Heat recovery from shower water

[acresswell]

In our new house, we'll have 2 shower cubicles at first floor level almost directly above the thermal store.

I'm therefore interested in recovering some of the heat from the drainwater and transferring it to cold water entering the store.

The recoh vert system (http://www.shower-save.com/recoh-vert.html) seems to be the best-advertised, but at £575 the price is definitely off-putting.

Itho (http://www.itho.co.uk/products/heating-hot-water/shower-heat-recovery) seem to be bringing out a competing product.  Anyone know any details about price or performance? I don't think a lot of their website.

I've found a thread on the AECB website http://www.aecb.net/forum/index.php?topic=1735.0 which also mentions a warmit product  (http://www.aki.co.uk/warmit) but it was first mentioned in 2009 and nothing seems to have happened with it.

Anyone know of any alternatives or got any experience of them in action?

Thanks

(I've no connection to any of the companies mentioned)

[mespilus]

A simpler solution may well be the heat exchanger from a combi boiler,
either bought as a 'spare part',
or,
depending upon your nature,
scavenged from discarded combis in skips,
(the source of the two I have acquired),

plumbed in to the pipe containing hot water exitting your TS?

[A.L.]

hello,

Anyone know of any alternatives or got any experience of them in action?

the people who make the ecocent heat pump have what they call a "squirrel", a cylinder with a coil to recover waste heat, see very bottom of this page www.esavep.com/products/hot-water-cylinders. Sorry no further details

[acresswell]

I've no objection to using a scavenged combi boiler heat exchanger...
  Will it get jammed up with the inevitable long hair? (wife, daughter and dog... I barely have any left   )
  What are they usually made from?  Stainless steel?
  It'd be easy to connect the incoming water, but I'd have to bodge something on the drainwater side to give me 40mm or 50mm connectors in and out.

The squirrel looks interesting. I was afraid it was going to use a heat pump (but it doesn't seem to).  It seems to be a glorified tank with a coil in it.  I suspect that I could do something similar with an old cool box and a coil of cooper tubing.  My only concern is that after the shower, there'll be a quantity of drainwater and also clean water (in the coil) sat at perfect temperatures for legionella.  With the other devices, although there'll be some clean warm(ish) water sat in the coil, the dirty water drains away. The water in the coil will therefore cool more quickly, reducing the likelihood of problems with legionella.

Any other thoughts?

[acresswell]

Just re-read Mespilus's post...

plumbed in to the pipe containing hot water exitting your TS?

I was expecting to put it on the pipe where cold water enters the thermal store, with the other side of the heat exchanger taking the drainwater from the showers above...  to try to pre-heat the water going in to the thermal store

[Justme]

How much energy is actually in the shower water once it gets to the drain?

I was thinking that a 10kw electric shower (easier way of working out the total energy than a gas / TS shower) on for a 5 min shower is only 0.8kWh most of that will be heating your body & the air in the cubical then the shower sides & base will absorb most of the rest.

Just how warm do you think the water in the drain will be?

Try putting the shower on & catching the water at the base in a jug with a temp probe in it.

Will each shower have enough volume & latent heat to warm the exchanger never mind the incoming water?

I would put money on you saving more by reducing the temp & flow slightly than capturing the waste. Much cheaper too.

[jwbellarby@gmail.com]

an easier solution would be to have a coil around the shower waste to preheat the water going to the shower, that way it is being used when most effective. I've seen several diagrams on the web of doing this and almost did it ourselves on our new build but not enough time

James

[Fionn]

Hi all,
        I came across what I believe is by far the best and cheapest method of achieving grey water heat recovery here recently - http://www.theyellowhouse.org.uk/themes/heatwat.html#h14

Basically grey water from sinks and showers goes to a holding tank for reuse for flushing toilets. The key however is that the tank is within the building envelope so any energy retained in the water is returned to the air inside the house.

