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Author Topic: Thermal store with gas ch  (Read 936 times)
Solarchaser
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« Reply #15 on: May 16, 2019, 08:04:34 PM »

I already have the gas combi boiler, its downstairs in the kitchen, it does what its supposed to, but it uses gas to heat things, and on days of excess solar, I could use electricity instead.

For me, the simplest thing is to put a thermal store in the loft, right above the main bathroom, as then all I'm doing is adding a loop between the bath cold water feed and the bath hot water feed.

If I then close the combi hot water valve, I get hot water from the store.

In a nutshell, that's my plan, but it has to pass a couple of tests.
The first being cost.

CountryPaul, the drain normally wouldn't have any water in it, it would really be a vent, but I could use it as an emergency overflow also.
Normal wastepipe survives the odd boiling water deluge,  and tbh if it was getting boiling water down it, then the tank has completely failed, I'd expect it to be dry unless the tank is burst.
Re building regs. I'll have a look, but I'll likely just ignore them if they dont suit, though if you are right about 4m for 40mm, I'll probably be fine anyway.
Good points re the stratification,  I've been looking at the harvi which heats one element till it cuts out, then can heat another (and then another) so should hopefully deal with that issue, though if I'm honest I think I'd prefer a little pump to circulate the dirty water inside, if that's even possible, as it's a pretty warm environment for a water pump.

RIT, that's kinda what I was hoping you WOULDN'T say.
I think motorised valves will be prohibitively expensive.

Fair point about faulty valves, pressure differentials means it couldn't actually cause any harm, just nuisance cycling of the combi I guess, or the odd bit of cold water in the hot worst case.

When the extension went on to the house I completely redone all the plumbing, so theres isolation valves on every branch, and I'd definitely be fitting full bore valves on both ends of the store.

I'd hope to save quite a bit.
I'm paying around 1200 a year for gas and electricity.
So I think theres a good potential to save 2-300 a year by not using leccy showers and reducing the gas on hot water usage.
So if I look at an optimistic 5 year payback, then 1500 on a store, Solar diverter and valves seems reasonable I think.

As you say Brackwell the weather is not dependable, especially in not so sunny Scotland, but I've consistently got over 3Mwh a year on my 4kw array, so I'm confident that 8 months of 12 I should have excess solar now I've added a further 6.6kw array.
But obviously that wont help November to February, or weeks of full overcast rubbish, and as you mention, visitors etc. which is why I want to be able to seamlessly switch back to the combi if the store is not hot enough.

Hence thermostatically controlled motorised valves.
When store is cold, the supply to it is isolated and combi runs as normal, when store is hot, combi valve is isolated and store is open.

How did I get to 4-500L? I've looked at many specs around the 210L tanks which are good for 2-3 showers, and there are 6 people in my house, so 4-500L seems reasonable.

I note that many people when going down the solar route, first of all look to reduce their usage, some manage it dramatically.
And while I did change most white goods to energy saving equivalents and of course all the house bulbs are leds, my main goal isn't to reduce usage as such, more to create enough excess that I can live my life as usual, while saving money doing it.

Because with the best will in the world, I live with a woman who just loves to use kw's
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Countrypaul
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« Reply #16 on: May 16, 2019, 08:42:35 PM »

Quote
How did I get to 4-500L? I've looked at many specs around the 210L tanks which are good for 2-3 showers, and there are 6 people in my house, so 4-500L seems reasonable.

Are you sure that is only for 2 -3 showers?  If your store is at say 70C and you blend it down to 40C with 10C cold water that would give you close to 400L of shower water. If each shower takes about 8mins** that is close to 60L per shower, so you would easily get 6 showers out of the small store.

I am told that teenage females tend to have much longer showers, I know my wife who definitely is no longer a teenager certainly does, where as me and my lads tend to be less than that.

Do all six need showers at the same time? If not then a smaller TS backed up by the combi might be more efficient, especially if getting a 4-500L store up therewould be very difficult. It took 2 of us to get a 430L TS up one flight of stairs (600mm diameter copper with 75mm PUR - from Newark), so a larger steel one might be a significant challenge!
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Solarchaser
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« Reply #17 on: May 16, 2019, 10:13:02 PM »

I have to admit, since I have no real world experience of a store. I'm purely taling the manufacturer's blurb at its word.

If your real world says a 210 would be fine, then I'm tempted to just go with that, and if it's not enough I could double up in time, and that would likely make more sense, in a few ways, not least the physicality of maneuvering one into the loft.

And if one is enough then if I still have spare pv power I could fit one for the central heating too. Hmmmm
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Countrypaul
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« Reply #18 on: May 16, 2019, 11:32:05 PM »

I can't say that one 210L TS would be enough for you, as I said I don't know if you have 5 heavy users in the house or not  Grin

I know I put in a 430L store which was the largest I could get in and it provides the DHW and central heating year round, but is not heated purely by PV as yours would be.  My store normally runs upto 80C (some eople I believe run upto 90), that extra temperature can provide a significant amount of extra hot water. If the cost of heating the water is negliable (you already have the PV) then again you might get away with a smaller store at a higher temerature.

Whilst 2 smaller stores might give you more flexibility (and starting with one might remain just one) it would have to be expected that the 2 stores would have greater losses than a single store, though putting them close to each other with insulation round the pair might minimise the difference.

I don't know the weight of the stores you have been looking at or the structure of your loft access, but I know a 430L copper store took two of us just to carry it up the stairs and along.  You might be able to hire a "lifter" that builders use for hoisting beams up etc but then that would all be additional expense that might be better spent on other things. Only you will be able to make those decisions, but those of us who have installed similar things can try and give you the benefit of our experience whether good or bad to help you minimise the bad ones.
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