Please help with my DIY solar heater

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aquamarine

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Mar 9, 2009
101
Midwest
I want to build my own heater like the one on:
http://ffaat.pointclark.net/blog/archiv ... eater.html
I am hoping someone here has knowledge about these things. I am not very good at DIY and working with tools and not strong. But I really need a heater and this type works for many people, so I have begun this project.

First of all, I purchased three 100 foot rubber black air hoses. Did I mess up by getting air hoses instead of garden hoses or irrigation hoses? Will they not be as effective for some reason? They are meant to withstand high PSI, are non-kink. They have metal couplings at each end. Will those rust? Should I cut off those metal ends? Should I coat them or anything? I'm thinking it was a stupid move but it's hard to find hoses that are 100 foot and black and not pvc or reinforced... and not too fat or skinny... and not really expensive. I feel like garden hoses might be made to not absorb the heat as much. If I have to, I will return those hoses. I would want to know as soon as possible so I can send them back and get others soon.

If I have to return them -- does anyone have a link to a place to buy 250+ feet of good hose? If I am going to keep these hoses -- I would appreciate some advice on what type of connectors to buy (although Lowe's people can help advise me too). Thanks.

Secondly, I am unsure of how to calculate how big my final coil will be (which then tells me how big of a piece of wood to buy for the background). I was hoping to make a rectangular shaped frame instead of square but am willing to do square if it's easier. I think that rectangular would be nice because of not taking up as much ground space, and it would rise higher and i think it would catch more sun rays that way. I know that the guy in the post was using 200 ft and his frame was 4 ft x 4 ft. My air hoses are 3/8 inner diameter and 5/8 outer diameter, and my method of affixing the hose to the wood would make it take a little more space, so more like 2/3rds of an inch per loop of coil. Of course not all 300 feet would go in my frame, I would leave about 24 feet outside the frame.
 
Not to bring in some negative comments, but have you sat down and planned this out thoroughly?

What is the motivation for trying a DIY setup? I know you mentioned size, but with a pool your volume, and my beginners knowledge of solar systems (just installing mine now), how much temperature difference do you expect to get with that small sq. footage?

Have you looked at some of the cheap Fafco panels?

Those, in my opinion, would be the cheapest and most expandable entry point for starting a solar system.

I can understand the DIY route for a hobbyist, or someone really into building stuff, but if you dont have much DIY/Tool experience, the project will most likely cost you more money in the end than buying a complete system, and not work nearly as well.

Just my 2 cents.
 
On that page, there are many comments... many are getting 6+ degrees increase. Of course depending on the size of their pool, how much hose, etc. Some are making their heaters for under $150 total. I would cover mine with Optix to trap in the heat and that is supposed to be significant too. I've thought about it plenty, the only problem so far is that I may need to get a different hose. And then it would be nice to get some input on size/connectors but I can stumble through any of it.
 
Again, just my opinion, but I would think that since an air hose is a pretty thick walled rubber hose, and since rubber is an insulator, thick would be bad (not much heat transfer).

Good luck with your setup though, and keep posting updates, ill be interested to follow it.
 
By far the most efficient and economical solar heat is from using commercial panels purchased on eBay and installing them yourself. The commercial panels use construction techniques that give significant advantages, are next to impossible to duplicate at home, and are more cost effective than anything you can build from scratch in other ways.
 
Well in my case... 1) I don't want to install onto my roof, or take up a lot of ground space. Also this one will be fairly portable, when not filled with water, so that I can tweak the angle or even change the angle in the middle of the day or the morning. 2) I do not want to hook into my existing pool piping or anything else, I want to just have these hoses hang into the pool. 3) I want to use a solar powered pump with panel, which is already on its way, and they aren't as powerful unless paying a lot. But the one I got should be very good, a lot of the DIY people on that page seem to be doing fine with one that is only something like 1/8th as powerful as what I ordered.

I do think I should return the air hoses and get water hoses. That's a pain since I ordered them online, but this is worth doing right of course. I don't like the 5/8" OD anyway, I would like a 1/2" OD I figure or 3/8" OD.

