Setting Condensing Boiler Flow Temperature
- Thread starter Chris_J
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Oh absolutely, but that restriction is not a result of restrictions in the (smaller) radiator itself. That was my point to our friend, or at least I think it was - this thread seems to have gone on a bit of a wild goose chase so apologies to the OP for my contribution to that...
Indeed, having to throttle the LSV more is a good demonstration that a smaller radiator doesn't restrict the flow more than a big one. If it did then there'd be no need to do so - in fact it would be self-balancing if this was the case.
Mathew
yes, but if there is still a demand on the boiler it will short cycle an that is bad for the boiler an for the customer. so that exactly why it is important to have a good sized bypass rad, to stop short cycling.
at least this way if its set up with a 20c drop it should be fully condensing.
at least this way if its set up with a 20c drop it should be fully condensing.
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Haha, no problem. Thanks for the very entertaining thread!
I'm actually at work at the moment, so it's a great way to pass the time
That's right.
The relevant factor is actually the flue gas temperature as this determines the amount of water vapour which the flue gas can hold; any excess will be turned into water. The lower the flue gas temperature, the less water vapour the flue gas can hold. The flue gas pass over the pipes containing the returning water, so they are cooled down, and the water vapour condenses.
M
mysteryman
There is much misunderstanding in this thread.
Delta T is the difference between return and flow temperature, eg 30/50 is Delta T 20, not 30 or 40 as stated.
A boiler burning Natural Gas, or methane, will begin to condense at a return temp below 53, but for full condensation you need the flow below 53C. Band B boilers, with cobbled-on secondary heat exchangers, are now illegal for this very reason - they can't condense fully.
All boilers are not 'carp' - there are some excellent models readily available, the best ones being designed around weather compensation.
You do NOT need to oversize radiators. For 95% of the heating season the heating demand is only a fraction of the maximum. Weather comp will keep a good system with normally sized rads fully condensing during this 95% of the heating season.
Delta T is the difference between return and flow temperature, eg 30/50 is Delta T 20, not 30 or 40 as stated.
A boiler burning Natural Gas, or methane, will begin to condense at a return temp below 53, but for full condensation you need the flow below 53C. Band B boilers, with cobbled-on secondary heat exchangers, are now illegal for this very reason - they can't condense fully.
All boilers are not 'carp' - there are some excellent models readily available, the best ones being designed around weather compensation.
You do NOT need to oversize radiators. For 95% of the heating season the heating demand is only a fraction of the maximum. Weather comp will keep a good system with normally sized rads fully condensing during this 95% of the heating season.
No.
Delta-T is the difference between the mean of the flow and return temperatures, and a notional room temperature of 20°C. So, for example, with a flow of 80°C and a return of 70°C the mean is 75°C. This gives us a Delta-T of 75-20 = 55.
Misunderstanding? You bet, but it's yours I'm afraid.
Mathew
Actually you are both right in your own way.
Delta T is only a term used to denote a temperature difference.
That can be Mysteries flow/return of a boiler ( what he advises on all day )
It can also be the flow/return of a radiator.
Also the difference between the mean temperature of a radiator and the room temperature!
In fact you can use it to describe a temperature difference between any two things!
Tony
Delta T is only a term used to denote a temperature difference.
That can be Mysteries flow/return of a boiler ( what he advises on all day )
It can also be the flow/return of a radiator.
Also the difference between the mean temperature of a radiator and the room temperature!
In fact you can use it to describe a temperature difference between any two things!
Tony
It can also mean a time difference - look it up on the NASA website.
I assume you have more than two rads!
Add up the output of all your rads, What does it come to?
Lol, sorry.
(571x4)+(286x3) = 3142W
Plus a towel rail, so say 3.6kW.
Hmm, kinda low right?
(571x4)+(286x3) = 3142W
Plus a towel rail, so say 3.6kW.
Hmm, kinda low right?
Those rad outputs seems very low. Are they definitely the type without fins on the back?
The Vokera 29A produces a max heating output or 24kW (29kW for hot water). The spec does not state what the minimum output is but I have calculated it as about 6kw from the gas rate data.
This means that, even when the boiler is running at minimum output, it is producing much more heat than your radiator need - about 60% too much!
This means your boiler will be continually short cycling (stopping and starting), because the temperature will rise very quickly as there is nowhere for the excess heat to go.
You said earlier that you calculated the heat requirement as about 13kW. Did you use the calculator I suggested and did you deduct the 2kW allowance for hot water?
Either way, it would appear that your radiators are seriously undersized. Does that agree with your experience?
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