The ventilation rate procedure provides a prescriptive method for determining minimum ventilation requirements. It accounts for pollutant sources from both the building and its occupants, and allows the designer to account for the efficiency of different ventilation systems when delivering outdoor air to the breathing zone.
Proposed addendum f was first released for public comment in September 2011 after some users of Standard 62.1 indicated the ventilation rate procedure was “too complicated,” according to Standard 62.1 chair Roger Hedrick. He said the 62.1 committee agreed that application of the multiple-zone recirculating system equations described in Section 6.2.5 and Appendix A can be complex.
“When designing multiple zone recirculating ventilation systems, Table 6-3 provides a default value of Ventilation Efficiency (Ev) based on the largest value of the zone primary (Zp) outdoor air fraction, for all the zones served by the system,” he said. “However, if Max (Zp) exceeds 0.55, then Appendix A must be used to design the system outdoor airflow. Addendum f attempts to simplify the design process by providing a simplified default approach for cases with Max (Zp) greater than 0.55.”
The earlier review draft set the default value of the zone primary outdoor air fraction based on a default minimum zone primary airflow set as 30 percent of the zone design primary airflow.
“The public review comments pointed out that this formulation did not work mathematically under certain conditions,” Hedrick said. “This new public review version instead simply allows Ev to be set to 0.6, unless a higher value is provided by Table 6-3 or by using Appendix A. Use of a relatively low value of Ev will result in higher outdoor airflow rates, but using the default will simplify the system design process.”
Also open for review is addendum i, which would add limits for low humidity. Recent studies have shown that excessively low humidity may result in unacceptable indoor air quality. The Standard 62.1 committee is interested in the appropriateness of the relative humidity limit and the climate zones where the requirement applies. The addendum is open for an advisory public review, meaning comments received allow for constructive input and need not be resolved or formally acted on by the project committee.
In addition to addenda f and i, three more addenda are open for public review until April 22. They are:
• Addendum h – Table 6-1, includes ventilation rates for “Sports arena (play area)” and “Gym, stadium (play area).” Both space types have ventilation rates based on floor area only, the per person rate is zero. Users of the standard have expressed interest in applying demand controlled ventilation to these space types, which is effectively prohibited by the lack of a per person component to the ventilation rate. This proposed addendum replaces both of these space types with “Gym, Sports Arena (play area)”, with Rp = 20 cfm/person and Ra = 0.06 cfm/ft2 and assigns this new space type with an air class of 2 rather than class 1 from the first publication public review version.
• Addendum k adds an exception to the recirculation limits on Class 4 exhaust airstreams from laboratory hoods which would allow use of heat wheel energy recovery in some cases. The exception defines several criteria which the airstream must meet before such heat recovery can be used, and the heat recovery system must limit recirculation airflow to less than 0.5 percent of the outdoor air intake flow.
• Addendum l adds a refrigerated warehouse space type to Table 6-1, providing revised ventilation rates for these spaces. These rates include a “People Outdoor Air Rate, Rp” which will require ventilation during periods of expected occupancy, but do not include an “Area Outdoor Air Rate, Ra” which will allow the ventilation rate to be zero for refrigerated warehouses with no occupants.
Also, addendum j is open for public review until May 7. The proposed addendum would add requirements to the Indoor Air Quality Procedure (IAQP) for determining minimum ventilation rates which require consideration of the combined effects of multiple contaminants of concern on individual organ systems. This “additive” effect is already implicit in the Ventilation Rate Procedure. This proposed change is intended to improve the IAQP by requiring consideration of these additive effects that are well established in the literature for many organ systems, according to Hedrick.
For more information, visit www.ashrae.org/publicreviews.
Publication date: 04/09/2012