FGA Readings and Interpretation

[dontknowitall]

Time for me to ask a series of questions - if I'm allowed:

Flue Gas Analyser readings - what do they mean/how are they calculated?

Ratio: What does it mean? I think it's something to do with one gas compared to another.

Net Efficiency: What's it net of and how is it calculated?

Gross Efficiency: What is is measuring? Obviously efficiency of the boiler but what does that mean?

CO2 - If the customer's lost their manual what's a good figure to aim for?

O2 - Between 5.5% and 6.0% - but what does this mean?

Finally, an easy one:
CO - What's the maximum (ppm) you would allow before you put an axe to the boiler?

Most of the above are related in some way to other readings/questions in the list above.

Trouble is that I've been told how to service boilers, what readings to make sure I'm getting but no one's explained in clear English how all these things relate to each other!!

I'd be really grateful for some help with the above. An internet link describing/explaining would be just as helpful.

Many thanks, in advance.

 

[kirkgas]

Time for me to ask a series of questions - if I'm allowed:

Flue Gas Analyser readings - what do they mean/how are they calculated?
they are the result of taking a sample of what is being produced by the combution process to confirm if the appliance is working properly/dont really know how they are calculated other than to say the machine is built to carry out the specific function so whatever is built into the machine does what it says on the tin

Ratio: What does it mean? I think it's something to do with one gas compared to another.
ratio is CO/CO2, which is the amount of CO and CO2 being produced in relation to each other (again provoding evidence as to how well the appliance is burning the fuel)

Net Efficiency: What's it net of and how is it calculated?
this is the amount of "useable" heat produced per m3 of gas, measuring in net is the more modern way as it discounts the % of water vapour in the calculation. it is calculated by measuring the amount of gas used against the heat produced

Gross Efficiency: What is is measuring? Obviously efficiency of the boiler but what does that mean?
as above but the gross figure includes the % of water vapour

CO2 - If the customer's lost their manual what's a good figure to aim for?
THIS IS A SCARY QUESTION, YOU DON'T GUESS THESE TYPES OF THINGS,GET THE MI OR LEAVE IT ALONE, however knowing about combustion assists i this, ie "perfect combustion" will produce absolute results, i think perfect combustion will produce 11.2% CO2

O2 - Between 5.5% and 6.0% - but what does this mean?
i think this means there is a problem depending where this reading is coming from, you should get 20.9% O2 outside

Finally, an easy one:
CO - What's the maximum (ppm) you would allow before you put an axe to the boiler?
some boilers quote ppm so again check MI before actioning again get training notes for CPA1 etc to get action levels for appliances

Most of the above are related in some way to other readings/questions in the list above.

Trouble is that I've been told how to service boilers, what readings to make sure I'm getting but no one's explained in clear English how all these things relate to each other!!

I'd be really grateful for some help with the above. An internet link describing/explaining would be just as helpful.

Many thanks, in advance.

this is my take on your Q's (haha i'm sure someone will see errors and advise me accordingly) i would suggest you research combustion as you will get useful info by going back to basics

 

[dontknowitall]

WOW!! What a helpful response. Many thanks Kirkgas especially as I wasn't expecting such a comprehensive answer so quickly. Re the CO2 I've been taught (oil) that I can't go wrong if I aim for 11.0% - 12% so 11.2% makes perfect sense. My OFTEC inspector told me that one about O2 being between 5.5% and 6.0% !!! Maybe Kerosene is measured differently on the FGAs?

Thank you again - an answer like that makes this forum really great!!

 

[ramsey75]

hi
what does Xs air mean and pressure when using my analyser on flue gas i understand the other readings
thanks > new to oil servicing

 

[Reg Man]

I can give some answers to your questions, I am not sure this web page could stand up to the amount of data for the answers. This is something that would probably be a days training for an experienced engineer. As Kirkgas says go back to basics. Combustion/fuel air mix/CO/CO2. One little tip: RATIO is the amount of CO sampled in a quantity of CO2. I might have a high level of CO but if the CO2 is also high it don't mean the combustion is poor.