ASHRAE 62.1: A review of key requirements and concepts

07/15/2013


Air classes

The concept of air classes is a fundamental aspect of the standard that can have a significant effect on the basic HVAC system layout and design. ASHRAE divides indoor air into four classes that describe the level of contamination within the air in a given zone. Air classes are important because they govern the ability to recirculate air both within a given space as well as within a given system. Systems that serve spaces that have multiple air classes need to be carefully designed to ensure compliance as when air streams combine, the mixed air stream takes on the air class of the worst stream.

Class 1 air is considered generally clean and without significant odor and is representative of the air in typical office or classroom areas. Class 1 air can be recirculated to any space type. Class 2 air is considered moderately contaminated or odorous and is restricted in its recirculation. Examples of Class 2 air zones include daycare facilities, dining areas, retail sales areas, and fitness facilities. Class 2 air can be recirculated to other similar Class 2 or 3 areas or Class 4 areas. However, Class 2 air cannot be recirculated to Class 1 spaces. This can have a significant impact on the design of multi-zone HVAC systems. For example, a multi-zone variable air volume (VAV) system serving a school cannot use a common return if the system serves a daycare or pre-school classroom unless that zone is separately exhausted and not returned to the main Class 1 system.

There is typically less risk of system design errors when it comes to Class 3 and 4 air zones—these are air zones with significant contamination, highly objectionable odors, and potentially dangerous contaminants (in the case of Class 4 air). There is less risk because most designers, contractors, and owners (and codes) clearly recognize those zones and exhaust them by default. These zones include janitor’s closets (3), lab exhaust (4), and commercial kitchen (4) exhaust. The main difference between Class 3 and 4 is that Class 4 air cannot be recirculated even within the space of origin.

For systems with heat recovery that are exhausting Class 2 and Class 3 spaces, the standard does allow for minor amounts (10% and 5%, respectively) of recirculation due to leakage across the energy recovery device. This allows a dedicated outside air system (DOAS) to effectively recover heat while maintaining acceptable IAQ.

The three procedures

The provision of adequate ventilation air to spaces occupies the bulk of the standard and is its most widely known area of scope. ASHRAE has divided the determination of adequate ventilation air and the methods of compliance into three procedures—ventilation rate, IAQ, and natural ventilation.

By far, the ventilation rate procedure is the most widely used and adopted, and it consists of the fairly familiar requirements for certain quantities of outside air for different space types. The required rates within the ventilation rate procedure have changed over time as the science of IAQ has grown and evolved over time. In the 1970s, at the outset of the standard, the ventilation rates were much lower than those required today. Likewise, the current version of the standard splits the ventilation requirements into two categories—area-based and occupant-based rates. The area-based rates are intended to cover the ventilation required to dilute pollutants generated by the non-occupant loads within the space—such as furniture off-gassing. The occupant-based rate then covers the ventilation required due to occupant-source pollutants, such as CO2 emissions and body odor. A detailed coverage of the ventilation rate procedure is beyond the scope of this article.

The IAQ procedure is probably the least used procedure in the standard, though it is the most flexible approach to ventilation. It is probably most appropriate when the indoor pollutant sources are very well known and atypical to the standard spaces already documented within the ventilation rate procedure. The IAQ procedure allows the designer to calculate the ventilation requirement based on specific pollutant emissions within the space and the quality of the outdoor air. However, because emissions for many sources are poorly understood and can vary widely, this procedure carries more risk for the designer and a higher burden of knowledge in researching the specific emissions rates of all the possible pollutant sources in the zone.

The natural ventilation procedure provides rule-of-thumb design parameters for naturally ventilated spaces to guide designers to a basic approach that is suitable for most non-complex single or double-sided natural ventilation schemes. One key aspect of the 2010 edition of the standard is the requirement for naturally ventilated spaces to also have a mechanical ventilation system designed to either the ventilation rate procedure or the IAQ procedure. This requirement is only waived if the system is an “engineered” system that is approved by the authority having jurisdiction and/or has automatic controls that ensure the openings will provide adequate ventilation whenever the space is occupied. This requirement for a backup mechanical system was added to ensure adequate ventilation during period when manually operable windows might otherwise be closed—such as during very cold or hot weather or when outdoor air is objectionable (such as spring allergy season).

Start-up and operations

ASHRAE 62.1 also governs system start-up and operations. For sophisticated contractors and operators, the requirements are probably second nature. However, they can serve as a good guideline for less sophisticated operators and also are a good reminder of aspects of operations to design around and include in the operations and maintenance manual.

ASHRAE’s Standard 62.1 provides the foundation for our understanding of achieving acceptable IAQ. It has a much broader reach into the building design and operations than many realize. It should be noted, though, that the science of IAQ is always evolving and that the requirements of ASHRAE 62.1, like most other standards and codes, represent the minimum requirements for acceptable IAQ. Designers should evaluate the literature, other regional standards (such as U.S. Green Building Council’s LEED and CEN CR 1752), the specifics of their project, and their client’s goals to ensure that systems meet their project’s overall needs.


Peter Alspach is an associate principal and mechanical engineer in Arup’s Seattle office. His expertise is in HVAC systems design, building physics analysis, and façade engineering. Alspach is a member of the Consulting-Specifying Engineer editorial advisory board, currently serves as the secretary of ASHRAE SSPC 55, and is a board member for IBPSA-USA. 


<< First < Previous 1 2 Next > Last >>

Leslie , OK, United States, 07/17/13 07:10 AM:

very good, how about posting CO2 levels in IAQ for K12 schools. It is in
62.1. Except it does not set a max CO2 for optimal
living or education.
Anonymous , 08/06/13 07:03 AM:

Very good article
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
2016 Product of the Year; Diagnose bearing failures; Asset performance management; Testing dust collector performance measures
Safety for 18 years, warehouse maintenance tips, Ethernet and the IIoT, GAMS 2016 recap
2016 Engineering Leaders Under 40; Future vision: Where is manufacturing headed?; Electrical distribution, redefined
SCADA at the junction, Managing risk through maintenance, Moving at the speed of data
Safety at every angle, Big Data's impact on operations, bridging the skills gap
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Applying network redundancy; Overcoming loop tuning challenges; PID control and networks
Driving motor efficiency; Preventing arc flash in mission critical facilities; Integrating alternative power and existing electrical systems
Package boilers; Natural gas infrared heating; Thermal treasure; Standby generation; Natural gas supports green efforts

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role of plant safety and offers advice on best practices.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me