Boiler sizing from cubic area, or actual usage

[Wildcat1961]

87.7 GCV = 96.47 NCV.
99.4 GCV = 109.34 NCV.
Unless Combustion is near stoich then 99.4 GCV would be a mis-leading claim.

 

[John D v2.0]

Net means heat only, gross means including the latent heat of evaporation of the condensate.
Net was used in the days when condensing was not considered, but now that doesn't make sense.
To get close to 100% gross is possible if no heat leaves via the flue.
I'm thinking that means effectively a heat pump from the flue gas, or combustion supply air warmer than the heating return temperature.

 

[Wildcat1961]

Net means heat only, gross means including the latent heat of evaporation of the condensate.
Net was used in the days when condensing was not considered, but now that doesn't make sense.
To get close to 100% gross is possible if no heat leaves via the flue.
I'm thinking that means effectively a heat pump from the flue gas, or combustion supply air warmer than the heating return temperature.

Is that right..
Should we set Combustion @ stoich (100% GCV)?

 

[John D v2.0]

Is that right..
Should we set Combustion @ stoich (100% GCV)?

That wouldn't be 100% efficient at the stoichiometric ratio that just makes sure no air not needed for combustion goes through the flue . But that air that does go through will still end up warmer than the input air hence wasted heat.
If you somehow filter out the nitrogen that's 80% wasted heat removed. But you'd still have the last 20% which you could retrieve with a heat pump (heat pumps are over 100% efficient so you could get over 100% overall on your boiler by letting the air back outside cooler than when it came in.)

But at that stage you're really better off just getting better insulation in your house!

 

[Wildcat1961]

O2 is required for combustion.
“Air” being referred to as ‘xsair’

 

[John D v2.0]

O2 is required for combustion.
“Air” being referred to as ‘xsair’

No one is suggesting air isn't needed.
Gas is also needed, which does raise the point that the incoming gas temperature is as relevant as the incoming air.
Interesting that someone made a new word for "air"

 

[Wildcat1961]

Interesting that someone made a new word for "air"

The above comment just shows your ignorance as far as Combustion is concerned.
Why feel the need to post on a subject you know nothing about?

 

[John D v2.0]

The above comment just shows your ignorance as far as Combustion is concerned.

Showing off behind fancy words is not evidence of being an expert.
I think you'll find my previous posts on this thread above are basic physics and entirely accurate.
Your habit of making useless posts in reply to mine in the hopes of eliciting something you feel like you can make a smart comment about is not very impressive.

Edit: of course there's every chance my posts is not accurate andand happy to learn, but you seem more interested in trying to seem clever then helping.

 

[Wildcat1961]

Showing off behind fancy words is not evidence of being an expert.

Fancy words?

I think you'll find my previous posts on this thread above are basic physics and entirely accurate.

Then at least get ‘net’ and ‘gross’ the correct way around.

Your habit of making useless posts in reply to mine in the hopes of eliciting something you feel like you can make a smart comment about is not very impressive.

You certainly don’t impress the professionals on here with your mis-leading comments/advise.

Edit: of course there's every chance my posts is not accurate andand happy to learn, but you seem more interested in trying to seem clever then helping.

If you’re not sure the advise you give is accurate then don’t post simple.

 

[John D v2.0]

Then at least get ‘net’ and ‘gross’ the correct way around.

Mate I don't know what you have against me but if you have to pretend I made a mistake to score points don't bother replying to my posts.

 

[Wildcat1961]

Mate I don't know what you have against me but if you have to pretend I made a mistake to score points don't bother replying to my posts.

Pretend you made a mistake?
It’s in black and white as to what you posted.

 

[bernardgreen]

The bottom line efficiency is how much of the heat produced by burning the gas gets into the water be it water taking heat to radiators or water to the hot taps...............The bottom line efficency is not used for marketing. Marketing use a "rated efficiency" which not going to be achieved in the average home.

In some combi boilers the bottom line efficiency is zero for several seconds after a hot tap is turned on. Gas is burning but the temperature of the water leaving the bolier is the same as that entering the boiler. The method used to calculate the "rated efficiency" of the boiler ignores that period of zero efficiency. It is invariably excluded from the equation. Ignored / excluded even though that period of zero efficiency will occur many times a day when the boiler is installed in a home.

 

[Kaymo]

Ok, had some work to do on the outside of the house yesterday so just trying to catch up now.

Ignoring the efficiency of the hot water heating for the moment, I am interested in the efficiency of the boiler. To be honest I hadn't thought about a latent heat effect, but I suppose this makes sense if there is condensing involved. However, correct me if I am wrong, but in the case of a gas boiler, is it not more of a case that the condensing unit is just recovering some of the heat that is being wasted in the combustion process?

I can't believe that any gas boiler is more than 100% efficient, or it would be marketed this way. I am thinking of efficiency in terms of 24kW of heat is created by a boiler, how much of that is useful heat, i.e. not lost to the outside through the flue. Surely that is the only worthwhile measure of efficiency?

 

[bernardgreen]

I can't believe that any gas boiler is more than 100% efficient, or it would be marketed this way.

The qualifier (hi) allows for this spectacular claim of 127.6 %

or is it 122%(hi)

 

[Kaymo]

If this claim is real then there would have to be something else going on beyond just combustion and recovery of the heat from combustion?