CHP vs condensing boiler

[elenikalyva]

Hi All,

I would appreciate if you guys can give some light to the following:
As you all know a building can often fail the BRUKL compliance and then pass when CHP plant is added in place of a regular condensing boiler for heating. Can anyone explain why this happens and whether you believe the BER with CHP is correct since CHP plant has a very much lower thermal efficiency than a condensing boiler when producing heat. I do understand that CHP plant is displacing grid electricity but I would like to know how the BER is calculated when using CHP.

Thanks in advance.

Regards,

EK

[RossThompson87]

Hi,

When you add CHP to your model the heating/hot water should get worse. As you say the thermal efficiency of the CHP is often much worse that a boiler.

However you get credit for the electricity generated by the CHP. A deduction is made from the BER to account for this.

Basically the software does the following:

BER reduction from CHP electricity (kgco2/m2.annum) = electricity generated in (kWh/year) x grid displaced electricity fuel factor / floor area


I hope this helps

Ross

[elenikalyva]

Hi Ross,

Thanks for your quick reply. Can you advise from where I can view the electricity generated by the CHP?

Also, from carbon emission factors both on-site and off-site generated electricity are very similar (current 2013 factors are the same) and hence the question how can the CHP provide this level of improvement?

Thanks,

Eleni

[RossThompson87]

Hi,

You should be able to get a graph of the CHP generated electricity in Vista. If you look under the energy section.

The improvement is accounted for on the basis that the CHP generated electricity would have had to have come from the grid if the CHP wasn't there. So you get a benefit for not using grid electricity if that makes sense.


Ross

[elenikalyva]

Hi Ross,
Thanks again for your reply. I do understand the benefit of not using grid electricity, but I do not understand how the carbon savings with CHP are so significant since the carbon emission factors of grid supplied and grid displaced electricity are very close and in the case of 2013 Regs the same.
Eleni