Saturday, January 13, 2018

David's DIY drainback solar water heating system

David has designed and built a very nice solar water heating system for his energy efficient home. It is a drainback system that uses an EPDM lined, non-pressurized wood tank for heat storage.

Some of the highlights of Dave's system...
  • Tank design suitable for limited height crawlspaces.
  • Nice tank frame design using half lap joints for the corners
  • Used new old-stock commercial collectors at a very good price
  • Efficient heat exchanger installation
  • Using used and recycled materials kept the cost of the system down
David with his three drainback collectors
David's system consists of three collectors mounted vertically on the south wall of his house. The heat storage tank for the system is in the crawl space under the collectors. Its a drainback system, so for freeze protection, the water in the collectors drains back to the heat storage tank when the pump turns off.

The collectors were obtained on Craig's list as "new old-stock" for a very good price.
The heat storage tank is a non-presurized, wood framed, insulated with polyiso rigid foam, and then lined with an EPDM liner - this is a design that has been used on quite a few Build It Solar projects, and works well.

David with heat storage tank in his 29 inch deep crawl space.
The heat exchanger uses a 300 ft coil of pex pipe that has been used successfully on several Build-It-Solar projects. The scheme that Dave used to support the pipe coil and space the coils out is very nicely done and likely provides a worthwhile gain in heat transfer efficiency. One nice thing about this style of heat exchanger is that it stores several gallons of fully preheated water right in the coil.

PEX coil heat exchanger with nice coil separation and support scheme.

See all the details here...


Gary
January 13, 2018

1 comment:

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