An update on ASHRAE 62.1

Our expert MEP Roundtable panel discusses the major changes to the 2010 edition of ASHRAE 62.1 and how these modifications will alter mechanical system design, building performance, and energy codes compliance.



Meet Our MEP Roundtable Participants

  • David P. Callan, PE, CEM, HBDP, LEED AP, Senior Vice President, Environmental Systems Design Inc., Chicago
  • Mark A. Cascia, PE, CEM, LEED AP BD+C, Senior Expert Application Engineer R & D, System Applications Group, Siemens Industry Inc., Buffalo Grove, Ill.
  • Roger Hedrick, Director of Technical Resources, Architectural Energy Corporation, Boulder, Colo., and chair of ASHRAE SSPC 62.1.

CSE: Describe the major changes to the 2010 edition of ASHRAE 62.1. When will these changes go into effect?

Mark Cascia: The major changes to the 2010 edition of ASHRAE 62.1 compared to the 2007 edition include several modifications. Revisions to the IAQ procedure and the additional requirements for natural ventilation systems, clarification of the ventilation rate procedure for multiple zone systems (especially VAV systems) in a rewritten Appendix A, and the addition of a section addressing demand control ventilation (DCV) to clarify the circumstances when ventilation during operations can be reduced from the zone design ventilation rates are among the major updates.

Dave Callan: The changes in the standard are immediate. However, building code authorities will likely adopt the standard in part, or whole, as their code review cycles dictate. This usually means a delay of a year or so. The standard update revises the ventilation rate procedure, clarifies exhaust requirements, clarifies natural ventilation requirements, and links natural ventilation requirements with mechanical supplemental systems for wider ranging climates.

Roger Hedrick: Taken from the foreword to 62.1-2010:

  • Deletes Section 6.2.9, which had addressed ventilation in areas with smoking. Ventilation for such spaces is no longer covered by the standard.
  • Provides minimum requirements to clarify when ventilation systems must be operated.
  • Relocates natural ventilation requirements to a new Section 6.4, adding a prescriptive natural ventilation procedure to the existing ventilation rate procedure in Section 6.2 and IAQ procedure in Section 6.3. The standard also now requires that most buildings designed to meet the natural ventilation requirements include a mechanical ventilation system designed to meet the VRP or IAQ procedure requirements; mechanical system operation must be activated whenever conditions preclude operation of the natural ventilation system (e.g., due to thermal comfort, noise, security, or other issues).
  • Relocates Table 6-4 and other requirements related to exhaust systems to a new Section 6.5, since exhaust requirements apply to all buildings, regardless of the procedure used to determine outdoor air intake flow rates.
  • Revises the IAQ procedure to make it more robust. In informative Appendix B, provides a table of volatile organic compounds that designers might want to consider as possible contaminants of concern. To encourage designers to consider “additively” (a basic consideration in the prescriptive VRP) when applying the IAQ procedure, some guidance from the ACGIH has been included in the informative text.
  • Adds additional requirements related to the design of demand-controlled ventilation systems.
  • Revises requirements for separation of outdoor air intakes from exhaust and relief air outlets by using classes of air already defined in the standard rather than descriptions of the air quality.
  • Adds some occupancy categories to the ventilation rate table (Table 6-1) and revises ventilation rates for a few occupancy categories.
  • Deletes ventilation requirements for health care spaces since they are now covered by ASHRAE/ASHE Standard 170-2008, Ventilation of Health Care Facilities.
  • Adds minimum filtration requirements related to PM2.5, and changes minimum air cleaning requirements related to ozone to reflect changes in the U.S. EPA’s ozone reporting procedures. Table 4-1 is moved to an informative appendix to facilitate updates when the EPA makes changes to the NAAQS.

CSE: How will the modifications to the natural ventilation rate procedure alter the mechanical system’s design?

