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ASHRAE STD 62.1

Ventilation for Acceptable Indoor Air Quality

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Organization: ASHRAE
Publication Date: 26 June 2019
Status: inactive
Page Count: 6
scope:

FOREWORD

The 60°F (15°C) indoor-air dew-point limit avoids the microbial growth problems frequently observed when humid outdoor air infiltrates into buildings that are mechanically cooled. Microbial growth is common during cooling seasons and especially when cooling and occupancy are intermittent. Examples include in schools during summer vacations, apartments and condominiums that are intermittently occupied during summer months, college dormitories and military barracks that are unoccupied for long periods, and health care buildings and hotels in hot or humid climates that contain both naturally ventilated and mechanically cooled spaces

Humidity-related requirements of earlier versions of Standard 62.1 were intended to address both mold growth and comfort concerns by limiting indoor humidity to 65% rh. That requirement, however, did not explicitly extend to unoccupied hours when microbial growth often accelerates. More importantly, because it did not establish a coincident dry-bulb temperature, the 65% rh limit did not limit the mass of water vapor available for surface absorption during periods when cooling is intermittent to conserve energy.

Microbial growth is governed by the availability of moisture in the surfaces of building materials, coatings, furnishings and mechanical systems. The relative humidity (RH) of the air does not affect microbial growth until the water vapor is absorbed or condenses into the surface. Limiting the indoor-air dew point rather than the RH limits the total mass of water vapor available for condensation or absorption. Further, limiting the dew point to 60°F (15°C) prevents actual condensation until the air contacts a surface that is cooler than 60°F. Few surfaces are cooled that low in buildings, even allowing for typical cold-air leakage into interstitial spaces and the frequently less-than-perfect insulation of pipes, valves, and duct work.

This specific limit is a compromise between energy and microbial growth concerns. Lower indoor dew points would further reduce risk. For example, a 55°F (13°C) maximum dew point is the guidance contained in the 2001 and 2008 Humidity Control Design Guide for Commercial and Institutional Buildings and in the 2015 ASHRAE Handbook- Applications, Chapter 62, "Moisture Management in Buildings," and Chapter 23, "Museums, Galleries, Archives and Libraries." The 55°F dew-point limit is also required for all high-performance buildings as defined by the General Services Administration's 2017 PBS-P100, Facilities Standards for the Public Buildings Service. But a dew-point limit of 55°F (13°C), while certainly an improvement appropriate for reducing risks and improving comfort in high-quality buildings, could also increase energy consumption in unoccupied buildings in highly humid climates, especially when a building is not airtight. A dew-point limit of 60°F may provide a more affordable balance between the equally important concerns of reducing energy consumption and reducing risks to occupant health from microbial growth.

As noted by Section 5.9, Exception 1, buildings or spaces that are neither equipped with nor served by mechanical cooling equipment can be exempted from the dew-point limit, because their surfaces tend to stay warm during humid weather, which helps avoid moisture absorption and the risk of microbial amplification.

Note: In this addendum, changes to the current standard are indicated in the text by underlining (for additions) and (for deletions) unless the instructions specifically mention some other means of indicating the changes.

