Indoor climate The adaptive approach to thermal comfort

Transcription

1 Bachelor of Architectural technology and Construction management Indoor climate The adaptive approach to thermal comfort 7 th semester dissertation academic report Author : Tudor Mihai Panaitescu Consultant: Poul Børison Hansen

2 Dissertation title: Indoor climate the adaptive approach to thermal comfort Consultant: Author: Poul Børison Hansen Tudor Mihai Panaitescu Student identity number: Number of copies: 2 Number of pages: 35 All rights reserved no part of this publication may be reproduced without the prior permission of the author. NOTE: The dissertation was completed as part of a Bachelor of Architectural Tecnology and Construction Management degree course no responsibility is taken for any advice, instruction, or conclusion given within!

3 Contents List of ilustrations... Error! Bookmark not defined. List of tables... Error! Bookmark not defined. 1. Introduction Problem formulation Background information Problem statement Research questions Delimitation Summary of working process Research methodology Choice of theoretical basis Professional relevance and choice of subject Abstract Key words The thermal reception and comfort of humans Warm and cold receptors Temperature sensation and thermo-receptor activity Temperature sensation related to thermal comfort Acceptance of temperature drifts The effect of air movement on thermal comfort and sensation Discomfort caused by vertical air temperature differences... 12

4 3.2.1 Preferred temperature Local sensation and discomfort Heat and Cold aclimatization Heat acclimatization Cold acclimatization Health Adaptive thermal comfort Adaptive aproach to thermal comfort Adaptation Physiological adaptation psychological adaptation behavioral adaptation Field Studies, experiments and findings Adaptive comfort Standards General conditions Characterization of outdoor climate Range of acceptability Conclusions References... 34

5 LIST OF ILUSTRATIONS Fig.1 - regression lines represent the level of discomfort measured by the percentage of people that were feeling discomfort for 90 min and 180 min (Olesen, Fanger, Sholer, 1978, Indoor Climate symposium, p573) Fig.2 - measurement of relative heat loss in different areas using a thermal manikin (Olesen, Fanger, Sholer, 1978, Indoor Climate symposium, p574) Fig.3 - shows sweat loss in comparison with skin temperature when resting (Gonzalez, 1978, Indoor Climate symposium, p743) Fig.4 - shows sweat loss in comparison with skin temperature when exercising (Gonzalez, 1978, Indoor Climate symposium, p744) Fig.5 shows responses in terms of absolute heat production in individuals from various ethnic backgrounds (Gonzalez, 1978, Indoor Climate symposium, p747) Fig.6 - shows percentage of satisfied Pakistani workers (Nicol and Humphfreys, 2001, p.48) Fig.7 shows a comparison between PMV static model and adaptive model HVAC buildings (Hensen and Centerova, 2001) Figure 8 shows a comparison between PMV static model with NV adaptive model in buildings (Hensen and Centerova, 2001) LIST OF TABLES Table 1 shows average values of preferred temperatures (Olesen, Fanger, Sholer, 1978, Indoor Climate symposium, p.571) Table 2 shows results for comfort or discomfort caused by vertical air difference (Olesen, Fanger, Sholer, 1978, Indoor Climate symposium, p.572) Table 3 shows the results for annual energy consumption of a standard office using a computer simulator (Hensen and Centerova, 2001)

6 1. INTRODUCTION 1.1 PROBLEM FORMULATION BACKGROUND INFORMATION This report is a compulsory part of the 7 th semester of the Architectural technology and construction management program and it represents the final dissertation. The definition of thermal comfort is highly important in deciding a building s energy use and thus it s sustainability. Therefore, the aim of the report is to present studies and experiments bearing upon it PROBLEM STATEMENT Conventional ways of achieving what is understood today as a thermally comfortable indoor environment require a considerable amount of energy. Today, the overconsumption of energy leads to environmental damage, thus an urgent need to reduce the energy consumption is imperative. One of the main problems is in approaching thermal comfort in indoor climates is that current standards such as ISO/EN 7730 and ANSI/ASHRAE 55 are more or less based on a static model of thermal comfort. Only physiological aspects are considered when defining thermal comfort, when in fact there are many other influential aspects. The climate change and increasing pollution that we experience today requires a decrease in the demands for indoor climates when it comes to the thermal environment. Even though thermal sensations may be quite strong in environments that do not meet the desired thermal comfort, the human body has an amazing capacity to regulate its temperature through adaptation. A sustainable achievement of thermal comfort in indoor climates is often more complex than a question of setting standards in order to meet the occupant demands. In the future thermal comfort should be the result of the equal interaction between the building and occupants. In order to achieve thermal comfort in indoor climates people will need to focus on 1

