[Greenbuilding] Drain Waste Heat Recovery

[Tom St. Louis]

Power-Pipe and GFX will not slow any waste water on its journey, the inside 
core is standard unmodified Drain Waste Vent (DWV) copper pipe. They just
reclaim the energy, though Power-Pipe's design and function does provide a
lower pressure drop with excellent energy recovery. This combination allowed
Power-Pipe to be the only Canadian Energy Star Program compliant Drain Heat 
Recovery
unit, maybe the same thing could happen in the USA too some day soon.

See http://www.renewability.com/index.htm

The pressure drop must be considered in the plumbing supply design to lessen
complaints. People want both good volume and pressure without fluctuation
when more fixtures are turned on. If the technology is out of site and out
of mind and still works then the fear of change and the fear of choosing
this investment in drain heat recovery will soon be forgotten. Rewards of
lower energy costs derived from smart multiple systems integration that
people can see in the wallet is happiness. Other effects like less CO2 are
great too.

There is a reason to have multiple heat exchangers (HX) if you want the best 
ROI.
The optimum flow rate for 3" and 4" dia falling film heat exchangers is 2 to 
3 GPM. If
multiple fixtures drain to one heat exchanger at the same time, the film
inside is thicker which hinders heat recovery. The key is to have multiple
fixtures used consecutively that drain one after the other at 2 to 3 GPM 
flow over a
longer period of time. For example, if you have one shower that four people
use, one person after the other, you could have four 12 minute showers, 48
minutes of 2.5 GPM heat exchanger activity resulting in faster pay back for
that one HX unit. Four showers flowing to one 4" dia HX works economically 
because odds are that all 4 showers would not always be in use at exactly 
the same time.

If you are lucky and have the ability to create separate gray and black
water plumbing (usually cold from WC flushing) in your system, you could 
have
heat recovery from the most likely hot or tepid gray water, and then do gray
water reuse post HX. Again think "Smart Systems Integration". Maybe more 
cost up front but potential hugh long term return.

Tom

----- Original Message ----- 
From: "John Straube" <jfstraub at civmail.uwaterloo.ca>
To: "Alan Abrams" <alan at abramsdesignbuild.com>
Cc: <GREENBUILDING at listserv.repp.org>
Sent: Tuesday, June 26, 2007 4:17 PM
Subject: Re: [Greenbuilding] GFX Drain Waste Heat Recovery


> This is not too hard to imagine working. I dont think you need to buy one 
> GFX or Powerpipe heat exchanger per floor, or even one per stack in a 
> multiunit building. I would not be surprised if you could do a whole 
> vertical run in a tall building with really good bang for buck (sure you 
> loose some heat from the uninsulated pipes, but the capital cost per 
> shower just dropped really really low). Ideally, I would think you could 
> break the system up at each pressure reducing valve (say every 6 floors in 
> your case) per stack. This would still be a really good payback scenario, 
> likely under a year even with the expense of retrofit vs new build.
>
> Alan Abrams wrote:
>> Dr V--
>>
>> Imagine a 40 yr old 250 unit 18 story high rise with, oh, say, maybe 25
>> stacks that are at least 6" diameter by the time they get to the garage
>> ceiling, maybe some of them running horizontally for a ways to join with
>> others--into who knows, maybe 15 stacks that take it below grade...many 
>> of
>> them quite a ways from the water heater.  Of course no way to synch the
>> preheat circuit with any given shower, but you know two or three hundred
>> peeps are gonna take a shower between 6-8 am every day...
>>
>> Is it madness to take this thought any farther?
>>
>> -Alan Abrams
>>
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>>
>>
>>
>
> -- 
> Dr John Straube, P.Eng.
> Associate Professor
> Dept of Civil Engineering & School of Architecture
> University of Waterloo
> Waterloo, ON Canada
>
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