The demand weighted fuel factor for the Bivalent System is higher than when calculated by hand using the forumula from paragraph 53 of the 2010 NCM modelling guide, why is this?

The equations used within the VE are different to those documented in the NCM modelling guide however you should find that they arrive at the same result. In a DSM compliance calculation we derive two values; a weighted efficiency and a weighted CO2 factor. The NCM modelling guide however has an equation that has a conversion factor that includes both efficiency and fuel factor.

The calculated weighted efficiency is calculated as:-

where

*HEff = Weighted Efficiency
Ln = Fraction of Load supplied by system n
Effn = Efficiency of System n*

The bivalent carbon emission factor is calculated as:-

where

*CEFBivalent *= Weighted CO2 Emission Factor

*CEFn *= CO2 Emission Factor for system Fuel

*HEff *= Weighted Efficiency

*Ln *= Fraction of Load supplied by system n

*Effn *= Efficiency of System n

The demand weighted fuel factor given in the NCM modelling Guide accounts for both Efficiency and CO2 factors. It would therefore be directly applied to any heating load whereas with the approach taken in the DSM route the load would first be divided by the weighted efficiency to determine Energy then multiplied by the weighted fuel factor to determine CO2.