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CS-2009 EAp2:Minimum Energy Performance

Exhaust air energy recovery in the baseline

Profile picture for user verona
FABIO VIERO
Head of Sustainability
Manens S.p.A.
LEEDuser Premium Member
16 thumbs up

Hello all, my question is: when do i have to consider the exhaust air energy recovery in the baseline building’s AHU? The 90.1 User’s manual reports that exhaust air Energy recovery is required for fan system that are larger than 5000 cfm and which also require a significant amount of outdoor air (70% or more); but what does this 70% refers to? To the proposed building or to the baseline building? And in the last case, how can I value this 70%? In the summer design day, winter design day or other? Thank you very much. Have a good day!

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Profile picture for user sheffer
Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Tue, 04/24/2012 - 16:30

Hey Fabio, The trigger for the Baseline energy recovery requirement is the Proposed OA. Since the OA must be identical in both models (in the absence of demand controlled ventilation), when you apply the Proposed OA to the Baseline system if the OA% in the Baseline is over 70% of the Baseline cfm then the Baseline system must have energy recovery. So any Baseline system with an OA requirement below 3,500 cfm never needs energy recovery. OA is typically sized on primary airflow so in most cases the summer design day.
Profile picture for user verona
FABIO VIERO
Head of Sustainability
Manens S.p.A.
LEEDuser Premium Member
16 thumbs up

Thu, 04/26/2012 - 10:15

Hi Marcus! Don't you think that the worst condition of this 70% is the winter design day? The OA flow rate is constant during all the year but in this situation the total air is less than the summer condition (i have a VAV system). Anyway, i can calculate both the situations and only if both were less than 70% i could not consider the heat recovery. Do you agree? Thanks a lot. Have a good day!
Profile picture for user sheffer
Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Thu, 04/26/2012 - 13:33

Whichever one, summer or winter, gives you your primary airflow peak should be used. Over here it is usually the summer design day. Agreed, if the peak is less than 70% then no heat recovery in the baseline.

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