I.5 Thermal Comfort

Intent
Provide for occupant thermal comfort through control of ambient temperature, and operative temperature which includes wet bulb, dry bulb and globe temperatures, relative humidity (RH), mean radiant temperature (MRT), and air velocity.

Required Performance Criteria

1. Maintain continuous indoor exposure to ambient temperature in continuously occupied spaces less than 80°F and greater than 64°F. For transition spaces (entries, hallways, exterior walls) temperatures may fall outside the limits for continuously occupied spaces to save energy.
2. In continuously occupied spaces where MRT asymmetry could be a problem (for example: spaces such as glass atria, rooms adjacent to boiler rooms, and areas under an exposed roof structure), maintain the wall, floor, and ceiling surface temperatures within 20°F when taken from all continuously occupied positions OR Maintain no continuous indoor exposure to greater than 0.30 asymmetry in MRT across three body plane hemispheres (front-back, side-side, top-bottom)
3. Maintain air velocity greater than or equal to 10 fpm for continuously occupied spaces. Exception: Spaces with natural ventilation or mixed mode ventilation are exempt from I.5C during the times that they are operating in a natural or mixed mode ventilation mode.
4. Maintain interior relative humidity (RH) greater than 20% and less than 50% in continuously occupied spaces. Exception: Spaces with natural ventilation or mixed mode ventilation are exempt from I.5D during the times that they are operating in a natural or mixed mode ventilation mode.

Recommended Performance Criteria

5. Full compliance in keeping thermal variables within ASHRAE 55-2004 winter and summer comfort zones.
6. Vary dry bulb temperature (DBT) via building control system so as to avoid thermal boredom. Produce ramped drifts of up to + 2.0°F/hr in peak-to-peak variation around neutral temperature. Note: Operative Temperature (OT) is also known as Wet Bulb Globe Temperature, (OT or WBGT = 0.7 Natural Wet Bulb Temperature + 0.3 Globe Temperature)

Compliance Tools and Resources

• ASHRAE 55-2010
• Woodson, W. E, Tillman, P. & Tillman, B. (1992) Human Factors Design Handbook, 2nd Edition. McGraw-Hill, NY.
• Calculate or simulate thermal comfort using guideline performance criteria and other appropriate thermal comfort indices. Operative Temperature is determined by dry bulb temperature, relative humidity and mean radiant temperature (DBT, RH, MRT), and air velocity. Calculation can also include the effects of Clo value (the insulation value of clothing), physical activity and time. See especially ASHRAE Standard 55-2010 and the Human Factors Design Handbook for explanation of conditions and measures to provide for thermal comfort. See other references, particularly Engineering Data Compendium and NASA MSIS for handling special condition problems. See Handbook of Environmental Psychology for discussion of thermal issues for particular settings (e.g. offices, industrial environments) and for perceived control of thermal variables.