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GBlist: Drainwater heat recovery
Domestic water heating is a significant energy end use in almost all
housing, but has, I believe, been neglected compared to HVAC and
envelopes. Drainwater heat recovery looks like one technology that
can improve system efficiency.
As mentioned by Craig DeWitt, the GFX (from Vaughan Manufacturing in
MA), is a very simple system, basically a copper drain line
(typically 5 feet long) with copper supply tube wrapped around it.
The supply tube carries cold water on its way to the water heater
and/or directly to showers. When there is simultaneous flow of warm
drain water and supply water (when showering or otherwise by
luck), the drainwater preheats the cold supply.
The GFX has proven performance in a lab setting, with an
effectiveness of about .60 (i.e. captures about 60% of theoretically
available energy) during simultaneous flow. It has not been subject
to any rigorous field trial yet, but I have a proposal out to a
number of utilities to install and monitor systems in occupied homes
to obtain this information.
We at NAHB Research Center, working on behalf of Vaughan, have
also just completed the evaluation of the GFX required to obtain
an IAPMO listing, which will help with code acceptance.
The concept of a heat exchanger combined with storage capacity, to
allow heat recovery when supply flow and drain flow are not
simultaneous, makes sense from a pure energy perspective.
However, adding storage raises practical issues such as added cost
and complexity (added storage volume on either drain side or supply
side, and controls and pump if storage is on the supply side), and
code acceptance issues, especially if drain side storage is added.
I'll watch for more ideas on this.
Phone 800-638-8556 x706
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