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Thread: Solar pool heater. Should I cover?

  1. #1
    DIY Senior Member CanOfWorms's Avatar
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    Default Solar pool heater. Should I cover?

    I have a solar heater for my pool that is 100' of black landscaping pipe tightly coiled on a piece of plywood that I painted black.
    It works in the heat of day, but not as efficient as I would like.
    I have to run the water through slowly and I use a secondary pump.
    My question is this...
    Will I get more heat if the whole operation is covered with plexiglass? I was going to test this with some clear plastic wrap like a clear plastic drop cloth.

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    DIY Senior Member Smooky's Avatar
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    A car setting in the sun gets a lot hotter with the windows shut than it does with the windows open.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by CanOfWorms View Post
    100' of black landscaping pipe tightly coiled on a piece of plywood that I painted black...not as efficient as I would like.
    That pipe might not be a good conductor of heat, and the plywood is actually an insulator rather than a collector. But yes, putting it all in a Plexiglass housing will help trap/hold the heat so more of it might get through. This summer I plan to make a pool heater (for a 1000-gallon pool) with an automotive radiator inside a Plexiglass housing,
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    DIY Senior Member CanOfWorms's Avatar
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    That radiator will work, but will it absorb sunlight?

    If you really want it to heat up you should take a look at the solar oven that Peace Corps has been teaching people in Africa to make. It reaches as high as 275 degrees.
    If you followed those plans and used a few toyota radiators you might get better results.

    As per the black hose, it heats the water for sure.
    I used it last year and it worked.
    But you need to be smart about it. Turn the pump off at night, and put a solar (bubble wrap type) cover/heater when not in use,
    Another big issue is that you need to get the flow to be rather slow through the element or it really doesn't seem to work.
    I used a splitter with a valve cracked to send a slow flow through the coil and the other end straight to the pool.

    It made the pump whine.

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    DIY Senior Member CanOfWorms's Avatar
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    I just saw that you are in Amsterdam. I was there in July and I barely broke a sweat the sun didn't go down until 10 or 11 pm.
    I mean it was not anywhere near hot.
    If you are going to do this in Amsterdam you will need to take advantage of those 18 hour days.
    If you have an above ground pool and are not concerned about appearances. You should consider painting the outside black or having a black plastic skirt that you can wrap around.
    Also, the ambient temp of the ground cools the pool. This year I am going to put a 2" layer of mulch with a plastic liner under the pool. I don't know if it will work, but it might.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by CanOfWorms View Post
    That radiator will work, but will it absorb sunlight?
    As long as it is black, it will get hot when the sun is up and not blocked by clouds or whatever.

    Another big issue is that you need to get the flow to be rather slow through the element or it really doesn't seem to work.
    I used a splitter with a valve cracked to send a slow flow through the coil and the other end straight to the pool.

    It made the pump whine.
    A radiator has a slow flow internally because of its capacity in relation to its inlet and outlet size, and I will likely also use a ball valve to restrict the overall flow. Also, that "whine" means the pump motor was doing less work than it is capable of doing and is drawing less power than when it is pumping at full capacity. Let it run with a wide-open flow and its RPM will decrease and it amperage draw will go up.

    At the other end of all of this, my pool gets too hot for comfort in the middle of Louisiana summers...and I resolve that by adding a pointed-up sprinkler head on my filter pump's return line to gently spray water into the air and have it fall back into the pool cool. After giving that a try, I was quite surprised by how well that works. I can hold 1000 gallons of water below 90 degress even while it is sitting in the sun on a 105 day.
    Last edited by leejosepho; 05-14-2013 at 04:57 PM.
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    DIY Senior Member CanOfWorms's Avatar
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    I got the posters confused. I see you are in Arkansas not Amsterdam.
    I don't really see a solution. The water does not heat up if i run it through full speed.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by CanOfWorms View Post
    The water does not heat up if i run it through full speed.
    That is why cars have thermostats in their cooling systems: To slow the flow so the heat has time to move from one component to another.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    DIY Senior Member CanOfWorms's Avatar
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    Quote Originally Posted by leejosepho View Post
    That is why cars have thermostats in their cooling systems: To slow the flow so the heat has time to move from one component to another.
    Can you expand on how you would do this? I am interested in the application.
    Doesn't an automotive thermostat just open or shut?
    How would this affect the pump? How would you rig it?
    Wouldn't it cycle on and off releasing boiling hot water into the pool?

