Oct. 6, 2011: Alternative to ASHRAE Standard 62.1 Ventilation Rate Procedure Proposed
ANSI/ASHRAE Standard 62.1-2010, Ventilation for Acceptable Indoor Air Quality, sets minimum ventilation rates and other requirements for commercial and institutional buildings. 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.
Some users of Standard 62.1 believe that the ventilation rate procedure is “too complicated,” said Roger Hedrick, Standard 62.1 chair. “While the 62.1 committee disagrees with this in most cases — the basics of the VRP are quite straightforward — the committee agrees that application of the multiple-zone recirculating system equations described in Section 6.2.5 and Appendix A can be complex.”
Proposed addendum f, open for public review until Oct. 16, provides an additional default value for Vpz.
“Difficulty determining an appropriate value for Vpz seems to be a frequent issue with users of the multiple space equations,” Hedrick said. “The committee decided that supplying a default value would simplify application. However, the default value is necessarily conservative. In a large number of applications, determining the ‘lowest zone primary airflow value expected at the design condition analyzed’ will result in a value for Vpz that is higher than the default, resulting in a reduced outdoor air intake requirement.”
Other addenda open for public review are:
• Addendum h (open until Oct. 16). Table 6.1 in the standard includes ventilation rates for “Sports arena (play area)” and “Gym, stadium (play area).” Both space types have ventilation rates based on floor area only, with a per person rate of 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. In most cases, the overall ventilation rate for these spaces is expected to decrease, possibly significantly, according to Hedrick.
One concern about allowing CO2-based demand controlled ventilation in these spaces is that the volume per person in these spaces is typically large, which means that CO2 concentration changes will have longer than usual lag times behind occupancy changes, he noted.
• Addendum g (open until Oct. 31). Currently users are directed that for space types that are not listed in Table 6-1 they should select the space type from the table that is most similar to the space being designed. However, some space types are actually ventilated using the exhaust ventilation requirements of Section 6.5 and Table 6-4. This proposed addendum adds language directing the user to select the space type that is most similar to the space in question from either Table 6-1 or 6-4, and to design the ventilation for the space according to Section 6.2 or 6.5, as appropriate
For more information, visit www.ashrae.org/publicreviews.
Publication date: 10/03/2011