Drain-Water Heat Recovery

Drain-Water Heat Recovery Saves Energy

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Drain-Water Heat Recovery, including:

  • Design and build strategies
  • Necessary codes
  • Application how-tos
  • Using materials

A simple device saves significant amounts of energy

These systems have speedy payback
The energy department estimates that energy losses in hot water amount to 80% to 90%, a good argument for installing a drain-water heat-recovery (DHR) system.

In a gravity-film heat exchangerDevice that transfers heat from one material or medium to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from one airstream to another. A copper-pipe heat exchanger in a solar water-heater tank transfers heat from the heat-transfer fluid circulating through a solar collector to the potable water in the storage tank. (GFX), drain water flows through a copper pipe that is wrapped in smaller diameter copper tubing. Heat from the drain water is transferred to incoming water. Heat exchangers are made from solid copper so they are durable, and there are no ...

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Sat, 02/11/2012 - 16:51

Response to John Scime
by Martin Holladay, GBA Advisor

Here is one set-up sometimes used for slab-on-grade homes:

I'm not necessarily advocating this approach -- it lacks the no-moving-parts efficiency of an installation that depends on gravity -- but you could do it if you want.

Sat, 02/11/2012 - 00:04

Edited Sat, 02/11/2012 - 12:45.

How close to your heater for best efficiency?
by John Scime

I love the idea of the DWHR pipes - simple and effective. My trouble is that with a slab-on-grade build - where you cannot easily go through a floor joist to connect directly - you would end up running a lot of tubing in an less-than-direct fashion. I figure with my configuration, the DWHR outlet would be 18 - 20 feet from my on-demand water heater. Would my newly heated water cool down over that length of run, thereby deminishing the effiency? This would be a big concern given the capital cost.

Any thoughts?

John, near Ottawa

Wed, 08/26/2009 - 06:51

Install Considerations / Details
by Mike Guertin, GBA Advisor

You have to consider the install details before buying a GFX. Vertical orientation is critical for the film to form on the drain pipe walls and the longer models are more efficient than the shorter models. So you have to locate the tallest vertical drop from the main drain line to the sewer / septic pipe exit for the best efficiency.

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