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The human body is enveloped in a natural convection that is created by the body’s own metabolic heat. This natural convection does not cover the body’s surface equally, however, so disturbances caused by outside airflows are also not equal over the body surface. In this study, horizontal local airflows of various temperatures and velocities were directed at two locations on the bodies of several subjects: the backs of the necks and the left sides of the ankles. In this paper, the subjects’ perceptions of temperature and air motion at both locations were compared during experiments held in winter. Airflows directed at the ankles were perceived to be higher in temperature and velocity than identical airflows directed at the back of the necks, while airflows directed at the neck produced greater thermal comfort than identical airflows directed at the ankles. Therefore, the percentage of dissatisfied (PD) was smaller at the neck than at the ankles. In practical terms, to prevent the sensation of being cold, low-temperature airflows directed at the ankles should be avoided, and to increase comfort at the neck, high-temperature, high-velocity airflows should be avoided. Keywords: back of neck; ankle; local airflow; sensation; thermal comfort 1. Introduction and Gonzales and Nishi (1976). People living in hot and humid climates enjoy a good The conditions of thermal comfort differ for the back breeze, but the same breeze will cause discomfort to of the neck and the ankles. Homma (1988) suggested those living in cool and mild climates. Although air that the human body is enveloped by rising airstreams, movements are needed even in cool climates to increase and the velocity corresponds to the highest acceptable comfort and freshen the air in enclosed living spaces, air velocity for comfort. Toftum, Zhou, and Melikov these air movements can produce unwanted cooling (1997) showed that at 20˚C and 23˚C, an airflow from effects. Rather than directing the airflow against the below was perceived as being the most uncomfortable whole body, it is more practical to send air to a specific followed by airflows towards the back and front. At 26˚C, location on the body that is sensitive to the temperature the airflow from above and towards the back caused the and velocity of the airflow but will not be disturbed by most dissatisfaction due to the draught, but generally it. To find such a location, the mechanism of sensation only a few of the subjects perceived discomfort at this caused by local airflows should be divided into two temperature. Homma (2001) studied the physical side stages. The first stage is physical stimulation of a body’s of the thermal comfort of a local draft. A thermal manikin surface by the airflow. A local airflow may cause local was used to compare the effects of the draft at the back differences in the stimulation of a body surface because of the neck and at the ankle. The results indicate that it travels through a natural convection boundary layer. local airflows affect the ankles more strongly than the The second stage includes physiological perception of necks. the airflow at the surface and the generation of sensation In the present study, local airflows with a range of from the perception. velocities wider than that defined by ASHRAE and ISO Various research results have been published on local standards as allowable velocities were directed at the sensation. Houghten et al. (1938), and Fanger and back of the neck and at the ankles of the test subjects. Christensen (1986) suggested that the backs of the necks These locations were chosen because the natural were less tolerant of cold drafts than the ankles. On the convection of body heat starts at the ankle level and fully other hand, the importance of the temperature in the develops at the neck level. The differences in the subjects’ lower part of a room was suggested by Wyon et al. (1969), perceptions of temperature and airflow, and their feelings of comfort were examined. If a draft is felt more strongly *Contact Author: Listiani Nurul Huda, Graduate Student, at either of these locations, it is effective to limit the Department of Architecture and Civil Engineering, Toyohashi draft only at this location. This study used human subjects University of Technology, Toyohashi Japan, 441-8580 in order to find a range of comfort that reduced Tel: +81-532-44-0111 (ext. 5607); Fax: +81-532-44-6831 discomfort at these locations. In order to distinguish the e-mail: firstname.lastname@example.org physiological responses of a human body, the following (Received November 8, 2003 ; accepted April 6, 2004) laboratory experiment was conducted. Journal of Asian Architecture and Building Engineering/May 2004/62 55 2. Design and Procedure of Experiments electrical current to the modules; switching the direction 2.1 Design of the electrical current changed the direction of the heat The experiments were carried out in the climate flow. chamber of the Building Environmental Laboratory, The change in the temperature of the airflow was Toyohashi University of Technology (TUT), Japan, completed in five minutes by supplying more power than during the winters of 2002 and 2003. Four different was required to maintain the temperature. The applied combinations of temperature and air velocity were airflow had low turbulent intensity. The standard