Waste Wattage: Cities Aim to Flush Heat Energy Out of Sewers

Around the world, and more recently in the U.S., cities are realizing that the water leaving our homes and offices?specifically, warm and hot wastewater?is an astoundingly powerful source of energy. One estima te is that Americans flush 350 billion kilowatt-hours of energy into the se wers each year?roughly enough to power 30 million U.S. homes. Citie s are taking notice, and taking steps to install sewage heat recovery syste ms to get a piece of that energy resource.

Using existing technology developed for geothermal to do this. Clog free he at exchangers might get tricky dealing with raw sewage though.

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bloggs.fredbloggs.fred
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Imagine being the poor guy having to clear the fatberg out of the heat exchanger. You're a volunteer?

Jeroen Belleman

Reply to
Jeroen Belleman

and

e

S.

That's the first thing that came to my mind: fatbergs.

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bloggs.fredbloggs.fred

Ah, we see Mueller raising his head again!

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 Thanks, 
    - Win
Reply to
Winfield Hill

I've often thought that showers would be a good candidate for heat exchangers. Water heated to 37'C then hitting 37'C bodies often with

37'C urine added. (We know you do.)

Problem is, the cost of such a device buys a lot of hot water. In some ways, energy is too cheap.

Also, a proportion of the water could be recycled, as in back to the shower head.

Cheers

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Clive
Reply to
Clive Arthur

Good luck with that. There is already a problem in the UK with fatbergs forming in London sewers because far too much fat is entering the sewage system and congealing into a horrible mess.

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Martin Brown
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Martin Brown

I was considering wrapping the cold-water inlet of my water heater around the shower drain pipe. Epoxy or solder or something, or just use a water jacket. That wouldn't change the sewage path.

It wouldn't be worth the effort, as our utilty bills are reasonable now.

That 350 billion KWH number looks big to me, almost 10% of the total energy consumed in the USA.

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John Larkin         Highland Technology, Inc 
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John Larkin

I saw such a device advertised maybe 10-15 years ago. It attached to the tub drain and needed the under-tub space to go vertically down for about 3 feet, then the usual trap and connection to the sewer pipe. I vaguely recall their ad going on about needing the large diameter for contact area and to slow the flow rate, and to be vertical so stuff wouldn't build up on the inner wall at that low flow rate, and that tall to get all the heat they could. The outside was wrapped with copper tube that was plumbed into the water heater inlet. The inside may have also had a spiral groove for more area, it's been too long to remember for sure. That height looked like a deal breaker, and after seeing the ad a few times I never heard of them again :-).

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Carl Ijames
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Carl

hat the water leaving our homes and offices?specifically, warm and hot wastewater?is an astoundingly powerful source of energy. One es timate is that Americans flush 350 billion kilowatt-hours of energy into th e sewers each year?roughly enough to power 30 million U.S. homes. C ities are taking notice, and taking steps to install sewage heat recovery s ystems to get a piece of that energy resource.

e heat exchangers might get tricky dealing with raw sewage though.

eat-recovery/

Right- they only make sense when a lot of users are sharing what becomes a common drain. I just don't see it in a single family residence, especially when these heat exchangers sell for $450 apiece, and you would need a lot o f them. If people turn their hot water heater down to 110oF, and use energy star appliances, clothes washers and dishwashers, which also minimize wate r usage, flow limiters on shower heads I think are 2.5 GPM, which is plenty , they should come out ahead. I think the commonly available and cheap 99% efficiency electric water heater, at my $0.11 rate, estimates at $400 for a n entire year for a family of four.

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bloggs.fredbloggs.fred

and

e

S.

emoved-from-london-sewer

eat-recovery/

That's exactly why everyone needs a backflow preventer valve where their dr ain-waste piping leaves the house.

