Pool Collector Using PEX Tubing and Aluminum Fins

This is Tom's design for a pool heating collector that uses PEX tubing for the collector risers with pressed aluminum fins.
 
The collector is very simple to make, and the combination of PEX tubing and no glazing makes it a very inexpensive collector to build.   I believe that it will be  a very efficient pool heating collector --  at least as efficient as commercial plastic collectors. 
 
The collector is not glazed, so overheating of the PEX should not be an issue, but the PEX should be protected from any direct exposure to sunlight by either the aluminum fins, or, in areas not covered by the fins, the PEX should be painted or covered.
 
Tom has worked out a very neat way to allow the use of simple irrigation system T fittings to assemble the risers to the manifold.  The larger manifold will allow several collectors to be hooked up end to end without starving the last collector of flow.   Be sure when hooking up collectors end to end to run the supply and return to opposite corners of the collector array -- this way the flow path length through each riser is the same.

Tom formed the grooves in the aluminum fins that fit closely over the PEX with this press that he made.  For those of use with less machine shop skills, this sledge hammer method can be used -- its more work, but it works fine for a few collectors.
 
Thanks very much to Tom for providing this description and pictures of the pool collector!!
 
Update: Tom has a new website with additional info on his solar projects and products...
 
 
 
 Update from Tom after first full season of use -- October 2009:

Pool Solar collectors:

The system worked without a hitch all summer long.  The 8 panel array yielded about 160,000 BTU's per day, which on a pool the size of the one I was working on amounted to one degree a day.  Unfortunately, we had one of the coldest summers on record, and the cold nights robbed heat faster than we could generate it.  Overall, the pool owner (a friend) was happy with the system and noticed every sunny day he was gaining heat.  About the only drawback is the "unglazed collectors" collected pine needles from nearby pine trees.  The system was drained and prepped for winter last week.
 
 
 

Tom's Description

I've designed an unglazed swimming pool collector, pretty much the same design as yours, but keeping everything as cheap as possible. I'm using 4' x 8' x 1/2" treated plywood for the back, a border of treated lumber that recesses the "edge" of the plywood for weather protection, and 1/2" polyisocyanurate under the absorber. I like the insulation on top of the board for two reasons. No thermal loss between the absorber/hose area and the wood, and the exposed back is a durable material (the plywood). I like the manifold design for drainback, and it works nicely for a "modular" panel (each 4' x 8' panel is a separate module). With this concept, I can add or subtract modules based on the pool size.
 


Treated plywood backer board with edge
edging to protect the plywood edges from the weather.


Note the press together irrigation fittings used
to connect the manifold and risers.
 


 


Close-up of the injection molded irrigation fittings.
 


5/8ths PEX tubing heated up a bit and pushed
into place on the fitting -- no clamp required.

 

The "T"s I am using for my connections are a "Lasco" irrigation fitting, actually a 1/2" injection molded plastic fitting which works great with 5/8" PEX. I just heat the end of the PEX for 15 seconds with a heat gun and push the softened PEX onto the fitting. It grips the PEX so well no clamps are required. I found another source for the fittings (at a local plumbing distributor) that's cheaper than the Lasco ones I've been getting at Home Depot. Apparently there are several vendors making the black irrigation hose and fittings.

 

The plastic (injection molded) irrigation "T"s are 1/2" all three directions.  For my last order on those, I got the cost down to $.33 a piece.  I'm using 5/8" PEX for both the manifolds and the risers.   I had about 800'-900' of the 5/8" PEX left over from another project.  I would have liked larger manifolds, but everything was working out so cheap I thought I would give this design a try. 

 

The websites for the cheaper "T"s and the Lasco fittings are listed below. Either the Lasco or "Seal Well Products" will work. It just depends on where you can find your best pricing in you local area. Home Depot stocks the Lasco product, and the "T"s ran about $.62 a piece there. The Boshart, known as B.I.I. product (Seal Well) show list pricing on their web site. I purchased these for $.33 each locally, so the list pricing is quite a bit higher than you will pay if you can find them at a plumbing "wholesale" store.

http://www.boshart.com

http://www.lascofittings.com/
 

 


Four completed collectors

I think the PEX will work good for the pool collector. The absence of glazing should eliminate much possibility of over heating it. I plan to design an on/off switch for the array, and then add an over-ride control that turns the pump on if the absorbers hit 200 degrees. You can always run the array at night or leave the pool cover off if the water is actually getting too warm (don't think that's going to be a problem up here).

Collector Cost

 
  Solar Pool Heater Costs      
               
    Option 1     Option 2    
Material Unit Price Quantity Cost   Quantity Cost  
               
3/4" OSB 10.78 1 10.78     0  
1/2" Treated 26.95   0   1 26.95  
1/2" Poly Insulation 11 1 11   1 11  
               
2"x4"x8' Treated 3.1 2 6.2   2 6.2  
!/2" Barbed "T" Fittings 0.42 16 6.72   16 6.72  
1/2" PEX 0.43 66 28.38   66 28.38  
               
.018" x 8" Aluminum 0.42 60 25.2   60 25.2  
               
Screws     5     5  
Paint     10     10  
MI Sales Tax     6.38     7.35  
Labor 6.5 0 0   0 0  
Total     109.66     126.8  
               
Optional Material costs              
5/4" x 12' Plastic Decking 24.95 1 24.95        
2"x6"x8' Treated 5.95 1.5 8.925        
18" x 12' Alum Soffet 15 2.5 37.5        
             

 

  

 

Tom

 

Tom will answer email questions -- you can reach him at: toms1 AT chartermi DOT net  (replace At with @, DOT with .)

 

Tom's Other Projects

Tom has sent in several great renewable energy projects ...

 

 

 

I'd offer one small alternative to Tom's design to think about.

The alternative would be to leave the insulation board out and apply the aluminum fin directly to the plywood.  The thinking behind this is that 1) for most pool collecting applications, the pool water will be cooler or nearly as cool as the ambient air, and when this is the case, the insulation is not really needed because there is no heat loss, and 2) by having the fin in direct contact with the plywood, it will be easier to staple it down so that it fits very tightly against the PEX riser tubes -- this is important to get good heat transfer from the fin to the riser tube. 

Part 2 is not so much of an issue for Tom, in that his press forms a very good fin groove that snaps on the tube, but it is more of an issue for fins formed with  this sledge hammer method .  Along the same line, I would use a bead of silicone in the groove before stapling it down -- the silicone fills any tiny air gaps that might remain between the aluminum and the PEX.   The silicone is 10 times more conductive than the air it replaces, but any remaining silicone filled gaps must still be very very thin for good heat transfer.

 

Gary March 31, 2009