Ev (System Efficiency) for Constant Volume 100% Outdoor Air Syst

Omer, With constant volume systems, Ev still needs to be determined from Table 6-3 in Standard 62.1. The value of Ev will be based on the highest Zp (breathing zone ventilation rate / design supply airflow) value of zones connected to the system. You are correct that with a 100% outside air system, Ev doesn't affect the final result.

Omer, I understand the confusion here. Please refer to 6.2.4 (Equation 6-4) to calculate Vot (assume Ev = 1). You input your actual design OA in the LEED letter template and the template determines whether you're 30% over 62.1 requirements by comparing to the calculated Vot value. You may want to attach a brief narrative describing that you have 100% OA units. It looks like the template could use a check box for 100% OA conditions.

Omer, for this type of system, Ev does not apply. The 100% outside air system simply needs to provide the appropriate breathing zone ventilation rate to each zone. Secondary recirculation applies more to fan-powered VAV box systems.

Hello, we have an issue similar to Omer's and would like to hear Roger's advice. For EQp1, we aren't sure what calculation methodology to use for our design approach. It is a multi-unit residential building, and the ventilation system is exhaust-only. Fans in the kitchens and bathrooms run continuously and exhaust directly to the outdoors, with no recirculation. These fans run in excess of the requirements per the Ventilation Rate Procedure. The review team has asked us to demonstrate specifically how sufficient outdoor air is provided to other living areas, such as the bedrooms and living rooms. Is there an established calculation methodology for this design approach under EQp1? We have reviewed ASHRAE 62.1, but haven't found an answer. Factors such as air distribution effectiveness don't seem to address exhaust-only systems. In summary: how should we calculate the air supplied to each living space (ie bedroom, living room) for an exhaust-only/ infiltration-only system? Thanks in advance.

Kate, this is a great question. You can use an exhaust-only system, but will need to adjust the ventilation effectiveness to account for "induced ventilation." Ez could be 0.8 if induced ventilation (under the main door to the unit, for example) is opposite from the exhaust point. It may be 0.5, if the induction point is near the exhaust point. You want to make sure that the corridors outside the units are provided with sufficient make-up air to maintain an appropriate air balance for the building as a whole. The user's manual provides additional guidance on multi-family residential applications.