investigated. In the two temperature experiments, the deviation of the airflow was 0.02 m/s when the velocity temperature of the local airflow was adjusted in at the nozzle face was 0.25 m/s. It increased to 0.08 m/ increments of 5˚C while the air velocity was maintained s when the velocity at the nozzle face was 1.00 m/s. at 0.5 m/s. In one experiment, the temperature was adjusted upwards, from -10, to -5, to 0, to +5, and finally to +10˚C from the laboratory temperature. This combination was labeled tuvc. The reverse temperature sequence was labeled tdvc. In the velocity experiments, the velocities of the local airflow were adjusted from zero to 1 m/s and vise versa in steps of 0.25 m/s, while the temperature was maintained at the ambient temperature. In the increasing-velocity experiment, labeled tcvu, the local airflow velocity started at zero Fig.2. Section of Draft Producer and peaked at 1 m/s. In the decreasing-velocity experiment, the velocity adjustment schedule was reversed, starting at 1 m/s and ending at zero, and was 2.2 Procedure labeled tcvd. The schedules of the experiments are shown The subjects were TUT students, who were paid for in Figure 1. their participation. The subjects’ physical data are listed in Table 1. Each subject was exposed to all four conditions of the experiments. In the winter of 2002, the subjects wore school clothes that were normal for the winter season. In the winter of 2003, the subjects were requested to wear a combination of uniform clothes. During each experiment, the subject sat quietly at a desk and read. Table 1. Data subjects in the temperature and velocity change Fig.1. Schedule of Temperature/Velocity Changes The laboratory was thermally well isolated from outdoor temperature changes. The temperature was controlled to between 22˚C and 24˚C. In an experiment lasting 95 minutes, the temperature change was less than 0.5˚C. The temperature gradient between 0.1 m and 1.1 m above the floor was less than 0.3˚C. The mean radiant A local airflow was directed at the back of the neck temperature was identical to the air temperature in the and at the left side of the ankle of the subject. The areas where the experiments were conducted. During the distance between the nozzle and the objective location experiments, the average outdoor temperature was 5˚C was 0.4 m. During the experiment, the subject was and the relative humidity was between 55% and 60%. exposed to the airflow and asked to fill out a Two draft producers were constructed using thermo- questionnaire consisting of semantic questions on modules that pumped heat to or from one side and thermal sensation, perception of airflow, and thermal discharged it to the other side of the module, and either comfort at the two body locations. cooled down or warmed up the blown air. A section of The subjects were allowed 20 minutes to acclimate to one draft producer is shown in Figure 2. The temperature the thermal conditions in the laboratory. During this of the local airflow was controlled by means of the period, they received instruction on filling out the 56 JAABE vol.3 no.1 May. 2004 Listiani Nurul Huda questionnaire. During the next 75 minutes, the subjects sensation in all four experimental conditions ranged from were exposed to local airflows having one of the above -0.829 to 0.744 for the necks and from -1.110 to 0.618 four conditions. Five consecutive 15-minute periods for the ankles. consisted of stepped changes in either temperature or Figure 4 (a) shows the results of the temperature- velocity. Three times during each 15-minute period, the change experiments. All of the lines for thermal sensation subjects noted their responses on the questionnaire. (See at the necks and the ankles increased with temperature. also Figure 1.) After the experiment, the responses were The gradients of the regression lines were lower at the converted into numbers for statistical evaluation. The ankles than at the necks. For the airflow with a questionnaire is shown in Figure 3. temperature difference of -10˚C, the thermal sensations at the neck and ankles were slightly cool. The thermal sensation increased gradually as the temperature rose, and approached neutral sensation at an airflow temperature difference of +10˚C. Most of the votes indicated cooler sensations at the ankles than at the necks. The gradients of the regression lines had different trends in the two velocity-change experiment, as shown in Figure 4 (b). In the velocity increase experimental condition (tcvu), the regression lines were steeply negative at both body locations. The values for the ankles Fig.3. Design of the Questionnaire were less than those for the necks. When the air velocity was 0 m/s, the average votes at the necks and ankles 3. Results The means and standard deviations of the subject’s ranged around a slightly warm sensation, and shifted to votes regarding thermal sensation, airflow perception, a range around a slightly cool sensation when the air and thermal comfort were calculated using the SPSS- velocity was 1.00 m/s. All of the votes at the ankles were Statistical Package. The results are shown in Table 2. lower than those at the neck. In the velocity-decrease The ANOVA test, which had a confidence interval of experiment (tcvd), the gradient was very gently but 95%, shows the votes to the three questions for the four still negative at the necks, but was positive at the ankles. When