Dual Heating

[Stuart]

We have a traditional hot water system that uses a storage tank for the hot water, the heating of the water is primarily through a gas boiler with an electrical immersion heater as back up.

I would like to connect the electric immersion heater up, so it works when the Gas boiler switches to heat the water. Thus reheating the water at a much faster rate.

I have tried to adjust the thermostats so they work in tandem, but have been unsuccessful, either the water is heated to too high a temperature or the electrical immersion does not kick in.

I was thinking of some sort of relay device that would switch the electrical immersion heater on when the motorised valve is switched to open, but what sort of relay would I buy and where from.? And if this was implemented would it still just heat the water to the same temperature as set for the gas boiler or would the water still be overheated?

[meow2222]

16A contacts, 240v coil. Try rapid electronics, or any other electronic/electrical supplier.

yes, as long as your gas system has a tank thermostat. There are some old systems without one, with those you'd get overheating, which can be a safety issue.

NT

[cynic]

Why? Unless your hot water cylinder is too small you are simply helping it with a more expensive fuel source. You would be far better fitting a bigger, insulated cylinder

[Stuart]

Some stab in the dark calculations

purchase new tank and have fitted £500 ?? differance between gas and electric 2p /kwh ??

2 hours per day * 365 = £14.60 per year

payback time 34 years

the present situation of every body wanting baths one after the other will dissapear in a couple oy years time.

[Dave Plowman (News)]

Rapid do a suitable one - 60-4383 - which is a 30 amp DPST with 240v AC coil for 6.45 plus vat. It's PCB mounting and could be mounted on a bit of veroboard with the appropriate tracks beefed up with some 2.5mm copper stripped from TW&E and soldered to it. Fit 15 amp chock blocks to the ends of the 2.5mm for external connections. And then mount it all in a suitable box - I'd use an 'adaptable' metal one with knockouts, and earth the casing. Use insulated spacers to fit the veroboard to the box, and remove the tracks near to the mounting points. I think you'll find it difficult to find a ready made 'box' to do this job at a reasonable price. The above should cost no more than about a tenner.

? And if this

The water will heat to the highest set thermostat - I'd set the immersion one slightly below that of the boiler.

[timegoesby]

Fit a TMV blending valve on the DHW outlet pipe from the cylinder. About =A330. Then have the cylinder water stored at 75 to 80C. The TMV drops the DHW temperature to 50-55C or less. This stores more energy and effectively increases the size of your cylinder, and still heated with cheap gas.

[timegoesby]

Totally unnecessary. Read my previousl post.

[Dave Plowman (News)]

You've already told the OP what your 'solution' is. I have simply answered his question.

[John Rumm]

What sort of boiler is it?

Conventional or condensing?

What flow temperature do you usually run it at?

How long does the current setup take to recover the water temp? What sort of cylinder is it? i.e. what capacity and is it a normal indirect one or a fast recovery type?

Sounds like you have too much hysteresis in your stats.

Depends on which stat you use to control what. You may get better results by adding an additional strap on tank stat to control your relay, and then turning up the one in the immersion so as to effectively remove it from the equation (for all purposes other than as a safety backup).

Also look at what cylinder temperature you are currently requesting on the cylinder stat. It might be you could tweak it up some more to allow more cold to be mixed with the water at the point of use.

(A higher tank temp is partly a "one shot" solution in that recovery via the boiler will take a long time finish off the last bit of temperature rise, since the temperature differential between primary CH water and cylinder temp will be small toward the end of the heating phase. It does however mean the first tank full will go a bit further)

[timegoesby]

Because you couldn't think of anything else, as you don't know about water systems. The OPs idea is the wrong one and I put him on track.

[Dave Plowman (News)]

And I'd guess you haven't a clue about electronics.

No you haven't. Trying to heat and store water at 80c with a standard cylinder is a daft idea.

[Andy Hall]

At least Drivel would have suggested having one with 2m of insulation.

OTOH, he was always one for glossing over inconvenient details.

[timegoesby]

Yes, that is why I don't give advice on it.

You are the resident prat.

[timegoesby]

Sounds good to me.

Like it will cost around =A330 for a TMV and save money on expensive electricity, even if the insulation is not that great. In airing cupboards the clothes act as insulation. You may not have noticed.

Another prat.

[Dave Plowman (News)]

You drape the clothes to be aired round the cylinder? Good grief.

BTW - hot air rises. That fact should help you air clothes better and explain why they don't insulate the cylinder, or at least by only a tiny amount.

[Roger]

The message from [e-mail] contains these words:

An uncanny echo of Dribble there. I am beginning to doubt they are siblings, more likely two facets of a split personality. I wonder how many more there are out there that aren't quite so obvious.

[EricP]

There's a small unit round the back of Huddersfield that turns them out. They can knock up a DIMM in a couple of days, a Drivel in a week and this new model takes about three hours. :))

[Lurch]

On Sun, 13 May 2007 14:10:26 +0100, "Dave Plowman (News)" mused:

I've seen a house burnt to the ground because someone piled clothes up on the cylinder. Eventually the immersion heater (could have been the pump or valve, everything was switched on and buried under clothes and towels, hard to tell what actually started it) gave up and just set everything alight in the middle of the night.

[Dave Fawthrop]

|!On Sun, 13 May 2007 14:10:26 +0100, "Dave Plowman (News)" |! mused: |! |!>In article , |!> wrote: |!>> Like it will cost around ?30 for a TMV and save money on expensive |!>> electricity, even if the insulation is not that great. In airing |!>> cupboards the clothes act as insulation. You may not have noticed. |!>

|!>You drape the clothes to be aired round the cylinder? Good grief. |!>

|!I've seen a house burnt to the ground because someone piled clothes up |!on the cylinder. Eventually the immersion heater (could have been the |!pump or valve, everything was switched on and buried under clothes and |!towels, hard to tell what actually started it) gave up and just set |!everything alight in the middle of the night.

So you would both be against those new fangled foam insulated cylinders, and the older glass fiber insulating jackets which we had long ago? That is IMO taking Risk Averseness to new depths.

[Lurch]

On Sun, 13 May 2007 16:54:31 +0100, Dave Fawthrop mused:

No, I'm not saying that anything in a cupboard with a cylinder in it catches fire, I'm saying that unwise positioning of items can lead to it.