With energy costs rising and water in short supply I am thinking it is wasting both on my upstairs hot water supply as I have to run quite a bit of water until it runs hot.
I have a modern combi boiler located in my downstairs kitchen that supplies all my water and upstairs I have an en-suite shower and wash basin.
What might be my best options without the setup cost being unrealistic.
Geoff Lane
Probably nothing that is really worth doing.
A few options:
- You could move the boiler upstairs - e.g. airing cupboard, other cupboard or loft. This moves the problem because then you will have the dead leg problem when you us the kitchen tap. It probably makes matters worse because more than likely you use the kitchen tap more times than water upstairs and it is each of those occasions that results in loss.
- As above but fit an electric sink water heater. This would be a more expensive way to heat water.
- Fit a hot water cylinder and roof tank for upstairs use. This can be heated from the CH side of the boiler by adding convention motorised valves and controls. However you will get a small anount of standing loss from the cylinder - perhaps a 100W or so. In the winter this doesn't matter because it' added to the house heating. It would give the advantage of a more copious supply of HW than the combi manages. Another variant of this would be to fit a thermal store and this would provide mains pressure HW.
Probably the last of these are the only ones that make sense because they offer improved functionality as well.
(a) re-route the hot pipe to be a shorter length.
(b) install a smaller diameter pipe if possible, to reduce the volume of standing water
(c) insulate the pipe, this will reduce cooling between uses
(d) pretend it's Olden Days again and wash/shave at the kitchen sink.
Owain
I think you have just discovered the Achilles heal of Combi, but the waste isn't any greater, less probably overall, than having stored hot water. Its the interminable wait for hot water at the wash basin. Unlike stored hot water, running the tap faster can't solve the time problem. So, stick with what you have until you can't stand the wait at the washbasin then install an instaneous water heater. The shower isn't such a big problem because the wait is a smaller proportion of the activity and who really wants a 10kW electric shower.
Jim A
Irrespective of how the water is heated a given length of hot pipe that cools is a given waste of heat.
Not quite so sure about that..but I'll let it pass.
The instantaneous water heater will be less efficient anyway because it will be electric, and that is already supplied to you at probably no better than 50% thermal efficiency, whereas a good boiler does more.
You can achieve a similar result with a pumped flow and return hot water system..and it probably costs no more in the long run if well insulated.
its only Combis I don't like so I'll let that pass.
Jim A
I know gaswas always considered cheaper that electric but is that so now.
Geoff Lane
Blimey, I remember when I were a lad there was no running hot water, a gas boiler had to be lit for a bath :-)))
Them were the days..
Geoff Lane
On Sun, 01 Oct 2006 18:48:50 +0100 someone who may be Geoff Lane wrote this:-
In general yes, even allowing for boiler and system inefficiencies and pumping. However, there are cases where an electric water heater is cheaper than gas fired centralised systems. An example would be a remote little used sink, such as by a toilet near the front door, which is often best provided with hot water by an electric heater under the sink. It can also be the case with an old boiler and long uninsulated pipe runs that summer use of White Meter (Economy 7 down south) electricity to heat water is a similar cost to using the boiler.
Much electricity in the UK is produced by gas. Such plants have been run in preference to coal plants for many years, with coal partly relegated to load following (which it is not particularly well suited to).
I've been thinking of doing exactly that. My system has a hot water tank in the airing cupboard and the kitchen sink at the far end of an extension. It takes 4.5 litres of run-off before the hot comes through from cold. The first 6 or 7 meters of pipe is 22mm because that also feeds the bath, the remainder being 15mm.
The scheme I have in mind is to tee off a return under the kitchen sink as close to the tap as possible, and route this back to the DHW cylinder in plastic pipe, insulating this and the feed at the same time.
I then have to think of the best place to put the pump and how to switch it on or off. As the tap is only used in burst of activity I discounted continuous (or more likely time switched) running as probably being at least or more wasteful as running off the 4.5 litres a few times a day.
I then thought about switching it with a temperature sensor in the tee. This maybe a bit better than continuous run but not much, as the although the pump would cycle on/off, the water would still be maintained at a hot temperature.
Then I wondered about a simple switch in the kitchen to turn it on whenever someone wants the tap. Hmmm... would we actually do that in advance of needing hot water. Probably not in many instances, so we would still be cussing while the 4.5 litres ran off.
Then I had the idea is to have a PIR sensor to detect activity in the kitchen preparation/sink area and have this activate the pump. This fits in well with my plumbing and power arrangement as the hot feed comes in along the top of wall units, so the pump could go on top of those, and there is also power up there feeding the hob extractor fan.
Next is how best to use the PIR detection signal. I'm thinking of powering the pump, once the trigger is received, for just long enough to get the 4.5 litres through, so we don't have continuous hot in the return. The flow will then start to cool if the tap is not actually used, so the pump will need re-triggering after maybe 5 or 10 minutes, so long as the PIR is still detecting a person present.
I'm not sure whether to put the pump in the flow or return. Because of the long pipe run the flow rate is not that good, so a pump in the flow side could also boost that. It would however need some way of ensuring it is switched on whenever the tap is turned on (otherwise it would impede the flow instead of boosting it), so it needs a flow sensor to over-ride the PIR system, and this sensor needs to be between the return tee and the tap, otherwise it will sense the return flow and keep the pump running for ever. The alternative of putting the pump in the return allows a smaller, cheaper, quieter pump to be selected, but doesn't have the boost benefit.
The pump obviously has to be potable water rated, so shower pumps are out.
Now to the return pipework. At first I though that because only 4.5 litres need be drained back through it, it can be 10 or 12mm, but then the flow rate would be fairly slow, and we may finish up still having to wait for hot to arrive. I need to do some calculations on rates, pump pressure and bores. However, putting the pump in the flow may give enough circulating pressure to permit a 10-12mm return. That would certainly simplify the installation, and minimise heat loss.
Finally the connection of the return to the DHW tank. Feed it into the
22mm cold feed at the bottom? No, that would stir the cold layer at the bottom of the tank up to the top! It needs to feed in near the hot top, but perhaps not the very top, given it will dump up to 9 litres of cold into the tank when first switched on (9 litres is the max assuming the return is the same bore as the flow). So do I need to make a new tapping into the tank, say 1/4 or 1/3 the way down (how?), or can I get away with a surrey/essex flange at the top. This will have to operate in reverse flow to the normal use as a shower take off. And what if I later decide to install a pumped power-shower? The shower at present is fed from the bath tap, and could do with a boost. This needs a bit more thought.So to summarise, I would put a flow switch close to the tap, a tee just upstream of it, a plastic return pipe (10, 12, or 15mm?) from the tee back up to the DHW tank, connection method to be decided. The boost pump goes in the flow on top my wall cupboard (or possibly fixed to the floor if noise is going to be a problem). A PIR is fixed high up, pointing at the work area, and a bit of delay/logic circuitry goes in a Maplin box nearby, and the mains power gets taken off the extractor-hood supply. This allows the unit to be isolated by the fan isolation switch for servicing.
Any comments, and especially suggestions for the make of pump and connection to the DHW tank.
Thanks
Phil
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