My version of home-made solar water heater

Jump to latest Follow Reply
D

dccordell

0
May 30, 2013
19
West Monroe, La
I know it seems silly to have to have a pool heater in Louisiana, but our ABG pool seems to be stuck at about 76-78 degrees, which is just a little too chilly for comfort. I'm sure when day time temps get into mid- to high-90's, water temp won't be a problem. Until then, we decided to try to heat the water.

After reading all of the threads about solar tube water heaters, looking at a few other sites, and all of the solar water heater images on Google, it was apparent that basically all we needed was to pump water through a hose on the roof and back into the pool. I had a spare water pump from my saltwater aquarium (may or may not hold up to pool chemicals), so all we needed was tubing.

It looked like the method used by others of winding the tubing onto wood, metal, or PVC brackets was a pain in the butt, especially when it comes to securing the tubing with zip ties, wire ties, etc. I wanted to avoid this part altogether.

Also, it seems to me that by coiling the tubing right next to each other, some sun light contact is lost that could be gained by leaving small gaps between the tubes so some side-heating of the tube can occur. Maybe my thinking on this is wrong, but it makes sense to me for now...

So, I decided to just lay some tubing on our porch roof (300ft, minus the runs to/from the pool), and secured each end of the tube onto 2x4's. This allows the tubing to get more sun contact by not being secured side-by-side, prevented the problem (pain) of coiling the tube onto a mount, and therefore only took about 30 minutes to install!

A note on the pump: So the pump I have is 700gph. Initially I thought that the head pressure would slow this pump down a lot, but then I realized that since the water is going up and right back down to the pool, without any air breaks in between, head pressure isn't an issue. However, the friction loss in the tubing and fittings does slow down the flow far from the 700gph.

The water going from the pool right now is 76, and coming back from the roof is about 80. Not a huge increase, but hopefully over a day or two, it will bring the pool up enough to take a swim.

A quick question: Do you guys think the tubing on the roof would heat more efficiently on the shingled roof rather than the metal roof? The metal gets super hot, but when clouds pass over, it quickly cools, and so does the tube and water. The shingle roof however seems to store the heat, and stays warm for a while under clouds. Also, should I add another 200-300ft on the roof to heat the water even more? It has been running for 3hrs this morning with no pool temp increase yet. Thoughts?

 
Solar heating is all about sqft of sun exposure, if your pipe is 1" diameter ... at best you have 25 sqft of heating (which is not much). I had 2500' on my house from a previous owner that did not do as good of a job as I wanted and I hated dealing with all the leaks.

Solar heating is also most efficient at high flow rates, you are better off heating a lot of water a little than a little water a lot. And pumping through very long small pipes is inefficient. YOu would be better off with shorter tubes plumbed in parallel. Also, having the space between the tubes allows air to travel around them which actually cools the pipes. Not sure if the shingles or metal roof really will make much of a difference.

These days it seems to generally be more cost effective to just buy the true solar panels ... on Ebay you could get a 4'x20' for around $200 I think.
 
So it appears as though I didn't do enough research before trying to throw some black tubing on the roof to heat my pool water. :)

Since then, I've determined that the 1/2" tubing I'm using (actually .7" outer) provides about 5.83 sq. ft. per 100 ft. section. At Lowe's, 100 ft. tubing is $14, putting the home-built tubing version at $2.40 per sq. ft., not counting any fittings needed, and assuming I've done my math correctly!

I found a 40 sq. ft. version on Doheny.com for $115, which is about $2.86/sq. ft.
As you mentioned, jblizzle, there is several versions on ebay, with mostly similar prices. One is an 80 sq. ft. for $198.95 after shipping, putting it at $2.49/sq. ft. A little cheaper than Doheny's.

I realized that Home Depot has this tubing for $10, instead of $14, bringing the price of a home-built tubing model down to $1.71/sq. ft. Not bad! If my local store had the 500 ft. for $45 in stock, the price would be even better.

Overall, I think if I had realized that there were these cheaper options on Doheny's and ebay, I would have started out with one of those instead of building my own.

Having said that, mine does work to a small extent. The pool has made it up to 80 during sunny days, which haven't been common during this crazy weather we've been having. Even with the cover, it keeps dropping back to 76-77 at night, which is making it harder to keep at or above the 80 mark.

I think we'll wait to expand this heating system until fall when we'll be needing the heat again. Then we'll probably go with one of the models listed above.
 
The big difference is your typical home built will not last as long, and more importantly circulates all the water through a long loop, where the commercial panels send it through many parallel tubes. It is all these parallel tubes that reduce back pressure, and allow for optimal heat transfer. So even with equal surface areas the commercial panels are likely to provide 30%+ more BTU's of heat for given area. You could improve that by running multiple parallel runs with your home built tubing, but this adds considerably to the header fitting expense.

Flexpvc.com sells some manifold parts that might allow you to rig parallel flow with the home made heater

Ike

ps. my fist solar heat system was a similar loop of black tubing on the roof
 
Quick question regarding using parallel tubes:

How do you prevent water from flowing more through one or a few of the tubes, rather than evenly (or almost evenly) through all of the parallel tubes... without using any valves?

I had initially pictured using 1/4" tubing connected to "manifolds", similar to the store bought versions I suppose. I couldn't figure out how to control which tubes would have more flow, so I moved on.

I guess with enough pressure, you force water through all of the tubes evenly, more or less?
 
The water will take the path of least resistance ... if the total travel distance is the same ... the flow should be similar in all the runs.

The DIY setup that was on this house I bought used I think had 8 different loops, but the length varied from 100' to 250' and then were just pileded on top of each other in places .... so likely the water was not the same in each run ... for all I know since the loops went up and over ridges and all piled up, some of the loops may not have even been getting flow.
 
dccordell said:
The DIYer inside me wants to be some of these, but at the prices on eBay and Doheny's, it's almost not worth the time to build it myself.
Click to expand...

You got it ... if you want to tinker, fine, but do not expect to save much if any money doing so anymore.
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply