Green Building Forum - Recovering the heat from shower water

Recovering the heat from shower water

Mike George — Sat, 29 Nov 2008 17:30:14 +0000

Met a chap today who is selling heat recovery units for shower waste water. He claims the heat exchanger is 60% efficient and the system has Certification to back this up. At a unit cost of around Â£450/ unit it would be interesting to see if the numbers stack up. Anyone looked into these?

Recovering the heat from shower water

jamesingram — Sat, 29 Nov 2008 17:32:34 +0000

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2957&page=1#Item_0

some talk about it here

Recovering the heat from shower water

fostertom — Sat, 29 Nov 2008 17:33:48 +0000

Lots of them about - is this about the thing in principle, or about a particular make? what make?

Recovering the heat from shower water

Mike George — Sat, 29 Nov 2008 17:46:36 +0000

James - thats a thread I have never looked at for some reason - thanks - will read it all and post there

Tom, apparently there is only one supplier in the UK - at least that's according to the guy I met - showersave.com

Recovering the heat from shower water

fostertom — Sun, 30 Nov 2008 00:17:19 +0000

There's the common vertical drop-pipe type, many versions from US/Canada, also a German one that's a flat coil that fits under the shower tray - in fact I have an idea it's an option on the Bette lift-out-floor shower tray.

Recovering the heat from shower water

Mike George — Sun, 30 Nov 2008 00:38:43 +0000

Yes, its the German one they are offering. Also the Bette tray for around Â£1200

Recovering the heat from shower water

TimSmall — Sat, 17 Dec 2016 10:43:06 +0000

8 years later, and they still seem to be about the same price... There's also a UK manufacturer about now (Recoup), with a part-plastic, part-copper design.

I made an all-copper one myself for < Â£100 in parts, but it's not WRAS compliant since no double-walled exchanger (EN 1717).

Yet another manufacturer gets around the double-walled requirement by mandating that it's installed upstream of the shower U bend (sold in the UK as Heatrae SHRU). Overall I suppose it's not as good, since if it springs a leak, it'll be chucking fresh water down the drain I suppose, but I suppose that's pretty unlikely (most likely to leak from the solder joins I suppose in which case all the leakage paths would be fresh water into the room). Nice to know you can do that design with the Â£100 DIY option, and still comply with the regs tho'.

I'm quite happy with mine as it allows me to run two showers simultaneously from a minimum size combi boiler (for me the boiler replacement savings outweigh the the running cost savings).

Also worth noting for these that if you're running from a combi boiler that the boiler will be running quite a lot more efficiently (maybe 90% instead of 70%) in addition to the obvious savings of cutting a basic 50% off the hot water usage.

Must get around to putting some temperature sensors on my DIY one, to do some real-life efficiency monitoring

My initial esimates gave a pay back period of around 15 years I think (including labour).

Cheers,

Tim.

Recovering the heat from shower water

TimSmall — Sat, 17 Dec 2016 10:44:58 +0000

Outer sleeve on, next is a standard Tee piece (not show), and finally the reducer (which is standard except it has the end-stop filled off so that it can slide over the inner pipe.

The criss-crossed wire is some scrap 2.5mmÂ² mains wire, stripped of its insulation. The purpose is to maintain an even gap between the outer and inner pipes (at some of the cross-over points I added a blob of lead-free solder to get the spacing correct), and also to introduce turbulence in the pre-heat water to maximise the mixing within it.

I thought perhaps without turbulence, the layer which travels next to the inner skin would end up warm, with the layer travelling next to the outer skin staying colder).

Recovering the heat from shower water

ringi — Sat, 17 Dec 2016 15:06:33 +0000

Put a double check value on the water feed before it goes into your shower heat recovery, so if you get a leak, it is unlikely to get back to your drinking water tap.

Recovering the heat from shower water

dimengineer — Sat, 17 Dec 2016 17:50:49 +0000

I just find it difficult to conceive that you'll ever recover enough good quality heat to make it worthwhile. At best, waterg oing down the plughole will be 35C max, if you get a 5C approach on the heat exchange thats a best of 30C. And 5C would be a good result.

So your shower uses what, 50 litres for the shower, and you can heat up the equivalent amount incoming from say 15 to 30C. Thats 50 x 4.2 x 15 kJ = 3150KJ. Less than 1 kWh per shower. If its gas heated thats less than 5p recovered. Shower every day, 365 in a years Â£18 saved.

So ona domestic scale I reckon its simply a non starter.

