I am turning a small box room into a wet room with a high flow shower. However id like to keep running cost right down so am considering trying to recover the heat in the waste water going down the plug hole to preheat the cold water going into the thermostatic shower valve.
I cant seem to find any products for sale in the uk that do this, so am considering making one myself.
Has anyone had a go at building one?
Steve
I'm thinking of the same thing myself, but don't know of any product. On problem is that the waste water contain scum and hair, bits of soap etc, and it's low pressure so cannibalising a boiler heat exchanger won't work. I'm thinking of coiled microbore piping ( several in parallel ) inside a flat box where the waste water can hang about for a few seconds. The other option is to redirect the trap outlet so that it goes to a length of 40mm waste pipe inside which some copper tube could be coiled for the cold water, the
40mm waste eventually conecting back up with the old waste outlet.many configurations possible, all with small problems involved
Andy
R.P.McMurphy brought next idea :
I would run an outlet copper pipe close to the cold inlet for as long a distance as possible, perhaps ensuring good thermal contact by soldering the two side by side and wrapping insulation round the pair. The larger the two pipes and slower the flow through them, the more heat will be transfered between them.
I havent, so take any info with this in mind. I figured a good idea might be to wrap 4 equal lengths of microbore round the copper drain pipe, soldering in place, and parallelling the microbores using a 4:1 manifold at each end. Typical lengths are 2-3' for the unit.
Reasons for paralleled microbore:
1.you get much more contact area with the drain pipe than you would with larger pipesBest thing to do with this water is to feed it to the cold inlet on a thermostatic shower, as you said.
If you're creating a setup, there is another way to gain heat at very low cost, with less return than your drain exchanger. That is to use a low cost high capacity solar collector between header tank and HW tank, with draining and bypass valves for winter. By low cost I mean a pancake of plastic pipe under polythene, on either flat roof or wall.
NT
Just a thought here - wouldn`t microbore be more prone to blockages from hair or anything else that went down the plug`ole ?
(i`ve got sod all experience of plumbing, just a wild question)
Colin Wilson explained :
He was suggesting using the microbore for the cold feed, wrapped around a copper drain.....
Good idea BTW (using microbore).
Oh! its a saving pennies thread. Ho-hum
-- Sir Benjamin Middlethwaite
No, but I did read a website once by a company (US-based IIRC) who did. Sorry I don't have the address but I do remember the following:
The right way to do it is to have a *vertical* drainpipe - the falling water then tends to form a thin film which adheres to the inside of the pipe. The inside of the drainpipe must be smooth i.e. you can't put a coil inside the drain pipe - it has to be around the outside. Obviously good thermal contact between heat carrying parts is essential - you can't just wrap a coil around; it has to be soldered or brazed. It goes without saying that plastic is right out, at last for heat transferring components.
As with all heat exchangers, the flow direction of the two fluids should be opposite otherwise you will never extract more than 50% of the available heat. i.e. if your drain water is falling vertically then your cold water flow should be upwards.
I can think of no easy DIY way of continuously brazing a copper spiral to a central tube. I would think that a more practical design would be to have two concentric tubes, with the drain flow in the central tube and the cold water flowing between the central tube and the outer tube.
HTH
This has come up from time to time as a suggestion.
I am fairly sure that copper waste pipe is compatible with the push fit waste fittings.
A problem I can aticipate if this works is that you will have to keep upping the flow rate from the electric shower using the temperature adjuster. You may run out of travel and need to have a shower which you can then put on half power.
You may well have already thought this through but the outlet from the microbore pre-heater should be at the plug hole of the bath/shower-tray.
I'd try 'tack' soldering the microbore to the water pipe using potable 'green' lead-free solder every 25cm or so and then come along after using CH/gas pipe leaded solder (which has a lower melting point) to finish the job.
