In our case enough to boil the tank, so we dont use off-peak. solar alone is sufficient so far from April to September. In fact it's a bit too much and a second thermal store is planned for next year. That one is likely to be a tonne of water.
And yes this is in Italy. A separate system is planned for the barn/tractor shed for washing down oil containers and sweaty tractor driver.
90MJ 30C woould be a bit cool even for underfloor heating I'd have thought. 40C minimum? Running the store down to that temp would also mean you'd need something else for DHW. To get the required heat transfer from the store to, on demand, hot water you need a reasonable temperature differential between your max HW temp and the store temp. HW would normally be at 50C or there abouts a 10C differential means a minimum store temp of 60C...
How big (sq m) are your solar thermal panels. Trying to get a handle on what I'm being offered. I'm not convinced that a 250l store and
3.23m^2 (apperture) is big enough, we have plenty of roof space for larger or extra panels.We do have a space heating requirement even during the summer. The current oil boiler normally only has a thermostat controlled holiday from space heating duty for at most a month. This "summer" the total number of single days it hasn't fired for heating is probably less than seven...
Use a hybrid thermal-PV panel with the PV running a heat pump from low temperature thermal panels into a higher temperature store. (Apparently there are actually commercially available systems that do that.)
PV to heat is never worth doing. Solarthermal to heat is a fraction the cost.
NT
That's why they sometimes run the UFH from a lower tapping - so it leave a reserve of hotter water for DHW purposes.
The big crossflow plate heat exchangers will actually work down to quite a small temperature differential - some under 5 degrees.
still a lousy idea
240 volts - and how much current?
Dont tell harry.....
couple of picoamps? :-)
I've just realised that steve firth is being even more of a tosser than harry.
A solar thermal panel will - if insulated properly and proteced from re-radiation.. - theoretically get up to the temperature of the sun, as long as you only take very small amounts off heat out.
We have two 30 tube panels. Each is a 3 sq m aperture. This is overkill for
280 sq m of floor and DHW given that we're in Italy.I suspect it's right sized for summer and may be small for the extreme ends of the season.
The UK house is oil fired but cunning Georgian builders ensured that it has huge thermal mass and that it heats up passively from the south facing windows. Even in December we have days when the boiler doesn't fire.
About optimum in my experience.
We have DHW set to 45C at present. My wife finds that to be excessive. I may try 40C next time I get to fiddle with the mixer valve.
You seem to be forgetting that the thermal store is stratified. DHW and radiator feeds are taken from the top of the cylinder. UFH is taken from the lower third. Similarly boiler flow is about halfway down, solar and solid fuel flow is taken from the bottom.
Depends on the pipe spacing. I'm no expert but our annexe runs happily at 27C.
John was suggesting that stratification and separate draw off points could take care of DHC. I think a separate cylinder fed from off peak might be simpler in use. There is the issue of pipe runs and time for hot water to reach the taps. A very large heating store might be best at ground level.
Initial thinking is that this may be an *upside down* house with a kitchen on the second floor.
regards
>In message , Alan Braggins writes
That makes a sort of sense. Ideally the overall system needs to be maintenance free and within the understanding of an oldish person. She is good with TV button sets:-)
regards
I am going to have to drop this for now. I'll get back when I know more.
regards
Isn't there some sort of recommendation for a minimum DHW temp? I thought it was recommended that 60C minimum was desired? (something about bacteria).
Also, how much insulation is considered minimum for a heat store? How much use would a larger store be compared to a commercial system like yours? (I was just idly thinking of a 3m x 3m x 3m hole under one of the rooms).
Thanks.
I will be building a 2cuM store, when roundtuits begin.
The temperature in the thermal store is 80-90C, there's no chance of legionella in there. You'd be raving mad to want water at 60C delivered through a domestic hot water tap, especially with old people or children in the home.
No "harry" it's true, not "theoretically true", it's true.
More bollocks from you, again. And you've admitted that the photovoltaic output from your panels in the same conditions is a pointless 20W.
I take it mathematics was just one of the many subjects that you failed at school.
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