Few Questions about a diy "pool heater"

[donberry]

I have a 24' x 52" round pool. Just ordered my solar cover now I am thinking about how I want to go about making a solar "heater".
I am thinking I am just going to go with the coiled pipe/hose idea but have a few questions and was wondering if anyone had any ideas....
1. I was thinking about just using the black coil pipe. Lowes has the 3/4" 100' rolls for around $45.00. I then debated using soft copper tubing and painting it black, but it would cost twice as much for 100' and would only be 3/8" - so a lot less water would be heated.
Would the copper be so much more efficient that the 3/8" 100' would work better than 3/4" 100' of plastic ?

which leads to question 2.
2. I could put the pipe on my garage roof. As it would be seen when you pull in the driveway, I would build a box to sort of spruce it up cosmetically - basically a wood box with maybe plexiglass for the cover. Since I would be building the "box" if i went with the roof idea, I would obviously paint the bottom and sides of the box black and could also put metal on the bottom of the box. For this, if it would help, was thinking about just using aluminum metal flashing that comes in 50' rolls x 6" and only costs under $15.00.
Would the aluminum be better than wood painted black and also, would the aluminum be better if it was painted black ?

Now the biggie, question(s) 3.
I was thinking, which is usually dangerous, that it would possibly be better to have the water remain in the "manifold" for a longer period of time, heating it up more. If the water is just flowing thru it, it would not have much time to heat up, but if the water were sort of trickling thru it, less water would be exchanged, but the water would be much hotter - am i correct in this thinking ?

100' of 3/4" pipe only holds about 2 1/3 gallons of water and since my pool has around 14 1/2 thousand gallons - that 2 gallons is going to take quite a while to make a difference......so the hotter it is, the better ?

Ideally, how many 100' coils should I use. Would obviously be a big deal if I did go with copper. 3 100' rolls of black plastic = $150 where the copper would run me $300+.....

Then, what i have no idea of, is exactly how big a pump I would need. I believe a slow flow would be better, but I imagine the trick would be getting a pump that would pull the water up to the roof - tho it won;t be pulling all that much I guess and gravity will help it getting down.

i know there is a ton of stuff around the internet on this, but after searching and reading for quite a while, these are the questions I still have - with I guess the biggie being how many rolls of 100' plus the size of the pump.

I could put the hose on the ground, on one side of the pool. The only downside is it does not get full sun until around noon - but then gets full sun until dark. the roof would get pretty much full sun all day - how big of a difference is that extra 4 hours going to make ? i am guessing quite a bit considering the minimal amount of water i will be moving.

or.........
would I get more heat by building a brick "fireplace" and making a copper manifold - i have all of the free wood I will ever need, but would be a pain to go out, start a fire and then keep it going all day long .

any ideas appreciated

 

[jblizzle]

Re: Few Questions about a diy "pool heater"

General remarks, as I did not read your post carefully:

Solar heating is about square footage exposed to the sun. Generally it is usually cheaper to buy the solar panels over a diy setup of the same area. Also solar heating is most efficient at as high a flow rate as possible. Better to heat a lot of water a little than a little water a lot.

Btw, I used to have over 2000 feet of one inch black tube and that was only about 200 sqft. I am going to be installing 500 sqft of panels in the next few months.

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[Mmonaco]

I bought used solar panels off Craigslist for $1.00 a square foot or less. I have almost 1000 sq ft of panels and the kids love it. That might be easier and cheaper than DIY.

 

[jblizzle]

Re: Few Questions about a diy "pool heater"

Mine came off craigslist as well. I had to order some extra parts but included the controller. Under $2 per sqft after the extra parts.

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[danpik]

almost everyone who is a tinkerer and owns a pool has tried the "hoses on the roof", black coiled pipe, etc solar heaters. Most get the same results. A mediocre heater for the money spent. I have seen some very creative solutions in the past befor solar heaters were comonly available and a couple of them actually worked pretty good. One in particular was a grid of tubes running thru the blacktop of a driveway. The owner was a heating system engineer/designer so he understood the calculations for the BTU/Hr, flow rates, etc. His brother was a blacktop contractor and was able to help with this project. Ultimatly there was over 2,000 feet of tubing in the driveway broken up into 10 zones. His inground pool was always in the high 80's to low 90's. Definatly not a DIY project.

As for the flow of the water in the system as the OP asked. A BTU is a BTU. In other words, the same amount of energy will be transfered per hour regardless of the flow rate.

I will have to agree with some of the other posts on this. A comercially available system is going to be money well spent vs trying to experiment with making something work. The companies that make these have already spent the engineering dollars to make these work. Personaly, I gave up on the solar and went with Nat gas. My pool is relativly small (18') at 50,000 lbs of water and a 100,000 BTU heater on a nice sunny day can get me easily 2+ deg of water temp increase/hr. I don't run it all the time as we are rarely able to use it during the week. I can fire it up on friday afternoon and have a nice comfotable 85-88 deg for the weekend if needed

 

[donberry]

okay, as u all seem to speak from experience, it will be either real solar panels or maybe gas heat.....thanks. I appreciate the responses.

