Thermal Alliesthesia, Biophilia, and IAQ
Everything’s better in threes. Part 5 of a series devoted to exploring the design implications of buildings as both part of the human phenotype and part of our selective environment.
In the last article in this series covering the design implications of the built environment’s dual evolutionary nature (that started here), I focused on thermal comfort, covering some of its relevant physiological, psychological, and social factors. In this article, I’ll build on that discussion and cover aspects of thermal alliesthesia relative to evolutionary mismatches and the evolutionary dual nature of our built environments. Then I’ll transition to the broader concept of biophilia and end with a discussion of a design strategy impacting indoor air quality (IAQ) that is sometimes portrayed as biophilic in nature.
Drilling down further into the nature of thermal comfort, we come to the phenomenon known as thermal alliesthesia. Simply put, alliesthesia is the change to a sensory experience (stimuli) that can be perceived as positive or negative relative to its impact on our internal state, and it can be applied to any of our senses. However, for the purpose of this article the focus is thermal alliesthesia.
So, if external conditions, that we perceive as hot or cold stimuli, move us out of equilibrium and put strain on our body as it works to maintain internal temperatures within the narrow band around 37°C (98.6°F), we then experience discomfort corresponding to feeling too hot or too cold. As external conditions (or actions like adjusting clothing layers) move us back into equilibrium, we then experience a sense of what’s been termed thermal delight (a term popularized by Lisa Heschong in 1979). The level of thermal delight, or pleasure, is proportional to the degree of disequilibrium experienced, also called the load-error.
The thermal sensations we experience that result in discomfort and pleasure are driven by the movement in and out of equilibrium, of experiencing a transition in thermal states. That’s primarily because our skin is equipped with heat flow sensors, not temperature sensors. These warm (heat gain) and cold (heat loss) thermal receptors occur at different depths within our skin and in different densities across our bodies. As a result, different parts of our bodies are more sensitive to heat loss and heat gain than others. So, if an environment’s specific manifestation of the general and local factors of thermal comfort discussed in the previous article results in an equilibrium in heat flow across our skin receptors (zero load-error or stasis), then it essentially creates an absence of experienced thermal sensations. See the following for additional information (I’ve barely scratched the surface).
Thermal comfort of heterogeneous and dynamic indoor conditions — An overview
Creating alliesthesia in cool environments using personal comfort systems
From thermal boredom to thermal pleasure: a brief literature review
Historically, however, ASHRAE and other international standards have focused on the homeostasis aspect of thermal comfort, using steady-state heat balance equations like the whole-body thermal-balance comfort (WBC) model referenced in the previous article. The end result is a building system designed to maintain a static, narrow range of thermal conditions to keep our core temperature within this narrow band around 37°C (98.6°F). And that’s certainly important from an evolutionary fitness perspective. Deviations in our core temperature outside of that band negatively impact our fitness levels (represented by our health and productivity) as well as the fitness levels of the organization’s we’re a part of. The larger the deviation and the greater the time involved, the greater the impact. Yet, as I’ve alluded to above, homeostasis is only part of the evolutionary story relative to thermal comfort.
I should note, though, that there is movement in the industry beyond the the goal of maintaining environmental conditions within a narrow temperature band via mechanically conditioned buildings. Adaptive comfort standards (such as ASHRAE 55’s Adaptive Thermal Comfort guidelines) and efforts to account for the local thermal comfort factors discussed in the previous article represent movement away from maintaining thermal stasis. But we have a ways to go.
It’s not hard to see how our long evolutionary history (extending well back beyond modern humans), in which the majority of our time was spent in exterior environments, or in shelters that maintained a much greater connection to the exterior, has designed us to sense the rate of heat flow as opposed to temperature itself. Maintaining our core temperature under varying environmental conditions was crucial for survival, and sensing our heat gain or loss is more adaptive to that end compared to sensing the environment’s air temperature (or even operative temperature) at any given moment. The former, translated into psychological experiences, provides earlier warning to how environmental conditions might negatively impact our core body temperature. Experiencing pleasure as our body moves back into equilibrium or discomfort as we move out of it are indicators of the need to take, and motivators to take, conscious action.
Examples of such actions covered in the last section include office workers donning mittens to deal with the frigid arctic conditions created by the AC and college students avoiding an unconditioned dining hall during the warmer months. Again, B = f(P, E). On the pleasurable side of things is an example of college students experiencing thermal delight (along with visual delight) during the colder months as they were drawn to strolling through a daylit corridor. For many students, it was a chance to experience some solar heat gain shortly after entering the building as they headed for the dining hall (potentially pausing along the way).