7 adaptive approaches in order to maintain thermal neutrality, not only on changing the indoor thermal environment in order to meet their comfort criteria. Today thermal comfort is achieved by using a considerable amount of energy in order to reach standards for indoor climates that are unsustainable. Would a decrease in the demands for indoor thermal environment lead to significant energy savings without affecting the thermal comfort? RESEARCH QUESTIONS How do humans perceive the thermal environment? How is thermal comfort defined? How acceptant can humans be to temperature changes? Can we use temperature drifts in order to save energy in the summers? What is the concept of adaptive thermal comfort? Are there studies to prove its viability? Can an adaptive approach to thermal comfort lead to significant energy savings? DELIMITATION The location of a building is one of the most important factor when it comes to the thermal environment. The information in this report is mostly relevant to hot climates and moderate climates. The report is going to present scientific research, from early studies and experiments regarding thermal perception and comfort, acceptance of temperature changes and air movement, heat and cold acclimatization to recent studies done on the thermal adaptability of humans to an indoor environment. All this is presented and analyzed in order to find out if the energy savings made by using an adaptive approach to thermal comfort would be significant. 2

8 1.2 SUMMARY OF WORKING PROCESS RESEARCH METHODOLOGY The report is based on: -Analytical research existing studies and experiments concerning the thermal aspect of indoor environments are presented and analyzed in order to make a critical evaluation of the material -Empirical research a hypothesis that an adaptive approach to thermal comfort can lead to important energy savings is made, thus investigations are going to be made in order to approve or disapprove this theory CHOICE OF THEORETICAL BASIS The report is based on secondary qualitative data, found in scientific reports published in the book Indoor Climate the effects on human comfort, performance and health at the First Indoor Climate Symposium (reference no. 1,2,3,4,5,7) and on scientific reports found on the web (reference no. 6,8,9). The report also relates to EN/ISO 7030 (International organization for standards) and ASHRAE (American Society of Heating, Refrigerating and Airconditioning Engineers) PROFESSIONAL RELEVANCE AND CHOICE OF SUBJECT The way that we are achieving thermal comfort in buildings today is based on changing or creating buildings that fit the occupant demands. I write this report with the belief that occupants of a building should adapt to the given conditions mode than they do today. I believe that building designers should be allowed to take the adaptive capacity of humans into consideration when designing a building. Therefore, this report will present information to prove or disprove this hypothesis. A sustainable building is always a result of an integrated approach towards designing. Therefore, it is essential that a Construction Architect should be aware of factors that can influence the comfort, performance and health. 3

9 1.3 ABSTRACT Early experimental studies in test rooms concerning thermal perception are presented in order to give a better understanding of thermal sensation, thermal comfort and thermoregulatory activity. Same studies have shown that small temperature differences are not consciously distinguished, therefore further research is presented on the acceptance of temperature drifts, which can be used to save significant amounts of energy. Two potential problems that may occur when using temperature drifts are air movement and vertical air temperature differences. These aspects are analyzed in order to verify the degree to which they affect occupants during temperature drifts. Based on the hypothesis that thermal comfort also depends on factors beyond physiology, the concept of adaptive approach to thermal comfort is presented in contrast with current standards. Different types of adaptation are presented, ranging from behavioral, psychological and physiological adaptation. Being more accurate than test room experiments, field studies show examples of how effective the adaptive approach can be. Studies that compare the thermal comfort standards with field surveys in order to see the differences in comfort temperature are discussed. Also, calculations of temperature ranges are presented. Based on these ranges, a computer simulation is presented which proves the effectiveness of the adaptive approach by calculated net energy savings. Finally, revisions that have been recently proposed to ASHRAE Standard 55, are presented and include a new adaptive comfort standard that can be applied in certain circumstances KEY WORDS thermal comfort, acceptance, adaptive approach, standards, energy savings 4

10 2. THE THERMAL RECEPTION AND COMFORT OF HUMANS A good understanding of how humans perceive the environment is needed in order to assess what is an acceptable indoor climate. Studies and experiments (Hensel, 1978) have been made in order to define the main processes related to thermal reception. The thermal reception of humans (thermo-reception) is a process in which different levels of heat energy (temperatures) are detected by living things (Encyclopedia Britannica). It involves temperature sensation, thermal comfort and thermoregulation of the body. The thermo-receptive structures in humans are found inside the body and in the skin. They signalize the thermal state of the environment and the body. Thermal comfort and temperature sensation can be separated psychologically and physiologically. Temperature sensation is objective, while the thermal comfort is related to the subjective state of the observer. The terms describing temperature sensations are cold and warm, and thermal comfort and discomfort is characterized by the terms pleasant and unpleasant or satisfied and unsatisfied. The origin of signals for comfort and discomfort are the thermo-sensitive structures in the central nervous system, thermo-sensors inside the body and structures involved in shivering, sweating and blood circulation. Internal and external thermo-sensors together create the general thermal comfort, but are also involved in local thermal comfort. The principle is the same in the case of thermo-regulation. Thermo-receptors in the skin contribute to the integrated signals for thermoregulation, but in the same time signals are mediated through channels that are separate and are involved in temperature sensation. The local sensations are almost independent from the general state of the subjects. 2.1 WARM AND COLD RECEPTORS Warm and cold sensations are mediated through separate pathways from specific warm and cold receptors located in the skin. (coetaneous nerves) Cold and warm receptors have been established in human subjects by recording single fiber activity from coetaneous nerves. It has been shown 5