the air velocity was 0 m/s, the thermal sensation experimental conditions. The votes were significantly at the neck was almost neutral and slightly decreased as different for the necks and the ankles and had a the air velocity increased, while it increased at the ankles. covariance coefficient (F) larger than 4, as shown in Table At an air velocity of 1.00 m/s, the thermal sensation was Table 4 shows a statistical analysis of the votes by slightly cool at the necks but slightly warm at the ankles. gender to the three questions in the questionnaire. The The votes for thermal sensation were significant, with gray colored portions indicate statistical results that were a probability (p) of less than 0.005 in all of four not significantly different. experiments and at both body locations. The thermal The ages, heights, and weights of the subjects had no sensation in the temperature- and the velocity-change significant influence on the responses for the three experiments differed significantly for the necks and the ankles, with a significance level of 5% and a p value of questions. less than 0.005. 3.1 Thermal Sensation The mean votes by males and females to thermal Table 4. Comparison of ANOVA results for male and female subjects Table 3. ANOVA results for tuvc, tdvc, tcvu, tcvd Table 2. Mean and Standard Deviations by Experimental Conditions JAABE vol.3 no.1 May. 2004 Listiani Nurul Huda 57 Fig.4. Thermal Sensation Votes by Temperature and Velocity Change Experiments Fig.5. Airflow Perception Votes by Temperature and Velocity Change Experiments 3.2 Airflow Perception the ankles, as shown in Figure 5 (b). At low velocities, The means for all the votes in the temperature- and the airflow was only very slightly perceived at the both velocity-change experiments by males and females locations but the perception became more definite when ranged from 0.298 to 0.808 at the necks and from 0.555 the air velocity was at the highest level. At air velocities and 0.713 at the ankles. The regression lines for the below 0.25 m/s, the perception of airflow was lower at temperature- and velocity-change experiments had the necks than at the ankles. At air velocities above 0.25 different gradients, as shown in Figure 5. In the m/s, however, the perception of airflow was higher at temperature-change experiments, the regression lines the necks than at the ankles. were lower at the neck than at the ankles. At the cooler The votes for airflow perception were significant, with temperatures, the airflow was perceived to be slight at the p<0.005 for all four experimental conditions and at both locations and decreased gradually as the both locations. Airflow perceptions at the necks and temperature difference increased. The perception of ankles in the temperature-change experiments differed airflow at the ankles was more definite than at the necks. significantly from those in the velocity-change In the velocity-change experiments, all of the regression experiments, with a significance level of 5% and a p lines increased as the velocity increased at the necks and value of less than 0.005. 58 JAABE vol.3 no.1 May. 2004 Listiani Nurul Huda 3.3 Thermal Comfort cooler at the ankles than at the necks. In the velocity- The mean votes by males and females for thermal change experiments, the perceptions of airflow were comfort for all four experimental conditions ranged from stronger at the necks than at the ankles, but this was -0.693 to 1.192 at the necks and from -0.953 to 0.983 at reversed in the temperature-change experiments, as the ankles. The average thermal comfort response was shown in Figure 7 (b). This means that the neck was higher at the necks than at the ankles in all four more sensitive than the ankles to airflow and that the conditions, as shown in Figure 6. ankles were more sensitive than the neck to temperature. The mean votes for thermal comfort in the tuvc and Figure 7 (c) shows many votes below the line of equal tdvc experiments increased slightly as the temperature sensation in the first quadrant. This indicates that the difference at the necks and the ankles increased, as shown airflow was more comfortable at the back of the necks in Figure 6 (a). In the lower temperatures, thermal than at the ankles. All of these relationships were comfort was higher in the temperature-increase significant, with p< 0.005. experiment than in the temperature decrease experiment for both locations. Thermal comfort was negative in the 3.5 Percentage of Dissatisfied lower temperatures at the ankles in the temperature- The percentages of dissatisfied (PD) were calculated decrease experiments. At the higher temperatures, all of from the comfort votes. When an average response was the thermal comfort votes approached the neutral below -0.5 over the full scale of -2 to 2, the response condition. In this condition, the ankles felt more was assumed to be one of dissatisfaction. Figure 8 (a) comfortable in the temperature-decrease experiments shows that, in the temperature-change experiments, the than in the temperature-increase experiments. Figure 6 average PD was about 14% at the necks, and about 21% (b) shows that the mean votes for thermal comfort at the ankles. At temperature differences below -5˚C, increased as the velocity increased at the necks and the female subjects had a higher PD at the necks than did ankles. In the slower air velocities, thermal comfort was