Due to variations in body type, experiences and culture, every person has a different definition of comfort. Yet, standards such as ASHRAE 55 continue to be written based on static, linear models, regarding occupants as receptors of their environments instead of active participants in it.[1]These standards are also based upon gender-biased data, often leaving women to live and work in environments designed for their male counterparts. A 2015 study published by Nature Climate Changestated that “buildings should ‘reduce gender-discriminating bias in thermal comfort’ because setting temperatures at slightly warmer levels can help combat global warming”[2]during summer months.Not only is thermal comfort an issue of inclusivity and equality, but also of energy usage and sustainability. It is the responsibilityof thermal comfort standards to share accountability for promoting sustainable buildings during a time of increasing pollution and rates of climate change.[3]Emphasis on thermal comfort has a growing importance in architecture through its potential significant impact on productivity, attendance, equality and sustainability.
ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy, was first written in 1966 “to specify the combinations of indoor thermal environmental factors and personal factors that will produce thermal environmental conditions accept- able to a majority of the occupants within the space.”[4]Standards like ASHRAE 55 are used by architects and engineers to provide a climate suitable for productivity of its users. The standards ultimately decide a building’s energy consumption and therefore its impact on the earth’s climate.[5]ASHRAE 55 takes into account four primary environmental factors (temperature, thermal radiation, humidity and air speed) and two personal factors (activity and clothing).[6]The standard does not require evaluation of comfort in existing buildings, but this can optionally be performed through an occupant satisfaction survey or physical environment measurements.[7]
Dissecting the standard
ASHRAE Standard 55 states that temperatures cannot fluctuate over 2.0º F in fifteen minutes or 4.0º F within an hour. Not only does this require greater energy usage to heat or cool a space to maintain a consistent temperature, but de Dear and Brager, co-authors of “Thermal comfort in naturally ventilated buildings: revisions to ASHRAE Standard 55,” question whether thermal monotony is always positive. They suggest “counteracting thermal boredom with fluctuating interior temperatures to meet our inherent needs for sensory stimulation.”[8]Maintaining a singular, narrow temperature range ensures that one part of the population is always dissatisfied with the interior environmental quality. However, by varying the temperature throughout the day, not only is energy saved, but a larger number of occupants are comfortable for at least some part of the time. De Dear and Brager comment that “Perhaps we should be aiming for a higher level of experiential quality in our environments, where ‘pleasantness’ rather than ‘neutrality’ are the goals.”[9]
ASHRAE 55 is based on the Fanger Predicted Mean Vote index (PMV), the most commonly-used model in research of thermal comfort.[10]PMV only integrates metabolic rate and clothing level in its heat balance equation, asserting the assumption that both remain constant in an office setting over time. Through this implication, “the comfortable and controlled building interior is determined to function as a place of separation from the indigenous climate and the seasons, where individuals have little opportunity to participate in their own comfort responses and are forced to accept the narrow thermal conditions with which they are provided.”[11]
When performing occupant thermal-comfort surveys, ASHRAE analyzes the data by dividing the number of votes between -1 and +3 by the total number of votes based on scale of -3 to +3, or very unsatisfactory to very satisfactory.[12]The resulting number is utilized as the percentage of occupants who approve of the thermal environment. However, this thinking is flawed and nearly manipulative of the system, considering that participants of the survey who say their environment is ‘slightly unsatisfactory’ are grouped with participants who actually responded that they were satisfied with their thermal comfort.
ASHRAE 55 uses metabolic rates to provide predictions of comfort levels among occupants. Metabolic rate, the transformation of energy to heat through activity, is defined per unit of skin surface area. The standard claims that their metabolic rate values are “valid for an average adult with surface skin area of 1.8 m².”[13]However, the average skin surface area for men is 1.9 m², while the same for women is 1.6 m².[14]This would provide an average closer to 1.7 m² for the average adult. This is also excluding children, whose average skin surface area is closer to 1 m².[15]Further, the PMV in its own right is problematic for determining a suitable environment for all types of people. The model does not take into account “factors beyond fundamental physics and physiology,”[16]such as culture, thermal experiences, interactions and context, which impact a person’s expectations for the environment, and therefore their perceived thermal comfort. “Thermal sensations, satisfaction, and acceptability are all influenced by the match between one’s expectations about the indoor climate in a particular context, and what actually exists.”[17]The PMV accounts for some behavioral adaptation like adjusting layers of clothing or changing velocity of local air but ignores the psychology of what makes people perceive spaces differently.[18]Comfort is also contextual. De Dear and Brager cite the example that “People living year-round in air-conditioned spaces are quite likely to develop high expectations for homogeneity and cool temperatures, and may become quite critical if thermal conditions in their buildings deviate from the center of the comfort zone they have come to expect.”
