Infiltration methods: TM23 or CIBSE Guide A

[Phil OLoughlin]

The introduction of alternatives for defining the infiltration method in VE DSM 2013 is baffeling me a little.
Question, why are we even given a choice?
Since we are, has anyone investigated when one 'helps' over the other please?

[RossThompson87]

Hi Phil,

This is actually mentioned in the NCM modelling guide. It appears various methods are allowed as long as the same approach is taken across the actual, notional and reference buildings.

It seems very odd as I thought the idea was to standardise these calculations so everyone gets the same result!

In terms of which one 'helps' I guess it depends what you are trying to do.

I imagine a low air change rate would give the best EPC rating.

If you have a heating system that is much better than the notional building, then a high air change rate would help emphasise this benefit.

I hope this helps

Ross

[Complex Potential]

Spot on Ross.

I personally don't like the TM23 method simply because the infiltration losses that result seem so tiny.

I'm not sure about whether TM23 gives a better EPC rating though because the reference building would then also switch to the TM23 method.