The elusive thermal comfort

What makes a person thermally comfortable and how to best achieve thermal comfort in e.g., an office environment? While most experts have always acknowledged that thermal comfort is a condition of mind that conveys one’s satisfaction with the thermal environment¹, how to best achieve thermal comfort still remains a long standing multi-billion-dollar problem². Indeed, despite almost a century of research on thermal comfort, its provision is still based on fundamentally flawed assumptions, achieves a lackluster performance, and requires excessive energy to operate.

In the not-so-distant past, thermal comfort standards required an authoritarian control that dismisses any user adjustment. The then influential minds in the field contended that people are thermally comfortable when they feel neither too cold nor too warm³ and the industry best practice was to restrict indoor temperatures within a narrow range of isothermal conditions with little to no air movement⁴.In these conditions, which are commonly known as thermal neutrality, the laws of thermodynamic would dictate that metabolic is influenced neither by cold nor by heat stress. Arguably, such an approach treats all humans as mere “passive recipients of thermal stimuli”⁵ and fail fails to account for personal peculiarities and many real-world thermal adaptations that influence how people respond to and interact with their thermal environments. Additionally, by its nature, this approach requires achieves a lackluster performance, and requires excessive energy to operate.

Thanks to the energy shortage due to the Arab Oil Embargo of the 1973-1974, energy conservation became a geopolitical priority. In particular, the U.S. government funneled significant funds into research related to energy-efficient thermal comfort provision. The resulting research⁶ showed that humans have developed adaptations (e.g., attire change, behavioral adjustments, physiological and psychological adaptations) that help cope with their non-comfortable thermal environments and that many parameters (e.g., past thermal history, physiological, and psychological process) play a vital role in people’s thermal comfort. As such, there exists no single temperature for thermal comfort. Instead, when faced with thermal discomfort, people proactively or unconsciously take action to stay comfortable. Consequently, instead of using energy-intensive thermal neutrality that keeps indoor air temperatures within strict temperature zones, acceptable thermal comfort could be achieved with wide thermal comfort zones at much lower energy. This approach, however, is very simplistic and ignores essential precursors to thermal comfort, and has functional restrictions that are often at odds with social norms and clothing etiquette⁷.

With the looming perils due to climate change and global warming, policymakers all over the world have enacted policies that curtail agents of anthropogenic climate change. These policies impose strict cutbacks in energy use in buildings. Ironically, although new building regulations aim at reducing energy footprints, in reality, newer buildings are more energy-hungry because they use inferior building fabrics and design and because of inefficiencies in how they are operated⁸. Moreover, these regulations, given the limitations of current thermal comfort provision technologies, can only aggravate the level of thermal discomfort in workplaces. For example, a mandatory energy-saving policy, which was introduced by the Japanese government in 2011, resulted in an increased thermal dissatisfaction and a reduction in productivity⁹. Thus, delivering thermal comfort at lower energy is a conundrum that requires a paradigm shift in how thermal comfort is provided¹⁰.