The pandemic has dramatically increased awareness of the role indoor environments play in protecting occupant health. When the Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) publicly accepted that SARS-CoV-2 transmission was primarily through air, ASHRAE; BREEAM; the Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA); and others recommended 100% outdoor air ventilation, regardless of the consequence on energy use.

As the pandemic eventually loosened its grip, thoughts shifted to extreme weather events, such as wildfires and hurricanes, that were devastating the properties of individuals and communities. These extreme weather events were accurately tied to rising atmospheric carbon levels and greenhouse warming — adding momentum to energy conservation goals and furthering interest to decrease buildings’ carbon footprints. Meanwhile, the war in Ukraine triggered soaring fossil fuel prices, creating economic pressures on building owners and managers to “do the right thing.” As building priorities vacillated between managing IAQ to protect occupant health and operating HVAC systems to decrease the carbon footprint, do we even know what “doing the right thing” is anymore?

Answering this question requires several steps. The first is to ask ourselves, “Why do buildings exist in the first place?” To shelter people? To publically announce the status of the building owner or “corner office” occupant? To showcase the latest gravity-defying design or indoor technology? The honest answer is probably “all of the above,” but, first and foremost, buildings must exist to shelter occupants from harsh outdoor conditions and create safe indoor spaces to live and work. The second step is to understand and utilize a solid base of data that connects occupant health outcomes with indoor temperature and humidity, microbiological, particulate matter, and exposure to primary and secondary gases. The third step is to monitor indoor spaces during seasonal and use pattern changes so that changes in HVAC settings continue to support occupant health.

Unfortunately, there currently exists a harmful disconnect between building and medical professionals that prevents the aforementioned second step. Mechanical engineers design and operate systems that result in IAQ that humans are exposed to without incorporating data on the short- and long-term health consequences. Consequently, the majority of set points for IAQ management result from statements on occupant comfort, odors, impact on building materials, and the “expert opinion” of engineers. Without the medical studies needed to verify these set points, a chasm has formed, and human health has suffered as a result.

The ASHRAE Infectious Disease Position Document released on Oct. 13, 2022, illustrates this disconnect. The most glaring example is the brief and dismissive comment, “Existing evidence for the effects of temperature and humidity on infection risk does not justify changes to ventilation and IAQ standards, regulations, and guidelines at this time.” Instead, the position document recommends, “ventilation, filtration, and the use of ultraviolet germicidal radiation and other technologies determined to be safe.”

This statement obscures conclusions from numerous well-controlled and statistically significant studies showing data on the protective health effects of mid-range indoor humidity. Research in epidemiology, infectious disease, mammalian immunobiology, cell biology, microbiology, and metagenomics point to the health benefits of relative humidity (RH) between 40% and 60% for at least three reasons:

1) Tiny airborne (infectious and noninfectious) particles to settle out of the breathing zone;

2) The infectivity of many (not all) viral and bacterial pathogens in exhaled aerosols is decreased; and

3) The protective respiratory immune system is optimized.

The lack of discussion in the position document on the health benefits of RH between 40%-60%, generally justified by difficulties in preventing moisture damage when thermal channels or cold surfaces result in condensation, has clarified that building professionals and ASHRAE are at a critical juncture.

Understandably, engineers are not routinely educated to think about the innate protective barriers of the human body any more than doctors and other clinicians are educated about building mechanical systems. Nevertheless, given the international voice of ASHRAE, this organization must take one of two paths. The first option is to clearly state that ASHRAE recommendations have nothing to do with human health and remove any mention of occupant well-being from the mission statement. The second, and more constructive option, is that ASHRAE recruits input from medical professionals, and the two disciplines learn to integrate their expertise to truly protect occupants.

ASHRAE must decide, as there is no longer a respectable middle road.