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Posted by Paul M. Eldridge on July 1, 2007, 11:47 am
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Hi David,
I can now offer better numbers with respect to our earlier discussion
concerning wastewater heat recovery. According to Retherm, a Canadian
supplier of this technology, their products recover *up to* 30 per
cent of the waste heat that flows down a shower drain.
Source: http://www.retherm.com/HowItWorks.htm
Their offerings range in price from $447.00 to $698.00 CDN.
Source: http://www.retherm.com/Products&Pricing.htm
I'll assume my cost falls somewhere in the middle of the pack
($572.50) and that I'm capable of installing this product myself, at
no additional cost. For argument's sake, I'll also assume I heat my
water electrically, at a cost of $0.1067 per kWh, and that my heat
recovery is, indeed, a full 30 per cent.
As previously mentioned, two five-minute showers at an average flow
rate of 2 GPM and at a 60F temperature rise represents roughly 10,000
BTUs of heat demand (2.93 kWh). At 30 per cent heat recovery, I would
expect to save 0.88 kWh/day or about 321 kWh/year. My annual savings
at $0.1076 per kWh are $34.53, which puts the simple payback at 16.6
years. That's about a 6 per cent return on my initial investment.
Obviously, the results would be better for larger families and/or
where shower length is longer but, again, in our case it made more
sense to spend our money on other energy saving measures that provide
a higher rate of return.
Cheers,
Paul
--- Original ---
>On Wed, 20 Jun 2007 23:48:31 -0500, david.williams@bayman.org (David
>Williams) wrote:
>
>>-> I did look at installing a GFX on my shower drain, but even at today's
>>-> relatively high fuel costs, the economic payback is not all that
>>-> compelling. In rough terms, two five-minute showers at 2 gallons per
>>-> minute and an average temperature rise of 60F represents about 10,000
>>-> BTUs of heat demand. That translates to be something in the order of
>>-> 0.35 litres of fuel oil per day or approximately 128 litres (34
>>-> gallons) per year. If the GFX could recapture half that (and that
>>-> might be somewhat optimistic), I would expect to save about 65
>>-> litres/year or about $55.00 at current fuel oil prices (i.e., $3.20
>>-> per US gallon). If there were teenagers in the household, it would be
>>-> a done deal, but since there are only the two of us and we're both
>>-> pretty water and energy frugal, I really couldn't justify it.
>>
>>-> Cheers,
>>-> Paul
>>
>>Still... $55 per year for ever is nothing to be sneezed at. I suppose I
>>spent about $100 to make my heat exchanger, so it paid for itself in a
>>couple of years. It's about 15 years old now, so I'm quite a few
>>hundred dollars ahead. And it causes no inconvenience whatsoever. Money
>>for nothing.
>>
>> dow
>
>Hi David,
>
>True, I don't want to suggest $55.00 is chump change, but I think a
>typical GFX retails for about $450.00 CDN (perhaps more given the
>recent run-up in copper prices) and I would probably need a plumber to
>install it. In my case, it made more sense to invest that money
>elsewhere where the energy returns would be much higher.
>
>Paul
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