Ventilation for Acceptable Indoor Air Quality
This article is the second installment of our Review of ANSI/ASHRAE Standard 62.1-2004. The first installment reviewed changes in the use of carbon dioxide as an indicator of indoor air quality.
The ANSI/ASHRAE Standard 62.1-2004 Ventilation for Acceptable Indoor Air Quality incorporates a number of significant changes to the previous standard – 62-2001. This standard incorporates 17 addenda that delete and/or replace many of the sections of the previous standard. In fact, there is relatively little that has not been changed. These changes are detailed below.
- The Standard numerical designation was changed from 62 to 62.1 because a separate new standard, “62.2 – Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings”, was developed.
- Many sections of the standard have been rewritten into “mandatory and enforceable language”. This allows for code enforcement agencies to incorporate provisions of the standard and then be able to fully enforce the requirements. There are a lot less “should”s and a lot more “shall”s.
- Because of the enforceability considerations, the standard is mainly applicable to new construction. But it may also be applicable to building additions, HVAC system replacement, “substantial alterations” to the building, or a change in the building’s use. These additional applications may depend upon the building codes that adopt the standard. Older buildings should be in compliance with the version of the standard in effect at the time the building was designed and built.
- Definitions have been added for “breathing zone”, “cognizant authority”, “industrial space”, and “zone”. The new definition for “breathing zone is essentially the same as the definition for “occupied zone” from the previous standard. The use of this term may cause some confusion for those familiar with Industrial Hygiene terminology. A “Breathing Zone” in Industrial Hygiene terminology refers to the area that one takes a personal air sample in for industrial hygiene air sampling. It is the area from which the employee draws air and has been defined as being as close as possible to the nose and mouth and a hemisphere forward of the shoulders with a radius of 6 to 9 inches. The definition of “breathing zone” from the ASHRAE standard is “the region within an occupied space between planes 3 and 72 in (75 and 1800 mm) above the floor and more than 2 ft (600 mm) from the walls or fixed air-conditioning equipment”.
Section 4 – Classification was deleted in its entirety and was replaced with a new Section 4 – Outdoor Air Quality. The outdoor air quality provisions of the previous version of the standard were in Section 6. The revised outdoor air quality provisions in Section 4 only include requirements to investigate and document outdoor air quality. The requirements for treating the outdoor air were revised and remain in Section 6. (Covered in Part 3 of this article)
Section 5—Systems and Equipment has undergone extensive revision. Paragraph 5-2, concerning Ventilation Air Distribution, was rewritten. Paragraphs 5.3, 5.4, and 5.6 through 5-11 were replaced. The new paragraph 5.3 deals with exhaust duct location, and the new paragraph 5.4 discusses ventilation system controls. The new paragraph 5.6 is an important addition concerning the location of outdoor air intakes. A new Table 5-1 has been included that specifies minimum air intake separation distances from such things as vents, chimneys, cooling towers, garbage storage, noxious or dangerous exhausts and other sources of hazards or odors. New paragraphs 5.6.2 through 5.6.5 deal with rain entrainment and intrusion, snow entrainment, and bird screens, respectively.
Paragraph 5.6 from the 2001 version, dealing with the use of local exhaust to capture contaminants was rewritten and renumbered as paragraph 5.7. Likewise, paragraphs 5.7 – Combustion Air, and 5.8 – Particulate Matter Removal, are now paragraphs 5.8 and 5.9. Figure 2 – Characteristics of particles and particle dispersoids, has been removed.
Paragraphs 5.9, 5.10, and 5.11 from the 2001 standard were deleted and replaced. Paragraphs 5.10 and 5.11 from the 2001 standard discussed humidity and moisture intrusion and their relationship to microbial growth. The oft-quoted range of 30 to 60% humidity is contained in paragraph 5.10 of the 2001 standard. The new paragraph 5.10 is titled Dehumidification Systems. It discusses the design considerations as they relate to humidity and does not mention microbial growth. It sets an upper limit of 65% humidity for occupied spaces. Although the previous paragraph 5.11 mentions drain pans, the new paragraph 5.11 – Drain Pans, provides much more detailed and specific design requirements. Once again, there is no mention of microbial growth.
New Section 5 paragraphs
Paragraphs 5.12 through 5.17 are new. Many of their provisions were contained in paragraphs that were deleted from the previous standard. Once again, these new paragraphs contain detailed and specific design information.
- Paragraph 5.12 – Finned-Tube Coils and Heat Exchangers, requires drain pans for condensate producing coils and heat exchangers. It also has a sub-paragraph – Finned-Tube Coil Selection for Cleaning that sets requirements for the design of coils to allow for cleaning.
- Paragraph 5.13 – Humidifiers and Water-Spray Systems, deals with water quality in these systems and obstructions within ductwork downstream of these systems
- Paragraph 5.14 – Access for Inspection, Cleaning, and Maintenance, is an important addition in that it provides detailed and explicit requirements for access to ventilation equipment and the air distribution system. Often, older systems have limited or no access to the interiors of equipment or ductwork.
- Paragraph 5.15 – Building Envelope and Interior Surfaces, provides requirements for preventing moisture intrusion into the building and condensation within the building.
- Paragraph 5.16 – Buildings with Attached Parking Garages, requires building design features to prevent vehicular exhaust from entering the building.
- Paragraph 5.17 – Air Classification and Recirculation, is a significant addition that requires that air within individual building spaces be classified into one of four classes (Class 1-4). The higher the potential for the air in a space to have odors or contaminants, the higher the numberical classification of the space. For example, a break room that is expected to have relatively few odors or contaminants is a Class 1 space, a private toilet would be a Class 2 space, a room for storage of soiled laundry would be a Class 3 space, and a chemical storage room would be a Class 4 space. There are of course exceptions, but the general idea is that you can’t recirculate air from numerically higher class spaces into lower class spaces. You can’t even recirculate Class 4 air back into the space from which it came.