What Is Room Temperature?

Understanding How We Measure Thermal Comfort

Chances are you are familiar with the term “room temperature.” We all have experienced work environments that are too hot, too cold or too muggy. Perhaps it is a conference room that always runs cold or a classroom that feels too stuffy. Typical occupants do not need to know why the room is uncomfortable; they just want it fixed – and fixed quickly!

Where does an engineer begin? And is there a single room temperature?

Changes in our activity, clothing and environment all affect what temperature is most comfortable

How to Measure Thermal Comfort

ASHRAE Standard 55-2023, Thermal Environmental Conditions for Human Occupancy states that thermal comfort is the “condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation.”¹ Comfort is inherently a subjective experience, and it is the engineer’s job to quantify it. The human body’s experience of thermal sensation is traditionally quantified by six environmental variables:

• Dry-Bulb Temperature: The air temperature measured by a typical thermometer
• Humidity: The amount of moisture in the air
• Air Velocity: How quickly the air blows across our skin
• Thermal Radiation: The exchange of heat due to hot and cold surfaces (this is most typically due to direct exposure to the sun)
• Clothing: The insulation provided by our own clothes (this is wonderfully quantified in units of “clos,” where a typical business ensemble is equal to 1.0 clo)
• Metabolic Rate: The amount of energy our body generates due to our activity level (this is equally wonderfully quantified in units of “mets,” where a seated occupant outputs 1.0 met)

These six variables work together to influence our body’s thermal exchange with the environment and, ultimately, what it feels. Many complex models have been developed over the last several decades to describe the relationship between these variables.² For this reason, there is no single room temperature for all applications.

Six variables simultaneously influence our perception of thermal comfort

How Is This Applied?

Engineers utilize ASHRAE Standard 55 to inform how comfortable their designs will be. This standard sets boundaries on each of these variables to ensure that the maximum number of occupants will be satisfied with the resultant thermal environment.

Additionally, if engineers design a space outside these boundaries, such as a tall hotel atrium with a significant solar load or a gym with highly active occupants, they can utilize ASHRAE Standard 55 to adjust the room temperature accordingly to offset the other variables.

But Why Do I Feel Cold While My Coworker Feels Warm?

Unfortunately, not all people experience the thermal environment the same way. We all have differences in our intrinsic metabolic rates and clothing choices. Additionally, a poorly designed HVAC system can result in unwanted temperature fluctuations between zones. The ideal building will keep 80% of its occupants thermally satisfied, though many fall short of this goal.³

So What Is Room Temperature, Actually?

Understandably, saying “it depends” is not a satisfying answer to this question. In most commercial buildings – where occupants are seated (met = 1.0) and are wearing business clothing (clo = 0.96), with typical humidity (Rh = 50%), low air velocity (velocity = 20 fpm) and no direct exposure to the sun – the room air temperature that is least likely to result in the perception of warmth or coolness is approximately 74°F (23.3°C).

So Why Price Industries?

Thermal comfort is the fundamental design goal of all air distribution systems. The solutions that Price manufactures all directly contribute to this goal:

• Grilles, registers and diffusers (GRD) must be selected to ensure supply air is being delivered to all corners of a room at a comfortable air velocity.
• Air terminal units control the amount of air delivered to a space. Their sizing and placement are critical to ensuring spaces maintain comfort as thermal loads change throughout the day.
• Controls sense the room temperature and communicate with the building system to achieve the occupant’s temperature set point.
• Sustainable systems, such as underfloor and displacement ventilation systems, can achieve thermally comfortable conditions while significantly reducing fan energy and air velocity.
• Noise control devices ensure building systems can run optimally without resulting in a loud, noisy environment.
• VAV diffusers provide smaller zones of control that achieve higher occupant comfort by using a dedicated thermostat and can integrate seamlessly with traditional VAV systems.

Where Can I Learn More?

We are glad you are curious! Here are a few resources to guide you on your thermal comfort journey:

• Price Engineer’s HVAC Handbook (Edition 2) Chapter 4, “Indoor Environmental Quality”: This chapter dives into further detail on the subject, exploring topics such as “What Is a Draft?,” “What Is Clean Air?” and “How Do I Know My System Is Ventilating a Room Efficiently?”
• ASHRAE Standard 55-2023, Thermal Environmental Conditions for Human Occupancy: This is the primary design standard for occupant comfort in the United States.
• Price Learning Portal (PLP) Learning Path #1 – Air Distribution Overview: This digital course provides fundamental information utilizing webinars, literature and Price HVAC Handbook
• Ask an Engineer: Price’s application engineers deal with these questions every day and will be more than happy to talk to you about it.
  
  

References

1. American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE), ASHRAE Standard 55-2023, Thermal Environmental Conditions for Human Occupancy (2023).
2. ASHRAE, “Thermal Comfort,” chap. 9 in ASHRAE Handbook – Fundamentals (2021).
3. Charlie Huizenga et al., “Air Quality and Thermal Comfort in Office Buildings: Results of a Large Indoor Environmental Quality Survey,” Proceedings of Healthy Buildings, vol. III (June 2006): 393–397.