Playing with Fire: Homeostasis and Alliesthesia Considerations in Architecture, Building Science and HVAC Design

Copyright © Robert Bean, R.E.T., P.L.(Eng.) for HeatSpring

Most people employed in the world of architecture, building science and HVAC understand the need for spaces which are thermally acceptable to the majority of occupants. But, as repeatedly demonstrated from my informal research, it appears the industry does not actually understand the principles of thermal comfort. Statistics obtained by polling industry audiences over the past 15 years across North America show 97% were unaware that Standards exists for thermal comfort and of the 3% which are aware only 1.5% own them and only 50% of them can actually converse with understanding, the principles described within. As such it remains a mystery to me that those who make a living selling thermal comfort equipment or promoting thermal comfort systems or designing thermally comfortable spaces do not know what thermal comfort is. Consider we would never want mechanics to work on our automobiles if they didn’t know about the mechanics of cars. Nor would we want heart surgeons to operate on our hearts if they didn’t know about hearts. It’s strange that society lets the construction industry practice “thermal comfort” when the industry generally doesn’t know the principles behind it. Clearly it’s a big topic, but let’s start by introducing two human comfort factor terms of, “homeostasis” and “alliesthesia” which practitioners ought to know when considering occupants and the design of buildings.

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By definition, homeostasis is the tendency of the body to seek and maintain a condition of balance or equilibrium within its internal environment, even when faced with external changes. Physiologically this includes vasodilation and vasoconstriction. “Vaso” is a blood vessel, “dilation” is to open or have less restriction and constrict is to close or have more restriction. This is how the body controls the flow of blood and thus the distribution of body heat. For example, to shed thermal energy the body increases the flow of blood to the skin which increases the skin surface temperature. An increase in the skin surface temperature increases the potential for radiant and convective transfer to the surrounding environment. If the architecture, building enclosure and HVAC system are of poor function such that the surrounding surfaces and air temperatures are near or higher than skin temperature then it becomes more difficult for the body to shed heat. When the body cannot cool itself, it triggers stress responses which are psychologically and physiologically based. To mitigate thermal stress responses in the human body, we have universally defaulted to using electrical and thermal energy derived from industrial processes (combustion) to condition our non-industrial spaces. From this one simple example you get a peek at the inside of Integrated Designwhich sits at the crossroads of building science, health science, hybrid HVAC systems, interior systems, and the study of energy and energy efficiency.

Alliesthesia can be defined as the change to a sensory experience that can be perceived as positive or negative. It applies to all senses which help define the broader definition of indoor environmental quality. Proponents of adaptive thermal comfort and naturally ventilated spaces use alliesthesia to draw attention to the benefits from exercising ones thermal regulatory systems. Unfortunately, some who prescribe exclusively to this philosophy of design, choose to ignore subjective thermal boundaries that when breached can also cause psychological and physiological stress responses in some individuals. Stress responses can also be invoked with the “lack of control” or “inability to adapt”. You may ask how this is possible in a space designed for adaptation. Well, it’s a mistake to think that buildings designed for adaptive comfort and natural ventilation equates universally to equal distribution of authority over opening windows or operation of space heaters or use of personal fans. These spaces are not immune from failure if individuals lack the authority to operate the building features, cannot thermally adapt due to business or personal cultural practices or have physical, physiological and psychological challenges. For these individuals in these scenarios the conflict and resulting stress is nothing more than extensions of the proverbial “thermostats wars” in traditionally designed spaces.

 It’s easy to promote “green” building strategies until one considers the growing population of people who unintentionally can’t execute on the principles.

So what are the consequences of stress due to thermal conditions? Mortality and morbidity statistics from the world of healthcare demonstrate the dangers of overheated or under heated spaces especially amongst the elderly population or those populations that have limited control over their environments such as infants and the infirm. These populations cannot always adapt physically, physiologically and psychologically as such become victims of bad buildings especially in the presence of climate changes of consequence. Consider someone with arthritis or Parkinson’s trying to open windows or put on or remove clothing? It’s easy to promote “green” building strategies until one considers the growing population of people who unintentionally can’t execute on the principles.

But what about the general population? At what point and to what intensity in the “normal” human body does infrequent, sporadic or sustained thermal stress become harmful? Since the body responds to stress in several ways including the release of hormones cortisol, epinephrine and norepinephrine it would serve us well to not trivialize that which we might not fully understand. Consider the works of Dr. Christopher Wild at the International Agency for Research on Cancer, World Health Organization who coined the term “exposome” and industry colleague Dr. Gary Miller from the, “The Human Exposome Project”. Those involved in this study, believe that “the role of our environment is underappreciated and are studying how the environment influences our health, both in negative and positive ways.” As noted by researchers, “We believe that pursuit of a Human Exposome Project, similar to the Human Genome Project or the BRAIN Initiative, will help reveal the importance of the environment in our lives.”

Though we have an understanding of the relationship between buildings and bodies it really is immature knowledge given recent studies in the epigenome and microbiome. It is for this reason I am pleased to talk about programs such as the WELL Building Standard®.  This Standard is “the world’s first building standard focused exclusively on human health and wellness.” As noted from its website, “It marries best practices in design and construction with evidence-based medical and scientific research – harnessing the built environment as a vehicle to support human health and wellbeing.” This resonates with me and assures students that our “boot camp” for recent grads of building and mechanical engineering and HVAC technology programs is a vital step in connecting the various aspects found within integrated design.

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About Robert Bean – Pres., ICC INc.

Robert Bean, R.E.T., P.L.(Eng.) is a registered engineering technologist in building construction and a professional licensee in mechanical engineering. He is president of Indoor Climate Consulting Inc. and director of He is a volunteer instructor for the ASHRAE Learning Institute and serves ASHRAE TC’s 6.1, 6.5, 7.4 and SSPC 55 Thermal Environmental Conditions for Human Occupancy; and is a special expert on IAPMO’s new Uniform Solar Energy and Hydronics Code committee. He has developed and teaches numerous courses related to the business and engineering of indoor climates and radiant based HVAC systems.

Robert is teaching: