I can understand a condensing combi being potentially a very efficient package if a combi is what is wanted, but DHW storage requires the mean water temperature to be above 60deg and a themal store temperature to be at the design temperature. I've seen 75deg mentioned. In a mainstream domestic market boiler that can only be achieved by the boiler flow setpoint being at least the required temperature year round. That reduces the condensing savings considerably, massively if useing a thermal store.
Couple a non-condenser to a thermal store and efficiencies rise to the mid to late 80% as the operational condition is stable and very predictable. Have a blending valve ensuring the 11C differential and the 80C flow is virtually guaranteed. SEDBUK's seasonal figures do not apply. Part load does not apply.
Condensing boilers coupled to thermal stores, where the store is to be 80C, do not perform much better than a good regular boiler, and cost substantially more (I know the price is dropping like a stone). Have a larger thermal store, or better a heat bank, and store temp of 76C, as some do, and couple a condensing boiler with 22C temp diff with the load compensation control switched off then a 54C return temp is guaranteed using a blending valve, and efficiencies rise with the condenser.
The beauty of using a thermal store is that a boiler can be quite basic and simple. The Quantum boilers Heatsave is ideal as it does not modulate.
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This is a good quality boiler.
Initially condensing boilers were thought not to be suitable for thermal stores. Not entirely correct as a condenser will always be more efficient as it merely has a larger heat exchanger. The store makers made them larger and dropped the operating temperature to 75-76C and used blending valves on the boioer flow and return ensuring low return temps to the boiler most of operational time. Boiler makers produced a wider Delta T. Then they were far more efficient, but not to the maximum efficiency that could be obtained from a condensing boiler.
The beauty of using a blending valve on the boiler flow and return on a heat bank or thermal store is that the water in the store only requires one pass through the boiler for the store to be up to temp. This makes the setup quite efficient all around.
The wider the Delta T on the boiler the better for efficiency. Makers will state a Delta T of say 22C, contact their Tech dept and they will usually go
4-5C over that, so a regulated condensing return of 50C can be achieved in many cases increasing overall efficiency.
The message from "Ian Middleton" contains these words:
Figures won't impress dIMM, he just doesn't understand simple arithmetic.
As to the example above I doubt if any likely scenario could feature a much better saving but the saving here on the gas bill is only £50 per year, about 23% at current prices, hardly more than half the 40% dIMM constantly bangs on about.
Meanwhile £2.5K could have been earning say 5% (£125 per year) until really needed. If borrowed the situation would be much worse.
Even under the new rules, it will still be possible to fit non condensers under certain circumstances. There is a "scoring" system that you use to tot up points attributed to various factors (distance to flue terminal, availability of condensate drain etc). If you reach a big enough score, then you are allowed to install a less efficient boiler.
I was "informed" by my mother a while ago that according to a programme broadcast on radio 4 a while back, there was no point in my installing a condensing boiler! (apparently someone was arguing that fitting condensing boilers to old systems would have no benefit for many of the same reasons as you chap seems to be suggesting).
It took a while to explain all the various reasons why that argument was flawed, very simplistic and ignored most of the factors!
Absolute tripe. I know in some areas the estate agents highlight that an economic gas condensing boiler is fitted. When people view and see a brand new boiler that is certainly is a selling point. That means no expenditure on heating for many years to come.
So, you think that a kitchen with conventional flued boiler that looks 30 years old will be treated the same as one with a brand new cheap to run condenser on the wall? Get real.
As the property TV progs have shown, selling a house straight away can mean £1000s saved or gained.
IIRC the opinion of the Estate Agent posters here was that any working heating system was a view equally and a broken one a serious defect (with more than it's fixing price implicated in the purchase price).
It is the case that a condensing boiler may well be more efficient than a conventional one at the higher end of the temperature range.
However, you are implying that by fine tuning the operating temperature on the flow side to 76 degrees, that something wonderful happens, the angels sing and you can be up to your chin in a bath of
10 litres.
There is not a sudden Holy Grail to be achieved at 52-55 degrees return temperature with a condensing boiler. All that happens is that the efficiency curve takes a steeper slope.
What you are actually describing is a compromise which in practice makes very little difference from the perspective of whether condensing is happening or not.
In other words, miracles don't suddenly happen at 0.1 degrees below the dew point.
Not so. A 50-55% efficient cast-iron clunker replaced by a high efficiency condenser with TRVs, and ate-of the art controls, quick recovery cylinder etc, will give approx 40% (older boilers are nor suited to quick recovery cylinders as they cause the boiler to condense). Remember the old boilers efficiency would have tailed off over the years. I have come across this sort of efficiency hype.
A few weeks back I seem to recall you trying to tell us that sticking a store in between boiler and rads was always a "good thing", and that it would raise efficiency. ISTR a number of people pointing out that while this may well be the case for a dumb non modulating boiler, with a most modern boilers all you were doing was bolloxing the boilers closed loop control system by sticking a large energy storage term into the sums, that would only serve to upset the boilers ability to load compensate.
Well done IMM, you are beginning to pick some of this stuff up it seems.
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