Since the greywater portion of the heat exchanger must operate under very the low pressure head of a gravity drain and still flow at an adequate rate, it must be quite large in diameter. It is essentially a drain pipe and is no more likely to get clogged than any other drain pipe. Since the water is not standing in the heat exchanger but just flowing through, it doesn't have the required gestation time for significant biological growth -- just like most drain pipes don't grow stuff, unless they have standing pools of stagnant water due to poor slope design (hair going down the drain, or mineral deposits are obviously a different issue). Given that this heat exchanger is the same diameter as any other drain plumbing, I don't see biological fouling as a significant issue.
The heat exchanger path for the incoming cold water is indeed much smaller with a higher pressure loss (usually, a small spiral tube wrapped around the greywater drain pipe), however it is clean water, and is no different than the heat exchanger for any on demand water heater. The effectiveness comes from the fact that showers are essentially continuous flow systems with no time delay from inflow to outflow. The exact time that hot water is flowing down the drain, is the same time that incoming cold water is flowing through the outer tubes of the heat exchanger. They work very well under these conditions. Uses such as clothes washing, dishwashing, anything that involves drawing hot water, using it for a while, then discharging it to the drain, they have little effect on, since the hot water discharge does not coincide with the cold water draw to the input of the water heater. If showers use a significant portion of an average household's hot water, then greywater heat reclamation would seem to make sense. Zeke On 10/13/05, Tom Irwin <[EMAIL PROTECTED]> wrote: > > Hi John, > > > Just because graywater has some heat in it does not make it economically > recoverable. Graywater is a wonderful breeding ground for fungi and bacteria > that will definitely grow and clog heat exchange tubing. I think it will be > a huge headache and a waste of capital and time. Think about the problems in > trying to recover shower water at 40 or 45 C for a 10 or 15 minute period. > That´s only a 20 or 25 C differential for a very small amount of time. It > seems ridiculous to me. > > Tom Irwin > > > > > > ________________________________ > From: John Hall [mailto:[EMAIL PROTECTED] > To: Biofuel@sustainablelists.org > Sent: Wed, 12 Oct 2005 23:16:44 -0300 > Subject: Re: [Biofuel] Grey water heat recovery and low tech Solar > collectors???? > > > Jim, > There are commercial grey water heat recovery systems out there. They > recover 50% to 75% of the heat going down your drain, largely while taking > showers. According to the DOE studies conducted. Check > http://www.gfxtechnology.com/ > There is one other company that makes a similar product for about the same > price of $375 and there are tax incentives for these. > > I do not agree that they would not be worth it for the money since most > homes use about 30% of their energy bill heating water. This should cut > that about in half. > > Regards; > John > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > JJJN > Sent: Monday, October 10, 2005 8:15 PM > To: Biofuel@sustainablelists.org > Subject: [Biofuel] Grey water heat recovery and low tech Solar > collectors???? > > Hi folks, > > I was looking for some ways to help save some energy this winter. I > found two places that may help, but I know nothing about either and > wonder if it is worth the investment or not. They are: > > 1) Solar collectors > > 2) Grey water heat going down the drain > > Can anyone give me some pointers in these two areas? > > Thanks in advance > > Jim > > Wisdom to all > > _______________________________________________ > Biofuel mailing list > Biofuel@sustainablelists.org > http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org > > Biofuel at Journey to Forever: > http://journeytoforever.org/biofuel.html > > Search the combined Biofuel and Biofuels-biz list archives (50,000 > messages): > http://www.mail-archive.com/biofuel@sustainablelists.org/ > > > _______________________________________________ > Biofuel mailing list > Biofuel@sustainablelists.org > http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org > > Biofuel at Journey to Forever: > http://journeytoforever.org/biofuel.html > > Search the combined Biofuel and Biofuels-biz list archives (50,000 > messages): > http://www.mail-archive.com/biofuel@sustainablelists.org/ > > > > > _______________________________________________ > Biofuel mailing list > Biofuel@sustainablelists.org > http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org > > Biofuel at Journey to Forever: > http://journeytoforever.org/biofuel.html > > Search the combined Biofuel and Biofuels-biz list archives (50,000 > messages): > http://www.mail-archive.com/biofuel@sustainablelists.org/ > > > > _______________________________________________ Biofuel mailing list Biofuel@sustainablelists.org http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Search the combined Biofuel and Biofuels-biz list archives (50,000 messages): http://www.mail-archive.com/biofuel@sustainablelists.org/
