Standards of Human Comfort

Standards of Human Comfort Relative and Absolute Michael Boduch and Warren Fincher csd Center for Sustainable Development UTSoA - Meadows Seminar Fall 2009 Standards of Human Comfort: Relative and Absolute Michael Boduch Warren Fincher Figures 01 and 02. Humans maintain comfort levels in very diverse climates. For something so desirable, comfort While discomfort is about can unfortunately be a nebulous approaching extremes, comfort concept. The room that makes is primarily about determining one person put on a sweater can ranges. Various organizations, make another wish they were in such as American Society of shorts, and some people focus Heating, Refrigeration, and Air- better in contemplative silence while Conditioning Engineers (ASHRAE), others need ear-splitting music the International Organization simply to get motivated. In these for Standardization (ISO), and differences, however, is the kernel to the European Committee for understanding the nature of comfort: Standardization (CEN) have each that it is phenomenological. written publications that establish these ranges in detail. Yet while Our interface to the world is through these standards provide a set of our senses: touch, sight, hearing, conventions that can be approached smell, and taste. Each one of these as targets, the experience of comfort senses can lead to a greater or remains a product of our senses. lesser degree of comfort, and they can act independently or in concert. Thermal Comfort For instance, our sensation of cold can be so overwhelming that Temperature is the most significant we literally shut down our bodily component to the experience functions, yet at other times we will of comfort in a space. Our tolerate discomfort for a pleasurable bodies perform within an internal experience, such as standing in temperature range much narrower the rain and mud for a concert. than external temperatures. In the Indeed we are more likely to be process our bodies’ metabolism in agreement on the absence of generates heat, which must dissipate comfort. into the surrounding air or surfaces. 1 UTSoA - Seminar in Sustainable Architecture When external temperatures are Differences in temperature within a high, this process becomes more room or across a body can create a difficult and we may overheat or feel sense of discomfort (see Figure 03). Relevant Publications warm. When external temperatures When temperatures from different are low, the rate of heat loss surfaces diverge, we sense a surface ASHRAE Standard 55 3 becomes more rapid, and we may as radiating heat or “giving off” cold. ISO 7730 4 feel uncomfortably cold. When the ceiling is the contrasting EN 15251 5 surface, we note discomfort when Surfaces of a Room. When the ceiling is greater than 9˚ F (5˚ assessing thermal comfort in a C) warmer or 25˚ F (14˚ C) colder temperature to provide a sense confined space, we must examine than the other surface temperatures of discomfort. High levels of both the general temperature in in the room. We allow a greater relative humidity can work against the room, as well as the uneven divergence of wall temperature the evaporative cooling effects of distribution of heat in the room. from alternate surfaces temperature sweating and leave the body prone Typically when people refer to before we sense discomfort, 41˚ F to over-heating. Further, high levels temperature, they mean the (23˚ C) for warmer walls and 18˚ F of relative humidity in inclement 1 temperature of the air; however, (10˚ C) for cooler walls. As well, a winter weather produce a greater our experience of thermal comfort vertical air difference from our feet to sense of cold.6 depends on more than simply air our head shouldn’t exceed 5.5˚ F (3˚ 2 temperature. The mean radiant C), otherwise the high temperature Human beings are sensitive to slight temperature entails averaging gradient highlights one part of the temperature changes, yet cannot the temperatures of each surface body as feeling notably warmer or perceive differences in relative in the room. Combined with the colder than the other. humidity levels within the range of air temperature this produces an 25% and 60%, which is the primary overall measure, the mean operative Relative Humidity. While reason that this range is often cited temperature. However, even this temperature is the most as the baseline.7 If relative humidity measure has its limitations, as how important factors in generating a falls outside this range, there are close a person wil be to a particular phenomenological sense of thermal notable effects. When relative surface is usually variable, and in comfort, many other climatic factors humidity gets too high, discomfort these cases different surfaces will contribute. Relative humidity plays a develops, either due to the feeling of 8 dominate at different times. large part in conjunction with the moisture itself, which