Ok although I am in principle largely in favour of the 'leave-the-plug-in' method but I have recently been thinking about getting that mains incoming cold water up a few degrees particularly in the winter with the solar DHW panels already stretched to say the least.

The idea so far is split the incoming mains near entry to house as you do with one line going to 'boiler' and one to the taps. Passivhaus pipe lagging (50mm all round).

The boiler one doesn't actually go to the boiler it goes to the unvented cylinder through a flat plate heat exchanger in the thermal store powered by solar, wood stove boiler and immersion or gas boiler in that order.

If I were to get the baths and showers to direct their waste water to a tank before leaving the house, I then create an enormous coil holding 50 or so litres of cold incoming water this way the water can sit for a good long while but still keep my mains pressure hot water.

Thought I could construct said coil from 30m or so 22 HDPE pipe, ie as it comes of the roll. Alternately 4x 10mm copper coils 22-10mm manifold at each end. Sling the thing out in a 100l tank, perhaps larger to fit the coil and then stick something in the middle of the coil to reduce the volume.

How to I empty the waste tank bottom first? (to keep the hottest water at the top in the longest) Is the 4x 10mm coil a dumb ass idea?, Does HDPE not conduct enough?

As you can tell, thinking aloud really... all input welcome...

J

http://www.shower-save.com/pdfs/Recoh-vert%20grey%20water%20heat%20recovery.pdf
This is the shower heat-recovery thing mentioned, and includes an additional skin between contaminated and mains water "which is obligatory in most countries".

Thin film heat recovery seems to be quite popular in the USA/Canada:
http://www.gfxtechnology.com#
http://www.renewability.com/dhrt.htm
http://www.watercycles.ca/
http://www.shower-save.com/pdfs/Recoh-vert%20grey%20water%20heat%20recovery.pdf

No sure how this UK system opperates. The description suggests that it may be prone to maintenance issues though (I get the impression that it is a sump type design)
http://www.aki.co.uk/page/warmit

Mark

James,
Thin film technologies, such as GFX and Recoh, only work well for continuous flow devices like showers as they pass the incoming cold water through the heat exchanger to preheat it before it enters the domestic hot water heater (SHW tank or whatever).....They are not suited to much else. That said much of the DHW is used from bathing rather than taps so if you avoid baths in favour of showers you can reduce your DHW consumption quite substantially (and avoiding showers in favour of a wash hand basin for every other day helps even more).

These system are, apparently, relatively low maintenance (I can certainly believe it compared to sumps and tanks.) The GFX information really help to explain the technology and there are a number of independent reports on this particular system. I've not heard of one being used in the UK and would be interested to hear about anyones experiences if they have.

I think that sumps and tanks have many potential problems with bacterial and mould growth since it won't be hot enough to kill the nasties. Legionaires could also be a serious risk.

Mmmh perhaps easier said than done...

The gunk and nasty thing perhaps mitigates toward the single length of HDPE so that the outgoing grey water can never get at the the fresh incoming cold. re the nasties and, 'spose I would have to arrange a weekly purge or something, with gunk trapped and dealt with once month.

Thing is it just seems to make no sense to chuck out 50% of the heat in the water you've just done all you can to get up to temp and then bring in a few hundred litres of icy cold water...

There has to be a way!!

J

JackyR,
I had never heard about legionnaires being formed in warm `clean` mains water,surely this can also happen where cold pipes run alongside hot or even if a cold pipe runs under a hot roof?
It must scupper alot of hot water ideas.
How real is this danger and are there specific regulations.

Thanks,

Chris

Here's that paper again, but clickable: http://energytech.at/pdf/task26_4_industry.pdf

That heat recovery system for showers is nearly 500 quid.

My idea was 'store' the water in a 50m long 22mm pipe but by store I mean say a few hours, the grey water is also 'stored' but for a similar amount but in a tank shortly before discharging in to the soil outlet therefore never the twain meet.

The preheated water then passes on to the plate heat exchange in the thermal store to get lifted up to operating temp. As the grey water will be at most 25 degrees or so the preheat won't make in preheated water that hot, but if its coming in at 2 degrees in the winter even lifting it to 10 would make a decent impact.

Jim,

good idea about the tank, would be keen to use relatively off the shelf bit of gear, not sure how much water would be in the coil but the transfer would be better.

J

Someone pls check my sums.

Assume 22 mm pipe to have internal diameter 20 mm, therefore radius 10 mm = 1 cm.
Capacity of 1 cm length of 22 mm pipe is therefore π x 1 x 1 x 1 = 3 cm^3 (approx).
Capacity of 50 m of 22 mm pipe = 50 x 100 x 3 cm^3 = 15 000 cm^3 = 15 litres.

This feels wrong - and James talks of only 30 m of pipe holding 50 litres...

So if you do this put the details on here because i'd probably be able to DIY it as well - mmmmmmm - give it a try anyway. And i'll be deeply up to elbows renovating house next summer so could build it in......if it work

Cheers.

james
i've seen a similiar system used to preheat the water main for a combi-boiler with the tank acting as a thermal store heated by a solar thermal panel. the tank the right way up though.
The water in the coil would have heat transferred to it as it passed through the grey water even after the 'stored' volume was used up. the problem would be as you suggested earlier removing the sludge without getting covered in it. some kind of diverter to soil pipe , on the access trap could be used to drain down and clean
Diy only, but going back to your first idea , how about
a 50 gallon+ cold water storage tank used to store the grey water outside , in a insulated box near a gully or soil pipe
fit a 28+mm gate valve to drain down into the gully and off to the sewerage farm, also fit 110mm access plug in the bottom to clean out
at the top of the tank fit a 50mm waste over flow into the 110mm soil pipe(with a u trap) or staight to the gully-trap
stick your water main 50m coil in the tank and fix it near the top ,below the overflow .
lid on and insulate the watermain pipe into house etc..
Second hand kit would be best as I 'd imagine the energy recovered would take a while to payback the embodied energy of new
materials.
If you're prone to the occassional use of bleach cleaner, this would enter the tank and maybe help reduce the growth of festering funk inside.

cheers Jim

mmmh..... some consideration of the exchange rate and the following graph, cause our you hero to reconsider the GFX...

I'm not sure that I follow the concern over Legionella...

From what I can see of the Recoh units, the waste water from the shower travels through a heat exchanger with a double barrier meaning that there won't be any contamination of the incoming mains water. This water is then drained away as usual.

Where could the contamination occur?

With a temp diff of at most 23 degrees (your estimated <25 degree sump, 2 degree winter mains - but measure mains as figures vary wildly) and 28 mm HDPE, surely it'll take hours to have a noticeable impact on the incoming cold water? And the temp diff may often be much less.

So you'll get pre-heated water in slugs of 26.5 l max, hours apart. A bath is usually 50 to 150 litres, a low-flow shower 4 to 10 l/min.

It's not that you wouldn't get a few joules out of this system in the winter, it's that I just can't imagine it being worth the embodied energy, including installation energy, and cleaning cost (chemicals, water, your time).

The proprietary shower kits are narrow-piped, copper and operate at higher temps, so their heat-recovery figures should be much better. But the financial figures... whew!