ASHRAE 55’s comfort range spans only three degrees Fahrenheit (Appendix B), while men and women have been shown to prefer temperatures up to five degrees apart.[19]Not only does this small range of allowed temperatures limit the population of occupants that can be thermally comfortable, but it also results in higher energy usage. Static comfort temperatures keep air-conditioners and heaters running almost constantly, even in unoccupied areas. Significant energy costs are caused by “providing this constant supply of uniformly conditioned, cool, still and dry air…as are the environmental consequences associated with this vast energy end-use.”[20]
Thermal Comfort Survey analysis
A total of 68 participants completed a thermal comfort survey (Appendix A), similar to that of ASHRAE 55, evaluating each individual’s thermal comfort in the University of Maryland Architecture Building. The survey collected data consisting of gender, age, weight, race and location in the building. It asked the participants about their satisfaction with the temperature of their space, as well as their temperature during warm/hot and cool/cold weather. Finally, each participant could answer how they control their personal thermal comfort in the Architecture Building and provide further comments.
Unlike ASHRAE 55’s scale, this survey allowed participants to rate their satisfaction on a scale of -2 to +2, instead of -3 to +3. As previously stated, ASHRAE 55 considers -1 to +3 a satisfactory response. In this scenario, it is reasonable to assume that ASHRAE 55 would consider a rating of 0 to +2 to be satisfactory, in which case 72.3% of participants would be considered satisfied with their thermal comfort. However, I would argue that only a range of responses between +1 and +2 are fair to be deemed satisfactory responses. In this case, only 33.8% of participants are satisfied with their thermal comfort in the Architecture Building. This comparison highlights a drastic difference between what ASHRAE considers to be a fair calculation of a population comfortable in their environment, and the actual population comfortable in their environment.
The results of the study revealed correlations between both gender and weight, and thermal comfort. Female participants tended to be more dissatisfied with their thermal comfort than male participants (Figure a1). Females also responded as colder in warmer months, while males tended to be too hot during the same time of year. (Figure c1). With regards to weight, 33% of those over 180 pounds are often or always too hot when it is warm or hot outside, while 37% of those under 140 pounds are often too cold at the same time (Figure c2).
Due to a lack of diversity in participants’ race and age, accurate correlations could not be conceived from the study. However, even discounting correlations, the study reveals that there is a vast range of how people feel in the same space with the same outdoor weather conditions. One constant temperature cannot possibly account for all of these participants, representative of the occupants of the Architecture Building. The most commonly cited way of adjusting personal thermal comfort by participants was adding and/or removing layers. This puts comfort in the hands of the occupant instead of the architecture. It is the responsibility of the building to keep occupants comfortable. People should not be forced to wear winter coats inside or constantly have to leave the building in order to maintain their thermal comfort.
Proposal
ASHRAE 55 currently prescribes “a static model of thermal comfort that views occupants as passive recipients of thermal stimuli driven by the physics of the body’s thermal balance with its immediate environment,”[21]without taking accountability for sustainability of architecture. This assumption of universality has led to an “exaggeration of the need for air conditioning.”[22]A variable temperature standard, which ASHRAE 55 has come to employ in recent years, links temperatures indoors to the climate outdoors. This is especially plausible in naturally ventilated buildings, which have an assortment of positive attributes.