is unable to evaporate from the skin, or due to increased friction between skin and clothing with skin moisture.9 When relative humidity gets too low, skin and mucous surfaces <25˚F cooler >9˚F warmer become drier, leading to complaints about dry nose, throat, eyes, and skin.10 In particular, discomfort in >5.5˚F Dierence working environments, which are prone to significant eyestrain, such as an office with a computer, is exacerbated (see Figure 04).11 <18˚F >41˚F cooler warmer Velocity of Air. Air velocity plays a role in the perception of thermal comfort. In hot weather, as the body tries to cool itself, the flow Figure 03. Allowable temerpature variances of air across the body will assist 2 Standarrds of Human Comfort evaporative cooling from sweating. When air has a high relative humidity, the air next to the sweating summer and winter comfort zones body may become saturated with moisture, but by moving the air next to the body away and bringing 90 in fresh, lower-humidity air, the evaporation of sweat can continue. Mechanisms of convection can 85 “warm” zone further move the heat generated by metabolic processes from the skin 80 and into the surrounding air. All this condensation ºF issues in winter; leads to continued cooling, and the static mold higher the velocity of air, the more 75 electricity in effective is the process. winter; dry eyes As helpful as airflow can be in temperature, 70 warm and humid conditions, it can be problematic in others. In cool settings, the same processes of 65 “cool” zone evaporative cooling and convection, which play a key part in cooling the 60 warm body, may cool the inhabitants beyond their levels of comfort. Aside from the cooling effect of airflow, the air speed itself can cause discomfort 10 20 30 40 50 60 70 80 90 (see Figure 05). Generally, airflow relative humidity, % slower than 100 feet per minute feels either pleasant or goes unnoticed. summer Higher than that, and the flow of air winter can within an enclosed space can Figure 04. Comfort zones for summer and winter. provoke distraction (up to 200 fpm) and annoyance (above 200 fpm).12 The Role of Color. As a further complication, temperature is not air velocity impact air velocity in feet per minute (fpm) completely determined by our sense of touch. The presence of particular colors found in a space can influence our perceptions of temperature as well as climatic 50 fpm and less 50 -100 fpm 100 - 200 fpm 200-300 fpm 300 fpm + qualities. Experiments reveal that unnoticed pleasant generally pleasant, from slightly drafty requires corrective but causing a to annoyingly drafty measures if work rooms painted in hues between blue constant awareness and health are to be or green can feel colder than rooms of air movement maintained at high efﬁciency with red or orange walls by as much as 7ºF (3ºC).13 Metabolism. The biggest source of difference in perception, however, Figure 05. Air Velocity Impacts. 3 UTSoA - Seminar in Sustainable Architecture may be our individuality. Our abosorbed, or reflected. The color of perception of surrounding items, bodies generally do a terrific job at a surface represents the frequency and glare can be reduced with light regulating temperatures, but each of the spectrum reflected back to from multiple sources. What is body has a different metabolism the observer. A surface that is white interesting, however, is how these that can change over the course of has most of the spectrum reflected items are only part of the story of years or in the space of a day. Our back equally, whereas one that is visual comfort, and how sometimes metabolisms differ based on long- black has had most of the energy it may be desirable for each of these term factors such as genetics and absorbed. answers to be subverted. sex, medium-term factors such as seasonality, and short-term factors The main focus on visual comfort Role of Other Senses in Interpreting such as exercise or diet. And has traditionally been light levels, Visual Cues. One problem is that metabolism even changes based on contrast, and glare, and upon though we receive light solely with external temperature, further making these there is agreement on many our eyes, our perception is often complex attempts to definitively principles. The first is the more conflated with a reaction occurring anticipate an experience of thermal intense the task, the brighter the light concurrently to our other senses. comfort by the designer, leaving required. This is the main reason For instance, the light that falls from the inhabitant of the architectural operating rooms are much brighter the sun is simultaneously perceived space to engage in a variety of than offices, which are in turn much with the warmth on our skin, which individualistic solutions for regulating brighter than living rooms (see most find a pleasurable experience.

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