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Thread: Pool temp going down with solar on

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    Pool temp going down with solar on

    I just bought a house in San Diego with a 13k gallon in ground pool. It had a single speed pump which we replaced with an Intellifo VS. Before changing the pump, the pool was always above 80 with just solar heating. Since replacing the pump, it has been closer to 72.

    I have played with the rpms extensively. With 240 sqft of panels, it appears 36gpm would be appropriate. Using the spreadsheet from this site looking at rpms and watts, 2100 rpm should pump that. I've tried 2100 with 13psi up to 2400 with 16psi and the water temperature does not rise over 3 days.

    I heated the pool to 78 this morning and it has dropped to 74 since then. Outside temp is 89 and the panels have been in full sun.

    How can I solve this?

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    Mod Squad jblizzle's Avatar
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    Re: Pool temp going down with solar on

    I am not sure that you can easily equate RPMs and watts and flow rate.
    Really, you should only need about 24 GPM for panels that size, beyond that the heats gains are a diminishing return.

    Are you sure you have reasonable expectations?
    What are the low air temps?
    Are you using a cover?

    If there is sun hitting the panels and there is water flowing through the panels, then you are adding heat to the water. Could be that you are losing heat due to evaporation or cool air at night faster than your solar can add it.

    How big is your pool?

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    Re: Pool temp going down with solar on

    Dumb question, but are the panels off at night?

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    Re: Pool temp going down with solar on

    Sorry, I did give the pool size in my post but added a signature.

    My expectations are based on the pool temp prior to changing the pump. The day temperature has consistently been high 80's and night consistently low 70's, now and before. Nothing has changed other than the new pump and the lower pool temp.

    I am not using a cover and wasn't before.

    The panels are connected to a controller and off at night.

    I just noticed that even at the higher rpms I do have bubbles in the return. So maybe the VRV is not closing? If so, is it easy to replace?

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    Re: Pool temp going down with solar on

    I might have found something. There was quite a bit of air in the pump basket. I cleaned and re-lubed the o-ring but the bubbles were still there.

    There is a valve just before the pump with the other pipes labelled skimmer and vac/drain. The valve can turn off the pipe labelled skimmer with the other off position going to the side of the tee that doesn't go to a pipe. I turned the valve so it opens to both pipes coming in (skimmer and vac/drain) and the air bubbles in the pump basket and returns are gone.

    Could air have been pumping through the panels and lowering efficiency?
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    mas985's Avatar
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    Re: Pool temp going down with solar on

    Probably not by very much.

    But the change in water temperature could just be because of a change in weather conditions. Dew point and air temperature plus wind speed play a big role in the amount of heat that a solar system can deliver. I looked at your weather and it appears the last few days have been quite winding which can account for a reduction in heat gain.


    I heated the pool to 78 this morning and it has dropped to 74 since then. Outside temp is 89 and the panels have been in full sun.
    What was the starting temperature? Is the pool in the sun too? Are you using a solar blanket?
    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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    Re: Pool temp going down with solar on

    The starting temp was 72 this morning. I heated it with gas to 80 (sorry, typo, not 78) this morning. I turned the gas off at 11am. It is now 7:45 and the temp is back to 74.

    The pool is in full sun all day. I do not have a cover.

    I guess it just doesn't make sense that the weather hasn't changed. We always have an afternoon breeze and it hasn't been any different. My thinking is that something is off since the only thing that has changed is the pump.

    Any idea what speed or psi I should try running it at?
    12,000 gallon IG plaster
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    Re: Pool temp going down with solar on

    What are you using to measure the temps?
    Paul
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    Re: Pool temp going down with solar on

    What is the usual time the solar is turning on and off?

    When did you switch out the pump?
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    Re: Pool temp going down with solar on

    Hope you can figure it out.
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    You can lead a horse to (clear) water, but you can't force him to swim in it!

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    mas985's Avatar
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    Re: Pool temp going down with solar on

    I think your issue is one of heat loss and not heat gain which you confirmed with your test yesterday. 8 degree heat loss in that short of a time is pretty high and somewhat unusual.

    Where you running solar at the same time as the gas heater?

    Did you continue to run the water through solar after you stopped the gas heater?

    Also, are your panels installed on the roof and how high is the roof?
    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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