Cascia: Since mixed mode (natural and mechanical) ventilation systems are becoming more attractive design options, ASHRAE Standard 62.1-2010 establishes a new requirement that natural ventilation systems shall include mechanical ventilation, with only a couple of exceptions. In most cases, mechanical ventilation will now be required to supplement natural ventilation. Therefore, mechanical system designers will now be required to make provisions to supplement natural ventilation with mechanical ventilation. The only exceptions are:

  • a natural ventilation system has been engineered as such and is approved by the authority having jurisdiction
  • the natural ventilation system complies with the requirements in section 6.4 of the standard and the openings cannot be closed during periods of occupancy
  • the zone is not served by heating or cooling equipment.

Callan: We believe the intent is to ensure that buildings designed with natural ventilation in extremely hot or cold climates have a supplemental mechanical system to be used when occupants are expected to close operable windows.

Hedrick: In buildings or spaces that previously met the requirements of Standard 62.1 using natural ventilation, no mechanical ventilation system was required. Under 62.1-2010, all such spaces (with limited exceptions) will be required to have a mechanical ventilation system installed that complies with either the ventilation rate procedure or the IAQ procedure.

CSE: Explain the updated clarification for exhaust system requirements. How will this apply to all building types and classifications?

Hedrick: Table 6-4, which provides requirements for exhaust airflow from certain space types, was previously located in Section 6.2, which describes the ventilation rate procedure for designing a ventilation system. If the ventilation system was defined using the IAQ procedure or natural ventilation, then compliance with Table 6-4 was not required. In 62.1-2010, Table 6-4 moved to Section 6.5 in the standard. As a result, the exhaust requirements defined in the table must be met, regardless of the ventilation system design procedure used.  

Cascia: Exhaust ventilation is now a standalone section in the standard (section 6.4) and applies to all zones or systems, regardless of the design procedure used (a natural ventilation design, the ventilation rate procedure, or the IAQ procedure).

Callan: This revision is primarily administrative and clarifies the confusion that exhaust requirements apply to all designs, despite the method of compliance chosen.

CSE: How has the calculation changed for the IAQ procedure? What components of the IAQ calculation are now more robust? Which other IAQ requirements were clarified in the new standard?

Cascia: The IAQ procedure was modified with a new Addendum R to the standard. The modifications clarify that the procedure is an alternate method for calculating ventilation rates that can provide credit for reduction of concentrations of contaminants in the indoor air by means other than ventilation, such as filtration or air cleaning. The procedure was strengthened by removing an approach that merely required that it be proved “successful in similar buildings” without defining “successful” or “similar.” As revised, the procedure now requires calculations for any application of the IAQ procedure. Informative Appendix D in the 2007 version of the standard was revised by Addenda B and I in the new edition. Certain errors were corrected and nomenclature was revised to be consistent with the body of the standard.

Hedrick: The calculations required for the IAQ procedure are that mass-balance calculations be performed to show that contaminant concentrations will meet the criteria set for them. These calculations have not changed in the 2010 version of the standard. What has changed is that the ability to use “design approaches that have proved successful in similar buildings” has been made more stringent. In particular, a subjective evaluation in the previous design must be performed to demonstrate that the design is successful, and “similar” has been defined, in an attempt to ensure that a previous design will be used appropriately.

CSE: What types of energy-efficiency requirements for ventilation systems are included in ASHRAE 62.1? How is this different from previous editions of the standard?

Hedrick: Standard 62.1-2010, as in previous versions of the standard, does not explicitly address energy efficiency. Energy efficiency is considered in that the committee attempts to set ventilation requirements that are adequate, but not excessive. Also, the standard provides a number of methods for designing acceptable ventilation systems, allowing designers flexibility to optimize their designs.

