Gross/Net Efficiency after service.

[toptec]

Just filing papers away today and I noticed a small tear off note on the back of the RGI's invoice after he carried out a service of my Worcs Junior 28i a few weeks ago.

The printed note shows the boiler as having a net efficiency of 96.3% but a Gross efficiency of 87.3%.

Just curious really as to the differences between the two - Gross what? and Net what? What causes the reduced readings?

Regards All

 

[bengasman]

Net and gross efficiency are pretty much a theoretical exercise to do with how much heat is recovered from the gas used .
The figures you specified are unlikely to be correct.
It is even more likely that the engineer actually measured them, and it is complete nonsense to write them on a report after a service.

 

[gassafeman]

Someone else who has recently purchased an FGI and has no idea how to use it!

Paul

 

[toptec]

I remember him using some sort of sampler. It produced this printed note I have. Why would it be likely he used it, Bengasman? ... do you mean unlikely?

If it is as useless as you say why on earth bother doing it and even worse bother attaching it to the invoive. The note says that the machine is a Unigas 1000 by the way. From your and gassafemans response I gather this is not a requirement of the service/safety check!

 

[gassafeman]

It is not, and provides useless guidance as to the operation / efficiency of your boiler!

Paul

 

[Agile]

To calculate the efficiency in the normal basic meaning you would need to measure the amount of gas the boiler consumes and then measure the amount of heat the boiler produces. That would be very difficult to do!

The flue gas measuring equipment gives an efficiency reading calculated from the gas percentages in the flue. Its a kind of combustion efficiency measurement and has little significance to the real world.

Some people tell the customer that their boiler is xx.x% efficiency as if its a reflection of their skill in servicing the boiler!

Tony

 

[bengasman]

I remember him using some sort of sampler. It produced this printed note I have. Why would it be likely he used it, Bengasman? ... do you mean unlikely?

Yep, unlikely as it may sound, I meant unlikely.

 

[bengasman]

It could be that his analyser could only print out all the results, in stead of just the CO/CO2 ratio. This ratio can be used as "proof" that the boiler works fine.
This would have some sort of logic, although I never bother proving that the boiler is fine after I serviced it, or do a lgsr.

 

[toptec]

Some people tell the customer that their boiler is xx.x% efficiency as if its a reflection of their skill in servicing the boiler!

It's funny you should say that............... he mentioned it a number of times but I was too busy painting the sunroom ceiling to pay any attention. . Nice bloke though, are all you fitters 5'2"?

 

[Agile]

Did he come all the way from Bournemouth?

 

[toptec]

Ok, I asked for it......... Why Bournemouth?

 

[Steve69the69Gas]

Cos we know a vertically challenged one from there

 

[Boilerman2]

The Difference between Net & Gross is the Latent Heat Gain, On a Condensing Appliance Combustion Efficiency should be Quoted as Net as the latent heat in the flue gasses is recovered by the heat exchanger