Recovering the heat from shower water

wookey — Sat, 17 Dec 2016 18:31:24 +0000

I think you are looking at it from the wrong end. If the shower is 45C, then that means half the energy is coming from the heat exchanger rather than the heater so your showers are approx twice as efficient as they were (modulo start/end effects). That sounds worth having. Certainly for Â£100, less so for Â£450, although if your shower tray costs Â£1200, then it's neither here nor there!

Recovering the heat from shower water

joe90 — Sat, 17 Dec 2016 18:33:00 +0000

I wanted to make my own but came to the same conclusion that payback was not worth the effort. Better to put that effort in insulating/draughtproofing the house.

Recovering the heat from shower water

SteamyTea — Sat, 17 Dec 2016 22:03:08 +0000

Could you not make one that used a heat pump and a coil to preheat a header tank of water.
Would require a bit of certified refrigerant gas working and an vented shower system.

A lot of the energy from a bath or a shower goes into the air, a good heat recovery unit will help in the winter.
My water temperature rises and falls by 15Â°C between winter and summer (mean is 13Â°C). In the winter it can drop to 5Â°C and up to 20Â°C in the summer. May be easier and cheaper to fit a trace heater/small immersion heater to the incoming mains and run it from some PV.
Some sums would be needed.

My bath/shower probably uses around Â£100 of E7 electricity a year. Which is really way too low to spend more than Â£50 quid on.

My water costs more than the heating

Recovering the heat from shower water

djh — Sat, 17 Dec 2016 23:43:01 +0000

Posted By: SteamyTeaCould you not make one that used a heat pump and a coil to preheat a header tank of water.

I doubt that the duty cycle / length of time it would operate / quantity of heat in shower waste would make the investment in a heat pump worth while. Probably better to accept the lower source temperature but vastly longer operating hours of a normal ASHP.

Recovering the heat from shower water

SteamyTea — Sun, 18 Dec 2016 06:31:03 +0000

I agree, though there are ways to make a very small heat pump act like a larger one for a short period of time.

The main problem of over cooling waste water would be gunking up of the waste pipe.

Recovering the heat from shower water

joe90 — Sun, 18 Dec 2016 12:25:07 +0000

If I remember correctly Tony,S idea was to leave bath water in the tub after a bath and let the heat warm the room then empty once cold. Not possible with a shower unless you shower in a bath and put the plug in.

Recovering the heat from shower water

Viking House — Mon, 19 Dec 2016 21:06:21 +0000

Well done Tim, I like people who make things, your apparatus looks great! I'm also a fan of Combi Boilers, heating cylinders of water is inefficient and they waste a lot of space in a house. The problem with Combi's, as you've mentioned, can be insufficient water pressure and the capacity of the boiler to heat 2 showers simultaneously. Your heat exchanger idea should substantially boost the ability of a Combi to power 2 showers. I saw some shower heat recovery units http://www.wagner-solar.com/waerme/produkte/waermerueckgewinnung.html at this years Passive House Conference that were Passive House Certified to recover up to 65% of the heat used when showering.

If we build Passive Houses with Tri-Solar Roofs, FreshR HRV and Shower Heat recovery we should be able to run the houses with a small amount of electricity.
FreshR and Solar Heating cuts the heating demand from 15kWh/m2.annum to 1kWh/m2.annum.
Solar Heating and Shower Heat Recovery can cut the hot water demand from 20kWh/m2.annum to 1kWh/m2.annum.
3-4kW of Solar PV can cut the electrical demand by 60%, the rest can be powered by straight electricity, eliminating heat pumps, but it shouldn't cost any more than Â£100/annum to run the house.
My best performing 180m2 house uses â‚¬140/annum for heating, hot water and electricity, it has no PV.

Recovering the heat from shower water

SilverSpray — Sun, 05 Jan 2020 23:16:03 +0000

I bought, but due to floor construction and chosen showers 3 x Zypho shower heat exchange units.
Looking to sell them on Vs put them in landfill.
Apparently sold under licence to Megaflo, in the UK for over Â£1,000 each.
If I got Â£250 + P&P, I'd be happy.

Recovering the heat from shower water

SilverSpray — Mon, 06 Jan 2020 11:41:54 +0000

I've been doing a Google search and found 2 reviews of the Zypho's:

https://www.kbbreview.com/15941/news/zypho-shower-heat-recovery-system-are-now-available-in-uk/

https://specificationonline.co.uk/articles/2018-06-07/zypho/after-successful-trials-zypho-shower-heat-recovery-device-now-available-to-improve-uk-energy-efficiency

Makes me wish we'd been able to install them, but that's not how it went and hopefully somebody else can benefit from them.