Cascia: A new section to Standard 62.1 was added in the 2010 edition addressing DCV. Compared to a system that ventilates at the design airflow during all occupied hours, a DCV system can save significant amounts of energy. Standard 62.1-2010 now defines DCV as “any means by which the breathing zone outdoor airflow (Vbz) can be varied to the occupied space or spaces based on the actual or estimated number of occupants and/or ventilation requirements of the occupied zone.” Addendum G was also changed to require documentation of assumptions, sequences, and setpoints for any DCV system. In addition, for multiple zone systems, in order to reduce energy consumption, Standard 62.1-2010 adds clarification language to reinforce the requirement that VAV systems should be designed to use the minimum expected primary airflow in the critical zone.

CSE: What changes will be required to the BAS controls to ensure compliance?

Hedrick: The standard does not require the use of a BAS to comply with the standard. Use of a BAS may make it easier to use dynamic reset of outdoor air intake flow rates, but this is not required.

Cascia: To ensure compliance, maintaining the minimum prescribed airflow rates in each zone is required. Although zone CO2 sensing is not required to implement DCV, and there continues to be some concern in the literature about CO2 sensor accuracy and its affect on control, CO2-based DCV methods continue to persist in the industry due to their increased energy savings potential. There are published equations that can calculate dynamic CO2 setpoints required for each zone to maintain minimum ventilation, based on dynamically changing variables. These variables are the number of people in the zone, the activity level of the people in the zone, the zone area, and zone-air-distribution effectiveness. BAS DCV control programs will be required to implement these equations using CO2 sensors to ensure that minimum airflow compliance conditions are met with minimal energy consumption as these variables change over time.

CSE: There are aspects of ASHRAE 62 that are not within the purview of the mechanical engineer (building-envelope vapor barriers, operation and maintenance by the owner, construction period recommendations). With many jurisdictions effectively referencing ASHRAE standards from their statutory requirements, what risks or responsibilities does the mechanical engineer absorb related to these other disciplines?

Callan: At our firm, we have not been presented with this liability issue related to architectural provisions of this standard. The liability question is a non-issue because it is outside of what is expected of the engineer’s standard of care. The same applies to the 90.1 energy conservation standard. Architects are becoming better educated and more aware of the technical requirements of the standard, for which they are responsible.

Cascia: I am not a lawyer and so I cannot give a strictly legal answer, but mechanical design engineers should only be held legally liable and responsible for the aspects of design under their purview and control—aspects of the project that include developing and publishing a design intent document, sizing and efficiency ratings of mechanical and HVAC equipment, and developing or reviewing sequences of operation. Accountability for the IAQ and energy performance levels of a building project should reside with the responsible contractors hired to provide these performance levels.

CSE: The new working of the natural ventilation procedure implies that if natural ventilation is pursued, mechanical ventilation systems are also required except where one can guarantee that the windows will not be closed during times of occupancy or when the space has no heating and cooling. What is the driver behind this decision to change the language?

Hedrick: Concerns were expressed to the committee that buildings were complying with the standard using natural ventilation in situations where it was not likely that the natural ventilation openings would be used as intended to provide ventilation. In particular, high-rise residential buildings were mentioned. The committee was convinced that a mechanical ventilation system capability needed to be available to the occupants because there are many times when occupants do not wish to open the windows due to noise, thermal discomfort, security concerns, etc.

Cascia: The driver behind the decision is simply that mixed mode (natural and mechanical) ventilation systems are becoming more attractive design options compared to pure mechanical ventilation due to the energy savings potential of these systems. Some mechanical ventilation (with appropriate controls) is increasingly seen as necessary to ensure minimum ventilation requirements are always met during occupied hours, even for mixed-mode ventilation systems.

Callan: Engineers have raised questions regarding IAQ in buildings designed for natural ventilation. We understand that in some cases, while designers were well intentioned, they may not have considered the impact of closing windows during adverse weather conditions. The purposes of these standards are to ensure a higher quality of building design with broad considerations. Therefore, a building that meets the standard should be able to provide high IAQ in any weather condition, which prompts the need for mechanical backup when the windows are closed.

CSE: Similar to the previous questions, how does this change the interface with the “natural conditioning” language of ASHRAE 55?

