Greetings, The project I'm modeling has several DOA AHUs. Every AHU has a single CO2 sensor located on the return duct next to the unit. There are however AHUs which are serving several different rooms, but the CO2 sensor is only one on the assembly part of the return duct. Should such units be modeled as DCV. There is another question to this issue. The number of people in the room (occupancy) is defined by the designers and these numbers do not coincide with min ASHRAE 62.1 rates (they are smaller). The OA air flows however, for both Proposed and Baseline are equal. Also the air quantity (cfm/pers & cfm/ft2) is as per ASHRAE 62.1 rates, only the Occupancy Density - not. The question is (in respond to the reviewers remark): How to make Baseline to reflect ASHRAE 62.1 min. rates whereas the OA is already defined by the Proposed and the occupant density do not coincide with ASHRAE 62.1 default values. Your advice on the matter will be highly appreciated. Thanks.

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Thu, 12/04/2014 - 17:00

In the system that serves multiple spaces with a CO2 sensor in one of the returns, you should only model DCV in the space served by the sensor and not in the other spaces. Do not use the ASHRAE default occupancy if you know the actual occupancy. The proposed outside air should be based on the design for all systems, in all cases. The Baseline outside air should be based on the ASHRAE 62,1-2007 calculated outside air from the corresponding system in the proposed if the proposed system has DCV. If it does not have DCV then the baseline is identical to the proposed.

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