11 that cold and warm receptors are silent at constant skin temperatures. The maximum frequency of the static activity is in the range between 17 and 36 degrees C for cold fibers and between 41 and 47 degrees C for warm fibers. Studies show that cold receptors respond with an overshoot in frequency when they are faced with dynamic cooling, followed by an adaptation to a new static level, while dynamic warming leads to an undershoot and adaptation to a new level. In the case of warm receptors, the responses are in the opposite way, with an overshoot in dynamic warming and undershoot in dynamic cooling. 2.2 TEMPERATURE SENSATION AND THERMO-RECEPTOR ACTIVITY Specific warm and cold fibers mediate warm and cold sensations. It has been shown by experiments that warm or cold sensations can be selectively blocked by certain local anesthetics. The cold and warm sensations are not always conscious, whereas stimulation in small areas and small temperature changes excite receptors unconsciously. The sensations are only observed when a certain number of impulses per unit of time reach the central nervous system. The threshold for a conscious sensation is about 80 impulses/ second for a single cold receptor and 9 impulses/second for a single warm receptor. 2.3 TEMPERATURE SENSATION RELATED TO THERMAL COMFORT The sensation of a subject is dependent of his previous feeling of warmth. For example, warm stimuli applied on the hand of a hypothermic subject are considered pleasant and cold stimuli are considered unpleasant, the opposite phenomena were observed in the case of a hyperthermic subjects. Based on experiments and studies Herbert Hensel concludes whether the general state of thermoregulation may also modify the local cold and warm ranges. Subjects were exposed to different rooms with different temperatures, respectively 10 C, 30 C, 50C and C. The arm of the 6

12 subjects was thermally insulated from the ambient conditions and the hand was exposed to linear thermal stimuli +1.5 C/min and -1.5 C/min. In addition to that, the other hand was exposed alternatively water baths of 20 C and 40 C in order to judge the degree of pleasantness on a subjective scale. The environments of 10 C and 50 C did not alter the local cold threshold, but the pleasantness of cold stimuli is significantly modified by different room temperatures. The experiments show that the situation is different in the case of warm ranges as they increase to a certain extent with increasing room temperature. Therefore these findings signify that the sensory pathways for cold and warmth have different proprieties. The average skin temperature modifies the pleasantness of a dynamic warm stimuli applied to the forehead even though the internal body temperature is unchanged. The same principle applies to the pleasantness of static thermal stimuli exposed to the hand. If the palm is kept at 25 C and the room temperature is increased so as to bring the mean skin temperature from 31 to 37 C, the perception of the hand turns from unpleasant to pleasant. This affective change must be related to the thermal receptors located in the skin alone as the internal body temperature remains constant. This information directly implies that pleasantness or unpleasantness is not always related to the internal body temperature. Herbert Hensel s (1978) findings have showed that cold and warm receptors have different proprieties. Also he explained that the thermal comfort can be separated physiologically and psychologically, thus signalizing from the first International Indoor Climate Symposium in 1978 that discomforts don t always relate to physiological needs. Another important finding is that some changes in temperature are not always conscious and that small temperature changes are not distinguished by subjects. This last information implies that building occupants can tolerate certain degrees of temperature change. Further analysis is going to be made in this report on the acceptance of temperature drifts. 7

13 1. ACCEPTANCE OF TEMPERATURE DRIFTS Studies have been made at John B. Pierce Foundation laboratory (Larry G. Berglund, 1978) regarding the acceptability of indoor temperature drifts with the outside condition and the human adaptability to certain conditions such as natural heat or cold acclimatization, topics which are highly related to thermal adaptation of humans to the indoor environment. Traditional indoor environments have had constant temperatures. However, if the inside temperature of a building is allowed to drift with the outside condition, while the environment remains thermally acceptable to the building s occupants, important energy savings both for new and old buildings can be made. For instance, in the summer a building could be precooled with refrigeration or outside air at night when the performance coefficient is normally higher and outside temperatures lower. Then the temperature can be allowed to drift upward without cooling or with reduced cooling. Many solutions can be found according to the principle mentioned above such as using stored chilled water, increased building mass and/or a temperature ramp control system. Such designs can reduce the electrical demand during the day eventually leading to net energy savings. Larry G. Berglunds experiments conclude that slow temperature drifts of C/h are almost indistinguishable from traditionally preferred constant temperature by sedentary persons. The neutral temperature is determined by the clothing level of the occupants. A 0.5 C/h temperature drift which causes the ambient temperature to deviate from the neutral by 5 C wil meet the thermal acceptability demand of 80% (80% of inhabitants do not feel discomforts) according to Berglund s studies. An interesting observation made by Berglund was that during the first 2 hours of the drift, thermal sensations did not follow the temperature condition, meaning that the subjects were complaining less than expected in the first 2 hours compared with the remaining time, regardless of the fact that the temperature change was constant. The explanation for this occurrence can be the higher outer temperatures the workers were exposed to, thus increasing their heat tolerance. This can be due to the increase in body internal body temperature while exposed to the outside heat, thus being exposed to a lower 8

