With even the best boilers only modulating down to a certain level and TRVs as standard equipment, boiler cycling seems to be inevitable. Just how damaging or wasteful is it? I'm guessing not a lot, assuming of course it isn't happening every few seconds.
Boiler cycling, the ultimate evil or not?
- Thread starter ianniann
- Start date
A
ALEC1
Hugely damaging and wasteful... the boilers are designed to tick over with modulating controls or weather compensation..
savings with these controls have been reported as high as 30% thats just up dating the controls on condensing boiler
savings with these controls have been reported as high as 30% thats just up dating the controls on condensing boiler
Assuming this is true, how do you propose to achieve this when "ticking over" requires 1kw and most boilers won't modulate down below perhaps 5kw (or 10kw for many combis)?
'Hugely damaging' maybe over stating it... but have the boiler in a steady state could make the difference with a boiler lasting 10/15/20 years. the easer you make your boilers life the better its chances for the long haul.
ianniann you look to have a very keen interest in all of this for not being a installer or system designer...
ianniann you look to have a very keen interest in all of this for not being a installer or system designer...
Hmm ,I don't know about that , car's are very rarely working at maximumn ??? we use alot of J&S boiler's & they are vary rarely working at maximumn , only when they 1st come on , short cycling depend's they generally stay on at minimumn ! unless its H.W only .
Lot's of manus ect make all type's of claim's about this control & that ect ,
How much money can be saved , so & so forth , I have my doubt's , it's a bit like the sedbuck figure's for boiler's , based on average's , assumption's on useage , ignore how it produce's H.W , ultimately the consumer will pay a very heavy price for all this technology , in year's to come , the great condensing experiment is only in it's what 5th year ??
Lot's of manus ect make all type's of claim's about this control & that ect ,
How much money can be saved , so & so forth , I have my doubt's , it's a bit like the sedbuck figure's for boiler's , based on average's , assumption's on useage , ignore how it produce's H.W , ultimately the consumer will pay a very heavy price for all this technology , in year's to come , the great condensing experiment is only in it's what 5th year ??
http://www.hwch.co.uk/kidd.html 5th year? depend on who you ask...
it may be new to us but it does not make it new... a lot of boilers nowadays try and self load/range rate them self. don't want to plug XYZ boiler make here but some boiles for example look at the flow and return temps to see how much energy the system is emitting and range it self to that.
it may be new to us but it does not make it new... a lot of boilers nowadays try and self load/range rate them self. don't want to plug XYZ boiler make here but some boiles for example look at the flow and return temps to see how much energy the system is emitting and range it self to that.
Very few thing's are new , condensing boiler technology can be I beleive , be traced back to 1946/7 , stirlig engine's 1800 & something ?? condensing boiler's may well have been used in Europe since the 1970's , but we now have a massive range on the market , & ultimately every one will end up paying for this technology , at some time in the future , reliability is collectively down the toilet , pollution has only been moved , I am somewhat scepticle about the various claim's made by those who have a vested finacial interest ( manu's) in promoting / selling there product's to joe public .
I just can't resist when I see something that looks like BS
Either way I can't lose. If it turns out to be BS then I've learned something. If it turns out to not be BS then I've still learned something.OK, let's make this specific because I don't seem to be getting through. A common fairly smart boiler is the Vaillant EcoTec Plus. They modulate down their burner power to try and match the needs as best they see them. The lowest modulated power level I could find for any boiler in the range is 5KW for the 415 system boiler. That is way over any conceivable level of "trickle heating". It is higher than the heat loss of my entire house in the middle of winter, so any boiler operating at this level will sooner or later overheat (either the house or its own water) or switch off (ie. cycle). So my question remains, how is it possible to avoid cycling the boiler even with the most sophisticated controls? And how important is it to try?
A
ALEC1
People and the industry confuse load modulation with set point modulation.
It is true that all condensing boiler modulate down on lad, that is when the boiler thermostat is set at maximum the the gas consumption decreases, but the flow temperature remains at the maximum load.
However, almost all boilers destined for europe are manufactured to much higher standards, these are namely to modulate the set point as well.
The room controller (modulating controls) decides the deviation from the set point and tells the boiler at what temperature to fire at. So if there is a big deviation ie the set point is 20c and the temperature has fallen to 16, it will fire at maximum say 75c. If the deviation in .5c, it will fire in the low 40c's
The benefit is obvious. At lower temperatures the boilers dont work so hard, and given that every mechanical component has a given life span the less it works the longer it will last. In addition gas is burnt at higher efficiencies, well below the dew point of gas combustion.