It might just be possible to turn a typical 9kW Electric shower into a
20kW shower typical from a combi.Just to save a +lot+ of hassle I'd put some 1/4 turn bypass isolators around the gizmo - you'd be pretty pissed off if you found you could not get the water through fast enough in August to shower safely.
Note that only the better stocked PMs will have 35/42/50 mm Cu pipe.
And then wrap the whole thing in thick insulation.
'meter-of-copper-pipe-with-microbore-soldered/braised-to-it' route. where can I get the copper pipe from of the right size that will fit straight into the ubend from the shower? what size? also concerned about making sure flow rate is not restricted....how many 10mm or 8mm microbore will I need to wrap around the copper waste pipe to keep a free flowing run from the 22 mm supply?
Oh by the way im not using an electric shower, im using a thermostatic shower valve,
Steve
Loads of people. Go for a simple two concentric tube contra-flow design. Obviously the drain tube is in the middle, and make this as big and thin walled as you can. Anything with multiple tubes is asking for blockage trouble, or slow drainage flow which is nearly as bad. They need to be concentric or you'll not get a usefully large enough surface area - it doesn't matter how closely you solder the tubes, it's the water-copper interface that has the highest temperature drop across it.
Not too much weight of metal, or the steady-state flow might be fine but it takes too long to warm up,.
Any book on model engineering boilermaking will give you the construction details, but you can get away with simple flat plate endplates, you don't have to flange them - just use small bent stakes in the endplates so as to hold the tubes central while you solder them. Use silver solder, in two grades, to assemble it. This allows you assemble it in two stages and still use soft solder to install it in place.
As the drain tube has to run half-empty (or else it will glug) then some designs use a horizontally squashed oval tube, so as to have better metal-water contact area with less-full tubes. This is still easy to make.
Make a simple spreadsheet up too and run the numbers for the heat transfer - it's worth putting some real figures on it.
Compared with the cost of the water these devices use the fuel cost is fairly low. Application of some Black Bodge Tape to the shower head would be far more effective.
This has come up in the past. You are right a US company, GFX, makes a drain heat recovery that works and is feasible. I looked at it in aid to extend the size of the cylinder. A quick Goggle gives
Just a half-baked idea: How about combining it with a grey water recovery system? Thus the hot grey water is stored in a tank where it hangs around giving time for heat recovery until someone flushes the loo. You could get a good spiral of cold water pipe in the tank. Perhaps the tank could also cool into a room as "radiator"? Pass the water to the tank through a radiator? Think on't.
Chris
Vertical orientation does maximise efficiency, but isnt practical for downstairs, and horizontal pipes also work ok.
Soldering a microbore spiral onto the copper drain tube isnt hard in principle. You just wrap another 1/4 turn on, solder, wrap another 1/4 turn, solder etc. Note you wrap all 4 microbores on in parallel, not one after the other. Straightforward, pretty slow, probably quite satisfying.
The xsa of 4x8mm microbores is equivalent to one 16mm pipe, and 4x 10mm pipes has the xsa of one 20mm pipe.
The idea mentioned of slightly squashing the centre section of the pipe to ovalise it would of course help maximise efficiency, as long as its not overly squashed, nor squashed too near the ends.
NT
Resistance to flow is also strongly dependent on the diameter of the pipe, ie the distance between peak flow in the middle of the pipe and near zero flow at the pipe material.
Don't buy a power shower or put your cold inlet inside and lying on the bottom of the waste pipe so that the warm waste water will heat up the cold
yes, since its only a shortish pipe length I didnt want to get into it too much, but its true enough that reistance will be higher than a standard 16 or 20mm pipe, so 10mm microbore would probably be a better choice.
NT
As I said in my reply ">> Note that only the better stocked PMs will have 35/42/50 mm Cu pipe." The 42mm pipe will fit in the outlet of the shower trap. And I think it will fit into pushfit waste fittings aswell as compression type (of course).
Since there are 4x10 to 1x22 'manifolds' available I think you should go with that on pragmatic grounds.
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