The current standard does not allow for enough occupant control, which contributes to energy savings and satisfaction. Occupant controls include “opening windows and doors, turning on fans or personal heating/cooling devices, adjusting thermostats, changing clothing, migrating to more comfortable parts of the building, and ingesting warm or cool drinks.”[23]Even offering control of air-conditioning systems can result in less energy usage. For example, “a properly designed occupant-controlled HVAC system can save a substantial amount of energy (13% for the Washington DC climate), while providing increased comfort.”[24]While providing occupants with control over their environment is necessary, “satisfaction benefits of providing occupant perceived control are contingent upon controls being well maintained and simple enough for users to understand.”[25]In a 1995 study, nearly half of the office building occupants surveyed “expressed a desire for a different thermal environment than the one they had, even though the majority of offices surveyed fell within the standard ASHRAE comfort guidelines.”[26]Occupant-controlled HVAC has been shown to increase worker productivity and attendance, reduce conditioning in unoccupied areas, reduce energy consumption, increase building layout flexibility, and eliminate inadequate ventilation areas.[27]
It is a paramount aspect of design for occupants to participate in the indoor climate feedback loop, instead of become passive recipients of conditions delivered to them.[28]In contrast to the aforementioned example of people acclimated to air-conditioned environments, “people who live or work in naturally ventilated buildings where they are able to open windows, become used to thermal diversity that reflects local patterns of daily and seasonal climate variability. Their thermal perceptions—both preferences as well as tolerances—are likely to extend over a wider range of temperatures than are currently reflected in the old ASHRAE Standard 55 comfort zone.”[29]It is the role of standards like ASHRAE 55 to promote variability in indoor temperatures in order to provide pleasurable instead of simply neutral environments, appeal to a larger variety of people, and promote sustainability in architecture.
[1]de Dear, Richard J. Brager, Gail S. “Developing an Adaptive Model of Thermal Comfort and Preference.” 1998.
[2]Belluck, Pam. “Chilly at Work? Office Formula Was Devised for Men.” 2015.
[3]Nicol, J. F. Humphreys, M.A. “Adaptive thermal comfort and sustainable thermal standards for buildings.”2002.
[4]ANSI/ASHRAE Standard 55-2017.
[5]Nicol, J. F. Humphreys, M.A. “Adaptive thermal comfort and sustainable thermal standards for buildings.” 2002.
[6]ANSI/ASHRAE Standard 55-2017.
[7]Ibid.
[8]de Dear, Richard J. Brager, Gail S. “Thermal comfort in naturally ventilated buildings: revisions to ASHRAE Standard 55.” 2002.
[9]Ibid.
[10]Nicol, J. F. Humphreys, M.A. “Adaptive thermal comfort and sustainable thermal standards for buildings.”2002.
[11]Ibid.
[12]ANSI/ASHRAE Standard 55-2017.
[13]Ibid.
[14]MedicineNet.
[15]Ibid.
[16]de Dear, Richard J. Brager, Gail S. “Thermal comfort in naturally ventilated buildings: revisions to ASHRAE Standard 55.” 2002.
[17]Ibid.
[18]Ibid.
[19]Belluck, Pam. “Chilly at Work? Office Formula Was Devised for Men.” 2015.
[20]de Dear, Richard J. Brager, Gail S. “Thermal comfort in naturally ventilated buildings: revisions to ASHRAE Standard 55.” 2002.
[21]de Dear, Richard. Brager, G.S. “Developing an Adaptive Model of Thermal Comfort and Preference.” 1998.
[22]Ibid.
[23]Nicol, J. F. Humphreys, M.A. “Adaptive thermal comfort and sustainable thermal standards for buildings.” 2002.
[24]Glicksman, Leon R. Taub, Steven. “Thermal and behavioral modeling of occupant-controlled heating, ventilating and air-conditioning systems.” 1995.
[25]Nicol, J. F. Humphreys, M.A. “Adaptive thermal comfort and sustainable thermal standards for buildings.” 2002.
[26]Glicksman, Leon R. Taub, Steven. “Thermal and behavioral modeling of occupant-controlled heating, ventilating and air-conditioning systems.” 1995.
[27]Ibid.
[28]Brager, Gail. Paliaga, Gwelen. de Dear, Richard. “Operable Windows, Personal Control, and Occupant Comfort. 2004.
[29]de Dear, Richard J. Brager, Gail S. “Thermal comfort in naturally ventilated buildings: revisions to ASHRAE Standard 55.” 2002.