DIY solar pool heater advice

[mabris]

I’m looking to set up a DIY solar water heater. I wanted to get an idea of if my plan seems doable, and I had some questions about the plumbing.

The collector will be lying horizontally on a flat roof about 10 feet above the pool pump. The collector will consist of about 300 sqft of ¼” vinyl drip line irrigation tubing. I envision many parallel coils of tubing, all mounted on black-painted pegboard with zip-ties. The ¼” tube will feed off of (and ultimately into) a ½” drip irrigation tube using barbed connectors. There may be multiple of these ½” feeder lines and they would connect to a 1” line through some manner of manifold.

From the pool pump plumbing, I would have a ball valve for shutting off flow to the collector and check valve for the feed line, all at the 1.5” PVC size. Then there would be some sort of reducing fitting to get me down to the 1” irrigation tubing.

There would be no fittings other than a reducer for the 1” line feeding back into the 1.5” PVC.

I had a question, though. I’ve seen most DIY set-ups with both the output to and input from the heater on post-filter side of the plumbing. How can I ensure that there is enough pressure drop between the two tie-ins that it flows all the way up to the roof? Do I need some sort of diverting t valve at the line inputting into the heater? Can I put the output to the heater post-pump/pre-filter and the return line post filter?

Do I need a vacuum break in the tubing up on the roof?

 

[JohnT]

Welcome to TFP.

In order to carry the flow of one 1.5" PVC line, you will need over 350 of the 1/4" drip lines in parallel. The transition from 1.5" PVC would require 9 parallel 1/2" drip tubing connections on each end to maintain full flow. Stepping down to 1" complicates it even further. Maximizing flow is very important to efficiency, so you don't want to step down to a single 1" line. You'd need three 1" lines to carry the full flow, with each of these branching to 3 of the 1/2" lines, with each of the 1/2" lines branching to 100 1/4" lines, with all of it coming back together at the other end. Far better to go directly from 1.5" to 1/4". Commercial panels are made with 1.5" or 2" manifolds on each end which connect to the actual collector tubes.

The key thing to remember is that you don't want hot water coming out of the heater. Hot water is an indication that your flow is inadequate. Efficiency suffers as warmer water loses more heat as it's moved, and the panels lose quite a bit of heat as they heat up. Ideally you want the panels to remain at pool water temperature, with a lot of water warming only slightly as it passes through.

To control flow, you put a 3-way valve at the output of the pump to control the amount going to the panels.

 

[mabris]

I don't want to divert the entirety of pump output to the collector, do I? I had assumed that only a portion would be diverted.

 

[dmanb2b]

stick with a fafco panel or equivilent...unless you've got time to spare, imo they provide a much cleaner look and are designed for your pool circ system. I know $200 per panel may sound like a lot, but there is a lot to be said for free heating of the pool

 

[JohnT]

I don't want to divert the entirety of pump output to the collector, do I? I had assumed that only a portion would be diverted.

For highest efficiency, you want maximum water flow. This gives you the smallest possible delta T, which means the least heat loss.

 

[luckyman_apd]

A lot of people gave me the advice to go with a fafco panel, but like you, I'm very handy, and I didn't want to pay the huge upfront cost. I think I would need 12 panels according to their recommendations. I can tell you that I HAVE built my own out of 3/4 inch PE pipe. I'm going to rework it with 1/2 pipe when I get more time later this summer. On my system I have a check valve immediately on the return side of the filter (very important to prevent backflow into the filter. I have an elbow to send the flow up to the roof. After about a foot or so, I have a tee with a ball valve so I can divert flow from ever going to the roof. I also have a ball valve on the vertical pipe to shut water from going to the heater if I need to and it can all go through the bypass. Around 6pm the my upper roof casts a shadow over my coils so they no longer are needed, so I stop flow up to them. I used the PE pipe in coils. They are 100' rolls of pipe, and the headers or manifolds are 1.5 inch. I have 4 coils total, and I connect them to the headers with a tee and a 3/4" threaded reducer and a PE threaded connecter (with a hose clamp on top). Each coil collector costs around $35 to make.

I get little bit of heat from them, and my pool is steady at 85 degrees right now with a solar blanket as well. It does not produce enough heat to start my season early, but with a few changes it should be good enough. A few points to answer your questions.

With an engineering background, as far as efficiency goes, as long as the water is moving, you'll get the same heat. For example, if you run 10 gallons a minute through the system, let say it raises the temp of that 10 gallons 1 degree. you could cut the flow to 5 gallons a minute, and you will get a 2 temp rise, but it's less water. SO mix that with 5 gallons 2 degrees colder, and you get a 1 degree rise in a total of 10 gallons. You have to keep a few things in mind. If the water is coming out HOT, then you are losing efficiency. You are essestially wasting heat by not capturing as much as you could be. However, if the water moves through there too fast, and you're gaining only a 1/4 of a degree difference, it's gonna take a long time to have a cummulative effect. I ALWAYS keep the diverter ball valve open slightly. I never send all the water except for when I first get it going to push all the air out. (I use a check valve as a vacuum breaker. I use a 3/4inch one attached the end of the top manifold) I've spent a total of $350 with all the pvc pipe, glue, ball valves and check valves ( you will also need on on the return from the roof to prevent backflow up to heater ( you want to keep that water circulating, and not stalling). I'm gonna change from 3/4 to 1/2 inch, and double the length from 100' coils to 200' coils. That should produce enough for me. If not, at $12 a roll for 1/2 pe pipe at lowes, I can always add a few more. It only took me one full weekend to make and install the whole thing.

 

[JasonLion]

Obviously it is possible to build everything from scratch, but unless you are getting the materials for free, you will get more heat per dollar spent by buying an inexpensive commercial panel on eBay and installing it yourself.

As JohnT said, an efficient setup requires many many parallel runs of small pipe. That is difficult to construct and the large number of connections tend to lead to leaks. Commercial panels have solved this problem and don't cost all that much. Even the least expensive commercial panels are around 80% efficient. The DIY systems I have seen don't even come close to matching that efficiency.

 

[luckyman_apd]

efficiency, and actual out of pocket costs are two totally different things. I didn't have the money to buy a commercial one, but the relatively low cost of building my own I am able to produce enough "free" heat to satisfy my needs, after I make the modifications later this summer. Could I get more heat faster from a commercial setup? Of course, but overall, I was able to put up less up front, and still be satisfied.