-municipalities would probably reject the idea
-septic tanks are not large enough for the required footage of pipe
-piping could cause blockage of sewer flow
However the idea could be efficient , considering the gray water flow at a consistant temperature. Dont think the sludge would be a problem either , as it would probably aid in heat transfer , coating and surrounding the pipe , mixed with water.
Service on the loop could be bad though.
Dont know if this would be going "green" or going brown.
Airesearch thanks for your ththoughts. As far as the municipality is concerned I think the biggest problem will be making contact with the right person who is open to new ideas. As far as plugging the line at this point I am not to concerned with that problem right now. I would be looking at using larger diameter pipe to keep a larger GPM flowing over the loop so should be plenty of room. I figure the number crunching as to pipe size and required GPM would come later depending how receptive people are to the idea.
Dijit lol. I make my living working in or around sewage. Let me tell ya for the most part it is not bad then probably just like other jobs there are days you can't take enough showers.
There are variables to temp but for the most part in my area 55 would be average. It has been a while since I have looked at temps for I usually am looking at depth and velocity. I can get solid numbers this week if you would like.
One issue with using your sewage system as a heat source - removing too much heat could lead to an increase in viscosity of the sewage, interfering with flow and ultimately making it easier for the system to have freeze problems.
Not being familiar with sewers or septic, I also wonder if reduced temperatures in a septic system could interfere with the natural bacterial processes that break down the organic materials in the sludge (or whatever you call it).
There were some studies and actually homes modified so that all of the waste heat from the drains were tied into a heat exchanger that preheated the water going into the hot water heater and it really saved a bit of money/energy.
But the costs for installation were pretty high. Still, one heat exchanger located inside the home at the main outlet of the home sure would extract some heat from all that hot water going down the drain, I would think. That would elimanate all contact with the local sewer authorities but would bring you face to face with plumbing inspectors.
"The American Republic will endure until the day Congress discovers it can bribe the public with the public's own money.
- Alexis de Toqueville, 1835