The 2004 version of ASHRAE Standard 62.1 Ventilation for Acceptable Indoor Air Quality will soon be available. This sometimes controversial and closely watched standard, which sets minimum ventilation rates and other requirements for commercial and institutional buildings, will be of interest to many different entities in the HVAC industry. The latest version will contain all the addenda that have been approved to date and will take the place of the previous standard, which was published in 2001.

The goal throughout the revision process of Standard 62 has been to update the standard based on more recent information and to convert the 1989 standard into mandatory and enforceable language. This has been difficult at times, as some have pushed to make the standard more strict while others have argued it should contain the minimum requirements in order to be adopted by code bodies.

As can be expected, 62.1-2004 contains some significant changes from the previous version, including 17 new addenda. The major modifications involve changes to the ventilation rate procedure, changes in wording concerning environmental tobacco smoke, changes to requirements related to indoor relative humidity, and new outdoor air assessment and cleaning requirements.

New Ventilation Rates

One of the more controversial changes made to the standard concerns new prescribed ventilation rates, which are described in addendum 62n. Historically, the standard included a cfm/person requirement for a number of different space types, but the revised standard takes into account the fact that air pollutants are generated by building occupant activities and by the building contents. Therefore, the addendum bases ventilation requirements on the number of people a space is expected to hold, as well as the space's floor area.

"Engineers now need to calculate an outside air flow rate at the zone level for the people and their activities as well as for the building and the furnishings and then add them together," said Dennis Stanke, staff applications engineer, Trane Company (LaCrosse, WI) and vice-chairperson for SSPC62.1, the committee responsible for ASHRAE Standard 62-2001.

The procedure in addendum 62n specifies ventilation rates that can be measured for compliance verification and allows designers to determine appropriate rates and reduce the potential for overventilation in some densely occupied spaces. For example, in an office building, the procedure is used to determine the outdoor air requirement for each space type (e.g., offices, conference rooms, corridors), which is in turn used to determine the amount of outdoor air intake required at the air handler.

In the previous version of the standard, engineers were supposed to perform an efficiency-related calculation for multiple zone systems. However, this was often confusing because it was unclear as to which numbers needed to be plugged into the equation. With 62n, the procedure is spelled out much more clearly, noted Stanke, so people will better understand how to calculate the outdoor air intake rate. (To make multiple space ventilation calculations easier for users, a spreadsheet, 62n.VRP.xls, was developed and can be obtained under the SSPC62.1 directory at

This addendum was controversial for several reasons, according to Larry Schoen, P.E. of Schoen Engineering Inc. (Columbia, MD), who chaired one of the SSPC62.1 subcommittees. "Some of the people from the building products and chemical products industries felt that calling something an area rate was implying that their products were polluting the indoors. The standard said nothing of the sort, but they were concerned about that implication," he said.

Others were concerned about the addendum's complexity. However, Schoen said that the automated load calculation programs that are readily available today make it easy to perform the necessary computations.

There were also many different viewpoints concerning just how much air is needed in a space. Some believe that higher rates mean better air quality, but others wanted lower ventilation rates because of the outdoor air conditioning penalty associated with higher rates. In the end, it was decided that being a code-minimum document, the standard had to find rates somewhere between these two factions. (Addendum 62n can be downloaded for free via the "standards addenda index" shortcut on

While addendum 62n was more high profile, addendum 62y was also important for ventilation, because it adds an air classification table with respect to contaminants and odors. "We added that provision so that some of the makeup air for exhaust for toilets, for example, can come from areas that have what we call cleaner air," said David Butler, P.E., Engineering Resource Group Inc. (Jackson, MS) and chairperson for SSPC62.1

Butler added that he's also happy to see addendum 62a included, since this gives consulting engineers specific requirements for outdoor air intake locations with respect to contaminant sources. "That, to me, is a small thing compared to addendum 62n, but from a practicing engineer's standpoint, it's very important," he said.

Environmental Tobacco Smoke

It can be expected that anything concerning environmental tobacco smoke (ETS) is going to be controversial, and that certainly holds true for Standard 62.1. Some may remember that the prescribed rates in the ventilation table used to note that the rates would accommodate a "moderate" amount of smoking. That all changed in 1992 when EPA classified ETS as a Class A carcinogen, meaning there was no known safe minimum concentration of ETS.

Without a target concentration level, ASHRAE could not specify how much ventilation is required in an area to make it safe for humans to breathe. While the note concerning the moderate amount of smoking was removed from the table several years ago, addendum 62o clearly stated that the prescribed rates in the table apply only to spaces that do not contain environmental tobacco smoke. A similar note is included in the table of rates in addendum 62n.

If a space does allow smoking, a provision states that extra ventilation is required, but ASHRAE doesn't specify how much more ventilation is required. "There's a good reason for that," said Stanke, "Because we don't know how much more is needed. Advocates of human health would say that a space has to be like a wind tunnel if you're going to have enough ventilation to make it safe. We knew that ventilation had to increase, but we weren't interested in putting those really high rates, since nobody really knows how high the rates have to be, anyway. No cognizant authority has set a target ETS concentration."

The tobacco and hospitality industries objected, because they believe that the existing rates solve most ETS issues, and they don't necessarily want to increase ventilation rates. Another addendum (62g) will further address ETS and is in the works for a future revision of the standard. This addendum is expected to require classification, signage, and separation for areas where ETS is present.

Butler hopes that 62g will be finished soon, nothing that the fifth independent substantive comment review took place last spring. "We hope to have the board act on this addendum at our ASHRAE Winter Meeting in Orlando," he said.

