2nd Prototype of the DHW Pond Solar Water Heater


The Prototype 1 write-up has more detail on the thinking behind this horizontal pond concept -- read it first.


These are a few pictures of the 2 nd try at the horizontal pond type solar water heater.


Comments/questions/suggestions welcome Gary.


Some of the changes from prototype 1:


Changed to a sloping lid on the cover:

The flat lid tended to sag in the middle and collect dirty puddles of water.

The vertical sides that support the glazing have reflectorized Mylar to reflect more sun onto the pond -- this should help a bit when the sun is lower in the winter.

There will be a 2nd layer of film or bubble glazing just over the absorber -- not sure what kind as yet.

EPDM Liner instead of black polyethylene:

The polyethylene showed a lot of deterioration over just a couple months.

The EPDM should last for quite a few years.


Increased the area and the depth of the pond:

This allows more pipe coil for better heat exchange as the cold water flows through the pond, and more heat storage in the large volume of pond water. 

These changes were indicated by the testing on the small pond.

Changed the scheme for distributing flow over the EPDM layer:

This is in the picture -- the aim is get a more even flow.  Based on a little testing, this still leaves something to be desired, and I will likely change this.  Any ideas?

I also had a go at partially embedding the pond in the ground (see last picture) -- decided this was too much work and fussy to get the dirt arranged so that the insulation fit well.   Decided instead to just make the sides taller so that all the volume would be above ground.


This project is on hold until I can get the Solar Shed project going -- will probably get back to it during the summer.  I still think the concept has a lot of potential for a really cheap and easy to build water heater.


Cover on the pond, but


The prototype 2 frame with cover in background.  No insulation installed as yet.

The pond frame sits on gravel (for drainage), and has small footing blocks on each corner to allow easy leveling with shims.


The new slopping cover with reflectorized sides.



The EPDM absorber bonded to the rigid foam float with new flow manifold.

First cut at the new scheme for distributing water over the EPDM absorber.  The pipe down the centerline has many holes to distribute water into each panel.  The outer rim of PVC pipe dams the water so that it cover the full area of the EPDM.  There is a drain allow water to drain back down into the pond when the pump shuts off.

After a couple test runs on this, I'm not sure its the best solution -- any ideas?



The new PE pipe coils have about twice the volume and twice the surface area of the first prototype.