Biomass Boiler + CHP = 2010 headache?

[Complex Potential]

Hi guys

We've just taken on a design from another consultant who only carried out a 2006 Part L analysis. It has a biomass boiler and CHP which is causing me problems because the two appear to be messing each other up under 2010.

I'm sure this design was fine under 2006 when the notional building stuck with using natural gas but, now that the 2010 notional building matches the actual building's biomass carbon factor, the addition of a CHP unit is a massive problem. Here's why:

The system heat source is a biomass fuel boiler in conjunction with gas CHP (boiler rank 1 after the CHP). Of course, the notional building switches to the biomass carbon factor and its heating emissions drop to almost zero. Meanwhile, my actual building is using a big chunk of CHP which is on a gas carbon factor. Since the generated power is woefully inadaquate to make up for the difference in carbon factors we are in the daft situation of getting more favourable results if we remove the biomass boiler completely OR remove the CHP.

In fact, we even get better results if we get rid of the CHP and the Biomass entirely rather than having them both together.

This appears to be a rather toxic combination under 2010. Thoughts, ideas?

CP

[JohnLloyd]

You should probably model this as a Bivalent system. You'll need to do some additional calculations in Excel to work out roughly the percentage of annual heat you expect to be delivered by the biomass.

The Notional Building should then effectively use a gas boiler for a fair chunk of it's heat supply and you should find your CHP starts giving you a benefit.

[Complex Potential]

Thanks John

I was thinking along similar lines but I concluded I'd have to input the resulting carbon factor as a disctrict figure (causing the notional building to match it) because there appears to be no CHP option on the Bivalent side.

Am I missing something?

CP

[JohnLloyd]

Set up the bivalent system for your gas boiler and biomass boiler, and then tick the box for "Is this heat source used in conjunction with CHP?" on the Heating tab of the ApacheSystem.

That should work.