Thermal Store

[Steve Firth]

Up front, dIMM can piss off, I'm not interested in what he has to say.

My place in Italy is going to have several heat sources. Wood burner, solar and possibly an LPG boiler of some sort. A thermal store therefore seems like a good idea, particularly because SWMBO has decreed that the ground floor *will* have underfloor heating.

However there's a weeny problem or two, both electricity and water supplies are variable, and of course lack of availability of one has no relationship to the other. All of the thermal stores I have looked at are pumped, with three pumps on the majority of systems. That would mean no hot water on days with no electricity.

Is it possible to get a thermal store that will heat the incoming cold water mains without needing a plate exchanger?

[Grunff]

Yes. Our 'thermal store', which I converted into a heat bank (by adding an external heat exchanger, flow switch and pump), can do exactly this. It has a built in heat exchanger coil. Very long coil inside the cylinder. You pass cold water in and it comes out hot.

[Andy Hall]

Good to set out your store before starting :-)

I've seen one in a specialist place in California. It had a large heat exchanger inside the store consisting of a sandwich of plates rather like a plate heat exchanger but formed into chambers with gaps in between. In effect, it provided a large contact area for the cold water running through to be heated by the store water which was free to circulate around the plate sections. The exchanger was a lot larger than the typical plate heat exchanger and the overall store must have been at least 500 litres. I've never seen these in Europe, though.

Had you thought about solar electricity generation? A friend in California is into this and with solar panels on his roof is able to generate enough electricity on most days to run his electricity requirements apart from cooking. This includes several computers and associated equipment, lighting and charging his electric car. I don't know the size of the panels but the house is a mid sized suburban house - larger than Europe but not vast. Perhaps it would be worth considering this and using more conventional store and heating equipment. There would be more flexibility as well, in that if the electricity fails, there is quite a lot that you can't do. You might like some aspects of that of course :-)

[Christian McArdle]

Yes. In fact a "thermal store" is exactly this. The type with a plate heat exchanger is called a "heat bank". Although heat banks are better performing, if you have a reliability issue that outweighs this, then the thermal store would be best for you.

Another alternative is to have battery backup. This way you could keep the entire heating system going, and maybe some emergency lighting, especially if you have frequent short cuts.

Christian.

[Gordon Henderson]

How well did/does the internal coil work? I'm conidering such a tank to save a bit of space. (and money) Water through the coil will come from a loft tank and be pumped rather than mains, but the net effect ought to be the same. (Very low mains flow rate where I am) However, we have a rather large bath to fill, so wondering if it'll cope...

Gordon

[Doctor Evil]

Maxie, get in here. This one is insulting Dim Lin, the Oriental enchantress, the love of your life. What scum! The world is full of filth, Steve Filth.

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[s--p--o--n--i--x]

It may work out cheaper to get one of those little £44 generators from Makro to run the pump on the rare occasions the mains supply goes down.

sponix

[Grunff]

It actually works very well. We used it with the internal coil for several weeks before I switched to an external exchanger. My reason for switching to an exchanger was not because I wanted more capacity, but because I knew the coil would eventually scale up (very hard well water). With an exchanger, replacement is easy.

[Doctor Evil]

You now have a hybrid thermal store. Why did you add a plate heat exchanger? How did you pipe the coil/plate? How does it perform?

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[Grunff]

Because we have very hard water, I suspected that the coil would scale up within 5-10 years. Replacing a plate exchanger is easy.

The tank had several spare blanked off threads at different levels. I just used a spare pair, one about 1/3 of the way up, the other near the top.

There is little difference in performance. The only noticeable thing is a small increase in hot water delivery, because of the lower resistance of the plate exchanger compared to the coil.

[Doctor Evil]

You don't need a thermal store. You need electric over the sink heaters everywhere. When are you going to Italy for good?

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[Doctor Evil]

So, you disconnected the coil? It would have been better to have used the coil for the kitchen tap. As then you will prevent the pump from cycling on and off. If the kitchen tap is opened for a second, which is quite common, the pump will energise for no apparent benefit. You could have took the outlet of the coil into the plate. Around the flowswitch have a flow regulator, which is a cheap in-line isolator. This only brings the plate in when there are high flows.

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[Dave Plowman (News)]

What sort of current do these pumps take? Incorporating an invertor for supplying 230v from a car battery on a new installation isn't too big or expensive a job.

[Grunff]

Yes, but it's still there.

Not a bad idea. Except that in order to get hot water in the kitchen, you have to run the tap for at least 20 seconds. It's on the opposite side of the house.

[Doctor Evil]

A secondary circulation loop required here.

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[Grunff]

And one of those is?

[Dave Plowman (News)]

Can't say I've seen this solution in Ideal Homes. Do they fit neatly between the twin 'combi's'?

[Doctor Evil]

A DHW draw-off pipe taken from the store looping around to all the taps and back to the store. Hot water is pumped through the loop, so instant draw-off at the taps. A bronze pump on a timer (or a dedicated secondary circulation Grundfos will do) , a pipe stat and a few check valves. The timer keeps the pump off at night.

Do Google secondary circulation on IMM and how to fit on a heat bank or thermal store should be there.

In your case, I would connect up the coil from the cold supply, out of the coil and into the plate, to the taps and back to the cold supply. Two check valves have to be fitted near the cold inlet and the pump is fitted near the cold supply to the coil. Put in an in-line restrictor on the return to lower the flow so the flow switch does not cut in unnecessarily.

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[Doctor Evil]

Yes, right next to the cabers.

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[Grunff]

Maybe next time around. The house is now done. No more DIY for a good few years.