Shower waste water heat recovery

[snootsandfruits]

The other is fitted in a cupboard where you'd need a pipe anyway.

They've clearly sized them for the ceiling height of a standard house which does make me wonder what the efficiencies might be if you had taller ceilings.
Again this is a bit of a problem with a retrofit as historically the waste pipe is outside - and you'd not want to stick this thing outside. Most houses will not have a floor-ceiling cupboard below the bathroom, and may not be able to get suitable fall to their waste pipe after moving the shower outlet ~2.4m downwards.

Main market for these is volume housebuilders, who will NOT be paying £650 a pop.

That's a good point. Probably doesn't help me one bit, but I might see if any of the local plumbers' merchants can give me a better price.

[Paul_F]

Again this is a bit of a problem with a retrofit as historically the waste pipe is outside - and you'd not want to stick this thing outside. Most houses will not have a floor-ceiling cupboard below the bathroom, and may not be able to get suitable fall to their waste pipe after moving the shower outlet ~2.4m downwards.

We've designed that in for our house which is currently going through planning - both bathrooms are next to each other upstairs, and vertically above the utility/plant room.

[Tinbum]

I've done the same with mine. I hate pipes etc on the outside.

[snootsandfruits]

I also hate exterior pipes, wires etc. and have considered moving our waste pipe inside, but mostly to make potential exterior wall insulation easier as it *is* at the back of the house so doesn't bother me so much.

We've designed that in for our house which is currently going through planning

That being a WWHR unit, or just the waste pipe?

[Adokforme]

While I try to always put a positve spin on such ideas I'm really struggling to believe there is much heat remaining in waste shower water as it leaves the premises. After all cooling towers are based on the same principle to cool water before it even gets collected. Equally water splashing off another surface back onto my body has a cold feel. Our composite shower tray of substantial thickness sure takes out any remaining heat before the water even makes it into the ubend and then the waste pipe. I very much doubt the temp of waste water exceeds 20C.
Collecting waste heat from bath water might be a different proposition but I remember working at a research establishment in the seventies where a whole section was dedicated to waste heat recovery of such whereby a bladder was used to capture waste water from the bath prior to heat being taken and the water then finally drained. It was controlled by timers and monitoring equipment etc whereby the bath was "filled" and drained twice a day but I'm not aware of any such heat recovery system being marketed as a result!
I can only imagine that for any usable heat to be retained an inline preliminary thermal store would be required for the incoming cold to pass through prior to be drawn through the actual heated thermal store. But each to their own and good luck to anyone thinking of installing one.

[snootsandfruits]

While I try to always put a positve spin on such ideas I'm really struggling to believe there is much heat remaining in waste shower water as it leaves the premises. After all cooling towers are based on the same principle to cool water before it even gets collected. Equally water splashing off another surface back onto my body has a cold feel. Our composite shower tray of substantial thickness sure takes out any remaining heat before the water even makes it into the ubend and then the waste pipe. I very much doubt the temp of waste water exceeds 20C.

The composite shower trays are not particularly conductive of heat, and then they're not going be quickly radiating it away again when they get warm.
The initial temperature of the water flowing down the drain will of course be slightly lower, but I suspect it'll stabilise after the first litre or so.

I found the SAP calculation document I was looking for earlier:
https://www.ncm-pcdb.org.uk/sap/filelib ... 1.2013.pdf

Typical shower head water temperatures of 41ºC measured in the laboratory by Liverpool John Moores University (ref 7, figure 17 for mixer showers) indicate water temperature falls by 5.9ºC in the shower, giving a drain temperature of 35.1ºC, say 35ºC for simplicity.

35C water contains quite a lot of energy.

[Paul_F]

That being a WWHR unit, or just the waste pipe?

At the moment just the building layout - assumed WWHR, but not yet confirmed.

Collecting waste heat from bath water might be a different proposition but I remember working at a research establishment in the seventies where a whole section was dedicated to waste heat recovery of such whereby a bladder was used to capture waste water from the bath prior to heat being taken and the water then finally drained. It was controlled by timers and monitoring equipment etc whereby the bath was "filled" and drained twice a day but I'm not aware of any such heat recovery system being marketed as a result!

I've seen a few homebrew systems (one in Oxford springs to mind), but dealing with the gunk (soap scum, hair, etc.) which accumulates is a bit of a problem.

I can only imagine that for any usable heat to be retained an inline preliminary thermal store would be required for the incoming cold to pass through prior to be drawn through the actual heated thermal store. But each to their own and good luck to anyone thinking of installing one.

That's exactly how it works - they're installed vertically with the incoming cold water travelling upwards and the outgoing warm waste flowing downwards (surface tension holding it to the pipe). That gives a very good counter-flow heat exchanger. The pre-heated cold water can then go either to the cold inlet of the shower, the water heater cold inlet, or both in parallel.

Typical shower head water temperatures of 41ºC measured in the laboratory by Liverpool John Moores University (ref 7, figure 17 for mixer showers) indicate water temperature falls by 5.9ºC in the shower, giving a drain temperature of 35.1ºC, say 35ºC for simplicity.

35C water contains quite a lot of energy.

Incoming cold water is at ~10°C (12 month average), hot water to shower is 40°C and warm water to drain is at 35°C. This means that (40-35) / (40-10) = 83% of the heat in the shower water is going straight down the drain. That's the critical calculation -

[smegal]

I like the look of these, I guess on a thermostatic mixer shower, a slightly warmed cold feed would just reduce the amount of hot provided.

https://powerpipehr.co.uk/?gclid=Cj0KCQ ... OCEALw_wcB

My worry is that scum, hair etc can make a normal 32mm pipe drain slowly. I shudder to think what this'd look like inside after a while of use.

Scratch the above, this just looks like a copper pipe with a jacket. Probably wouldn't be too prone to clogging.

[Paul_F]

I like the look of these, I guess on a thermostatic mixer shower, a slightly warmed cold feed would just reduce the amount of hot provided.

That's exactly the idea. The alternative is using it to pre-heat the inlet water for a combi (or indeed a combination of both, which is the most efficient), in which case less fuel is burned to produce the same flow rate of hot water.

My worry is that scum, hair etc can make a normal 32mm pipe drain slowly. I shudder to think what this'd look like inside after a while of use.

Scratch the above, this just looks like a copper pipe with a jacket. Probably wouldn't be too prone to clogging.

Yeah, so far as the water is concerned it's basically a vertical pipe just like it would be flowing down anyway - and when was the last time you had a blockage in one of those?
One comment on that particular model - it's relatively small and that means fairly low efficiency (sized for minimum cost, to be fair). Something like this may be a better option - cost and efficiency are a bit better than the bigger Power-Pipe models, but it's more expensive than the one you screenshotted.

[myozone]

Years ago I thought of this to find someone who actually did it - He has a few other videos on the same theme.
Dave.