males. But at higher temperature differences, this was higher in the velocity-increase experiments than in the reversed. The PD was lowest for both genders at a velocity-decrease experiments for both locations, but at temperature difference of 0˚C. Above a temperature air velocities faster than 0.5 m/s, thermal comfort was difference of -5˚C, the males felt more dissatisfaction at lower. As the thermal comfort votes had complicated the necks than did females. At the ankles, females had a relationships with the four conditions of the experiments, lower PD than did males when the temperature difference the F values were significant only at the neck in the was below 5˚C. For other temperature differences, the velocity-change experiments (p<0.005). PD was higher for females than for males. At the ankles, the PD for both genders appeared to decrease as the 3.4 Comparison of Sensitivities of Necks and Ankles temperature difference increased. Both genders had the The thermal sensation, velocity perception, and lowest PD at the highest temperature difference. thermal comfort at the two locations in the temperature- The PDs for the velocity-change experiments are and velocity-change experiments are compared in Figure shown in Figure 8 (b). In general, the PD appeared to 7. Figure 7 (a) shows many votes below the two diagonal increase as the velocity increased. For both genders, the lines, indicating that the airflow was perceived to be PD was lower at the necks than at the ankles for air Fig.6. Thermal Comfort Votes by Temperature and Velocity Change Experiments JAABE vol.3 no.1 May. 2004 Listiani Nurul Huda 59 Fig.7. Comparison of Neck and Ankle in the Temperature- and Velocity-change Experiments Fig.8. Percentage of Dissatisfied velocities below 0.75 m/s. All of the PDs for females the mean value. This is shown in table 5. The average of were smaller than those for males in all of the velocity- the male and female votes are also plotted in Figure 9, change experiments. which shows that the frequency of the thermal comfort votes had different patterns in the temperature- and 4. Discussion velocity-change experiments even under common neutral 4.1 Influence of Temperature and Velocity conditions, which were a combination of a 0˚C In the discussion above, it was indicated that local temperature difference and a 0.5 m/s velocity. airflows with different temperatures or different air Average thermal comfort votes below -0.5 were velocities produced different sensations of thermal assumed to be indications of discomfort. Comfort votes comfort at the back of the neck and at the ankles. But it between -0.5 and 0.5 were assumed to indicate a neutral was found that the local airflow produced different condition. Average thermal comfort votes above 0.5 were sensations even for common conditions in the four assumed to be indications of comfort. experiments (tuvc, tdvc, tcvu, and tcvd). The frequency Slightly fewer subjects (about 1% fewer) felt distribution of thermal comfort votes tabulated by discomfort at the neck in the temperature-change combining the three votes at the common condition as experiments than felt so in the velocity-change 60 JAABE vol.3 no.1 May. 2004 Listiani Nurul Huda Table 5. Frequency of thermal comfort votes temperature-change experiments were concentrated in the neutral region, but in the velocity-change experiments, the votes were more evenly distributed. At the ankles, this was reversed. As defined in ASHRAE Standard 55, an allowable thermal environment is any environment in which 80% of the occupants accept the conditions. The experiments in this study were conducted under these conditions. The mean air velocity was under 0.18 m/s, and votes above - 0.5 in the 7-step scale were assumed to be indications of comfort. The present results showed that a local airflow with a velocity of 0.5 m/s at the two body locations was not disagreeable. In a study by B. Griefahn et al. (2000) on the significance of air velocity and turbulence intensity for votes to horizontal drafts in a constant air temperature of 23 C, the mean air velocity was directed toward various dorsolateral sites on the bodies of sedentary persons. The mean velocity varied in 4 steps (v : 0.1, 0.2, 0.3, 0.4 m/s) and the turbulence intensity in 3 steps (T : <30, 50, >70%). The results showed that draft- induced general annoyance (if draft-induced annoyance was stated for at least one body site) and draft-induced local annoyance as stated for the neck and for the forearm increased as air velocity and/or turbulence intensity increased. The present results of airflow perception at the neck and ankles agree with Griefahn’s results even though the air velocity range of the present results is wider than the mean velocity range of Griefahn’s results. Concerning rather sedentary persons, it seems that drafts are tolerable so long as the mean air velocity does not exceed 0.2 m/s and the turbulence intensity remains below 30% in an air temperature of 23˚C. In the present study, it was found that, throughout the present velocity range at both body locations, thermal comfort increased as the air velocity increased. In a study of convective heat transfer in a thermal manikin disturbed by local airflows, Homma (2001) noted that local airflows more strongly stimulated the ankles than the back of the neck. In the present subjective experiments, local airflows were perceived to be