In fact I regularly take out condensing boilers, not because they are inherently poorly designed, but because they are on-off controls.
The reason we use on-off controls is a bit of a mystery, but sedbuk only looks at boiler efficiency with the use of on-off controls and EST dont even put information about modulating controls on there website despite the fact they really do seem to save around 25% of gas over and above installing a condensing boiler.
It is true that all condensing boiler modulate down on lad, that is when the boiler thermostat is set at maximum the the gas consumption decreases, but the flow temperature remains at the maximum load.
However, almost all boilers destined for europe are manufactured to much higher standards, these are namely to modulate the set point as well.
The room controller (modulating controls) decides the deviation from the set point and tells the boiler at what temperature to fire at. So if there is a big deviation ie the set point is 20c and the temperature has fallen to 16, it will fire at maximum say 75c. If the deviation in .5c, it will fire in the low 40c's
The benefit is obvious. At lower temperatures the boilers dont work so hard, and given that every mechanical component has a given life span the less it works the longer it will last. In addition gas is burnt at higher efficiencies, well below the dew point of gas combustion.
In fact I regularly take out condensing boilers, not because they are inherently poorly designed, but because they are on-off controls.
The reason we use on-off controls is a bit of a mystery, but sedbuk only looks at boiler efficiency with the use of on-off controls and EST dont even put information about modulating controls on there website despite the fact they really do seem to save around 25% of gas over and above installing a condensing boiler.
A
ALEC1
to answer the specific question about cycling this can only be avoided on systems that has a heat loss output in excess of the minimum modulation capacity of the boiler.
System design is critical, that includes controls (must be modulating) and correctly sized pipes and radiators.
In small systems ie a flats cycling is pretty well inevitable.
On a "perfect" installation a modulating pump, linked to the burner, would ensure that the return was kept down and the burner level matched the demand with the modulating controls.
If a boiler is working to a set point fixed on the boiler, you will always get cycling, as the room temperatures rise, the trick of course is to let the flow temperature drop down as the room temperature rises... but not using a TRVS.
Yesterday I was in front of an ecotec boiler and the flow temperature of 50c actually dropped as I watched it with the burner on minimum...why? because the room sensor was satisfied or approaching it.
The burn was kept with a much lower return temperature still putting heat into the system at very high efficiencies... flue temperature around 35-40c the dropping flow temperature an irrelevancy as eventually it would stabilise...
System design is critical, that includes controls (must be modulating) and correctly sized pipes and radiators.
In small systems ie a flats cycling is pretty well inevitable.
On a "perfect" installation a modulating pump, linked to the burner, would ensure that the return was kept down and the burner level matched the demand with the modulating controls.
If a boiler is working to a set point fixed on the boiler, you will always get cycling, as the room temperatures rise, the trick of course is to let the flow temperature drop down as the room temperature rises... but not using a TRVS.
Yesterday I was in front of an ecotec boiler and the flow temperature of 50c actually dropped as I watched it with the burner on minimum...why? because the room sensor was satisfied or approaching it.
The burn was kept with a much lower return temperature still putting heat into the system at very high efficiencies... flue temperature around 35-40c the dropping flow temperature an irrelevancy as eventually it would stabilise...
But a boiler is nothing like a car.
The wear on a car travelling at 100mph is considerably greater than if it is travelling at 30mph. The load on the engine, brakes, suspension is considerably greater and will shorten the life considerably. Not to mention the increased fuel consumption.
If a boiler is running at maximum output the only difference, compared to minimum, is a faster running fan and a greater gas flow through the valve. The extra wear due to this is negligible.
I agree that most people confuse load modulation and set point modulation. Most installers only consider the latter and think of modulation as "automatic range rating". Manufacturers, particularly UK ones, are guilty of fostering this attitude.
I also think that most boilers are oversized, particularly now that Building Regulations specify a much greater level of insulation. I doubt if many new build houses need more than about 10kW for heating, which means that the boiler should be able to modulate down to 2-3kW. But most boilers only modulate down to 8 or 9KW and sometimes even higher if they are large combis.
A
ALEC1
Installers are an easy recipient of criticism in this...but as you say its the manufacturers who are to blame, not helped by not very enlightened advice being given to the government, by EST and SAP
The wear in tear comes in when everything have to be started and stop 100 times a day, every day.
fans ,gas valve, APS, spark gens, relays... all opening and closing, starting and stopping.
the boiler I had in mind for my example was my boiler, an intergas.
fans ,gas valve, APS, spark gens, relays... all opening and closing, starting and stopping.
the boiler I had in mind for my example was my boiler, an intergas.
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