Grey water heat recovery

[Baz]

Every now and then somone asks about this and I have come across this 'Heat Squirrel' at the bottom of the page about water cylinders .
http://www.esavep.com/products/hot-water-cylinders
Rather doubt it is ecenomically viable so one day there will probably be a building reg requiring it.
Might make sense in a hotel with higher water usage and a link into a GSHP to pull the heat back out into the DHW. "yes Sir, you can have a hot shower once we've washed the dishes."

[djh]

That seems to pass the grey water through the body of the device (henceforth known as "settling tank"). I'd think the inside of that would become a rather nasty sticky soup quite quickly.

There are some devices like flat trays and some like heat exchanger pipes but I've forgotten the names at the mo.

[desperate]

They used to have a system in the Magdalen (I think) Colledge in Oxford where Pa in Law used to work, it extracted loads of heat, but also money from the maintenance fund for plumbers to regularly un-block it. In the end they de-commisioned it as it was uneconomic At cactusville we try to minimse energy going down the drain by allowing bathwater etc to cool before pulling the plug

Desperate

[Stuart]

i remember reading about an American who had implemented a system wrapping a copper coil round the outside of a copper waste.
This would stop the clogging up. He discovered that the best saving was when showering as the waste is preheating the mains water as its being used.

Americans all seemed to be blessed with basements where all this tinkering is easy.

[wyleu]

At cactusville we try to minimse energy going down the drain by allowing bathwater etc to cool before pulling the plug
Desperate

Seems the easiest answer.

[Stuart]

I cant believe someone said bath on here and wasn't told off for not showering   

[Philip R]

If you remove heat from the grey water, the sewers will clag up as Desperate has discussed.

Also the missing heat will have to be added back at the sewage works, so the sludge can go to the anaerobic digesters.

As we move towards renewable gas from the sewage works being added to the gas mains, no additional odorant required!! the gas yields will be reduced if the effluent is cold.

In the future, sewage plants could be integrated with small scale local CHP / thermal generation plant,where the low grade waste heat from the condensers could preheat the sewage effluent ( It would need to be a good reliable heat exchanger. You would not want poo and pee contaminating your boiler feedwater) could be heated to 26 degC prior to be fed to the sewage works. Any dodgy sludge not fit for spreading on the fields could be co fired in said plant or be sent for gasification.

PS This would never happen in the UK because of different conflicating interests, technically incompetent politicians whom know Heinz all about science, Engineering, Technology and deeling with green issues!

Philip R

[EccentricAnomaly]

If you remove heat from the grey water, the sewers will clag up as Desperate has discussed.

Did he?  Where?  All I saw was some comment from him about the heat-exchanger thingy clagging up.

Also the missing heat will have to be added back at the sewage works, so the sludge can go to the anaerobic digesters.

Please tell me you're joking, aren't you?  Of course, we all know bath water only loses about 3.14159°C between going down the plug hole and arriving at the sewage works.

[SimonHa]

i remember reading about an American who had implemented a system wrapping a copper coil round the outside of a copper waste.

I think this might be the sort of thing you were thinking of: http://gfxtechnology.com/contents.html. I considered this quite carefully a few years back and decided it would be useful from a purely energy perspective. In fact when I was at uni one of the lab projects was to build something like this - IIRC they found its biggest drawback was the time it took to settle to a steady temp, though that would probably not be so critical for thermostatically controlled mixer valves. You could have a bend at the bottom with a trap to assist cleaning too.

I think the questions for me were both the carbon and financial payback for domestic use - there's a lot of copper/soldering involved for a relatively small payback. For commercial installations, e.g. a hotel, it could have a stronger case.

[smegal]

Also the missing heat will have to be added back at the sewage works, so the sludge can go to the anaerobic digesters.

As we move towards renewable gas from the sewage works being added to the gas mains, no additional odorant required!! the gas yields will be reduced if the effluent is cold.