I've planned and basically picked out everything else besides the hoses and hose couplings.

Some on that page are saying the water comes out really hot, like 100 degrees... IIRC... and I think some are getting 10+ degrees improvement. And most of them, as I mentioned, are not covering their hoses at all. Sounds nice to me, to have an area of your pool where you can go and be under nice hot water.

I also find the whole thing very interesting and I want to see it working for myself. I think I might get better at DIY by doing some more projects. It seems lower maintenance to me. And cheaper.

Oh, another reason is that I think in the winter, I could just put the hoses into my hot tub instead of the pool, to help heat it up and save some electricity. If it can raise the 20000 gallon pool by 6 degrees, it would raise the 400 gallon hot tub by a lot I figure.
 
For a pool your size, you'll need to scale this up. What those guys are doing is taking a 1/2" vinyl tube, like the mainline you would use in a drip irrigation system, coiling it in a spiral, mounting it to a board and running water through it. In sunlight, it will heat water. The question for you is how much heated water coming out of a 1/2" line is it going to take to heat a pool your size.

So, if you are sold on this concept, then you owe it to yourself to do it right. The easiest way to significantly increase your "heated water flow into the pool", is to build multiple spirals and run them in parallel. Imagine just one 1/2" tube putting hot water into your pool; now imagine a 3" tube putting hot water into your pool. If you happened to have a 3" tube spiraled onto a board in the sunlight, you'd want to consider this: Which water is going to get hotter faster? Water in a 1/2" tube, or water in a 3" tube?......Answer: Water in a 1/2" tube. Next question: Which water is going to move more efficiently? Water crammed into a 1/2" tube, or water in a 3" tube?.......Answer: Water in a 3" tube.

How can you get the best of both worlds? Combine the best aspects of each: Build six spirals of 1/2" tube. The next step is really important. Take the output from your pump and divide it into six....you'll need to design some type of manifold, the simplest would be a big pvc pipe connected to your pump, with six outlets off that pipe, one to each of your six spirals. This is parallel flow.

All the other details, such as pump power and capacity, the efficiency of covering it with this material or that, are for you to figure out as you engineer this. Why am I encouraging you to do this? Because I love tinkering and fabrication. It's fun to try something yourself. I know that as you build and use this, you'll learn about what does and doesn't work, and why. That process is what makes this entertaining, if it wasn't, we'd just go out and buy someone else's product.
 
Are you sure that 300 feet of 1/2" hose isn't sufficient? Most of the people on that page have smaller pools but some are the same size or bigger. The original poster on that page only used 200 feet. Also it would be in a very small box under a plexiglass type of sheet (Optix). The water would be flowing through quickly for half the day, every day. Yes, it takes days for it to first build up the heat.

Maybe this was a bad thread to start.
 
This isn't a bad thread. Again, lots of folks read these things; some simply buy the machine to do what they want, some are pro builders with a lot of expertise and background.......some of us just like to tinker. The key to tinkering is to never exceed certain limits. Those limits include costs, potential damage to equipment, and risks to personal safety. Example: electricity scares me. I don't mess with it. I know when to have a pro pick up part of a job. There may be an electrician floating around here who feels the same way about water chemistry....and so on.

Additionally, I often consult with engineer friends who can set me straight. My challenge is to fit my round goofy idea into the square hole of reality and physics. So, my advice for you, my friend: set some limits and have fun with this. I know that by doing this you are going to learn plenty.......lessons aren't cheap, so budget accordingly.

To your question: There is no doubt that if you take 300' of tubing and place it in the sun, you'll get hot water out of it. But it's important to understand that if I take three rolls of 100' of tubing and divide the water flow into the three tubes, it'll be more efficient. The water will get through the 100' foot tube faster than it will get through the 300' tube. It's true that by the time the water makes it's way through all 300' feet of your tube, it'll be hotter than what comes out of each of the 100' tubes. But by multiplying the water flow capacity by three, I'll end up exposing more pool water to heat.

