Dear all,

We are submitting a LEED project and have a query regarding ASHRAE 90.1 (2004) section G.3.1.2.8 - Design Air flow rates. It states that the baseline building should be modelled with fans serving the 'same functions and sized for the baseline system supply fan air quantity less the minimum outdoor air, or 90% of the supply fan air quantity, whichever is larger.'

We figure there are 3 different ways to interpret this sentence:

1) Model the baseline building with supply fans as normal, plus return fans with either 90% supply or supply minus outside air.

2) Only model supply fans but change the supply flow rate to 90% or supply minus outside air.

3) Does 90% mean supply minus 90% or supply minus 10%?

If someone could provide an example that would be very useful.

How do we incorporate the return fan power when reporting total fan power allowances, i.e. do we subtract return fans from the total?

Thanks in advance

Kat

Katherine Roberts