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CS-v4 EAp2:Minimum energy performance

ASHRAE 90.1-2010 - Unmet hours

Hi all,

I’m modeling for a project under LEED CS v4 according to ASHRAE 90.1-2010.

I know that unmet hours shall not exceed 300 .

In LEED 2009 in accordance to ASHRAE 90.1-2007 the Unmet load hours for the Proposed Design shall not differ from unmet load hours for the Baseline Building Design by more than 50 hours.

It is not so clear if now in the new version v4 this rate is canceled and if it is mandatory that the unmet load hours for the Proposed Design shall not exceed the unmet load hours for the Baseline building.

Could you help me?

 

Thanks.

 

Giuseppina Amorusi

LEED AP BD+C

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

Thu, 09/07/2017 - 13:08

The 50 hour difference was removed in 2010. The only requirement is the 300 hour limit for each model.
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LEEDuser Basic Member
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Mon, 03/05/2018 - 04:57

Can we increase the capacities to reduce the unmet hours?    
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Mon, 03/05/2018 - 15:53

It appears that they removed to provision that allowed projects to just increase the system capacity. In our experience there is usually a modeling issue that causes the unmet load hours like a thermostat setting, or airflow under-sizing. So I would double and triple check my modeling inputs. If you can't find the problem as a last resort you might be able to increase the system capacity or try to explain the reasons for the high unmet load hours.

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