If you use 300' of tube, you have to flow water three times as fast (layman's rough math) to get the same efficiency as the three separate 100' tubes. You'll need a powerful, fast pump to move water through that 300' tube; that water will be under high pressure and will shoot a nice jet of water into your pool. But what's the downside here? By speeding the water through that 300' tube, you haven't given it time to pick up heat. What if you put it through a 600' tube? Same thing. It'll be moving fast, under high pressure.....it'll pick up more heat because it's in the tube longer, but you'll need an even bigger, more powerful pump. Likewise, if you put water through three 100' tubes too quickly, they won't pick up enough heat.

Do some experimenting. Put your decisions through a "common sense" test.......in your original post, I can see that you began to realize the difference in heating ability between an insulated rubber hose, and a piece of black vinyl tubing. Consider those sorts of things, and proceed accordingly.
 
Hm. They were saying definitely don't use PVC hose, and that rubber is better. I was wondering if I should use braided stainless steel hose, and maybe I wouldn't have to use as much of it - that type of hose was expensive. Or was wondering about putting some metal inside the rubber hose.

Interesting about the pump power. Maybe it mostly evens out in the end? i.e. For whatever hose length/type/layout chosen, the pump may not matter as long as it gets the water through there? Because if the water is going through rapidly, sure it doesn't have much time to pick up heat, but you're getting 4 more passes of water in the same amount of time, so it only needs to pick up 1/5th as much heat. I suppose it's not even and neat like that.

I mean... it's not true that the pump would get the same volume of water through the 3 100 ft hoses as the one long one? I thought the pump just does X number of gallons per hour into the hose(s) and back out.
 

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With a fixed speed pump, the amount of water moving through the system goes down as the pipe diameter gets smaller and it also goes down as the pipe length gets longer. You simply can't move much water through a long narrow pipe, even with a fairly large pump. With a solar system you want to use fairly small pipes. To counter that you want to plumb them all in parallel. It is far far better to run many small pipes in parallel, because you get much more water flowing through the system.

The efficiency of a solar system goes up the more water you can push through the system. You want the largest possible flow, with a very small increase in water temperature. Heat transfer from the hot outside of the pipe to the water is more efficient the colder the water is. The warmer the water gets, the lower the heat transfer efficiency.

If you look at the efficient commercial systems, they have anywhere from twenty to hundreds of small pipes plumbed in parallel. That is what you need to do to make an efficient solar collector. Plumbing dozens of small pipes in parallel means lots of connections, which tend to add cost and reduce reliability. Commercial panels using direct plastic welding, which creates high quality reliable connections inexpensively, but it requires expensive equipment.

The total amount of heat you can get out of a solar heater depends on the collector area. The larger the collector, the more heat you will get. A very small collector will get some heat gain, but not enough to be worth the bother. Generally, about 10% of the area of the surface of your pool is the smallest solar heater that is worth bothering with. Most people aim for 20% to 40% as much solar collector as pool surface.

Another factor to keep in mind, is that using a solar cover will gain you more heat than a small solar heater, and it will make the solar heater more efficient. Without a cover, you will lose the majority of your daily heat gain each night.
 
First time poster. What a wealth of knowledge and experience here.

I am starting to build a similar system and actually that is how I eventually landed at this forum. The commercial panels are just longer than I wanted. I'm trying to get away with a smaller footprint.

I ended up getting 500 ft of 1/2" PEX tubing and am using polycarbonate for glazing (both available at HD or Lowe's). The boxes that contain the coils are 4 ft square. My prototype is built, I am guessing it has ~ 200 ft of tubing and I am just waiting for a sunny day here in Philly to test it out. In very short testing trials, depending on sunniness, it raises temp between 3-8 degrees with a flow rate of ~ 3 gal/min. This will not make a dent in a 25000 gal pool though. Eventually, I hope that 4-6 panels will be enough to warm the pool, extend my season, etc. If these work out, I will build a small structure over my pump, and these panels will be the "roof", with a total of 8x12 ft or so. The commercial panels would be more like a total of 16x20 or so.
 
