ASHRAE+62.1-2022+(1) - Page 072

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L7. VENTILATION FOR EXISTING BUILDINGS

This section provides guidance for determining compliance with the standard for existing buildings. Many sustainability and energy programs require that ventilation rates for systems comply with ASHRAE Standard 62.1; however, the methods for determining compliance vary widely. This appendix is intended to provide a standardized approach and clear guidance for practitioners who work with existing buildings.

A ventilation system in an existing building may be deemed to comply with the current version of Standard 62.1 if the system complies with all the sections in this appendix. The building may be deemed to comply if all systems in the building comply with all the sections in this appendix (Sections L7.1, Section L7.2, and L7.3).

L7.1 Filtration. Filtration complies with Sections L7.1.1 and Section L7.1.2.

L7.1.1 Filtration Before Coils. Filtration complies with Section 5.5, which requires a minimum of MERV-8 or ISO ePM10 filtration upstream of cooling coils serving occupied spaces.

L7.1.2 Filtration of Outdoor Air. Filtration complies with Section 6.1.4, which requires treating outdoor air with appropriate filters or air cleaners if local air quality conditions do not meet national air quality standards for PM10, PM2.5, ozone, or other outdoor contaminants.

L7.2 Outdoor Airflow. The following process may be used to determine if outdoor airflow rates comply with the VRP of the current standard. Occupied areas may be determined by measurement, dimensioned floor plans, or from the building manager’s data. Occupancy categories should reflect how spaces are currently used, which may differ from the original design intent. Check design criteria and assumptions documented according to Section 6.6, if available.

L7.2.1 Measure System Outdoor Airflow. Measure system outdoor airflow. Measurements may be made directly or by installed flow measurement devices in the system that are calibrated. This rate is Votmeasured .

L7.2.2 Determine System Type and Design Outdoor Airflow. Determine the system type and then follow the guidance in the appropriate section to determine the design outdoor airflow, Votdesign .

L7.2.2.1 Single Zone Systems. Determine Votdesign using Section 6.2.2. Section 6.2.2 provides Equation 6-3, which sets the system outdoor air intake flow equal to the zone outdoor airflow. Zone outdoor airflows are calculated in Equation 6-2 using the zone air distribution effectiveness ( Ez ) listed in Table 6-4.

L7.2.2.2 100% Outdoor Air Systems. Determine Votdesign using Section 6.2.3. Section 6.2.3 provides Equation 6-4, which sums all zone outdoor airflow requirements to determine the system outdoor airflow requirement. Zone outdoor airflows are calculated in Equation 6-2 using the zone air distribution effectiveness ( Ez ) listed in Table 6-4.

L7.2.2.3 Multiple Zone Recirculating Systems. Determine Votdesign using any process listed in this section. Calculations are ordered from simplest to most complex. The simpler methods typically result in more conservative (higher) ventilation airflows.

L7.2.2.3.1 Appendix G. Determine Votdesign using Informative Appendix G, which provides a table of minimum outdoor and primary airflow rates for specified occupancy categories in existing buildings: some educational facilities, conference rooms, corridors, office spaces, and libraries.

L7.2.2.3.2 Simplified Procedure. Determine Votdesign using Section 6.2.4 and the Simplified Procedure in Section 6.2.4.3, which provides a simplified method to determine system ventilation efficiency ( Ev ) based on occupant distribution. System ventilation efficiency values can vary from 0.22 to 0.75.

L7.2.2.3.3 Alternative Procedure. Determine Votdesign using Section 6.2.4 and the Alternative Procedure in Normative Appendix A, which provides credit for secondary recirculation but requires detailed system and occupancy information at the zone level. The system ventilation efficiency is determined by the ventilation efficiency of the “critical zone.” The alternative procedure provides credit for secondary recirculation.

L7.2.3 Determine Outdoor Airflow Compliance. If Votmeasured - Votdesign, the system complies with the outdoor airflow requirements of the VRP.

L7.3 Controls. Confirm that ventilation system controls comply with requirements of Section 5.18, which requires that minimum ventilation airflows be maintained under all load conditions through manual or automatic controls.

70 ANSI/ASHRAE Standard 62.1-2022