The argument against this arrangement is that your incoming water supply is likely to be at a lower temperature than the air in the house and thus a perfect  heat exchanger would harvest more of the energy from the grey water.
The perfect answer to this is to run your incoming cold water supply through the coil of the grey water tank (assuming you also use an old copper cylinder).
If doing this I would probably use an FPHE connected to the coil and run the incoming water through the other side, just to give double protection against any cross contamination.

Fionn

[MarkB]

Itho have two offerings - one in copper and one in aluminium. The copper version is roughly the same price (perhaps slightly less) as the Recoh-Vert while the aluminium version is a little cheaper and a little less efficient.

The Itho copper and Recoh-Vert have very similar efficiencies and the Recoh-Vert is considerably larger than the Itho.

I agree that there is very littel data available on their web site (at least when I last looked). If you ask Itho they will send you a copy of the installation instructions which include more details (I can email these if you send me your email address).

[spluger]

an easier solution would be to have a coil around the shower waste to preheat the water going to the shower, that way it is being used when most effective. I've seen several diagrams on the web of doing this and almost did it ourselves on our new build but not enough time

James

did this as an experiment on my old shower / bath

had a copper waste on it so took 15mm cold to shower, split to 2 x 10mm copper and wrapped around waste pipe for 18" then joined back onto cold to shower.

shower was a thermostatic mixer

never tested with temp probes but you could feel the difference between cold in and out by hand

sadly it wouldn't fit under my new shower tray and was swapped for some wood for the stove.

an other idea i had (room permitting) would be to send 10mm pipe through the plastic waste sealed at each end ensuring the 10mm copper was at the bottom of the waste and connected in a smiler fashion

again could not fit under my new shower tray 

David

[Fionn]

That's the thing with all these devices, they need to be installed somewhere that's awkward and tight for space. Not ideal for something that might potentially need cleaning either. Hence why I think the internal greywater tank is a good idea, simple and effective!

[acresswell]

Sorry, but I don't like the idea of DHW being pre-heated by a greywater tank...

When the shower is finished, the tank will gradually cool down through a range of temperatures that are ideal for bacterial growth... and the water for my next shower (which will be in droplets round my nose and mouth) will be sat incubating at those exact same temperatures. I couldn't care less about bacterial growth in the waste water (as long as I can't smell it) but I don't want bacterial growth in my shower water.

The recoh-vert or Itho will still need to cool down, but because they don't retain a mass of waste water they will cool much more quickly and therefore give much less opportunity for bacterial growth.

I can certainly see the value in keeping greywater inside the house to reclaim its heat, just not anywhere near my DHW.  Of course, if I had a GSHP or similar I would definitely think about installing a big greywater tank and running a bit of the slinky through it!

[Fionn]

That's a fair point and to be fair to the yellow house website people, they don't use it to preheat the water.
As regards a "big" grey water tank, I don't think there would be much point in making it any bigger than the amount of hot water you are likely to use in one go, I think 100L would be plenty unless you had a power shower.

[acresswell]

You're right, Fionn, it wouldn't need to be huge. 

Might go for slightly larger than 100 litres, though that does depend on the size of the household.  Typical gravity shower water useage is apparently 35 litres (http://www.uswitch.com/water/how-much-water-use/) so a household doing 5 morning showers and a washing machine load might generate more than 100 litres. Would want to be able to hold the grey water long enough so that all the heat had been extracted to reduce it to ambient temp. 

Presumably a tall thin tank would be best, to achieve stratification...and allow the outflow to be at the bottom so the coldest water is disposed of as new enters the tank...

...it almost makes me wish I'd got a GSHP to experiment with! 

[martin W]

the waste pipe heat exchanger made me think...

I could put a piece of 15mm copper pipe inside a 42mm waste pipe across the bottom so that the incoming cold could be pre heated by the waste cold going out. but over 1 or 2m in length how much heat trasfer would you really get?

Incoming mains - 6-15°C depending on time of year. Outgoing shower waster - 30-35°C max, so a delt T of 10-29°C. Actually in summer when incoming mains is around 15°C the shower waste is more likley 25°C.

anyone have any ideas on how to work out sensible temperture increase for 1m or 2m lenght of heat exchanger? 1°C, 5°C??