Major revisions for design and measurement of comfortable spaces are included in a newly published 2013 standard from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE).
ANSI/ASHRAE Standard 55-2013, Thermal Environmental Conditions for Human Occupancy, combines the 2010 standard and 18 published addenda into a consolidated standard. The core of the standard in Sections 4 and 5 specifies methods to determine thermal environmental conditions (temperature, humidity, air speed and radiant effects) in buildings and other spaces that a significant proportion of the occupants will find acceptable at a certain metabolic rate and clothing level.
Section 7 of the standard includes new requirements for the measurement and evaluation of existing thermal environments and is also applicable to commissioning.
The standard has been re-written with a renewed focus on application by practitioners and use of clear, enforceable language. Requirements are now clearly stated and calculation procedures appear sequentially.
Other noteworthy additions to the standard include an allowance for the cooling effect of air movement as a way to extend the upper limit of the comfort zone in naturally conditioned spaces and addition of a predictive model for occupant clothing behavior based on extensive field research. These additions provide new methods for improving occupant comfort while minimizing energy use, according to Gwelen Paliaga, chair of the committee that wrote the standard.
Documentation requirements to show that a design meets Standard 55 are contained in Section 6 and a sample compliance form is provided in appendix J. Both of these sections are clarified and streamlined for use by owners and third party rating systems.
The 18 addenda published since 2010 are summarized in detail in Informative Appendix M, and the most noteworthy changes are summarized here:
- The normative body of the standard, comprising Sections 3 through 8, have been rewritten and reorganized.
- Requirements are more clearly stated, definitions are added to Section 3, and informative supporting information has been moved from the body to informative appendices.
- Procedures are clarified and appear in a more sequential manner. For example, a “representative occupant” with representative “clothing insulation” and “metabolic rate” shall be defined as input into thermal comfort calculations.
- The cooling effect of air movement now applies to naturally conditioned spaces as well as mechanically conditioned spaces, and in each case correction factors are given that adjust the comfort boundaries when air movement is present.
- A new alternate procedure for estimating occupant clothing insulation based on outdoor weather was added. This procedure is based on extensive field research and can be used for design calculations, annual simulations and control of occupied spaces.
Major revisions to Section 7 procedures for measuring comfort in existing spaces including survey and physical measurement methods and a new section on evaluating and reporting results.
The standard now requires that two of the key comfort parameters, air speed and air temperature, must be calculated as an average that the occupant experiences at three heights across the body and over a period of time.
The cost of ANSI/ASHRAE Standard 55-2013, Thermal Environmental Conditions for Human Occupancy, is $95 ($81, ASHRAE members). To order, contact ASHRAE Customer Contact Center at 1-800-527-4723 (United States and Canada) or 404-636-8400 (worldwide), fax 678-539-2129, or visit www.ashrae.org/bookstore.