Schoen thinks it was a good idea to state that the ventilation rates apply only to non-smoking areas, because acceptable indoor air has to meet two criteria: health and comfort. "There is no known way to meet the health criterion, and there is evidence that ventilation will never do it," said Schoen. "The real engineering solution would be source capture - to put the smoker under a hood, but that's not practical."

Relative Humidity

There's no doubt that excessive moisture in buildings can lead to microbial growth. Previously, Standard 62 recommended that indoor relative humidity be maintained between 30% and 60%. In the new standard, thanks to addendum 62x, there will be no lower limit because there is no evidence that relative humidity is a health issue.

"We didn't feel there was enough scientific literature that said you're healthier if it's not too dry in the space," said Stanke. "But there is an upper limit of sorts at 65%. The standard doesn't say your system must be designed to ensure that the relative humidity never gets above 65%. Instead, it says your system has to be designed such that at a specific outdoor condition, which is the design dewpoint condition, your system design has to result in space relative humidity that's below 65%."

The revised standard contains a test point for humidity control, rather than an operative limit, because there are transient conditions such as a foggy morning or a rainy day, where a system might in fact result in conditions higher than 65% rh for some period of time. An operative limit for relative humidity would have forced many people to use humidity sensors, and it was believed that wasn't necessary for a minimum code language standard.

Butler added that the 62x addendum also requires proper pressurization of the building. "Maintaining a positive pressure relative to the outdoors controls the entrance of outdoor moisture and is a very common strategy used to prevent mold and mildew formation in a building," he said.

Andy Persily, of National Institute of Standards and Technology (Gaithersburg, MD) and former chairman of SSPC62.1, stated that addendum 62x also requires that the building envelope be designed to limit water entry in liquid form and via vapor diffusion and air leakage. The addendum also requires insulation of interior surfaces, such as cold water pipes, where condensation may otherwise be expected to occur.

Schoen added that a good designer would include many of these requirements anyway, but a lot of the envelope issues are outside the practice area of an HVAC engineer. "The requirement is there so that steps can be taken with the envelope to prevent the entry of moisture, which can be a significant problem."

Another addendum that concerns relative humidity is 62t, which contains specific requirements for drain pan sloping, outlets, sealing, sizing, and location to ensure that condensate from cooling coils is captured and drained effectively. This addendum also contains requirements for finned-tube coils to allow for access and cleaning. "Requirements for humidifiers and water spray systems are also provided, and requirements are added for system access to enable inspection, cleaning, and maintenance," said Persily.

Outdoor Air Assessment

The last major modification to the revised standard involves new outdoor air assessment and cleaning requirements. Persily noted this has been one of the more difficult aspects, because the outdoor air in some regions of the U.S. and other countries can be quite poor.

"In such cases, dilution ventilation with outdoor air can introduce significant outdoor contaminants, including particles, ozone, and carbon monoxide. The committee worked hard to develop reasonable requirements to address this issue," said Persily. "The previous version of the standard was not clear about what to do when the outdoor air quality is unacceptable."

Addenda 62r, 62z, and 62af all address outdoor air quality. Addendum 62r requires an assessment of the regional and local air quality, documentation of the results, and conclusions of that assessment, regardless of the type of ventilation being used (natural or mechanical) or the procedure being used to determine ventilation requirements. When using the ventilation rate procedure, if the PM10 levels exceed the national level, then particle filters rated at MERV 6 or higher must be installed.

Addendum 62z requires that air cleaning for ozone is the second highest daily maximum one-hour average concentration of ozone exceeds 0.160 ppm. "These data are available for the U.S. at the EPA web site," stated Persily.

He added that very few places in the country actually violate this limit. "If a building does exceed this limit, filters capable of removing ozone at an efficiency of 40% must be installed and operated whenever the outdoor ozone exceeds this concentration."

Schoen estimates that ozone problems that trigger Standard 62.1 requirements probably affect approximately 1% of all spaces, so it shouldn't have a big impact - yet. "It could become a bigger issue if our outdoor ozone problem gets worse. The good news is that for the 1% of affected spaces, a 1-in. panel filter impregnated with carbon will probably take care of the problem."

Addendum 62af includes a statement that notes the requirements of the standard will not necessarily guarantee acceptable indoor air quality in situations where the outdoor air quality is unacceptable and has not been adequately cleaned.

What's Next for 62.1

The committee working on the standard has undergone a major change in the last year: Basically the administrative subcommittee and the education subcommittee have taken the place of the previous subcommittees. The administrative subcommittee focuses on addenda and interpretations, while the education subcommittee focuses on education and research.

"I'm really pleased with how the new committee structure is working," said Butler. "Now we're able to make progress on two fronts instead of just focusing totally on addenda. We've been trying to do many things, but we simply couldn't because we didn't have the time."

For example, the committee is preparing Guideline 19P for users of 62.1, plus a user's manual, which will explain the reasoning behind some of the new provisions. In addition, the manual will answer applications questions and also show examples. An accompanying CD-ROM will contain automated design tools, which will make it easy to transfer the data to a spreadsheet. The committee hopes the manual will be available sometime in 2005.

"We found that so many of the problems that people were concerned about really dealt with or came from the fact that they didn't understand how to apply a lot of the requirements in the code," said Butler. He believes the user's manual and Guideline 19P will help alleviate some of these problems.

The committee has also started preparation for a series of informational seminars concerning 62.1 at the ASHRAE meetings. Butler hopes to be able to deliver Powerpoint presentations at regional meetings so that designers and code authorities will be able to get the information they need to enforce the requirements.

"All these things are very exciting," said Butler, "But it's also a vast departure from what the total focus of our committee in the past has been - trying to address addenda. We're down to very few addenda now, but we still have plenty of work to do." ES