I have to disagree with both of those. The amount of other water added to sewers combined with the distance travelled will eliminate the warmth of the waste. The AD's will still need heating to mesophilic temperatures.

All gas released into the mains has to have an odorant added, along with loads of other red tape that is irrelevant for such small quantities.

[smegal]

Also the missing heat will have to be added back at the sewage works, so the sludge can go to the anaerobic digesters.

As we move towards renewable gas from the sewage works being added to the gas mains, no additional odorant required!! the gas yields will be reduced if the effluent is cold.

I have to disagree with both of those. The amount of other water added to sewers combined with the distance travelled will eliminate the warmth of the waste. The AD's will still need heating to mesophilic temperatures.

All gas released into the mains has to have an odorant added, along with loads of other red tape that is irrelevant for such small quantities.

After a meeting today with someone in gas compression I have to admit I was wrong. You can get away with not adding odorant if you add to a 30 bar main (or above). The relatively small amount of biogas just gets mixed in with the rest of the gas.

[trubble]

i remember reading about an American who had implemented a system wrapping a copper coil round the outside of a copper waste.

I think this might be the sort of thing you were thinking of: http://gfxtechnology.com/contents.html. I considered this quite carefully a few years back and decided it would be useful from a purely energy perspective. In fact when I was at uni one of the lab projects was to build something like this - IIRC they found its biggest drawback was the time it took to settle to a steady temp, though that would probably not be so critical for thermostatically controlled mixer valves. You could have a bend at the bottom with a trap to assist cleaning too.

I think the questions for me were both the carbon and financial payback for domestic use - there's a lot of copper/soldering involved for a relatively small payback. For commercial installations, e.g. a hotel, it could have a stronger case.

I've made a similar thing to this - 54mm copper sleeved over 42mm copper, with reducing tees capping both ends and allowing cold mains into the bottom of the 54 sleeve, and warmer water out at the top, a cross-flow heat exchanger sort of thing. 2 metres in length, and when showering it does work - can definitely feel a difference in before/after pipe temps, although I haven't been scientific enough to use a temp gauge of any sort.
Is it worthwhile? Without ebay to get the bits from, probably not!
But it is an experment that does seem to have worked.

[SimonHa]

I've made a similar thing to this - 54mm copper sleeved over 42mm copper, with reducing tees capping both ends and allowing cold mains into the bottom of the 54 sleeve, and warmer water out at the top, a cross-flow heat exchanger sort of thing. 2 metres in length...

Wow - one in the wild ! Have you taken any photos? I'm interested in how you finished the ends with tees - I hadn't thought about this before. I don't know what the thermal difference between a wrapped spiral and a water jacket might be - the spiral might be better as the water takes longer to pass through the device, though the jacket might give better thermal conductivity (for the spiral, the tube only touches on one side, though the GFX uses oval tube I think).

I'm sure a few people on here would be interested to hear what the temp is at the bottom and top mid-shower if you ever get the chance - we could then do a few sums...

[trubble]

 
eta Right, success, a pic. Resize x 3. Uploaded. At last.
Top half is visible - this is during building work before plasterboard went onto ceiling.
Overall it's a good 2.3m in length, going right to the floor, where the cooled waste then goes under the floorboards in plastic and away.
54 tee with top reduced to 42 seals and caps the 54 around the 42. Reducing the branch to 22 means 22 pipe for mains water.
There's also a bypass with 3 gate valves as the soldering was difficult - held on 2nd attempt and been working for close to a year now.
Soldering comments will not be appreciated  
I'll have a go with thermometers but I haven't got the right strap on type - will test when The Management is washing her hair - should have a good 45 minute window there for measurements...

[Robl]

Bit of a late post this, but any updates on your system Trubble?
I've decided that I could incorporate something like this into our house, so Any feedback that you have would be very greatly appreciated.
Did you manage to measure the temperatures in and out of waste and cold water that the system achieved?
any problems noted in the last few months of operation?

Hope you see this, cheers RobL