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    DIY scratch-pad engineer leejosepho's Avatar
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    I was not suggesting a thermostat for what we are trying to do, I was just pointing out that a high rate of flow does not give heat enough time to move from the collector (tubing, radiator or whatever) to the fluid (water).

    Quote Originally Posted by CanOfWorms View Post
    Doesn't an automotive thermostat just open or shut?
    Yes, but there is typically a bypass somewhere so the flow of liquid is never stopped altogether.

    How would this affect the pump? How would you rig it?
    A low-pressure check valve could let water bypass the thermostat until it opened, and that combination would let the pump work at a fairly consistent rate of flow whether through the check valve or the thermostat.

    Wouldn't [a thermostat] cycle on and off releasing boiling hot water into the pool?
    Not with a low-temp thermostat.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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    DIY Senior Member CanOfWorms's Avatar
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    Quote Originally Posted by leejosepho View Post
    Not with a low-temp thermostat.
    What kind of low temp are we talking here?

    I think you might be better off just running 4 of these in series and running everything through it full force.

    Also the radiators wouldn't work for me because I use a saltwater system and it would eat up those radiators quickly.
    It kicks my pumps @ss too, but drips clear themself up on their own more often than with a non saltwater system.

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    DIY Senior Member CanOfWorms's Avatar
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    Or even better yet making a big (big enough) solar over and putting a few radiators stacked in there. You wil need the thermostat of sure because these things can bake bread.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by CanOfWorms View Post
    What kind of low temp are we talking here?
    Something below the "boiling hot" you had mentioned. I believe I have seen auto thermostats that are 130 degrees Fahrenheit (opening point to allow flow), and there might be some even lower than that. But yes, even that would be a bit warm if it hit someone directly where it entered the pool.

    Quote Originally Posted by CanOfWorms View Post
    Or even better yet making a big (big enough) solar over and putting a few radiators stacked in there.
    Then you would become dependent upon convection to get the heat to the radiators where it could then transfer to the fluid...and you could help make all of that more efficient by adding a solar-powered circulation fan inside the oven!
    Last edited by leejosepho; 05-16-2013 at 04:31 AM.
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    In the trades Dana's Avatar
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    Quote Originally Posted by CanOfWorms View Post
    I have a solar heater for my pool that is 100' of black landscaping pipe tightly coiled on a piece of plywood that I painted black.
    It works in the heat of day, but not as efficient as I would like.
    I have to run the water through slowly and I use a secondary pump.
    My question is this...
    Will I get more heat if the whole operation is covered with plexiglass? I was going to test this with some clear plastic wrap like a clear plastic drop cloth.
    You'll get more heat out of it with a higher pumping rate and lower output temp. Unglazed solar collectors are VERY efficient when run at low temp, (say 90F collector output, in 70F outdoor air). If you let it run hotter than that it's re-radiation and convected losses eat into that.

    Glazing cuts into efficiency by reflecting back a fraction of the solar radiation, but allows it to run at higher temps with lower loss. But the performance of the glazing is also quite variable, depending on it's material. Commercial flat plate collectors use low-iron glass with selective coatings to squeak a bit more out. Polycarbonate (Lexan tm) greenhouse glazing works better than plexiglass, but still isn't as good as even cheap clear glass.



    For what you'd spend in glazing to do it right you'd be better off buying cheap commercial unglazed pool heaters (or getting them for nearly-free on craigslist or something.)

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    DIY Senior Member CanOfWorms's Avatar
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    I think I would seal the top in plastic drop cloth to test it. This would only take a few minutes.

    Well this one is $70 on cl

    States it raises temp 5 degress in one week.
    Mine already works better than that.
    But it sounds like you are saying I should get the water flowing through this as fast as possible.
    Mine looks like this:
    100'

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