Boiler Efficiency

John.G

Baxi Solo 15 HE IE.
Controller Myson MEP 2C
Circ Pump: Heat Merchants HM5 130
Co2 8.30%
CO 28 PPM
CO/CO2 ratio 0.0003
Effic. 98.80%
Gas SP/WP 22.71/19.16 MB

A friend of mine recently gave me the some details of his HE Gas boiler including details of a FGA and was asking me some questions re the combustion efficiency etc which I will pass on and include some of my own.

Is the (combustion) efficiency of a HE boiler based on the net heating value of the fuel and the efficiency of a SE boiler based on the gross heating value? and if so why isn't the efficiency based on the gross heating value in both cases?.
In the case of a HE boiler operating in a partially condensing mode, does the FGA measure the amount of water vapour in the flue gases and then do the calcs or does it just assign a combustion efficiency % loss (wet gas loss) just based on the flue gas temperature?.
If a HE boiler was operating (for whatever reason) in a fully NON condensing mode is the efficiency still based on the net heating value of the fuel?.

Wearb

HE FGA settings on FGA assumes "all" of the latent heat is also recovered from the water vapour. The SE only measures combustion efficiency, but takes gas temperature into account for its final efficiency figure. The HE also takes temperature into account also.
Poor (unscrupulous) tech's can improve their efficiency readout, but testing before the system gets up to normal operating temperature, but doing that can throw all other figures off also.

For the above reasons, there can be a fairly big difference between seasonal efficiency and that measured with the analyser.

John.G

Wearb wrote: »

HE FGA settings on FGA assumes "all" of the latent heat is also recovered from the water vapour. The SE only measures combustion efficiency, but takes gas temperature into account for its final efficiency figure. The HE also takes temperature into account also.
Poor (unscrupulous) tech's can improve their efficiency readout, but testing before the system gets up to normal operating temperature, but doing that can throw all other figures off also.

For the above reasons, there can be a fairly big difference between seasonal efficiency and that measured with the analyser.

Thanks Wearb, so would it be true to say that if a HE Gas Boiler was running in non condensing mode with say 100C flue gas temperature that the displayed efficiency would be ~ 96%? which is the assumed latent heat of approx 8% for gas plus the ~ 88% efficiency if it was based on the gross heating value of the fuel.

Wearb

John.G wrote: »

Thanks Wearb, so would it be true to say that if a HE Gas Boiler was running in non condensing mode with say 100C flue gas temperature that the displayed efficiency would be ~ 96%? which is the assumed latent heat of approx 8% for gas plus the ~ 88% efficiency if it was based on the gross heating value of the fuel.

Assuming that you have done the figures properly (I don’t do gas) I think your calculation results and method seem correct.