Running condensing boilers in condensing mode

[Agile]

No the OP is not GB!

The OP has the ability to design simple relay based logic to control his simple system.

I dont really see what his problem is. He has several zones and all have independent room stat controls. So if one assumed the thermal characteristics of each zone were similar than any standard weather comp system would work.

In these days of high energy prices then I am surprised that he does not have or create double glazed windows.

Tony

 

[D_Hailsham]

No the OP is not GB!

The OP has the ability to design simple relay based logic to control his simple system.

And, presumably, you know that GB does not have that ability.

I dont really see what his problem is. He has several zones and all have independent room stat controls. So if one assumed the thermal characteristics of each zone were similar than any standard weather comp system would work.

I agree. The same assumptions are made for any house; i.e the thermal characteristics of all rooms are similar.

 

[Agile]

Weather comp assumes that all rooms are the same.

Of course they are not and other factors like solar gain during sunlight cause a differential effect.

Permanent differences can be fine tuned by careful balancing in most cases. Few people bother though.

Tony

 

[bengasman]

The condensing process does not start or stop at 55 C, above this temperature it gets rapidly less.
The problems you have come largely from having a poor quality boiler that is probably not quite installed as it should have been.
The difference in efficiency between the various band a boilers is negligible, the difference is in how the system is designed, installed, and how hot the boiler stat is set.
Designing a heating system is a skill that needs to be learned, what makes you think you had the knowledge to do this?

 

[holty]

Designing a heating system is a skill that needs to be learned, what makes you think you had the knowledge to do this?

shame that skill seems to be lost more and more these days.

 

[chadfieldpropertyservices]

Tony,
I don't have double glazing because it's a listed building in a National Park (don't go there!) I was lucky that they alllowed me to have an inside toilet!. I have used the art of balancing the system such that TRV's are unneccessary (and just something else that leaks or sticks)

As I have trawled through the various boiler manufacturers data, those that quote efficiencies all give better efficiency at lower supply / return temps ie 60/40'c is better than 80/60'c and 50/30 is even better, which lends me to believe that I am thinking along the right lines and I'm happy to lose some efficiency in hot water mode for the sake of a rapid heat up.

Yes, having looked into it further, a weather compensated boiler would probably do the job but is adding to the complexity of the system. In my life at the moment it seems that everything is packing up, the boiler, car etc and it is the electronics and technology that is failing, not only is the technology fragile and unreliable it is difficult to fault find and stupidly expensive to replace, Mum & Dads ancient cast irom potterton may not be efficient but it has cost them about two thermocouples in 25 years. I spoke to a guy yesterday that had just been to see a boiler his company fitted two years ago that was completely shot.
Remember that manufacturers are in business to sell Boilers and parts, not to supply reliable cost effective heating.

Bottom line is that I decided to have the ignition board replaced and it's running ok till next time.

Thank you all for your input but some of you do have an attitude (particulary those from Surrey and London)

 

[D_Hailsham]

The condensing process does not start or stop at 55 C, above this temperature it gets rapidly less.

Where do you get this idea from?

The temperature at which the water is condensed out of the flue gases depends on the dew point. This will vary slightly depending on the exact composition of the flue gases which will vary according to the impurities in the natural gas. This graph show how boiler efficiency varies with the flue temperature. The dew point in this case is 57°C

 

[Tipper]

You're not trying to 'condense' water out of the flue gas, you're trying to 'extract as much heat' as possible from the flue gas thus making economies on fuel usage.

Marine and power station engineers will know this as an ecomomiser and the issue there is to keep the exit flue gas temperature 'above' dew point to stop acidic condensate forming and rotting the carbon steel tubing (cheap and cheerful!) used. With the advent of better/cheaper stainless steels and the pressure to save more fuel, the 'economiser' can be allowed to condense.

Condensing is not the primary requirement but the by-product.

 

[D_Hailsham]

You're not trying to 'condense' water out of the flue gas, you're trying to 'extract as much heat' as possible from the flue gas thus making economies on fuel usage.

Are you saying that the fact that efficiency increase noticeably if the flue gas temperature is below the dew point is purely coincidental?

 

[Tipper]

The cooler the feed (return) temperature the more heat will be extracted from the fluegas into the feed water and therefore less fuel will be needed to get to the desired outlet temperature, therefore more efficient.

'Condensing' is still not the prime driver but it does show that the boiler is extracting more heat from the flue gases because it is running below the dew point and producing condensate.

Perhaps the high efficiency boilers would be better called 'economiser boilers' and they happen to produce condensate as a by-product due to the operation of the economiser reducing the flue gas to below dew point.

 

[Agile]

Tony,
I don't have double glazing because it's a listed building in a National Park (don't go there!)

Thank you all for your input but some of you do have an attitude (particulary those from Surrey and London)

Most listed buildings are allowed to have secondary glazing although I appreciate that not all will be. The planners have a big fight with the need to conserve energy. Its usually a local decision which means that it can often be reversed if you complain enough to the local MP etc. I do agree that many of the Nat Parks can be difficult but I usually managed to get TV masts approved because of the benefit it brought to the local residents.

I have an attitude of professionalism. That includes having boilers repaired by a qualified person.

Condensing boilers are called that to differentiate them from regular boilers.

Tony

 

[D_Hailsham]

The cooler the feed (return) temperature the more heat will be extracted from the fluegas into the feed water and therefore less fuel will be needed to get to the desired outlet temperature, therefore more efficient.

'Condensing' is still not the prime driver but it does show that the boiler is extracting more heat from the flue gases because it is running below the dew point and producing condensate.

Can't disagree with that. As far as Joe Public is concerned the boiler is more efficient when there is condensate produced than when it is not.

 

[chadfieldpropertyservices]

Actually its not just extracting more heat form the flue gas that just happens to produce condensate as a byproduct that gives the increase in efficiency. it takes a hell of a lot of energy to turn water into steam and you have to extract a hell of a lot of heat from steam at 100'c to turn it into water at 100'c, its the very fact that that the water vapour is giving up its latent heat of vapouisation INSIDE the boiler that gives Condensing boilers that potential to be super efficient.
Consiser this, "how much electricity does it take to boil a 2litre kettle and how much longer does it take to turn all that water into steam and boil it dry?"

I've just had a phone call from the tech manager of Ravenheat who confirmed that I was absolutely spot on with the way I had designed our sytem around their boiler with a cool heating circuit and hot cylinder circuit.
I may not have 25 years experience as a plumber but I don't have 25 years experience of sitting in a box being told this is the way its always been done either

 

[Norcon]

it takes a hell of a lot of energy to turn water into steam

But where is the water in a boiler?
I was led to believe carbon and hydrogen when burnt in a combustion chamber and combined with oxygen , will produce water vapour which then becomes superheated.
Isn't that one step ahead of water?

What is the difference between the amount of energy required to change water to vapour and the vapour to a superheated state?

 

[Tipper]

Time to dig out your steam tables!