themselves may be the deciding factor, annual average sun exposure only goes so far in a calculation if you live in an area where you tend to have clouds when you need solar the most, etc. Having said that more is always better, but if you live in a northern climate you may need to look into glazed panels, they don't provide nearly the amount of BTU transfer per surface area as unglazed in optimal conditions, but they do allow operating at much higher temperature differentials. (unglazed solar tends to work better when it is 70 degrees out and you want your pool 85 degrees, glazed works better when it is 40 degrees out and you want your pool 85 degrees)

    Ike
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    mas985's Avatar
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    Re: What can you tell me about solar heaters?

    Sacramento has fairly similar weather as ours and my experience has been that 75% coverage has been more than enough to meet our needs. However, we really don't like to swim when the air temps are cool (<80), but that is ok since solar does not work well with cool air temperature anyway.

    If we get a string of warm (80+) days in March, it is possible to bring the water temperature from the upper 50s to upper 80s in a few of days. So 30 degrees of heat gain is possible but conditions have to be just right. Wind and cold air can be killers for solar and we get a lot of wind where we are so not all days can be that productive. On a good day, I can get up to a 10 deg rise in a single day but I have also heard that others can do better than that. It all depends on the panel size.

    But during the summer and with the use of a solar cover, overnight heat loss is only a few degrees and the solar run time needs to be only about 1-2 hours per day to maintain 88F. I will usually set the solar temp to 86F and use direct sun heating for the rest.

    However, if I don't use a cover, it is a completely different experience. The daily temperature swings can be as much as +-8 F so run time needs to be most of the day and the evaporation is very high.

    This might also be useful for you (Sacramento):

    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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