The addendum revises the standard's ventilation rate procedure used to determine design ventilation rates. According to David Butler, P.E., committee chair, the procedure now is more straightforward, allowing designers to determine rates and reduce the potential for overventilation in some densely occupied spaces. Furthermore, the standard is now focused on minimum requirements.

In recognition of the fact that air pollutants are generated by building occupant activities and by the building contents, the addendum bases ventilation requirements on the number of people a space is expected to hold, as well as the space's floor area, Butler said. The "additivity" procedure is used to calculate minimum outdoor ventilation requirements for a building ventilation system.

For example, in an office building, the procedure is used to determine the outdoor air requirement for each space type (offices, conference rooms, corridors, etc.), which are in turn used to determine the amount of outdoor air intake required at the air handler.

The existing procedure, issued in 1989, contains a number of requirements that are difficult for designers to comply with and that do not allow designers to explicitly account for occupant density in a space, Butler said.

To make application of the calculation methods easier for users, a spreadsheet, 62n.VRP.xls, was developed. It can be obtained under the SSPC62.1 directory at ftp.ashrae.org. Addendum 62n can be downloaded at no cost via the "Standards Addenda Index" shortcut at www.ashrae.org.

Publication date: 07/05/2004