pool heater

[feelingasi]

ive recently aquired a 100 gallon fiberglass tank. my thought was to paint it black, stuff a bunch of 3/4 pex inside through 2 of the 4 2'' female tappings, and then pass the swimming pool water through the remaining 2 tappings. The tank is "verticle" with 2 2" taps on opposite bottom sides, one on the top side, and one directly on top. ive got most of my parts and there is a set of tees plumbed into the boiler system for this. anybody got any idea's on how much pex should go in the tank?

P.S. I'm not trying to build a 15000 gallon hot tub

 

[SolarAndWood]

Why not just throw a bunch of cheap black tube on the roof? In addition to the direct radiant heat, I bet the asphalt gets as warm as the tank will.

 

[feelingasi]

cus the closest roof to the pool is 30 feet high and metal. and i get about 3 times the snow as you do in the cuse. you can imagin the mess i'd have come cristmas. I've got about $50 invested so far and i'm kind of in the mood for a " boiler expirament"

 

[SolarAndWood]

I bet you get more than 3x than me...I'm almost in Lafayette. You are going to need a lot of surface area if you hope to warm up your pool this summer.

 

[tom in maine]

You need surface area to make a solar system work. A fence, a deck, even the bare ground (or lawn for that matter) will allow you to intercept more sunlight than a 100 gallon container. And it will work a lot better. The roof is best, but the others will do. Black poly pipe, while crude, does the job!

 

[feelingasi]

maybe i didn't explain it correctly, i want to use a loop of 3/4 pex inside the tank, pushing 180 deg water from my boiler thru the loop. then push pool water thru the tank body passing it over the coil. basically a homebrew version of an indirect hot water heater. the only reason for the black is maybe gain a little energy from the sun. i'm just curious as to how much pex would be needed to get decent heat transfer. my biggest fear is not putting enough in and having to rip it apart and start over. I'm thinking 100 feet, but i have no idea if this is even enough

 

[tom in maine]

I understand.
I think if you are firing this up with the boiler, you are apt to lose a fair bit of heat at the wrong times.
Painting it black will allow it to radiate more heat and given the volume/size of the tank, you might find performance suffers.
That being said, a 100 coil of 3/4" PEX cut in half and manifolded up to keep pressure drop down might be okay,

I would suggest a counterflow heat exchanger that could be as simple as an 8' length of 1.5" PVC with a center "core" of 3/4" x 10'
type L copper. The boiler water would flow in the copper and the pool flow would go through the PVC. These work well and are relatively
cheap to fabricate. You would use 3/4" Quiktite couplings on the ends to pass the copper through. The Quiktites would screw into some 1"male
adapters that would be cemented into the ends of the 1.5" PVC Tees that would be on the ends of the 8' PVC pipe.

This is probably not real clear, but it is basically a cheap DIY heat exchanger that works very well with a pool.

I will try to get this online sometime in the not too distant future.

Tom
Americansolartechnics.com

 

[Duetech]

FWIW I don't think the tank is big enough to effect the temp in a pool in any reasonable sense if there is a windy day involved. Pex is not noted for it's thermal conductive property. If you were using copper you would have a better chance of making an impact and probably not over 1/2" diameter. A 100 gal tank is not very big and will not grab that much energy compared to the energy that will be needed to influence the pool. You might be better off getting a weighted plastic tarp you can put in and pull out of the pool as needed. I'm not saying that your tank won't work to some degree but it would have to be isolated from the element of wind and you will have to get a lot of sun to heat a 100 gal tank. The idea of a solar type heater is a good one. You can make panels of black plastic tubes that sit on the ground and can be hooked in series that will charge faster and be usable sooner. For the tank though I'd recommend 100' copper or 400' pex. See this post "Going to an in-tank heat exchanger.. Advice needed." (just a little below your post) they mention a formula for copper/pex copmarison.

 

[feelingasi]

based on that i think i'll insulate the tank. i have some stuff around here called p 2000 left over from building my camp and insulating my crawlspace. it should work. the pool isn't very big and i agree that copper would be better. i do however fear what happens to copper when it comes in contact with chlorine, not to mention what it may do to the alkalinity of the pool. i spend enough money on chemicals. if nothing more, this tank/pool heater will serve as an excuse to run the boiler and make some DHW as i am currently paying "national greed" for that via elec. this will help get rid of some of those odd shaped pieces of wood that are to short or knarly to deal with during the heating season. see that... ever the optimist, i'll find good in anything, even if/when the pool heater fails to work.

 

[Gooserider]

I'm also a bit nervous about the idea of copper pipe (or pretty much any metal other than stainless) in contact w/ pool water, although it is my understanding that at least some pool heaters use copper for heat exchangers.

