How do we measure the six factors affecting thermal comfort?

Metabolic rate and clothing insulation. Evaluation of these factors typically involves observation. What types of tasks are the occupants in a facility or space performing? What types of clothing are the occupants wearing? ANSI/ASHRAE Standard 55 lists metabolic rates for various types of activities and insulation values for various types of clothing.

Air temperature, air speed, and humidity. Tools for measuring these factors are common in the HVAC industry. Some anemometers can measure all three at once. Check the measurement range, accuracy, and resolution of your instruments to be sure they can be used for a given situation with sufficient precision and accuracy. Also, be sure to keep these tools calibrated so you can have faith in their readings.

MRT. Tools capable of measuring MRT are few and far between—and expensive. In my research, I found a tool that can measure MRT along with many other factors affecting thermal comfort, but it costs more than $9,000! Until cost-effective solutions are developed, here are a couple of ways to determine MRT:

  • Insert a temperature sensor into the center of a pingpong ball painted flat grey to make your own globe temperature thermometer. Really. (To learn more, see “Performance Measurement Protocols for Commercial Buildings: Best Practices Guide.”) This will measure operative temperature, not just MRT, and can be used for most indoor environments with low to moderate air movement.
  • Measure the temperature of interior surfaces with an infrared thermometer, and use ASHRAE Thermal Comfort Tool to calculate MRT. Infrared thermometers are common in the HVAC industry and relatively cheap.

Summary

When evaluating the thermal comfort of a space, do not focus solely on dry-bulb air temperature; there are other factors—namely, mean radiant temperature, air velocity, clothing insulation, metabolic rate, and humidity—affecting thermal comfort. Measuring those factors and using ANSI/ASHRAE Standard 55 to determine the expected level of thermal comfort in a space is an objective method of determining if there is a thermal-comfort issue or it is just a bad Monday.

Reference

1) ASHRAE. (2012). Performance measurement protocols for commercial buildings: Best practices guide. Atlanta: ASHRAE.

 

Dave Moser, PE, is a senior engineer for PECI. Focusing on commercial-building energy efficiency, he manages the technical aspects of utility retrocommissioning programs, leads in-building retrocommissioning projects, and conducts research. He can be contacted at dmoser@peci.org.

 

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