But when the notor is accelerating from stationary to full speed it could be taking 20 times rated load, even more in some cases.
Hidden costs of changing to a combi
- Thread starter bernardgreen
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But when the notor is accelerating from stationary to full speed it could be taking 20 times rated load, even more in some cases.
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I think that the gas pressure was raised but now bigger pipes are put in to up the volume.Bob
Well you know BG it's a village fix.Bob
When natural gas was proposed in the 1960s, only two meter sizes were standardised on, U6 and U16. 6 cu/m hr (212 cu foot per hr) and 16 cu/m hr. They had many sizes. A U6 was designed to cope with the vast majority of domestic homes. Previously they had 3 cu/m hr (3/4" connections) and 3.75 cu/m hr (250 cu foot per hour). When converting to NG from town gas the distribution system could cope as pressure doubled with pipes already large bore to cope with town gas. The home gas installation pipes were instantly oversized. The CV of the gas was higher as well, able to deliver twice as much heat into a home down the same service pipe. A house was supposed to consume 6 cu/m hr if the need was there. They have cut back on this, skimping, taking an average for a district. A U6 can give approx 62kw of heat.
If there are distribution problems at peak hours, then get a combi with a small water storage vessel integrated, it will help. I know one fitter who fitted 28mm pipe from the meter to the combi and 32mm near the boiler to give internal gas storage when the combi kicked in. It worked - the burner was susceptible to pressure and flow changes. Matters like having 1" x 1" maintaps help a lot as well. It is a matter of attacking all points, until they put in a proper supply as they should have done initially. So a homeowner has to pay extra because the gas distribution people skimped. A 40kW combi in a supply that should be capable of taking 62kW is not even near maximum capacity.
If there are distribution problems at peak hours, then get a combi with a small water storage vessel integrated, it will help. I know one fitter who fitted 28mm pipe from the meter to the combi and 32mm near the boiler to give internal gas storage when the combi kicked in. It worked - the burner was susceptible to pressure and flow changes. Matters like having 1" x 1" maintaps help a lot as well. It is a matter of attacking all points, until they put in a proper supply as they should have done initially. So a homeowner has to pay extra because the gas distribution people skimped. A 40kW combi in a supply that should be capable of taking 62kW is not even near maximum capacity.
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Yup I'll go with that I did a lot of work for the firm who did the mods on the cookers when we changed over long time now but in lincolnshire i think it was press or priess who got the job and if you were going to sub off them you had to go to the tech Coll to be told all about it,mind you they paid well and on time good on them my agent who delt with me was Bill hemstock great bloke
very honest.Bob
very honest.Bob
Is that BG British Gas or a comment about the place where I live ?
Are you saying that a modern boiler can measure the pressure of the incoming gas as an analoge and then adjust the fan speed and other controls to modulate heat output. ?
William Press.
yes some can, they use a lambda sensor in the flue and adjust the gas valve accordingly, not all do but a modulating appliance is not a danger with a low inlet pressure, why can you not understand that ? Oh I forgot you know feck all about gas and combustion.
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Why anyone would want a combi unless they live in a caravan or small flat is beyond me.
You forget incorrectly......
What happens when the fan is at minimum speed and the gas valve is fully open and the lamda sensor (*) is still indicating excessive oxygen in the flue gases ?. Sensoble thing would be to shut the boiler down to avoid unstable combustion and/or repeatative flame out and re-starts. In which case how would the control system know when the inlet pressure was high enough to re-start.
(*) Assuming the lamda sensor is measuring ratio of oxygen to combustion products.
In many cases I don't think it's people wanting a combi, so much as the combi being a cheaper option if you have the water and gas service to make it a realistic proposition.
When I had my heating replaced, I had my venerable old cast iron BBU, loft cistern and copper tank replaced with a combi. Reason for choosing the combi was cost. A system boiler was slightly cheaper than the combi, but once a new loft cistern + copper tank + shower pump was added on the system was around £1,500 more expensive. A mains-pressure cylinder was similar but added annual servicing costs beyond the gas boiler service.
I'm only here for a couple more years so it didn't make sense to shell out the extra, however if this was a "forever home" then I would have gone with hot water storage plus solar heater panels.
It's a large 3-bed semi and the boiler copes well. If anything it's oversized as I've never heard it go full-blast even with the shower on full.
Because they are sold and promoted as being highly efficient and as well they remove the need to find space for a hot water cylinder.
They can give high values of efficiency when tested in laboratory conditions but many then fail to achieve those high values of efficiency when supplying hot water in every day domestic use.
As I said you do not have a clue about what you are talking about, if you did you would already know the answer
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