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NC-2009 EAp2:Minimum Energy Performance

Designed case AHU fanpower

Hello, Do we have to calculate design fan power from the formula HP=CFMx Total static pressure/6356 x fan efficiency or consider the motor fan power provided in the technical AHU datasheet in the designed case? We have currently used the design fan power formula and done the first submission. The reviewer has commented saying we have modeled with a lesser fan power compared to the technical submittal. So do we have to revise the model with Motor KW. Please clarify.

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Jean Marais
b.i.g. Bechtold DesignBuilder Expert
LEEDuser Basic Member
581 thumbs up

Mon, 09/19/2016 - 07:14

For the Proposed Model: Motor name plate (rated power) power is not to be used. The motor is always large enough to cover start up requirements, but for a simulation you need the energy of a running system. The AHU data sheet should profide a SFP for the entire machine (the internal pressure drops from coils, filters, etc. inside the machine itself ) at the design running condition + the connected ductwork system (external) and to move the air. The SPF includes all efficiency reduction factors. Just make sure that the AHU manufacturer has specified the equipment with the correct design volume flow and the actual hydrolic pressure loss from the outdoor, supply, extract and return ductwork.
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Mon, 09/19/2016 - 13:52

Proposed is modeled as designed based on the BHP of the fan motor. Show the reviewer what you have modeled and how it aligns with the design.

Tue, 09/20/2016 - 05:22

Thank you for the replies. Suppose a AHU has a Specific fan power of 4.7 KW and motor KW of 5.5. Then i understand we have to use 4.7 KW. Am i correct?
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Tue, 09/20/2016 - 12:47

yes

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