That said, my recollection is that PEX has about 1/3 the heat transfer ability of copper, so you would need three times as much length to get an equivalent heat transfer. If you use the search function you can probably find more details, but I think the people I recall using PEX to make exchangers in open storage tanks were using about 300' to sink their boiler output. However you might be able to get away w/ 100' since you aren't going to have the same issues of needing to get good heat transfer as the storage tank temp approaches that of the boiler. Assuming 180* boiler temps, you are probably looking at a minimum of 90* delta, probably more like 100-110*, which will transfer heat a lot better.

I would also forget about painting the tank as you aren't going to get significant solar gain from such a small surface , instead I'd look at seeing how much insulation I could pack around it...

Keep us posted on what you come up with, as I am also interested in pool heating - though what I'm thinking in terms of is doing a gravity loop from my future storage tank to a heat exchanger of some sort, likely some variation on that sidearm style that Tom was talking about earlier.

Gooserider

 

[tom in maine]

If you are going to do a counterflow hx, copper is fine. For that matter copper works well regardless of which design you go with, if the pool chemistry is okay.
If you want to be sure of not having corrosion issues in a counterflow, you can use cupro nickel, it is available, but is more than copper.
The counterflow hx is a lot less work and works extremely well for pools with a relatively small exchanger. They have, on occasion leaked, if the pool chemistry goes off, but never created any issue with the pool (like green water, etc).

PEX is actually about 1/100 the conductivity of copper. The relatively thin wall thickness is the equalizer.

You would need 3-6x more PEX to accomplish the same thing. I would not use PEX in a counterflow since there is a "time lag" associated with PEX that
is not as much of an issue in immersed designs.

Your biggest issue with PEX in the tank is going to be pressure drop, so cut a coil into several equal loops and manifold them.

If I was doing this, and I have done many, I would use a counterflow with copper otherwise a manifolded PEX will be okay.

 

['bert]

If you are interested in a DIY solar pool heater, here is one that I found. I did build one the results / cost ratio is very good. If i remember right it gave me about a 8*C rise in temp. Kind of a difficult forum so scroll down to about half way to post # 52 by Brian Clarke. (post numbers are in orange below each post)

http://ffaat.pointclark.net/blog/archives/107-DIY-Solar-Pool-Heater.html

YMMV

 

[Duetech]

Alberta Burner, That's the type of set up I was thinking about in my post above. Agreeable sunshine and few panels like the one in your link and I could probablyheat my dhw and keep my boiler warm (to avoid condensation) all summer long. I already have one circulator going most of 24-7. The panels are stowable and could be stored for the winter. It migh not have been worth the effor but the guy could have used a propane torch to "warm" the tubing to bend it so it would not have kinked while bending but he still has a pretty good DIY design. Thanks for the info.

 

[deerefanatic]

Here's an idea too... Make a serpentine pattern out of pex and sink it in the deepest end of your pool. The coldest water is down there..... You'd heat that, it'd rise to the top and the colder water would sink to the bottom.... Sort of a "radiant pool floor" if you will. Heat exchangers are great...... But there's nothing like heating the water directly........

 

[tom in maine]

If you can deal with the concept, dropping a coil directly into the pool will work fine.
You can simply drop a coil in, preferably manifolded to minimize pressure drop.
No need to do serpentine or anything fancy, a lump of tubing coiled together in the bottom will work well.
Stratification will make it convect and move more heat than you need.

 

[Gooserider]

I would avoid the coil in the pool approach for safety reasons... It would certainly work from a heating effectiveness standpoint, but I'd be concerned about the risk of someone getting tangled up in it and possibly getting stuck under the surface. :red: It may be a low risk, but it seems unnecessary to me...

Gooserider

 

[tom in maine]

avoid the coil in the pool approach for safety reasons... It would certainly work from a heating effectiveness standpoint, but I'd be concerned about the risk of someone getting tangled up in it and possibly getting stuck under the surface. :red: It may be a low risk, but it seems unnecessary to me...

That would be why the coil should be a mass on the bottom of the pool.
Getting caught in that would be reason for a Darwin Award.

I would prefer the counterflow hx, since it looks neater and would eliminate the however remote possibility of such a mishap.

 

['bert]

I would think a coil of any sort would be hard for your pool vacuum to clean well. Under steps is typically a starter spot for algae growth, some coils of tubing that you can not clean really well is just an opening for trouble. IMHO.

I one that I built only took about 4 hours and is run from a small sump pump. If you like I can take some pics.

 

[altheating]

I think I would opt for a stainless pool heat exchanger for about $350-$500. No hastle, no headaches and by the time you put your time and effort plus the cost of all the PEX and fittings it will be cheaper. I would stay clear of any cobbed up mess.