I've posted this earlier tonight, and I've done LOTS of research. It is true, you really aren't going to beat a prefab solar system from Fabco or one off of ebay. However, that doesn't mean you can't make an effective one yourself, but with the lack of using the roof, you might be dissappointed in your project. I have a similar sized pool to yours. I have built 4 coils connected in parallel out of 3/4 PE pipe. It is the black irrigation pipe from HD or Lowes. I find Lowe's has a better price and a better product. This pipe is very thin walled but very strong so it won't spring leaks, and it is a good conductor of heat, unlike rubber. The coils are made from 100' long coils and held together in a coil by using electrical conduit bolted in an x on both sided of the coil. The four coils are connected in parralel (meaning NOT end to end, all of them connect to a supply and return header). I get an ok performance from them. They won't raise the temp in a day, but after a week of good sun, it raised the pool between 5 and 8 degrees. I plan to improve this by rebuilding the coils with 1/2" PE pipe and making coils of 200'. THe pip is only $12 for a 100' roll. In all I can make a coil for $35 or less and just add it to what I already have. I didn't have 2 grand to drop on a solar system, so I figured I'd spend 200 bucks or so and try my own. So far it seems worth it, and I'll post more when I improve it. Here is a link where I got my idea from. I just modified what this guy did.

http://www.thecasualtraveler.com/solar.htm
 
To give you guys an idea of a cost comparison, I only paid a total of around $650 for my system, I am in the process of installing it now.

The break down was as follows:

$100 - System Kit
$260 - 80 sq. ft. of panel (this was a little higher than it would be for other people, since i had to buy 10' panels, not 20')
$200 - Goldline Automated Controller
$75-100 - All plumbing ( I had to redo my entire plumbing setup)

You can see that the $650 even includes an automated controller and valve.

While not as cheap as what you guys are putting together, it provides a whole lot more "bang for the buck" in my opinion.

I am definitely not knocking the DIY attitude, I personally have a degree in electrical engineering and my main hobby is robotics. heck, I have a CNC milling machine in my garage if that gives you any idea of my opinion of DIY.

I really am anxious to see how it turns out, and it's good to see someone on here (mokabb) that has one up and running.
 
Personally, I would be happy with the 5-8 degrees that takes a week to build up to. But yeah, I'll have to pay for a new cover & take it on and off some.

BTW. If I didn't already mention it, for me, a factor is that I wanted to be able to install it myself without help. I am not strong, don't own many tools, etc. I was definitely not going to touch my existing plumbing. [And besides I want my pump to be independent and free from cost (solar).]

Thanks for the info on the PEX from Lowe's. I'll head there as soon as I figure out if I want 1/2" in three 100' lengths or what. If they have 3/8" I'm thinking I should go for that? But not 1/4"? I know 300' total isn't that much for a pool my size, but may just go with 300... not sure... I'm wondering if I should do 300 now and hope it can get me at least 3-5 solid degrees and if I really want to, do another 300 later on? Or try to go for 500 now, or what.

What is the glaze for -- will it help efficiency or just help the tubes last longer or ?

Again I think most DIY heaters aren't covered from the wind. Also, some are not propped up at a good angle. Some do not have black on the background, or fully black tubes. Some that don't do as well are using materials that aren't so great like PVC is supposed to be bad.
 
I'm no engineer, but I have read a bit and hope that I some common sense. My thoughts are...

I'd be happy with 5-8 degrees per week.

I don't know that you'll get much flow out of a long coiled tube less than 1/2" in diameter - so even if the output feels hot, your total flow rate may not be enough to heat your pool unless you have numerous coils to make up for it.