14 temperature indoors even when drifting up. These findings imply that further research should be done on the topic of heat adaptation and acclimatization. Therefore, studies done by R.R. Gonzalez on natural heat and cold acclimatization are going to be discussed later in this report. L.G. Berglund concludes that rates of temperature drift higher that 0.5C/h lead to failure in meeting the acceptability threshold of 80%. However, the adaptive capacity has not been considered in the test rooms. If subjects would have had means of adapting to the given environment (for example: fans, opening windows, changing clothing) even higher temperature drifts can meet the 80% acceptability demand. These results indicate that there is a basis on which to search for solutions for energy conservation that can meet the occupant thermal comfort by letting the temperature drift with the outside condition. The potential savings will be determined by the building, local climate and internal loads. Temperature drifting can be particularly effective for existing buildings which have limited capacity for energy conservation compared to a new design. One aspect that needs to be mentioned is that the environment Berglund uses for these particular experiments was very homogenous, there was no air movement and there were no vertical air temperature differences. B.W Olesen from the Technical University of Denmark criticized Berglund s work. In a discussion from the First Indoor Climate Symposium in 1978 he stated: In your tests the environment was very homogenous, i.e. small air velocities, no radiant asymmetry or vertical air temperature differences. That is not always the case in real buildings. Many of the occupants will be exposed to local thermal influences and a drift in the temperature level in the room can cause discomfort and more than 80% may be dissatisfied. I think that this is something one should be aware of when using temperature drifts for saving energy. (Inoor Climate Symposium 1978, Discussion p.523) Berglund answered to Olesen s comment by saying that the conditions of his experiment are similar with the non-perimeter office areas. In such spaces, 9

15 continuous air movement can reduce the effect of vertical difference in temperature, but in the same time can threat as long as the contrary is not proven. There is a possibility that the occupants can be exposed to local thermal discomforts due to the fact that there are vertical differences of temperature in most building. Also, air movement can also be a potential problem. Therefore, further analysis regarding the effects air movement and of vertical temperature difference is going to be made in this report in order to measure if the extent to which the effects are caused is significant. 3.1 THE EFFECT OF AIR MOVEMENT ON THERMAL COMFORT AND SENSATION The convective heat loss of the human body can be affected by the air movement and eventually can affect the thermal sensation of the inhabitants. However, experiments done (D.A. McIntyre,1978) at the Electricity Council Research Center in Chester, UK are going to be discussed in order to analyze the magnitude of the air movement effects on thermal comfort and sensation. D.A McIntyre s experiments show that a isothermal jet of speed up to 0.25 m/s with a temperature of 23 C that is blown on the cheek does not produce a discomfort if the exposure time is short (2 min). In the case of longer exposures to air movement with a temperature of 21 C, the subjects proved not to feel any discomfort at speeds of 0.2 m/s. Therefore, the air movement speed and temperature are factors that may decide how the thermal affect is interpreted. In another experiment, people adapted to a cool draught of 21 C for 30 minutes. The initial sensation of cold has decreased or disappeared, even though there was no reduction in any feelings of discomfort. Therefore, the pleasantness and unpleasantness of a draught are determined by the subjects pre-existing feelings of warmth. D.A. McIntyre concludes that there are many difficulties in setting out the comfort threshold for air movement in order to ensure no discomfort from 10

16 draughts. There are other factors besides air temperature and moving air speed that influence the heat loss and thermal sensation of the body. The direction of airflow, body posture and temperature affect the heat loss and the nature of the variation of the air speed significantly affects the strength of the sensation. These are the physical factors that affect the heat loss. There is also a more subjective variation, person when it comes to pleasant or unpleasant sensations caused by air draught. The same air draught in the same environmental conditions can be pleasant for some subjects and unpleasant for others. In a large group of people is very probable that some people will feel uncomfortable, for reasons that may not be connected with the indoor environment. If given the opportunity to explain their discomfort to an environmental cause, some people will do so. D.A. Mclyntre s findings imply that detectable air movement can be described as causing discomfort even though it s actual physical effect minimal. D.A. Mclyntre shows in these studies that in many cases the discomforts produced by air movement are just a matter of subjective state and don t have a significant physiological effect at low speeds, on the contrary, the effect being minimal. The level of air movement is determined by too many variables, not only by the air conditioning and ventilation system. For example, a disturbance can even be caused by a person walking and can create air speeds of 0.5 m/s on a radius of 1 m. This has been observed experimentally by D.A. Mclyntre to cause complains from a person sitting in an office near the access pathway. This information implies that trying to regulate all the possible variables that affect the subjective discomforts created by air movement would be too consuming, regardless to say that there are little to no physiological effects when the speeds and temperatures have acceptable thresholds. However, high speeds of air movement can produce significant changes in thermal sensation and it is recommended to avoid such circumstances. 11

