Integrated Environmental Solutions Ltd
Frequently Asked Question
VE Module: VE Compliance
Why does my CO2 emission rise when I improve my u values?
The increase in BER is due to solar gains being essentially "trapped" in the building by the improved
envelope. Since the solar gain is trapped there is more of a heat build up in the model zones, so this
results in the cooling system using more energy. Although the heating system is using less energy in
winter due to the improved u-values, the additional cooling energy used in summer out-weighs this
winter saving. So overall the BER goes up. This can be seen below. Figure 1 has an external wall uvalue of 0.35W/m².K and an external glazing u-value of 1.95W/m².K
Figure 1
Figure 2 has an external wall u-value of 0.25W/m².K and an external glazing u-value of 1.2W/m².K
Figure 2
It can be see that the BER is higher in Figure 2 than it is in Figure 1 – despite the Figure 2 model
having significantly improved construction materials.
If the annual heating & cooling loads for both simulations are analysed it can be seen that the
improvement in construction u-values result in a decrease in annual heating energy, but an increase
in annual cooling energy.
Since the carbon emissions associated with cooling outweigh those carbon savings from the
reduction in annual heating energy – the total BER goes up for the scenario with the improved
uvalues.
Registered in Scotland No. SC151456 | Registered Office - Helix Building, West Of Scotland Science Park, Glasgow G20 0SP
Integrated Environmental Solutions Ltd
Frequently Asked Question
Registered in Scotland No. SC151456 | Registered Office - Helix Building, West Of Scotland Science Park, Glasgow G20 0SP