What I wanted in a system was the smallest one that would heat my pool so I can extend the season at least 2 to 4 weeks on either side. The recommendations that I saw for the commercial systems suggested ~ 8 2' x 20' panels if I recall. So, I'm hoping the glazing will increase the efficiency of "my" system so I can have halve the footprint. In theory, it will decrease the effect of wind on the coils and create a little "hot house". Maybe I'm just dreaming. I suppose if it worked others would already be selling it. I'll let you know as I continue the project over the summer. If it can do the heating, I will automate it, etc.

Oh, I bought the 500' ft length because the price/ft was significantly less.
 
Hm. Well I'd like to do five 100 ft 1/2" PEX tubes in parallel. I don't know anything about doing this. I am thinking I would just have to buy two adapters that go from 1 standard hose connector (assuming the solar pump is standard) to the small multiple hoses. Hopefully that is available or hopefully easy to put one together. If it's easy to do, then I might as well try to do more than 5 separate tubes.
 
I would suggest not doing the coating and instead put glass or acrylic over it. That's what I'll be doing, putting some wood on the sides, then covering it with non-yellowing plexiglass type stuff. Mini greenhouse.

Does anyone have suggestions for how I could figure out the square footage I need for my background piece of wood? Given that I want to coil 470 ft of 1/2" hose on there. I think 4 ft by 6 ft would work, or 3.5' x 7'.

Also I am trying to decide if I should simply spray paint the background wood black. I was planning to use a PVC coated metal grid inside to hold my hoses in place, which might help things heat up a little, I figure that will get spray painted too. Putting aluminum foil in there might help too, but I'm not wanting it to glare a lot... can I spray paint the foil black? I believe there was some discussion of this elsewhere that I read. Or maybe put some other metal backing.
 
Hi Aquamarine,

I would strongly suggest you don't waste time and money on the DIY solution. Unless you use several thousand feets of 1/2 pipe , you won't get any measurable results with a pool the size of yours.

Sure a few people on the site you mentionned are claiming 5-8 degrees increase in a week, but how much of that is due to the "pipe coil heater" vs just the normal effect of the ambiant temperature rising and sun hitting the pool surface?

The sun provides a finite amount of energy per square feet. No matter what you use: PVC, rubber, PE pipes or commercial panels you need exposed surface area to get that energy.

The math is pretty simple and once you understand it, you'll be able to better evaluate different solutions to properly heat your pool:

1- You need 8.34 BTU to raise 1 gallon of water by 1 degree F. I would estimate that your pool contains 20000 gallons of water, therefore you need 166 800 BTU to raise the temp of your pool by 1 degree F.

2- Now that we know how many BTU you need, we must determine how many you can get from your solar heating system. According to the data from the Florida Solar Energy Center, a very good commercial panel will give you around 1000 BTU per square feet per day. Therefore you would need 167 square feets (166 800 divided by 1000) of panel surface area to get that 1 degree increase per day on your pool. For your pool, that amounts to roughly 25% of the surface area, consistent with the rule of thumbs numbers mentioned by JasonLion (20%-40%)

3- You mentioned in your last post that you plan on building a collector using 470ft of 1/2 pipe. This translates to roughly 20 square feet of surface area. That will give you 20000 BTU per day if your system is as efficient as the best commercial panels. Using the rules above, that collector would give you a temperature rise of about 0.11 degrees per sunny day. :?

I'm sorry to play the role of the smarty-pants guy but please consider that I'm only trying to prevent you and others from wasting a lot of time and money.

As other mentionded, if you don't already have one, a solar cover will give you the best bang for the buck. After that, a pair of 4x20ft panels would give you that additional 1 degree per day, for around 400$.

Solar heating is great when you have the proper setup but can be a frustrating waste of time, money and effort if you don't.

I've seen a lot of inquiries similar to yours on TFP and other forums and I think that a "sticky" with some basic common sense information on solar heating would be a good idea. I know that it would have been good for me a few years ago when I wasted time tinkering with my own (useless) DIY pipe coil collector.

I now have 75% pool surface area in panels plus a solar cover and my pool is currently at 88F while my unheated / uncovered neighbours pool is at 73F :-D
 

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