Posted By: qeiplMy teenage nieces came to visit this summer and would have emptied the 300 litre HW cylinder if left to their own devices in the shower.

It made me think that some sort of timer valve on the hot feed to the shower mixer would be a good thing.
Every time the shower is turned on it sets the hot feed timer to run for a certain number of minutes, after which the hot feed is terminated for the same number of minutes.

It could incorporate a digital display that counted down how many seconds you had left before getting the cold water treatment.

I have to say that I've though about something similar although I was thinking about a motorised mixing valve that progressively made the water temperature colder the longer it ran rather than suddenly went from hot to cold. Not sure I'd ever be brave enough to implement such a thing though.

I looked at installing a shower drain water heat recovery unit - cost would have been around Can$500 (big copper to fix around a 4" cast iron drain pipe). I calculated the payback time to be around 40 years or so as my hot water heating cost was already low due to pre-heat from the GSHP. The path from the bathroom to the drain is relatively long in my house so a decent amount of the heat is emitted back into the heated enveloped anyway. Not so useful in summer, but I don't have hot showers in the summer anyway.

For places like gyms where the showers are running all the time, it makes perfect sense. Modern (commercial) laundries usually re-use the heat from drying and washing anyway.

Paul in Montreal.

Good point qeipl, easy enough with a new build, hot stack and cold stack, teed together above to vent through roof and joined together in manhole outside. Cold soil pipe insulated within slab and shortest route, hot soil pipe not insulated and longest route within slab.

I am working on a different idea at the moment, if I find my temp loggers I should get better data as I am working with 20 kg of water this time and a pumped heat exchanger. More to follow.

www.letsnotfixtheunbroken.com is broken

<blockquote><cite>Posted By: crusoe</cite>Condensation? No JSH, that's for old, cold houses, surely - and has never been a problem if ventilation is working properly - in most cases a window ajar, or open fire going. Modern, warm houses with full ventilation/heat recovery - not a problem! We're not talking swimming pool context here, simply a small bath.</blockquote>

Not me. Damon made the point about condensation. I agree with you, it's only a problem with poorly insulated houses (or should be).

<blockquote><cite>Posted By: qeipl</cite>My teenage nieces came to visit this summer and would have emptied the 300 litre HW cylinder if left to their own devices in the shower.

It made me think that some sort of timer valve on the hot feed to the shower mixer would be a good thing.
Every time the shower is turned on it sets the hot feed timer to run for a certain number of minutes, after which the hot feed is terminated for the same number of minutes.

It could incorporate a digital display that counted down how many seconds you had left before getting the cold water treatment. </blockquote>

Just fit a submarine shower valve. These are often just push button operated and give you a 30 seconds of water to wet yourself, then the water goes off while you lather up, then you push the button again and get another 30 seconds of water to rinse off. Bit of a bugger if you haven't fully rinsed off when the water goes off, because you only get two presses of the button every three days..............

There's nothing like a good experiment to show how something will work!

A system that retained hot waste water for a few hours, allowed the heat to be exchanged to incoming cold water (or air, if room heating was the objective) and then emptied the waste water away, would seem to have some merit. The snag is making something like this relatively simple. There needs to be a way of flushing the holding tank and draining it, as all the stuff I've read suggests that grey water goes very manky, very quickly, if stored in a tank for more than a few hours.

Sorry JSHarris/Damon confused.... though you did agree with Damon, JSH.

Touche PiM!

Steamy - link was a joke.... And I think your laudable commonsense experiement shows this to be, as a few of us who have been around the block a few times suspected, a very questionable use of funds. Well done.

We already have temperature-sensitive submarine valves, guys. Grumpy old guys like me falling asleep in the bath, waking up when it's cold, realising this - and letting the water out.

<blockquote><cite>Posted By: chrisinbrighton</cite>I have often thought about shower recovery systems and was wondering if a metal shower tray was used could the heat be taken directly from this -as opposed to the pipe.
It might be cold for your feet unless on an wooden? island above...</blockquote>

The Recoh-Tray is similar to this. The best image I could find of it is in this PDF file: http://shower-save.com/pdfs/Recoh-tray%20installation.pdf

Found this at Eco-build;

www.zypho.eu

no idea of price or efficacy.

You didn't miss much
Got to this and stopped reading.
OK, I read a bit more, the PDF of the technical stuff is here:
http://www.zypho.eu/images/Ficha_Tecnica_EN.pdf

Re One or two copper pipes between mains cold and waste water -

In our case the DHW tank is fed from a tank in the loft, so we have isolation from mains water for sure. Could I therefore make a simple&efficient copper heat exchanger that only has one barrier from cold to waste? As mentioned here, the waste would form a film on a vertical copper pipe, cold water running in a sleeve contraflow to this.
An important considereation is the pressure drop of commercial units, and I note that the type with microbore soldered around a copper waste pipe aren't suitable for gravity fed DHW.

I measured the temp of our shower, to get a bead on the numbers - there's a piccy of a graph I made below.
I measured the cold and hot feeds into the thermostatic power shower, and the U bend waste water temp. The flow rate under test was a rather embarrasing 10l/minute. I know this should be a lot less, but that kind of &quot;improvement&quot; would not go down well.

In brief, I calculated:
One typical shower used 1.8KWh of hot water
1KWh could be recovered if the hot feed only was preheated with 100% efficiency.
1.3KWh could be recovered if hot and cold feed were preheated with 100% efficiency.
The U bend water temp is 3degrees lower than the shower water outlet temperature - ie almost all of the heat really is flushed straight away.

Our daily use is 2.5 showers, and 7KWh of gas-&gt; hot water+cooking, which corresponds well to the above.

RobL

<blockquote><cite>Posted By: SteamyTea</cite>Halve your shower time is another way</blockquote>

Just fit submarine shower valves. They have a timer and on-off button. The first press of the button gives you 30 seconds of water, then the water turns off while you lather up. The second press gives another 30 seconds of water to rinse off. Any subsequent press of the button has no effect, so you're limited to 1 minute of shower water in total.