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NC-2009 EAp2:Minimum Energy Performance

Energy Recovery for Baseline Air Handling Units (LEED 2009)

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Craig Hossfeld
Associate
Whitman, Requardt and Associates, LLP
LEEDuser Basic Member
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My proposed design has multiple AHUs supplied from a dedicated outside air AHU (DOAS) . The DOAS will be over 20,000 cfm and will have energy recovery. The baseline system will be Packaged VAV System 5. Should the baseline system be provided with a DOAS with energy recovery, or is each baseline system considered independant, in which case energy recovery will not be required since each unit will have less than 70 percent OA? Thank you, Craig

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Jean Marais
b.i.g. Bechtold DesignBuilder Expert
LEEDuser Basic Member
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Mon, 02/17/2014 - 09:47

The key is to keep the ODA min amounts the same in both baseline and designcase models. With DOAS the designcase usually dictates the minimum amount of ODA required zone wise. This same requirement falls to the baseline case. The baseline case is not modeled as a DOAS system, but you may find that for some zones there may be little or no recirculation air as the ODA amounts may be far more than the required minimums of ASHRAE 62.1. It does present some trouble. I suggest making a table with the ODA fractions for the zones at design conditions, because if you have a zone that requires little or no ODA, but does require air for conditioning, it may receive too much ODA as the ODA fraction is set at the central AHU ODA mixing damper to accommidate all the connected zone ODA requirements which may be zone volume flow weighted. Like zones should be grouped. You may need to take a closer look at G3.1.1 Exceptions.

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