Document History

June 30, 2021
Ventilation for Acceptable Indoor Air Quality
FOREWORD The language of Section 5.10, “Maximum Indoor Air Dew Point in Mechanically Cooled Buildings,” has been interpreted by users to mean that the standard requires humidity sensors in every...
June 24, 2021
VENTILATION FOR ACCEPTABLE INDOOR AIR QUALITY
A description is not available for this item.
June 15, 2021
Ventilation for Acceptable Indoor Air Quality
A description is not available for this item.
January 27, 2021
Ventilation for Acceptable Indoor Air Quality
FOREWORD Addendum a clarifies that air density adjustments are permitted but are not required. At the publication of ANSI/ASHRAE Standard 62.1-2016, General Notes for Table 6.2.2.1, Note 3 was...
January 19, 2021
VENTILATION FOR ACCEPTABLE INDOOR AIR QUALITY
A description is not available for this item.
December 1, 2020
Ventilation for Acceptable Indoor Air Quality
A description is not available for this item.
November 19, 2020
VENTILATION FOR ACCEPTABLE INDOOR AIR QUALITY
A description is not available for this item.
November 19, 2020
Ventilation for Acceptable Indoor Air Quality
A description is not available for this item.
October 30, 2020
Ventilation for Acceptable Indoor Air Quality
FOREWORD Addendum d clarifies that open-circuit cooling towers, closed-circuit cooling towers, and evaporative condensers are all covered by the minimum separation distance requirements. Note: In...
October 30, 2020
Ventilation for Acceptable Indoor Air Quality
FOREWORD Unresolved objectors to Standard 62.1-2016 Addendum s noted that the definition for “unusual source” is unclear in distinguishing whether “rarely” refers to a source that is intermittent or...
April 17, 2020
Ventilation for Acceptable Indoor Air Quality
A description is not available for this item.
February 1, 2020
Ventilation and Acceptable Indoor Air Quality
A description is not available for this item.
October 16, 2019
Ventilation and Acceptable Indoor Air Quality
A description is not available for this item.
October 16, 2019
Ventilation and Acceptable Indoor Air Quality
A description is not available for this item.
ASHRAE STD 62.1
June 26, 2019
Ventilation for Acceptable Indoor Air Quality
FOREWORD The 60°F (15°C) indoor-air dew-point limit avoids the microbial growth problems frequently observed when humid outdoor air infiltrates into buildings that are mechanically cooled. Microbial...
June 26, 2019
Ventilation for Acceptable Indoor Air Quality
FOREWORD The Natural Ventilation Procedure was recently modified to require mechanical ventilation with certain exceptions. Addendum l provides specific requirements for the exceptions by providing...
June 26, 2019
Ventilation for Acceptable Indoor Air Quality
FOREWORD Table 6.5, “Minimum Exhaust Rates,” lists minimum exhaust rates for certain spaces in which contaminant generation has been deemed high enough that the contaminant cannot be diluted and...
June 26, 2019
Ventilation for Acceptable Indoor Air Quality
A description is not available for this item.
June 26, 2019
Ventilation for Acceptable Indoor Air Quality
FOREWORD This addendum adds a reference to ASHRAE/ASHE Standard 170 and an exception to direct users to use the ventilation rates in ASHRAE/ASHE Standard 170 for asepsis and odor control for health...
June 26, 2019
Ventilation for Acceptable Indoor Air Quality
FOREWORD The 2018 Facility Guidelines Institute (FGI) Guidelines for Design and Construction of Outpatient Facilities require certain outpatient spaces to meet local ventilation codes and not...
June 26, 2019
Ventilation for Acceptable Indoor Air Quality
FOREWORD Table 6.2.2.1, “Minimum Ventilation Rates in Breathing Zone,” includes educational space types, including “Classroom (age 9 plus)” and “Lecture classroom.” The first of these does not have...
June 23, 2019
VENTILATION FOR ACCEPTABLE INDOOR AIR QUALITY
A description is not available for this item.
June 22, 2019
Ventilation for Acceptable Indoor Air Quality
FOREWORD The current standard is silent on producing ozone within HVAC equipment. In some countries, ozone generators are accepted as air cleaners. In a recent poll of members of SSPC62.1, only 2%...
June 22, 2019
Ventilation for Acceptable Indoor Air Quality
FOREWORD Addendum ar modifies language in Informative Appendix E, “Acceptable Mass Balance Equations for Use with the IAQ Procedure,” to be consistent with the current IAQP. It also clarifies that...
June 22, 2019
Ventilation for Acceptable Indoor Air Quality
FOREWORD When Addendum r to Standard 62.1-2016 was published, the footnote to old Table 5.16.1, “Airstreams or Sources,” did not transfer to new the Table 6.5.2. This addendum reinstates the note...
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