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NC-2009 EAp2:Minimum Energy Performance

Fan power credit and packaged vav

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HOUCINE TLEMSANI
Mechanical Designer
MEP Engineering Solutions, Inc
LEEDuser Basic Member
8 thumbs up

I am working on a project where the base line system is a packaged VAV with reheat. ASHRAE 90.1 specify the packaged efficiency as 9.8 EER including the compressor heat rejection and fans. The question I am having is that if we are taking credit for the fan power pressure drops adjustment in the system in accordance with ASHRAE 90.1 are we allowed to change the packaged efficiency by including the fan credit allowance or no?

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Fri, 10/18/2013 - 20:55

It depends on your modeling software. Most of them separate the fan power automatically and you enter the EER as indicated in Table 6.8.1A without making the adjustment yourself.
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HOUCINE TLEMSANI
Mechanical Designer
MEP Engineering Solutions, Inc
LEEDuser Basic Member
8 thumbs up

Fri, 10/25/2013 - 19:36

thank's Marcus the trace 700 software does automatically separate the different components of the plant when packaged EER is used but will not add the fan power associated with the pressure drop credit to the total plant. OK assuming a 50 ton plant with a 9.8 EER the total plant allowed power is 61.22 KW. the energy break out of the plant 5 kw heat rejection. 25 KW compressor and 20 KW fan that is just assumptions. 90.1 pressure drop credit is allowing an extra 5 KW energy to be applied to the fan making the total power of the plant increase to 66.22 KW. resulting in an EER 9.646 is that correct or do you see any problem.
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Fri, 11/01/2013 - 16:21

Yes we do. The total plant power should not be increasing. If the fan power increases due to the pressure drop adjustment, the heat rejection and compressor power would be reduced to accommodate the extra supply fan power. You are separating the fans from the rest of the plant so you don't adjust the EER. You reduce the total by subtracting out the fan power.

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