Even though ASHRAE 90.1-2007 has been out for a few years already, I haven’t really dug into it as much as I should have. Mainly because the LEED® projects I work on are listed under version 2.2, which references 90.1-2004. Since the new LEED v3 rating system will reference 90.1-2007, I thought it would be a good opportunity to compare some of the differences in both the 2004 and 2007 versions. Although there are many revisions between the standards, one change I wanted to point out in this article concerns ventilation control.
Outside air (OA) is a very important component when it comes to energy use, especially in larger buildings where occupancy densities change throughout the day. If at any given time the system is bringing in more OA than needed, the system will use more energy to cool or heat the excess OA (depending on season). Standard 90.1-2004 only required systems with 3000+ CFM and average occupancy density of 10 ft2 per person to have Demand control ventilation (DCV). In 90.1-2007, DCV is required for spaces larger than 500ft2, having a design occupancy density of 25 ft2 per person and having either:
- an air-side economizer
- modulating OA damper, or
- systems with 3000+ OA
The big thing to note is the occupancy density. Basically, DCV is now required for systems that have a lower occupant density than it previously did. Comparing occupant densities from ASHRAE 62.1-2007, spaces such as malls, museums, and other spaces are required to have DCV if the above criteria apply.
For more information refer to ASHRAE standards 90.1-2004, 90.1-2007 and 62.1-2007.