17 3.2 DISCOMFORT CAUSED BY VERTICAL AIR TEMPERATURE DIFFERENCES Vertical differences in room temperature are occurring in most buildings due to the fact that warm air will always tend to rise and cold air will always tend to fall, thus creating the possibility for local thermal discomfort. B.W. Olesen together with M. Sholer and P.O. Fanger (1978) from the Laboratory of heating and air conditioning of the Technical University of Denmark have experimented with this phenomena in order to determine what are the limits of temperature difference between head and ankle for a subject in thermal neutrality so as to produce no feeling of discomfort. Thermal neutrality for a person is described as a condition in which he does not prefer nor a higher or lower temperature. Thermal neutrality depends on the activity, clothing and climate parameters like air temperature, mean radiant temperature and relative air velocity and humidity. Thermal neutrality is a necessary condition in order for a person to achieve thermal comfort. Four experiments are going to be discussed, with 16 subjects, 8 male and 8 female that were exposed to four different vertical temperature differences (0.4 C, 2.5C, 5.0C and 7.5C) between the ankle level and head level, the higher temperature being at the level of the head. Each experiment lasted for 3 hours. In order to achieve the temperature conditions mentioned above a special test room (fig.5). with electrical foil heating on the ceiling and upper walls and water cooed panels on the floor and lower walls. The front wall, including the door was made out of plastic foil (ployvnylchloride). In order to reduce the radiant emission and respectively the vertical difference in radiant temperature all the surfaces except the wall with the door were covered with aluminum foil. The room is placed in a hall with a controlled temperature of 21 C. The differences in vertical temperatures were monitored using 11 thermo elements at 11 levels between 0.05 m and 1.95m above the floor level. Also, the surface temperatures were measured. 12

18 The subject was sedentary on a chair that was sitting higher than the floor level so as the center of the subject is at the height of 1 m (fig5). The heights that represent the level of the ankle and head are 0.5m and 1.5m. In the first experiment of the the vertical temperature difference was small (0.4C), so the environment was approximately uniform. Each subject chose according to his wishes his own preferred ambient temperature. In the other 3 experiments, for the first 1.5 hours the temperature at the center of the subject was kept at the desired temperature identified in the first experiment. For the remaining 1.5 hours, the temperature at the center of the subject was changed at the request of the subject, the vertical difference remaining the same (2.5C, 5.0C, 7.5C) PREFERRED TEMPERATURE In the first experiment the preferred temperature was estimated as the average temperature of the 3 last measurements that were made in the last half an hour. The average values are listed in the table below. Table 1 Average values of preferred temperatures 13

19 3.2.2 LOCAL SENSATION AND DISCOMFORT In order to estimate whether there was a discomfort or not the subjects were asked to vote if they felt uncomfortable or not. The discomforts were measured between minutes 60-90, the end period when the air temperature was not changed and between minutes when the air temperature had been changed related to the subjects wishes. (Fig.8) The numbers and percentages of discomfort felt by subjects, and the average votes for all the local thermal sensations are listed in Table 2. Table 2 Results for comfort or discomfort caused by vertical air difference In fig.1 regression lines represent the level of discomfort measured by the percentage of people that were feeling discomfort. The 2 different lines represent the period of time that the subjects were exposed to the controlled 14

20 environment, 90 minutes and 180 minutes. The lines intersect the coordinate axis at 0.3 % for 180 minutes and 7% for 90 minutes, meaning that these percentages represent the number of people that feel discomfort when exposed to an uniform thermal environment. Therefore any value above 0.3% and 7% must be caused by the vertical air temperature. If it is accepted that 5% are experiencing discomfort due to a vertical air temperature difference, Fig. 10 shows that the maximum difference between head and ankles should be 2.8 degrees C.. Fig. 1 The most significant results from this study are measurements done with a thermal manikin; therefore fig.11 shows the changes of the heat losses from 15

21 different regions when exposed to vertical temperature differences. The change in the average heat loss was less that 4%. 16 Fig. 2 The experiments made at the Technical University of Denmark suggest that for sedentary people the vertical temperature difference between the head (1.1m) and the ankle (0.1 m) should not be more than 3-4 degrees C in spaces with high demands to the indoor climate. In this case, less than 5-10% of the population is expected to feel discomfort caused by vertical temperature difference. However, the subjects again did not have means of adapting to the given conditions. In the case of cold feet, clothing that has a better insulation property can be used as to achieve thermal neutrality. Also, experiments made with a manikin at the Technical University of Denmark conclude that the overall heat loss caused by vertical air

22 temperature differences is less than 4%. This value is not of significant impact and can be easily solved by adaptation to the given environment, for example by proper clothing in order to achieve thermal neutrality with no local discomforts. This solution is far less energy consuming compared with the amount of energy used to change the building environment in order to meet the 3-4C vertical air temperature difference demand and can also bring the occupants to thermal comfort. 2. HEAT AND COLD ACLIMATIZATION 4.1 HEAT ACCLIMATIZATION Heat acclimation is a thermoregulatory reaction of the body when exposed to laboratory heat stress. Summer acclimatization or natural heat acclimatization refers to physiological responses caused by the normal course of seasonal change or for indigenous populations. Laboratory heat acclimation experiments (R.R. Gonzalez, 1978) show that the thermoregulatory activity is increased after being stimulated to heat. The thermoregulatory activity is signalized by increases in sweat rate and skin blood that are happening with a lower displacement in internal temperature. Such effects have been tested by R.R. Gonzalez for the thermoregulatory relationship between sweating to body temperature, in the case of severe heat stimulation combined with physical exercises. Heat acclimation in hot-humid environments experiments proved to cause significant discomfort estimates. In the case of warm-dry heat acclimation the discomfort estimates are reduced, the thermal affect being perceived as pleasant. This effect is probably related to sweat evaporation. As previously mentioned in the report, H.Hensel has shown that the patterns of sensory inputs for thermal sensation and general thermal comfort have separate pathways. Thermal sensations are functions of rate of temperature change and air temperature, while thermal comfort and discomfort are regulated by sweating rate to thermal load. Thermal sensations do not predict responses of great magnitude especially in warm environments as they not expected to change significantly by any cold or heat acclimatization 17

