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Thread: Solar pool heater. Should I cover?

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  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 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
    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 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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    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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    In the trades Dana's Avatar
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    You want the difference in temperature between the water coming into the collector and what's flowing out to be 20F or less (eg: 68F pool water, 88F water coming out of the collector), but if the delta is much less than 10F you're probably chewing up more pumping power than it's worth. It depends on the absolute efficiency of the pump.

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    DIY Senior Member CanOfWorms's Avatar
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    Quote Originally Posted by Dana View Post
    You want the difference in temperature between the water coming into the collector and what's flowing out to be 20F or less (eg: 68F pool water, 88F water coming out of the collector), but if the delta is much less than 10F you're probably chewing up more pumping power than it's worth. It depends on the absolute efficiency of the pump.
    Last year the system I had worked. And though I did not measure it, it was acceptable.
    But my wife wants it really hot. Like over 80.


    I have the black sprinkler pipe hooked up to black rubber garden hose with fittings.

    The pump had a reducer and fed into that.

    Last year I was always screwing around with it because of one thing or another.

    What kind of pump to I need to work with my hose diameters?

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by CanOfWorms View Post
    Last year the system I had worked. And though I did not measure it, it was acceptable.
    But my wife wants it really hot. Like over 80.
    90 is comfortable for me, and here is what I have done:

    Name:  solarpoolwarmer.jpg
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    That hose was fairly warm before I began sending the water through it, and now it is much cooler. Beginning water temperature was 84, and I suspect I will have 90 in a couple of hours.

    Quote Originally Posted by CanOfWorms View Post
    What kind of pump to I need to work with my hose diameters?
    I am using an inexpensive pump and filter combo, but you might look for a TACO circulator:
    http://www.taco-hvac.com/en/products...nt_category=18
    Last edited by leejosepho; 06-11-2013 at 09:47 AM.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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