Thursday, April 3, 2014

DIY Shower Water Heat Exchanger

When you think about what goes on energy wise when you take a shower, its mind boggling wasteful. Your hot water tank heats up several gallons of water from about 60F to about 120F typically using about 6000 BTU worth of energy. The water flows over you once, and then right down the drain taking nearly all of that 6000 BTU of energy you just put into it right down the drain.

Tyler has worked out a pretty simple heat exchanger to extract some of the heat from the shower water as it goes down the drain and use this heat provide some of the heat to the incoming shower water.

The grey water heat exchanger is inside the ABS stack on the left.  It joins the
main stack on the right near the floor.

The grey water heat exchanger consists of a bundle of PEX pipes.  The cold water on its way to the shower runs through this bundle of PEX pipes which are inside the gray water drain from the shower.  So, the outgoing hot water draining from the shower transfers some of its heat to the cold water that is on its way to the shower.

The bundle of PEX pipes ready to go into the drain pipe.



The bundle of PEX pipes being stuffed into the grey water drain stack.

Be aware that in many places this single wall heat exchanger design would not meet code.

Tyler gives quite a bit of detail on the construction and performance of the heat exchanger -- all the details here....

Please leave any comments or questions in the comments section at the link above.

Also at the link above is some more information and DIY and commercial grey water heat exchangers.


Gary
April 3, 2014





3 comments:

  1. But why PEX pipes? They are insulated so there's very little heat transfer. Why not copper pipes?

    ReplyDelete
  2. Hi Dan,
    While pex has a conductivity many times less than copper, when you figure in the thermal resistance of the water layers, pex comes out about 3 times better than copper as a heat exchanger.
    Its much cheaper and its easier to work with.

    It seems to me that its worth experimenting with both pex and copper for this application.

    Gary

    ReplyDelete
  3. Oops! I meant to say "3 times worse than copper" in the comment just above.
    Gary

    ReplyDelete

 
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