Cascia: ASHRAE Standard 55 itself was last updated in 2004, but several addenda have been added since then (Addenda A, B, D, E, F, and G). However, none of these addenda affect the original “natural conditioning” language of ASHRAE Standard 55-2004. The standard defines naturally conditioned spaces as “those spaces where the thermal conditions of the space are regulated primarily by the opening and closing of windows by the occupants.” As currently worded, this definition does not preclude the use of mechanical ventilation to assist natural ventilation in supplying the ventilation needs for a space.

Hedrick: The mechanical ventilation systems required to be installed even if natural ventilation openings are available do not need to be operated when ventilation is provided by the natural ventilation openings. Therefore, it really has no impact on the building during these times.

CSE: A series of prescriptive rules about natural ventilation openings have been added, whereas older versions of the standard did not provide this guidance. Do you think that engineers are more likely to apply natural ventilation now that the guidance is embedded in the code as compared to having to justify an engineered system?

Hedrick: Previous versions of the standard included prescriptive requirements for opening sizes. However, the standard now recognizes that the ventilation provided by a given opening will vary based on the presence or absence of openings on opposite sides of the space. Therefore, the standard now allows natural ventilation openings to serve larger floor areas in a cross-flow situation compared to when openings are on one side of the space only. These new requirements are actually more permissive than previous requirements.

Cascia: Actually, prescriptive rules regarding the size and location of wall or roof openings to the outside air existed in ASHRAE Standard 62.1-2007 (see paragraph 5.1.1). ASHRAE Standard 62.1-2010 merely adds additional prescriptive rules about natural ventilation openings. Engineers will be increasingly specifying natural ventilation systems primarily because operation of these systems consumes less energy and there is a current push in the industry toward green buildings, and ultimately net-zero-energy buildings. For example, many of the [U.S. Green Building Council] LEED green building rating systems give credits (LEED points under the Energy and Atmosphere category) for natural ventilation systems.

Callan: No, because I think designers who were interested in designing naturally ventilated buildings simply have better guidance. Designers who shy from naturally ventilated buildings would not typically be swayed by the standard. The designer should be primarily concerned with the building, its climate, the application, and the ability for that climate to provide an acceptable passive design in all anticipated weather conditions. 

CSE: Will the new requirements require a change to manufactured components of an air handling unit or system, such as inlet dampers or outside air measuring?

Cascia: To maximize energy savings potential in DCV systems, CO2 sensing of the outside air and in each DCV zone will be required, as well as assurance that the baseline airflow will be no less than the building component (outdoor airflow rate multiplied by the area of the zone, Ra multiplied by Az), and the fan system will provide each zone with no less than the breathing zone outdoor airflow for the current zone population. This implies that total outdoor air intake for each air handler must be measured and that each DCV zone must have a means of varying the total airflow and calculating the percentage of outdoor air into the zone. Such a means can be accomplished by a BAS networked to a DDC-controlled VAV box with a damper, or a variable-speed fan-powered VAV box with an air measuring sensor and special programming to control the amount of airflow into the zone.

CSE: Costs of implementation—any anticipated increases/decreases?

Cascia: The addition of a CO2 sensor for measuring outside-air CO2 concentration and adding zone CO2 sensors for each zone controlled under a DCV strategy will be necessary added costs, as well as more commissioning time to verify that correct calculations are being performed in the BAS for zone population and the calculation of dynamic CO2 setpoints.

Callan: I wouldn’t expect a difference from a 2007 compliant building, except in the cases of a natural ventilated building that didn’t provide the supplemental mechanical ventilation system.

Hedrick: Buildings that complied using natural ventilation may now need to install additional equipment to meet the mechanical ventilation requirements of the ventilation rate procedure or IAQ procedure.

Read more on IAQ and other ASHRAE standards here:

LEED Certification May Not Guarantee Good IAQ 

ASHRAE 901.--2007 and Beyond

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