A proposed building is designed which the minimum flow rate on the VAV box is the minimum outside air ventilation rate. Based on the Ventilation Rate Procedure (ASHRAE 62.1), the System Ventilation Efficiency is 100%. Most thermal zones are controlled with Demand Controlled Ventilation which requires the baseline building shall be modeled to minimum outside air ventilation rate (G3.1.2.6). However, the VAV Minimum Flow Set Points (G3.1.3.13) sets the minimum flow rate to 0.4 cfm/ft2. Based on the Ventilation Rate Procedure, the System Ventilation Efficiency is 50% for the baseline model. The baseline minimum outside flow rate is double of the proposed minimum outside flow rate. Have I followed the rules of appendix G? Please send your comments.

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Wed, 06/25/2014 - 15:16

From Tyler, one of the engineers in my office - It looks like they’re using ASHRAE 90.1-2010 but are trying to recalculate the ASHRAE 62.1 minimum outside air requirement for the Baseline system. Section G3.1.2.6 of ASHRAE 90.1-2010 requires the Baseline outside air to be modeled using the minimum required ventilation rates as calculated for the Proposed systems in all cases, not only when demand controlled ventilation is modeled in the Proposed building. The only slight exception is (b), which allows the Baseline outside airflow to be recalculated using an Ez of 1.0 if the Ez of the Proposed design is >1.0, but even in this case the ventilation requirement is still based on the Proposed systems, not the Baseline.

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