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44734
Reply to
bloggs.fredbloggs.fred

at the water leaving our homes and offices?specifically, warm and h ot wastewater?is an astoundingly powerful source of energy. One est imate is that Americans flush 350 billion kilowatt-hours of energy into the sewers each year?roughly enough to power 30 million U.S. homes. Ci ties are taking notice, and taking steps to install sewage heat recovery sy stems to get a piece of that energy resource.

heat exchangers might get tricky dealing with raw sewage though.

at-recovery/

Better to put your money in Energy Star appliances than this thing. They al so economize water usage, that's a part of their energy consumption equatio n.

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bloggs.fredbloggs.fred

I can just imagine how gnarly that would get, with all the hair and soap and skin flakes decomposing in it. Cleaned out your bathroom sink drain recently?

Cheers

Phil Hobbs

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Phil Hobbs

hat the water leaving our homes and offices?specifically, warm and hot wastewater?is an astoundingly powerful source of energy. One es timate is that Americans flush 350 billion kilowatt-hours of energy into th e sewers each year?roughly enough to power 30 million U.S. homes. C ities are taking notice, and taking steps to install sewage heat recovery s ystems to get a piece of that energy resource.

e heat exchangers might get tricky dealing with raw sewage though.

eat-recovery/

I ran the figures a few years ago but can't find em. ISTR the exchanger cos

would also mean a smaller cheaper HW cylinder could be used, or for instant systems a lower power boiler.

NT

Reply to
tabbypurr

Vertical certainly has advantages but you can do it with a horizontal copper drain pipe.

NT

Reply to
tabbypurr

a common drain. I just don't see it in a single family residence, especiall y when these heat exchangers sell for $450 apiece, and you would need a lot of them.

I can't imagine what you'd do with a lot of them. Divide that cost by 8 to get a realistic diy construction cost.

appliances, clothes washers and dishwashers, which also minimize water usag e, flow limiters on shower heads I think are 2.5 GPM, which is plenty, they should come out ahead. I think the commonly available and cheap 99% effici ency electric water heater, at my $0.11 rate, estimates at $400 for an enti re year for a family of four.

So if you could feed 25% of that heat back into the cold supply to the show er & hot water heater you'd save $100 a year. If it's there for 20-30 years that's 2-3k saved. Not bad for under $100.

NT

Reply to
tabbypurr

We pay about $100 a month for gas+electricity, so anything past LED light bulbs isn't worth any effort.

I doubt that the sewage/cold water heat exchange would be very cost effective. The cold water would probably only pick up a few degrees. Turning down the water heater temp would probably be better. Take short cold showers.

What do you do at home to save energy? What do you drive?

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John Larkin         Highland Technology, Inc 
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John Larkin

ith

some

And that has a big impact on heat transfer. So what I designed used 2 horiz ontal tubes with a hand unscrewable connector at the u bend end to make use of a pipe cleaner easy. I wouldn't especially want to clean it though. The extra length helps, as does the ability of the copper to move heat from th e top of the water down to the bottom of the horizontal pipe. Near zero fal l also helps water rentention time & height of water in pipe, all of which aids heat transfer.

NT

Reply to
tabbypurr

that the water leaving our homes and offices?specifically, warm an d hot wastewater?is an astoundingly powerful source of energy. One estimate is that Americans flush 350 billion kilowatt-hours of energy into the sewers each year?roughly enough to power 30 million U.S. homes. Cities are taking notice, and taking steps to install sewage heat recovery systems to get a piece of that energy resource.

ree heat exchangers might get tricky dealing with raw sewage though.

-heat-recovery/

also economize water usage, that's a part of their energy consumption equa tion.

With a countercurrent heat exchanger it's theoretically possible to recover most of the hot/warm water energy leaving the house. Make one 25-50% effic ient and you can get a decent ROI, albeit not on a huge sum.

NT

Reply to
tabbypurr

I have no evidence either way, I just remember that in their ad they went on at length about how they couldn't keep a horizontal heat exchanger clean at a flow rate slow enough to keep the overall length down so to them vertical was the answer. Certainly horizontal would fit into a lot more locations.

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Regards, 
Carl Ijames
Reply to
Carl

Not everyone. We're at the peak of a hill.

We'd have to jackhammer the sidewalk to install and maintain one of those things.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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John Larkin

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