Dr. Gail Brager has previously linked thermal alliesthesia to health and productivity. One study she cited in support of this found that when exposing people to both constant and sawtooth temperatures with similar mean values, the former resulted in higher thermal satisfaction levels, lower stress levels, and lower fatigue levels (positively impacting focus, concentration, and general health). Dr. Brager, while pointing out such findings should be particularly relevant to business and building owners, acknowledges that more research is needed in this area to understand more of the details. I would suggest that some of these details are more likely to be discovered if said research was conducted within an evolutionary mismatch framework, as laid out in that article.
If thermal monotony and stasis, or constant temperature conditions, represent an evolutionary mismatch, then we should probably conduct some research focused on understand how different aspects of our thermal sensing and regulatory physiology operate under the varying environmental conditions of our ancestors (modern humans and before) compared to contemporary interior environments. Why does our thermal regulatory physiology appear to be optimally adapted to thermal variety? Why does thermal monotony appear to negatively impact our evolutionary fitness levels (including potential impacts on obesity)? Answering these questions could shed additional light on optimum operative temperature ranges, the contextual importance of the various thermal comfort factors involved, the nature and amount of environmental variation needed (range and frequency), and the functional and health impacts on other aspects of our physiology.
It’s also important to look at how this might change at our different stages of development (shaped by our evolutionary history) - fetal development to old age - as the answers may differ by stage of life. Even just reviewing the research done to date and reinterpreting it within this framework would provide useful insights and help guide follow up studies. In the end we’ll better understand how to optimize the building/occupant organism - how to better align our phenotype with the surrounding environment to optimize evolutionary fitness - and limit undesirable behavior (B = f(P, E)).
Such studies, grounded in evolutionary theory to help us understand and avoid evolutionary mismatches, could also help us get a better handle on the concept of biophilia (thermal alliesthesia is often tied to the concept of biophilia). This is essentially the idea that humans have an instinctive bond to other living systems – that we have an innate biological connection with nature – as proposed by biologists and naturalist Edward O. Wilson in his 1984 book, Biophilia (though the term was also independently coined by psychologist Erich Fromm in 1964). As I’ve written elsewhere, it’s not hard to see how biophilia is …
rooted in our evolutionary past, the majority spent as hunter/gathers who had a much deeper and more intimate connection to the natural world than what we have today. For example, the millennia our species [and our species’ ancestors] spent viewing the landscape around us on a daily basis led to a visual system (and the associated cues it provides to various aspects of our physiologies and psychologies) optimized for views of the natural world, not the interiors of our modern built environments. This is likely one of the reasons underlying research results that find pleasant exterior views that include vegetation can have significant impacts on office productivity, learning in educational environments, and patient recovery rates.
Wilson saw this innate connection manifested as a) a human fascination with the natural world that is both conscious and subconscious, capable of inducing involuntarily physiological and psychological reactions and b) an affiliation for the natural world that has an emotional component, including empathy for other creatures (human and non-human). These two manifestations have been linked to everything from Attention Restoration Theory and Stress Recovery Theory to feelings of happiness and the psychological need for belonging. Not surprisingly, though, an individual’s response to natural stimuli (or absence of natural stimuli), which can be positive or negative, will depend on a mix of biological/heredity and contextual cultural/environmental factors, as well as the individual’s life history. More research is needed to better understand all of this.
Multiple guides and schools of thought have been developed around the application of the biophilia hypothesis to design. Some of these include Terrapin Bright Green’s 14 Patterns of Biophilic Design, Stephen R. Kellert’s and Elizabeth F. Calabrese’s The Practice of Biophilic Design, and Stephen R. Kellert’s Nature by Design: The Practice of Biophilic Design, among others. However, the strength of the supporting evidence and research underlying the various recommendations made in these guides varies, as does their anchoring within an evolutionary framework. As researchers Giuseppe Barbiero and Rita Berto have stated:
The biophilia hypothesis [and by extension its application within design] must be compatible with our knowledge of evolutionary biology and psychology [and cultural evolutionary theory] to make it possible to reconstruct a plausible and coherent history of biophilia with what we know of Nature in the Pleistocene and Holocene eras, and of our cultural evolution in the Paleolithic and most importantly in the Neolithic era, when our relationship with Nature changed radically.