23 process. Therefore alterations in thermal comfort that occur during heat acclimation can be considered immediate reactions to those thermoregulatory responses. A study referred by R.R. Gonzalez finds that life in humid or dry environment confers 50% acclimatization when the ratio of sweat and body temperature responses are compared and that the physical activity of people has a role of great magnitude in responses to heat stress. The study also concludes that the main response to heat stress is a behavioral subjective change, the climate being the main variable for the degree and type of discomfort. Sensory and physiological responses may be very different from one individual to another, the variable being the task performed. Heat acclimated individuals, regardless of activity or clothing, should prefer higher ambient temperatures and higher acceptability of given warm environment when compared to a state in which the acclimation did not occur. Another study referred in R.R. Gonzalez s work (ref) concludes that natives that lived in certain hot-wet climates, with various occupations and assumed to be acclimatized, did have a preference for higher ambient temperatures up to 32-33C in the summer seasons. The results of different studies have been compared, and it was found that people s judgment of thermal neutrality is changed in the same direction as their thermal experience. Other studies explored the physiological and affective states changes happening during seasonal heat acclimatization in 20 young males. The subjects were tested in different times of the year, in June and respectively in August (after 45 days), while resting and doing light exercises, being heavily clothed and unclothed. Therefore, the effects of different temperature levels at 2 different clothing levels on body temperature were assessed in order to monitor the sweating responses for un-acclimatized and acclimatized subjects. The aim was to study the 20 subjects in the different clothing and activities; however, only 5 subjects have had complete physiological measurements during both tests. The air temperature was chosen in such a way that a temperature of 6C higher than the temperature considered neutral by each subject. The experiment concludes that there were no significant differences in the affective states of the resting subjects, clothed or unclothed. On the other hand, the subjects that were doing light 18

24 exercises preferred a warmer temperature, had lower internal temperatures, thought they sweat less and felt cooler Fig. 3 shows these results on the subjects by recording the evaporative weight loss. The skin wetness was determined as the ratio of observed evaporative weight loss to the maximum evaporative capacity. The highest skin wetness that occurred in the experiments done in June was less than 23%. Regardless that the conditions were the same in August, the skin wetness both for resting and exercising subjects and was significantly higher. Fig.3 Fig. 4 shows that the subjects that had direct sweat loss measurements had a displacement towards lower internal body temperature without changing the proportional control coefficient for evaporative loss. 19

25 Fig.4 The fact that acclimatized subjects prefer a higher ambient temperature can be explained by the lower internal body temperature. The most important phenomena that took place in these experiments was that to the same exposure and same conditions the skin wetness increased, the internal body temperature shifted towards the lower internal body temperature and the preference changed to a warmer environment. These responses apply to normal healthy individuals. Therefore, if reduced cooling and improved physical conditioning by some physical activities would be acquired by the general population the demand for energy can significantly decrease. The fact that the subjects preferred ambient temperature higher in August proves that the human perception of the thermal environment changes. Indoor temperatures could be allowed to rise during the summer months with only minimal dissatisfaction, leading to energy savings. 20

26 4.2 COLD ACCLIMATIZATION There are several difficulties in finding if cold acclimatization exists due to the fact that there are many variables that intervene. For example, the heat loss in extreme cold environment is closely linked with metabolism and body fat, factors which vary considerably in the population. Therefore, resting humans can maintain heat balance and be protected in the cold with minimal physiological challenge. However, exposure to extreme cold produces the most significant physiological adjustment. Skin cooling, reduced blood flow and increased metabolism the eventually leads to shivering are some of the body s mechanisms activated in a cold environment. However, the shivering mechanism caused by increased metabolism is not as efficient in humans as is other mammals, thus it cannot maintain total body temperature. Studies prove that long exposures to cold can create a mechanism alteration both in humans and animals. By testing fishermen from the Gaspe peninsula, it has been proven that there are some individuals that show a more rapid start of cold induced blood vessel dilation when exposed to very cold environments. These subjects appear to have less cold related discomfort than normal individuals. However, the Korean ama divers seem to be an exception as they don t show the same blood vessel dilation response. The response of these individual when exposed to very cold environments is a great narrowing of blood vessels. They have a greater maximal tissue for fat under the skin, and increased shivering threshold and an increased metabolic rate. The fact that there is a difference between the Gaspe fisherman and Ama divers implies that the type of cold acclimatization is different. Studies also show that an reduction of heat production mechanisms has been accounted in humans so that any increase in the average skin temperature from the given temperature in less in acclimated or acclimatized subjects than in non-acclimated and non-acclimatized individuals. Examples of these responses are shown in fig.5 (left panel) shows cold acclimation reactions in 2 different studies, before cold exposure and after prolonged exposure to a temperature of -6C, in a regime of 12 hours a day 21