cooler at the ankles than at the necks. The airflows were perceived more strongly at the ankles than at the necks in the temperature-change experiments, but this relation was reversed in the velocity-change experiments. Fig.9. Votes Frequency in Neutral Conditions Thermal comfort was higher at the necks than at the ankles in both the temperature- and velocity-change experiments; 91% of those in the temperature-change experiments. Even if the physical result has meaning, experiments felt neutral and comfortable while 90% felt the physiological and psychological sensations appeared so in the velocity-change experiments. The number of to be different in the present experiment. votes for thermal comfort was lower by about 4% for the temperature-change experiments. A larger number 4.2 Influence of Temperature and Velocity on Males of subjects (about 7% more) felt discomfort at the ankles and Females in the temperature-change experiments than felt so in The different perceptions of thermal comfort by males the velocity-change experiments; 75% of subjects felt and females were investigated by Rohles and Nevins neutral and comfortable in the temperature-change (1971). They found that males were significantly warmer experiments, while 82% felt so in the velocity-change than females during the first hour of exposure. In the experiments. At the necks, the votes during the present experiments, the exposure time was 1 hour and JAABE vol.3 no.1 May. 2004 Listiani Nurul Huda 61 15 minutes. But it included stepped increases and Acknowledgments st decreases in temperature or velocity. The average results This study was supported in part by the 21 Century of the temperature increase and decrease experiments COE Program on “Ecological Engineering for showed that the males felt more comfortable than females Homeostatic Human Activities” of the Ministry of in temperature differences of -10˚C and -5˚C at the necks, Education, Culture, Sports, Science and Technology, but above -5˚C, the females felt more comfortable. The Japan. males felt more uncomfortable than the females at temperature differences below 5˚C at the ankles, but References 1) ASHRAE (1992) ANSI/ASHRAE Standard 55-1992. Thermal above 5˚C, the males felt more comfortable. Males felt environmental conditions for human occupancy. Atlanta: American more uncomfortable at both locations throughout the Society of Heating, Refrigerating and Air Conditioning Engineers, velocity-change experiments. At the necks in the Inc., chapter 8 temperature-change experiments, the thermal comfort 2) B.Griefahn et al. (2000) The significance of air velocity and range of the males was wider than that of the females, turbulence intensity for responses to horizontal drafts in a constant air temperature of 23 C. International Journal of Industrial but at the ankles, the thermal comfort range of the males Ergonomics 26, pp. 639-649. was narrower than that of the females. 3) Fanger, P.O, and Christensen, N.K., (1986) Perception of draught in ventilated spaces, Ergonomics 29 (2), pp. 215-235. 5. Conclusion 4) F.H. Rohles and R.G. Nevins. (1971) The nature of thermal comfort Differences in temperature sensation, airflow for sedentary man. ASHRAE Research Report , pp.239-246 5) Homma, H. (1988) Examination of free convection around perception, and thermal comfort were found at the back occupant’s body caused by its metabolic heat, ASHRAE of the neck and at the ankles in the temperature-and Transactions 94(1): pp 104-124 velocity-change experiments. The ankles were more 6) Homma, H. (2001) An Experimental Study of Convection Heat sensitive than the back of the neck to lower temperatures, Transfer of a body disturbed by local airflow. ASHRAE Transactions 2002, Vol. 107, Part 2, pp.406-414 while the back of the neck was more sensitive to higher 7) Houghten, C.F. et al. (1938) Draft temperatures and velocities in temperatures and velocities. These findings may indicate relation to skin temperature and feeling of warmth. Transactions that low-temperature airflows directed at the ankles of ASHVE, pp.289-308. should be avoided. Also, to keep the neck comfortable, 8) J. Toftum et al. (1997) Effect of airflow direction on human high-temperature, high-velocity airflows should be perception of draught. Clima 2000, August 1997 Brussels, paper avoided. Increases in temperature and velocity, however, 9) K. Cena and J. A. Clark. (1981) Bioengineering, Thermal do not always reduce thermal comfort at the neck and Physiology and Comfort. Studies in Environmental Science 10. ankles even in winter. The PD was found to differ Elsevier Scientific Publishing Company. between locations and genders. These differences may 10) Richard R.Gonzales and Yosunobu Nishi. (1976) Effect of Cool be caused in part by the body’s natural convection and Environments on Local Thermal Sensation, Discomfort and Clothing Selection. ASHRAE Transaction. Vol. 76 (1), pp 76-86. by local differences in the perceptions of temperature 11) SPSS-Statistical Package Release 11.0E for Windows. and velocity. 12) Wyon, D.P. et al. (1969) Thermal Comfort during Surgical Operations, JIHVE Vol. 37, Oct., pp.150-168 62 JAABE vol.3 no.1 May. 2004 Listiani Nurul Huda
Journal of Asian Architecture and Building Engineering – Taylor & Francis
Published: May 1, 2004
Keywords: back of neck; ankle; local airflow; sensation; thermal comfort
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