Technical Archive: ANSI/ASHRAE Standard 55 Thermal Comfort Parameters and Appendix Errata

Note: This article is part of the ACLogics Technical Knowledge Archive, documenting indoor thermal environmental standards, building science comfort models, and official standard reference materials.

ANSI/ASHRAE Standard 55 (Thermal Environmental Conditions for Human Occupancy) specifies the combinations of indoor thermal environmental factors and personal factors necessary to produce thermal conditions acceptable to a majority of building occupants. This reference note documents standard comfort variables, comfort prediction modeling, and official errata corrections.

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1. Primary Parameters of Thermal Comfort

Standard 55 defines thermal comfort as the condition of mind that expresses satisfaction with the thermal environment. Achieving compliance requires evaluating six primary variables:

+-----------------------------------------------------------------------------------+
|                        ASHRAE STANDARD 55 COMFORT VARIABLES                       |
+---------------------+-------------------------------+-----------------------------+
| Parameter Category  | Environmental / Personal Factor| Standard Field Range        |
+---------------------+-------------------------------+-----------------------------+
| Environmental       | Operative Air Temperature     | 68°F to 78°F (Winter/Summer)|
|                     | Mean Radiant Temperature (MRT)| Surface radiative balance   |
|                     | Relative Humidity (RH)        | Dehumidification limit < 60%|
|                     | Air Speed                     | < 40 fpm (0.2 m/s) draft limit|
+---------------------+-------------------------------+-----------------------------+
| Personal            | Metabolic Rate (Met)          | 1.0 Met (Seated office work)|
|                     | Clothing Insulation (Clo)     | 0.5 Clo (Summer) - 1.0 (Win)|
+---------------------+-------------------------------+-----------------------------+

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2. Predicted Mean Vote (PMV) and PPD Modeling

Standard 55 incorporates Fanger’s Predicted Mean Vote (PMV) model, which evaluates thermal sensation on a 7-point scale (-3 Cold to +3 Hot). The Predicted Percentage Dissatisfied (PPD) calculates expected occupant dissatisfaction based on PMV:

$$\text{PPD} = 100 - 95 \cdot \exp\left(-0.03353 \cdot \text{PMV}^4 - 0.2179 \cdot \text{PMV}^2\right)$$

• Standard Compliance Target: Standard 55 targets a PPD of less than 10%, which corresponds to a PMV range between -0.5 and +0.5.

                           PMV vs. PPD Comfort Curve
    PPD (%)
     100 |                                         
      80 | \                                     / 
      60 |  \                                   /  
      40 |   \                                 /   
      20 |    \____                       ____/    
       5 |---------*---------------------*---------   Target: PPD < 10%
       0 +----------+----------+----------+----------> PMV
                   -0.5        0        +0.5

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3. Documentation Reference & August 2012 Errata

• Informative Appendix Bibliography: The appendix structure of Standard 55 provides comprehensive references to technical research papers, human subject environmental trials, and fluid dynamics literature.
• Official Errata Correction: An official ASHRAE Errata Sheet (issued August 28, 2012) corrected a foreword cross-reference, clarifying that references pointing to “Informative Appendix H” in printed editions were formally amended to point to Informative Appendix G.