27 for a duration of 2-3 weeks. The graphic in fig.5 concludes that for any given average skin temperature less heat is produced. This information implies a change in the response system caused by prolonged exposure to cold. In the right panel shown in Fig.5 responses in terms of absolute heat production in individuals from various ethnic backgrounds are shown. Fig.5 Interesting phenomena occurred in the case of the Aborigine and Alcaluf subjects. It seems that they allow their body to decrease in temperature without a response of increased metabolism. Studies referred by R.R Gonzalez have shown that the preferred temperature of winter swimmers compared with normal individuals, both clothed at 0.6 clo, is not different. The same studies have shown that female winter swimmers have had different temperature preferences compared to male winter swimmers. This information implies that the results are complicated by lack of metabolic data. 22

28 R.R. Gonzalez s studies show that the building temperatures in the winter have serious consequences on individuals, unlike the case of heat acclimatization. Therefore, discomforts caused by cold are harder to manage by the human body compared to body heating. However, in the discussion about R.R. Gonzalez s work from the International indoor climate Symposium from Copenhagen in 1973, I. Holmer has referred some evidence of some kind of psychological adaptation to cold. For example subjects exposed to cold perceive a given hand skin temperature as less cold compared with the subjects that were not exposed to cold. 4.3 HEALTH Health is one of the most important factors in choosing the adequate environment. The human needs regarding healthy survival to heat or cold stress are often more important than the subjectively preferred thermal comfort. However, in many situations like in elderly people or young children hypothermia is a common incidence. Wide numbers of people die in the Great Britain due to hypothermia. R.R. Gonzalez s concludes in his work that that in the winter it can be harder for the human body to adapt to the thermal environment in order to achieve energy savings. However, recent studies show that there are other types of adaptation besides the physiological adaptation that can be important in in order achieve thermal comfort. In the summer, the human body acceptability of thermal environment can play a significant role in strategies for energy saving. This applies for physically fit and healthy individuals; therefore close attention must be paid when dealing with less fit and debilitated individuals. L.G. Berglund s studies, followed by studies made by R.R Gonzalez created a basis for the concept of adaptive thermal comfort, as they have proven that humans have an astonishing mechanism of adaptation to the given environment. 23

29 3. ADAPTIVE THERMAL COMFORT 5.1 ADAPTIVE APROACH TO THERMAL COMFORT In the past, researchers did not consider sustainability when setting thermal comfort standards, thus the approach used for achieving thermal comfort leads to unnecessary energy consumption. Recently, studies have been developed on the adaptive approach towards thermal comfort (Brager and De Dear 1998). These studies are based on the hypothesis that factors beyond physiology and fundamental physics are important in creating people s thermal comfort. Such factors are: contextual factors (season, social condition, building design), demographic factors (gender, status, age) and cognitive factors (preference, expectation, attitude). In an adaptive approach, thermal comfort is achieved through an interaction between the building occupants and the environment they are occupying. The more possibilities are given to the building occupants to adapt themselves or to change the environment, the less instances of discomfort will happen. 5.2 ADAPTATION Adaptation presumes all physiological mechanisms of acclimatization and it concerns all psychological and behavioral processes applied by the occupants of a building aiming to improve the indoor climate to fit their personal requirement. (1) carte mica This definition sets a basis for 3 different categories of adaptation to an indoor environment: physiological adaptation, psychological adaptation and behavioral adaptation. 24

30 5.2.1 PHYSIOLOGICAL ADAPTATION Physiological adaptation to an indoor environment refers to genetic adaptation and acclimatization. (see chapter 4) PSYCHOLOGICAL ADAPTATION Psychological adaptation to an indoor climate refers to an altered perception and reaction to thermal information. In contexts where building occupants have a certain degree of control over their environment, their thermal sensation and satisfaction can be altered. People that live year-round in environments that are controlled by air conditioning develop high expectations, thus they may become unsatisfied easily if the thermal environment is modified from their comfort zone BEHAVIORAL ADAPTATION Behavioral adaptation refers to modifications that a subject can do to the indoor thermal environment, consciously or not, in order to change his thermal perception. The heat balance of humans is can be mediated by personal modifications such as changing the level of clothing, changing positions etc. and technological and environmental modifications such as opening windows, using fans and any other possible activity. 5.3 FIELD STUDIES, EXPERIMENTS AND FINDINGS The ASHRAE Standard 55 was initially related to the heat balance of the human body, based on the assumption that thermal sensation is strictly influenced by environmental factors. These standards are set based on experiments done in test rooms, which neglect the factors mentioned above. 25

31 Therefore field studies will be presented further in this report, in order to prove the effectiveness of the adaptive approach to achieving thermal comfort. A field study done in Pakistan by Nicol (1999), measures the percentage of workers that feel comfortable in an office building from Pakistan. The information was collected over a period of one year so the comfort temperature was changing continuously. The workers in Pakistan use air movement and other adaptive methods in order to achieve thermal comfort, fans often being available in offices. This is a remarkable example of how effective the adaptive activities of building occupants can be. The curve shows the average of comfortable workers and each point represents the proportion comfortable in a particular city and month. The results can be seen in fig.6. Fig.6 26

