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Forum discussion

NC-2009 EAp2:Minimum Energy Performance

Fan Power Calculation

Let's say we have a HVAC supply fan of a baseline which is calculated to be 3,000 cfm and the baseline fan power at 0.001 kW/cfm.This makes the fan power to be 3 kW. What if the same space has a wall mounted exhuast fan of 300 cfm. According to section G.3.1.2.9, do we have to alocate the allowance of 3kW to both supply fan of 3000 cfm and exhaust fan 300 cfm? This will make to average kW/cfm to be 3/3300 =0.00091 kW/cfm to be specified for both fans. Am I correct? Thanks

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Marcus Sheffer
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7group / Energy Opportunities
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Mon, 07/14/2014 - 13:38

The Section G3.1.2.9 calculations includes all of the fan power for that system (supply, exhaust, return and relief). You do not add them as the calculation is primarily based on the supply air.

Mon, 07/14/2014 - 13:53

So, in the baseline, there would be supply fan based on G.1.2.9 which has full kW from the calculation. the exhaust fan will have the flow (to maintahn same OA rate with the proposed) but the kW/cfm will be set to 0. Am I correct?
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Marcus Sheffer
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Mon, 07/14/2014 - 14:02

Once you calculate the total baseline fan power you can allocate it among the fans in the system. The best way to do this is proportional to the Proposed system but there is no requirement to do so.

Mon, 07/14/2014 - 14:59

Thanks, Marcus if we do the proportional fan power of the baseline. Then we just use the "supply" fan power (exclude exhuast fan power) to calculated adjusted compressor EER (system 3-4). Am I right?
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Marcus Sheffer
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Mon, 07/14/2014 - 15:49

The conservative approach would be to use the total G3.1.2.9 fan power to adjust the unit EER. If you want to use the supply fan power only based on your allocation of the fan power then you should be prepared to defend the allocation of the fan power. For example, if there is a corresponding exhaust fan in the space as you describe above and you have proportionally allocated the fan power you would be able to justify that the exhaust should be excluded from the EIR calculation.

Mon, 07/14/2014 - 15:58

Could you point me to another method besides G3.1.2.9 fan power to adjust the unit EER? or which section to read.
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Marcus Sheffer
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LEEDuser Expert
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Mon, 07/14/2014 - 16:16

I did not look to see if it would help but the next reference to check for clarification would be the User's Manual.

Tue, 07/15/2014 - 13:32

Thanks, Marcus. By the way, if we have a kitchen heavy duty hood of a restaurant. Can we exclude fan power of the baseline using exception 6.5.3.1.1b? (mentioned if current Section 1.4 table not have to report in fan power table). Hood fan power calucation method for the baseline was mentioned in 6.5.3.1.1 as well. It seems unfair if a total allowance of baseline fan power inculded kitchen hood fan. Such fan usually consume a lot of energy in design/proposed case.

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