Solar Pool Heater

A K'nex/TinkerToy/underfloor heating inspired solar heating system for your small outdoor pool.  Mine takes a 500 gallon pool from 65F to over 90F in one sunny Colorado day when used with the black pool cover.  I filled a 5 gallon bucket in about a minute with a 1800 gpm utility pump through the pictured setup with the water coming out about 4 degrees F warmer when the water was around 78 degrees already.    

To make this last longer I used ASA, PETG likely won't last long.  The manifolds can be PETG if they are kept out of the sun.

You will also need:

• 1000-1800 gph pool pump

• 2 garden hoses

• 1/4" irrigation tubing (I used 4x 100' rolls for an 8x8 grid that used 8x ~42' lines)

  • THE GRID USES ABOUT 7.8" OF TUBING, PER LINE, ON AVERAGE FOR EACH GRID SQUARE to give you a rough estimate

  • LLDPE is the best choice for flexibility, temperature, toxicity, and UV resistance.

• 16x 1/4" NPT to 1/4" push-to-connect fittings (the cheap 10-packs off Amazon)

• 2x 3/4" NPT to FGH adapters

• lots of thread tape

• lithium grease for the female threads on the manifold (protip for sealing PVC threads)

The connectors all have holes so you could mount it to black plywood and top it with polycarbonate or something, otherwise I just superglued mine together before adding the tubing which really holds it together.  

Print the manifold as thick as you can, and increase your extrusion multiplier by a tiny bit to help make it waterproof.  I did 8 perimeters and 20% honeycomb, 8 top and bottom, with a 0.6mm nozzle.  Use a brim to help with warping.  Don't expect it to be 100% leak proof under pressure.  It might be good to isolate either hole with the cutting and place on surface tools in your slicer to test YOUR fittings (mine worked fine) before you waste 300g of filament on the entire manifold.  If you are using a .4 nozzle, you might want to use a lower layer height as well.  

Print the grid pieces with at least 4 perimeters and 5 top/bottom layers.  No supports on the connectors!

The notched diagonals are only for the turns at the ends.  The blanks are structural only.  Sketch your grid out on paper first to get your part count.  mock assemble without glue, and test run a length of tubing on one of the middle tracks to verify your length before cutting the tube.

break the mock grid down and glue it back together square by square.  I would do a whole row of squares, then put those together, then add to that row each time I finished with all the squares of a new row first.  Gluing may not be needed if you are assembling it to a base of some sort with the holes.

Good luck!  I did all this on a Mini+ and MK4s in less than a week :)