32 Field studies (J.L.M Hensen and L. Centnerova, 2001) compares the comfort temperature of the static model based on the predicted mean vote (PMV) from ISO 7730 standards with experimental findings regarding comfort temperature in a large number of buildings and wide range of climate zones. The results are shown in fig.7 for centrally air conditioned buildings and in fig for naturally ventilated buildings. Fig.7 The diagram in fig.7 shows that the comfort temperature is very close to the predicted mean vote model. However, in the case of naturally ventilated buildings, subjects seem to have a higher acceptability towards temperature (fig.8). This phenomena can only be explained by the adaptive thermal comfort theory. 27

33 Fig. 8 Based on these findings L. Centnerova and J.L.M Hensen have calculated the required indoor temperature ranges for 90% satisfaction for the adaptive approach in centrally air conditioned and naturally ventilated buildings, located in an moderate climate (Prague, Czech Republic). The diagram in fig compares the calculations with standards based on EN/ISO7730. These findings prove that there are significant differences between the comfort temperature ranges obtained by using the adaptive model when compared to the standards. The graphic in fig.. shows for example that in the heating season, for naturally ventilated buildings using the adaptive approach, the minimum temperatures can be 2 C lower compared with the standards. 28

34 A computer simulation also made by L. Centnerova and J.L.M Hensen estimates the energy consumption of an standard office for 2 persons. Using the temperature 3 ranges that were previously presented, the absolute and relative total annual demand is shown in table. for 2 for different geographical locations facing different orientations. Table 3 1 Adaptive model for HVAC buildings 2 Adaptive model for naturally ventilated buildings 3- ISO EN 7030 standards Table 3 proves that in moderate climates, net energy savings can be made by using the adaptive approach both in centrally air conditioned buildings and even higher savings for naturally ventilated buildings. The ranges presented earlier are calculated in such a way that 90% of the building occupants are estimated to feel thermal discomfort and the minimum and maximum temperature is different when compared with the ISO EN

35 standards. Therefore, there is a need to include the adaptive capacity of humans in indoor climates. 4. ADAPTIVE COMFORT STANDARDS Revisions have been recently proposed to ASHRAE Standard 55 (Brager, de Dear,2001) include a new adaptive comfort standard that allows warmer temperatures in an indoor environment for naturally ventilated buildings during the summer season. The adaptive comfort standard is based on sets of data gathered from field studies in 160 air conditioned and naturally ventilated buildings, located in 4 continents. 6.1 GENERAL CONDITIONS ASHRAE Std. 55 presents the new adaptive comfort standard as Section 5.6 Optional method for determining acceptable thermal conditions in naturally conditioned spaces (Brager and Dear, 2001). This means that the traditional standard comfort zone is still applicable in all circumstances and the adaptive comfort standards is offered as an option only in specific circumstances. These circumstances are: - naturally conditioned spaces where occupants have control over thermal conditions by opening/closing windows, while windows should be easily accessible - The spaces are allowed to have a heating system, but the method must not be applied when it is in operation - The spaces are not allowed to have mechanical cooling systems - The spaces can have a mechanical ventilation system as long as it is with unconditioned air and in this case, windows must be the main factor of regulating thermal conditions 30

36 - Occupants should be sedentary and must be able to freely adapt their clothing to the indoor/outdoor environment - naturally conditioned spaces where occupants have control over thermal conditions by opening/closing windows, while windows should be easily accessible Some researchers have supported the fact that those adaptive comfort standards should be applicable in mixed modes building spaces (where both air conditioning and opening windows are present) or task/ambient conditioning where occupants have some control over some aspects of thermal conditions. The main point of the arguments was that personal control plays an important role in altering thermal expectations, therefore adaptive comfort standard is a more accurate representation of thermal responses in their realistic situations, compared with the laboratory studies. 6.2 CHARACTERIZATION OF OUTDOOR CLIMATE In the original analysis, adaptive comfort standard has been expressed through effective temperature. It has been later agreed that meteorological data was and a more accessible index. Therefore, adaptive comfort standard is defined as the arithmetic average of the mean daily minimum and maximum temperatures for the moth in question. 6.3 RANGE OF ACCEPTABILITY The original analysis concluded a regression line of optimum temperatures that were derived from temperature preference and thermal neutralities. It was decided afterwards that a range of temperatures, not an optimum temperature should be presented as part of adaptive comfort standard. The ranges of 80% and 90% acceptability were discussed. In the end, both ranges of acceptability were chosen, thus leaving the possibility to choose depending on the indoor thermal environment requierment. Also, 90% acceptability should be chosen in the case of buildings that can have significant vertical air differences. As the computer simulation presented previously in the report proved that an adaptive approach to thermal comfort led to net energy savings also in air conditioned buildings. The savings were not as significant as in the case of natural ventilation, but there were still net energy savings. This 31