K
karlskidmore
I'm not a heating engineer, but I have the feeling that my boiler could be oversized for the amount it is being used and therefore cycling too much as a result -- I would appreciate anyone jumping in to confirm or deny my assumption, plus ideas on how to possibly improve the situation:
The boiler is a [DLMURL="http://www.buderus.ie/buderus-downloads/buderus-manuals-to-download/gb112-manuals.html"]Buderus GB112[/DLMURL] and was right-sized for a 300m2 building using UFH (9cm concrete thermal mass), but, as we're only usually heating around 130m2, it is effectively oversized for our normal usage and, therefore, cycles on and off too rapidly (i.e. on for 6 mins, off for 5, repeat like that while switching programme is on -- I'm assuming that is too rapid?). The flow rate "heating characteristic curve" is configured as min:40C std:45C max:50C). The building type is "heavy" and is very well insulated. Lowest typical winter temperatures are between 5C and 10C.
The boiler can modulate the flame between 35% and 100% and it quickly modulates its output down to 35%, however, this is still not enough to reduce the level of cycling, as it quickly (within 5 or 6 minutes) reaches its flow set-point of 40C (with return flow around 28C / actually, it only turns off when flow gets to 44C). Ideally, if it could modulate down to 20% it could probably reduce the amount it cycles considerably while increasing efficiency. The "Heating Capacity Controller" dial on the boiler's front panel has been reduced to minimum, which prevents the boiler initially modulating above the minimum of 35%, which has helped marginally. I've already confirmed that there are no short bypass runs back to the boiler from disabled segments of the heating circuits, which could otherwise have influenced the return flow temperature too quickly. The individual manifolds do not have mixing valves -- this is instead centralised.
Are there any methods that would enable the boiler to modulate to even lower levels of output?
Could the gas input pressure be reduced to, in effect, reduce the nominal output?
The only alternative I can think of, to achieve the same (i.e. increased efficiency through reduced cycling), is to have a very repetitive switching programme, for instance on for one hour, off for two hours, on for one hour, off for two hours, ...., on for one hour, off for two hours, and so on. This way, the heating circuits could cool down sufficiently during off-periods to allow enough of a delta between flow and return to accrue before the next on-period and thus reduce cycling when it is on.
The guy who designed the heating system for this new build was a heating engineer (of the "all theory / no practice kind") and the Buderus approved guy who comes to service it is hardly an engineer at all (definitely has "no theory" to back-up his practice). I am not a heating engineer and don't pretend to be, but I do complete my own plumbing jobs (even having installed my own combi in a past life), so consider me just a generalist geek, left in the middle of all this, and living in a very remote rural (i.e. unsupported) area, but very keen to understand and take (efficient) control of this boiler.
So, any practical ideas on how I can tweak the system to reduce cycling / improve efficiency? Or is it already operating normally by typical installation standards?
Many thanks in advance for any help.
Karl
The boiler is a [DLMURL="http://www.buderus.ie/buderus-downloads/buderus-manuals-to-download/gb112-manuals.html"]Buderus GB112[/DLMURL] and was right-sized for a 300m2 building using UFH (9cm concrete thermal mass), but, as we're only usually heating around 130m2, it is effectively oversized for our normal usage and, therefore, cycles on and off too rapidly (i.e. on for 6 mins, off for 5, repeat like that while switching programme is on -- I'm assuming that is too rapid?). The flow rate "heating characteristic curve" is configured as min:40C std:45C max:50C). The building type is "heavy" and is very well insulated. Lowest typical winter temperatures are between 5C and 10C.
The boiler can modulate the flame between 35% and 100% and it quickly modulates its output down to 35%, however, this is still not enough to reduce the level of cycling, as it quickly (within 5 or 6 minutes) reaches its flow set-point of 40C (with return flow around 28C / actually, it only turns off when flow gets to 44C). Ideally, if it could modulate down to 20% it could probably reduce the amount it cycles considerably while increasing efficiency. The "Heating Capacity Controller" dial on the boiler's front panel has been reduced to minimum, which prevents the boiler initially modulating above the minimum of 35%, which has helped marginally. I've already confirmed that there are no short bypass runs back to the boiler from disabled segments of the heating circuits, which could otherwise have influenced the return flow temperature too quickly. The individual manifolds do not have mixing valves -- this is instead centralised.
Are there any methods that would enable the boiler to modulate to even lower levels of output?
Could the gas input pressure be reduced to, in effect, reduce the nominal output?
The only alternative I can think of, to achieve the same (i.e. increased efficiency through reduced cycling), is to have a very repetitive switching programme, for instance on for one hour, off for two hours, on for one hour, off for two hours, ...., on for one hour, off for two hours, and so on. This way, the heating circuits could cool down sufficiently during off-periods to allow enough of a delta between flow and return to accrue before the next on-period and thus reduce cycling when it is on.
The guy who designed the heating system for this new build was a heating engineer (of the "all theory / no practice kind") and the Buderus approved guy who comes to service it is hardly an engineer at all (definitely has "no theory" to back-up his practice). I am not a heating engineer and don't pretend to be, but I do complete my own plumbing jobs (even having installed my own combi in a past life), so consider me just a generalist geek, left in the middle of all this, and living in a very remote rural (i.e. unsupported) area, but very keen to understand and take (efficient) control of this boiler.
So, any practical ideas on how I can tweak the system to reduce cycling / improve efficiency? Or is it already operating normally by typical installation standards?
Many thanks in advance for any help.
Karl
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