Wanted: Waste water heat recovery for bath

stud26

Hi all,
I'm looking to install a waste water heat recovery unit under my bath, something like the Zypho IZI 30. Does anyone know where to get these cheap/discounted/secondhand. Everywhere I've looked is still quite expensive £450+.
Am open to alternatives or DIY options too.
Thanks in advance.

2nd_time_buyer

I guess the obvious thing is to leave the bath water in longer afterwards. Perhaps with a cover to reduce evaporation. I packed under out steel bath with rockwool which made a big difference to how long the water stayed warm.

Reed_Richards

Where are you trying to recover your heat to?  If it's just the room where the bath is then @2nd_time_buyer 's suggestion is as good as any.  If you are taking a shower leave the plug in.  

stud26

Thanks both. The idea is to recover the heat back into the shower feed, rather than heat the room/keep the bath warm.

But I like @2nd_time_buyer's rockwool idea, might do that too.

Magnitio

Reed_Richards said:

Where are you trying to recover your heat to?  If it's just the room where the bath is then @2nd_time_buyer 's suggestion is as good as any.  If you are taking a shower leave the plug in.  

https://zypho.uk/zypho-products/zypho-izi-horizontal/

Interesting products. But at the quoted price it would take a very long time to pay for itself.

waqasahmed

Magnitio said:

Reed_Richards said:

Where are you trying to recover your heat to?  If it's just the room where the bath is then @2nd_time_buyer 's suggestion is as good as any.  If you are taking a shower leave the plug in.  

https://zypho.uk/zypho-products/zypho-izi-horizontal/

Interesting products. But at the quoted price it would take a very long time to pay for itself.

There is another manufacturer I think. I think Zypho were just the first to market 

Like these guys 

https://recoup.co.uk/?gclid=Cj0KCQjww4-hBhCtARIsAC9gR3aEb95J0b05YjwPWfDgbcLSjxi_ZfUHy22n5zvCdSzJH9bSyK9zxEoaAi1OEALw_wcB

Assuming 50% recovery, and assuming 4 people use 30 minutes worth of shorting a day, surely that saves say 2.5kW? This is on the basis that a half hour shower would use around 5kW

zeupater

Hi

Years ago I saw a grey water heat recovery setup using little more than an old copper cylinder,a thermostat & a 2 way valve ....

The way I remember it, the cold water feed for the main DHW cylinder ran through the bottom coil of the old cylinder and, if there was hot water in the cylinder, preheated mains water (thus heat recovery) .... water in the old cylinder exited either through an overflow pipe mounted to the old HW top feed and if the water in the cylinder dropped below a set level the 2 way valve opened the old CW entry at the bottom of the cylinder to drain the contents ....

At the time I thought that it was quite a simple solution & pretty doable if you could accommodate the extra kit .... never really thought too much about it since though, just 'educated' MrsZ to swap to showers vs baths & reduced the shower head flow rates, which, although far harder, cost far less & probably far more energy efficient!

One thing I did think at the time, and never really got an answer to, was the effect of soapy residue & other matter (fluff, hairs etc) in both the cylinder & valve over time, but it's just a case of a little regular maintenance and/or incorporating a simple filter ...

Don't know what the rule tightening over the years means to whether you could still do it or not, but would guess that as it'd be totally sealed from both drinkable water & the domestic hot water then there shouldn't be any real problem as long as it's maintained/flushed/cleaned (low temperature contaminated hot water store ... yuk!) regularly, but then again, when did common sense last influence those introducing regulations!?

Don't know if it's useful, but it is the basis of a DIY solution if you have the skillset, but with the price of copper these days it wouldn't be worth the effort if you were paying someone to install ....

HTH - Z   

Reed_Richards

Suppose your hot water supply is at 60 C and you mix it with warmed cold water at 22 C to give you shower water at 41 C which cools slightly in transit so it enters the drain at 40 C.  The hot and cold flows will be equal and lets assume its a powerful shower using 12 litres per minute, that's 6 litres per minute of hot water.

Without the heat recovery your cold water is at 10 C so to get a mixture at 41 C you need 7.44 litres per minute of hot water.  So you are saving yourself 1.44 litres of hot water per minute.  Half an hours' worth of powerful showering would save you 43.2 litres of hot water (and use 180 l of hot water).

I used an online calculator that tells me it takes 2.5 kWh to heat 43.2 litres of water from 10 C to 60 C so the saving would be 2.5 kWh, exactly the figure @waqasahmed estimated.        

waqasahmed

Reed_Richards said:

Suppose your hot water supply is at 60 C and you mix it with warmed cold water at 22 C to give you shower water at 41 C which cools slightly in transit so it enters the drain at 40 C.  The hot and cold flows will be equal and lets assume its a powerful shower using 12 litres per minute, that's 6 litres per minute of hot water.

Without the heat recovery your cold water is at 10 C so to get a mixture at 41 C you need 7.44 litres per minute of hot water.  So you are saving yourself 1.44 litres of hot water per minute.  Half an hours' worth of powerful showering would save you 43.2 litres of hot water (and use 180 l of hot water).

I used an online calculator that tells me it takes 2.5 kWh to heat 43.2 litres of water from 10 C to 60 C so the saving would be 2.5 kWh, exactly the figure @waqasahmed estimated.        

The saving is probably much quicker if you're putting it in an electric one I guess. At current prices, that's around 18 months payback 

If it's mixer, less so, whether that be connected to a heat pump or combi. Currently, it looks like you'd need 1800 days or around 5 years before it pays itself back, when using a mixer shower

Prices are slowly coming back down too, so that payback period is actually increasing, not decreasing.

Another way of saving water whilst showering is to only use the water to rinse yourself. That's easier said than done when it's absolutely freezing but possible for most of the year 

Reed_Richards

In the example that I quoted, borrowing figures from the linked website, the drain water warms the cold water to 22 C so is cooled from 40 C to a bit more than 22 C.  If it's a drain in a bath then putting the plug in the bath and leaving the water to cool down to room temperature, around 22 C, would extract the same amount of heat into the room.  And it would cost you nothing at all!

I suspect that the heat recovery device would prove quite expensive to fit as it could need a lot of extra pipe work.  The only place where it might be fitted cheaply is where you have a shower above a bath that is fed from the bath taps, which are fed by pipes from below.  In that particular case you would only need a little extra pipework to divert the water feed to the cold tap via the heat recovery device.

Raxiel

We just leave the plug in as 2nd time buyer suggests, and let the water cool to room temperature before letting it go. Both baths and showers.

Not had any problems with humidity. Most of it stays in the bathroom which is fully tiled. We had historic problems (since fixed) with condensation due to poor insulation elsewhere so I have a few hygrometers around and they stay in the green on bath nights.