Any suggestions as to how many panels u would recommend for a 24' round pool ? I would guess I should get a 4 x 20 over a 2 x 20 ? I just did a cursory look and first site was selling a 2 x 20 and recommended 2 panels for a 24' round pool. Probably should be a minimum of 2 4 x 20 panels tho ?
I live in southern middleTennessee. October is normally in the 70's,, but who knows what normal is anymore. Would be nice if i could extend the season thru most of October.

 

[JasonLion]

Two 2x20s are just about the same thing as one 4x20, just more connections to make, so it is more of a price/connivence issue which size panels you get.

If you have room to lay out the panels and can afford it, two 4x20s (or four 2x20s) will give you a nice temperature boost. One 4x20 will help, just not as much. There is no clear dividing line, even a single 2x20 will have an effect. It is really of question of what you really want/are expecting.

 

[dmanb2b]

Two 2x20s are just about the same thing as one 4x20, just more connections to make, so it is more of a price/connivence issue which size panels you get.

If you have room to lay out the panels and can afford it, two 4x20s (or four 2x20s) will give you a nice temperature boost. One 4x20 will help, just not as much. There is no clear dividing line, even a single 2x20 will have an effect. It is really of question of what you really want/are expecting.

Ditto...I have the same size pool. I started with one 4x20 panel and now run 2. Huge difference and a solar cover at night to retain heat help extend our season by 1.5-2months.

I like Fafco solar Bear panels for AGPs...mine lay hidden behind my pool on the ground...been just fine for over 3 yrs now.

 

[donberry]

solar panels it will be, but unfortunately , tho I often spend more money than it would have cost me, I like to diy on things like this. I am the kid that was always taking apart the parents tv, radios etc.....
Also gives me an excuse to build a panel I have been wanting to for quite a while.
Sort of a different topic so will start a new thread for it.

 

[jblizzle]

Re: Few Questions about a diy "pool heater"

As for the flow of the water in the system as the OP asked. A BTU is a BTU. In other words, the same amount of energy will be transfered per hour regardless of the flow rate.

While it is true that a BTU ous a BTU, it is not true you get the same heat transfer regardless of flow rate. You get more heat transfer at higher flow rates.

Think of it this way, you are trying to cool the panels with water. At low flow rates the panels may still be warm so you are not using all the heat you could. To cool the panels the most, and heat the water the most, you want add much water passing through as possible.

Panels have a design flow rate that above which the additional gains are low, but below that rate you will lose a lot of efficiency.

Posted from my Droid with Tapatalk ... sorry if my response is short

 

[danpik]

Re: Few Questions about a diy

As for the flow of the water in the system as the OP asked. A BTU is a BTU. In other words, the same amount of energy will be transfered per hour regardless of the flow rate.

While it is true that a BTU ous a BTU, it is not true you get the same heat transfer regardless of flow rate. You get more heat transfer at higher flow rates.

Think of it this way, you are trying to cool the panels with water. At low flow rates the panels may still be warm so you are not using all the heat you could. To cool the panels the most, and heat the water the most, you want add much water passing through as possible.

Panels have a design flow rate that above which the additional gains are low, but below that rate you will lose a lot of efficiency.

Posted from my Droid with Tapatalk ... sorry if my response is short

True. There is an ideal window of opportunity for the heat transfer. too slow, which most people think works better because they feel more heat is not good. If you get the water up to the temp of the collector in the first half then it just flows thru the second half not collecting heat. As I mentioned in my first post this is why a comercially available system is better. All of the design work has been done which will include the flow rate that is best for the collector. I have to believe the ideal flow rate is a fairly small range for the highest efficiency.

 

[phonedave]

One other thing to consider if you do want to go the DIY route is the size of the tubing. Larger tubing is more flow, but it also does not conduct heat to the center of the tube - it is all about surface area. Water in the tubes will tend to be laminar flow, all the flow lines are paralell, the edges do not mix with the middle. Therefore a smooth temperatur graident exists between the edge and the middle. If you could make the flow turbulent, it would be much better.

Now, have never built a swimming pool heater, but I HAVE built a number of hot beer chillers (Hot wort to be technical) for home brewing. The best that I have seen are called convoluted counterflow chillers. The hot beer flows one way inside a copper pipe. The cooling water flows the opposite direction around the outside of the beer pipe - it is a pipe in a pipe - it has some interesting plumbing on the ends. That is the counterflow part.

As for the convoluted part. The pipes are twisted and "beat up", making the liquid flow turbulent.

I am not sure how somone would be able to use the counterflow idea for a pool, but the convoluted part would make sense.

-dave

 

[cramar]

I have a 20' pool and I'd say you need at least 2X4'X20' panels as a minimum, and you could probably use a 3rd one.

If your putting on a roof I recommend getting the true single 4'X20' panels and not the 2x2'X20' panels, the true 4' ones are less prone to slumping.
Also, the sunsaver 4' panels are rated for freezing so long as they are completely drained.

I'm very happy with my solar panels, they have provided us with far warmer water this year, there's even been days where I've shut them off as the water was getting too warm.
They may be more cost up front compared to a DIY version but from then on it's all free heat.