I should also note that this necessary alignment with our evolutionary past, depending on the specific physiological or psychological trait in question, could extend even deeper into our past, beyond the Paleolithic and our hominin ancestors. For example, certain functional aspects of our cardiovascular autonomic nervous system were likely initially set in place as a result of their adaptiveness to certain ancestors of our hominin ancestors.
One biophilia (and biomimicry / biomimetics) related recommendation that would have benefited from an evolutionary mismatch analysis is the use of ionization technology to clean the air indoors. Ions are naturally occurring within the atmosphere, humans are exposed to them (as we have been over the course of our evolutionary history) potentially contributing to physiological (fascination) and emotional (affiliation) responses, and they can naturally act to reduce atmospheric air pollution through various chemical reactions. It makes sense to consider capitalizing on this connection to the natural world and mimic these larger atmospheric chemical reactions indoors to clean the air.
But it also makes sense to ask if the resulting indoor conditions differ enough from our outdoor ancestral conditions to negatively impact aspects of our health (and therefore evolutionary fitness), making the indoor environment less adaptive to certain aspects of our phenotype. Speaking of our cardiovascular autonomic nervous system, I have elsewhere looked at how the exposure to ionization concentration levels high enough to effectively clean the air might impact the functioning of this system. The figure below summarizes the results of a) breaking down the system of traits relative to Nikolaas Tinbergen’s four characterizations of traits discussed in the evolutionary mismatch article and b) using a literature review to answer the following three questions:
Does repeated, long-term exposure to the ionization levels needed to be effective in removing pathogens and pollutants in real-world settings disrupt the cardiovascular autonomic nervous system’s mechanisms and therefore human health?
How does this exposure impact the development of the cardiovascular autonomic nervous system (and cardiorespiratory system more broadly) from conception to adulthood, and changes in how the system functions as a person ages past adulthood?
How do these levels compare to the levels our relevant evolutionary ancestors experienced in their environments (our ancestral environments)?
Refer to my chapter for more details, but basically the ionization concentration levels needed to clean effectively are higher than what humans typically experience within most contemporary natural environments (sometimes significantly so), with studies finding negative impacts on our cardiovascular autonomic system after five days of exposure at these higher levels. It is true that these concentration levels can be higher near waterfalls, rivers, mountain springs, and during or immediately after thunderstorms, but the exposure times and frequency of exposure in these cases are both more limited. Ionization concentration levels in the natural world are also significantly more variable than what are found indoors when these ionization systems are operating.
This variation in levels experienced, including experiencing higher concentration levels under more limited conditions, could be a contributing factor for why one study found that hours of exposure (as opposed to days of exposure) to ions at higher concentration levels had a positive impact (though multiple other variables must still be accounted for as well). As I stated:
If our cardiovascular autonomic nervous system evolved to most effectively function when exposed to the ranges of ion concentration levels found in contemporary natural environments (assuming this is an effective proxy for our ancestral environments) it is possible negative impacts could also happen at levels lower (or less variable) than what occur in nature. Only comparing the technology’s ion concentration levels to the low levels when the equipment is off may not be an effective test in and of itself.
All three of the above questions need additional literature reviews, followed by additional research as needed, to effectively answer them. We need to know if our contemporary natural environments, relative to ionization concentration levels, act as an effective proxy for the ancestral environments most relevant to the evolution of our cardiovascular autonomic nervous system. And what type of impacts occur after months or years of exposure versus days or hours, and how do these impacts vary by different demographic factors?
I’ll briefly add that the emerging field of exposomics which involves studying the exposome, a concept used to describe environmental exposures that an individual encounters throughout life, and how these exposures impact biology and health, would help answer questions such as this. And exposomics itself would benefit from operating within an evolutionary framework, increasing our ability to account for, and address, evolutionary mismatches related to the exposome.
As stated above, biophilic design strategies along with the underlying aspects of the biophilia hypothesis must be aligned with evolutionary theory and the evolutionary history of our species. Operating within an evolutionary theoretical framework, taking the potential for evolutionary mismatches into account, makes it more likely this alignment will occur, and therefore the alignment of our built environments with our phenotypic traits.
In the next article, we’ll transition to a wider angle lens and focus on the larger constraints society places on the decisions made during design and governing. We’ll shift from the building/occupant organism itself to the behavior of design and construction professionals, building owners, developers, committee members, government officials, etc., in the environmental context of the design / construction process, the development / updating of standards and codes, and the governing process itself.