Efficient gas boiler, show and tell

[trojanhawrs]

I mean an actual flow meter to measure the volumetric flow rate, something like this. That particular one requires a 24vdc supply and something to read the 4-20mA output. Then you use the formula here to calculate the heat transfer.

 

[Harry Bloomfield]

You might even see values above 100% due to the recovered latent heat from condensing (ErP data usually already includes latent heat value[GCV vs NCV]).

I cannot see how you could possibly hit 100% efficiency, there is always some waste heat from the flue of a gas boiler. The exhaust, will always be somewhat warmer than the air intake to the boiler.

 

[idealness8583]

I mean an actual flow meter to measure the volumetric flow rate, something like this. That particular one requires a 24vdc supply and something to read the 4-20mA output. Then you use the formula here to calculate the heat transfer.

Thank you! That's really interesting; this would be great to compare the heat output value from the precise flow rate perspective. I will consider it!

I cannot see how you could possibly hit 100% efficiency, there is always some waste heat from the flue of a gas boiler. The exhaust, will always be somewhat warmer than the air intake to the boiler.

I can't explain it properly either, there are definitely more questions than answers in all the numbers used and laws of physics are hard to dispute. But the overall comfort satisfaction is high

 

[Harry Bloomfield]

I can't explain it properly either, there are definitely more questions than answers in all the numbers used and laws of physics are hard to dispute. But the overall comfort satisfaction is high

80, 90, or 100% efficient - does it really matter? Ultimately, all of that energy will escape through the walls anyway

 

[trojanhawrs]

I cannot see how you could possibly hit 100% efficiency, there is always some waste heat from the flue of a gas boiler. The exhaust, will always be somewhat warmer than the air intake to the boiler.

I was curious about this too. It looks like it's to do with the assumption on how much energy a unit of gas contains. Energy content is gleaned by burning it and if you're not condensing the vapour it doesn't count towards the total. Obviously all boilers are condensing now but I guess they kept the net efficiency number as a comparison to the old ones.

 

[JonathanM]

I cannot see how you could possibly hit 100% efficiency, there is always some waste heat from the flue of a gas boiler. The exhaust, will always be somewhat warmer than the air intake to the boiler.

I was curious about this too. It looks like it's to do with the assumption on how much energy a unit of gas contains. Energy content is gleaned by burning it and if you're not condensing the vapour it doesn't count towards the total. Obviously all boilers are condensing now but I guess they kept the net efficiency number as a comparison to the old ones.

I did once try to get my head around it. If I remember correctly, it's a rather tortuous sleight of hand. It goes something like this:

In the days before condensing boilers, about 11% of the energy would be lost, in the form of water vapour, through the flue. These are sometimes called the "wet losses". And I think the argument was basically, because we are always going to lose 11% in this way, why include that in the calculation. So they came up with two ways of calculating efficiency. One is based on the gross calorific energy (gcv) of the gas and the other is based on the net calorific energy (ncv) of the gas . The ncv is basically 11% less than the gcv. As I say, it is a sleight of hand. They pretend that the energy content of the gas is 11% lower than it actually is. This makes the stated efficiency about 11% higher.

I think that ncv was mainly used on the continent and in the UK we used gcv. So, the same boiler, sold in two different markets, would have two different stated efficiencies, depending on which energy value is used.

The problem came when they started building condensing boilers. On the continent they often still use ncv, I think. As a result, boilers can have stated efficiencies of up to 108%. But that is the same as 97% efficiency in the UK. That's my best memory of how this all works.

 

[JonathanM]

I believe this is essentially the same boiler. First figure is Italy, second figure is UK

 

[idealness8583]

Thank you for sharing that data, it’s an interesting perspective (two countries) and a good point of reference in terms of what absolute values we are talking about.