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NC-2009 EAp2:Minimum Energy Performance

Minimum/Mandatory Requirements for, VAV TU?

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Jorge Torres-Coto
Building Systems Commissioning Engineer
Empirical Engineering, LLC
LEEDuser Basic Member
14 thumbs up

I have a Tenant Improvement that has VAV terminal units connected to an existing VAV AHU. The contractor and owner decided to save money and utilize stand alone control. Though the problem with their solution is that the thermostats only have ON-OFF function and cannot modulate between dead band and full cooling (since the project does not have re-heat). I have looked and cannot find much, aside from ASHRAE 90.1-2007 Addendum h, that states that a VAV TU has to modulate. I do not think I am wrong in assuming this control logic, since the opposite is both uncomfortable for occupants and a waste of energy for the tenant. IS IT OBLIGATED THAT THE VAV MODULATE IN LIEU OF ON-OFF (OPEN-CLOSE)? Thanks

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

Thu, 07/11/2013 - 14:35

Check out Mandatory Section 6.4.3.1.2 which requires a dead band. Does that help?
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Jorge Torres-Coto
Building Systems Commissioning Engineer
Empirical Engineering, LLC
LEEDuser Basic Member
14 thumbs up

Thu, 07/11/2013 - 19:06

Thanks Marcus The deadband covers the minimum, and that is clear and also a requirement to meet ASHRAE 62.1. Though I am not clear how the dead band relates to modulating from 0%-100% and anywhere in between in lieu of ON-OFF. As the system works now, when it is satisfied it goes to minimum. A regular VAV would hover around the current position it is at (X% open)
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Thu, 07/11/2013 - 19:08

I don't see anything in the mandatory provisions. Prescriptively there is 6.5.3.2 but that does not appear to address your issue. If there is a requirement in Addendum h then it is logical to assume that the issue is not addressed in the standard.
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Jorge Torres-Coto
Building Systems Commissioning Engineer
Empirical Engineering, LLC
LEEDuser Basic Member
14 thumbs up

Thu, 07/11/2013 - 19:58

Thanks Marcus I was in the wrong LEED Guide (my project is GID&C), thus since on this occasion they are not attempting performance compliance, they have to achieve the prescriptive requirements also. Though it is still strange that it is not required for a VAV to modulate for an office environment. I can understand a shut-off VAV for non-occupied spaces. Thanks

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