STUDY ON EVALUATIONS OF THERMAL ENVIRONMENT UNDER CROSS VENTILATION AND AIRFLOWS FROM AIR-CONDITIONING SYSTEM AND ELECTRIC FAN

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1 STUDY ON EVALUATIONS OF THERMAL ENVIRONMENT UNDER CROSS VENTILATION AND AIRFLOWS FROM AIR-CONDITIONING SYSTEM AND ELECTRIC FAN Yukari Iino 1, Masaaki Ohba 2, Akinaru Iino 3, and Tetsuo Annaka 3 1 Niigata Seiryo University, Japan 2 Department of Architecture, Tokyo Polytechnic University, Japan 3 Department of Architecture, Niigata Institute of Technology, Japan ABSTRACT The purpose of this study was to clarify differences between evaluations of thermal environment under cross ventilation and airflows from air-conditioning systems and electric fans. Nine subjects evaluated thermal sensation, thermal comfort sensation, airflow sensation and humidity sensation in an experimental room in the summer of 26. The surrounding ambient temperatures, relative humidity, and air velocity were measured simultaneously. The following results were obtained: (1) Airflow features of three airflows were clarified on the basis of turbulence statistics and fluctuations in time and space. (2) Changing frequencies of most sensation scales under cross ventilation were more than those under airflows from the air-conditioning system and their change ranges were wider. (3) The ratios of agreements between sensation scales over the whole body and those at respective body sites were higher under airflow from the air-conditioning system than under cross ventilation, because flow directions and fluctuations at respective body sites were different. Thermal sensation showed the lowest ratios of agreement of the four sensations. (4) When the air velocity was less than.5m/s, the cooling effects of cross ventilation for subjects were insufficient from the viewpoints of air velocity and airflow fluctuations based on the different results for four sensations. When the air velocity was more than.5m/s, various air velocity changes and airflow fluctuations in time and space made subjects feel more comfortable under cross ventilation than under airflows from the air-conditioning system. KEYWORDS Evaluation, Airflow fluctuation, Cross ventilation, Air-conditioning systems, Electric fans INTRODUCTION In humid areas with high summer temperatures, effective cross ventilation can greatly improve occupants thermal comfort. However, no method for more efficiently determining cross ventilation and no method for evaluating the cross ventilation environment has been firmly established in a systematic manner, and no effective factors of cross ventilation on thermal comfort sensation have been defined. This is because the unsteady-state environment is not easy to analyze and cross ventilation is also a mixed airflow in which indoor airflow is intermingled with outdoor airflow in a complicated manner. Our primary aim is to characterize qualitative features of cross ventilation as compared with those of artificial airflows from air-conditioning systems and electric fans on the identifiable basis of airflow phenomena and flow behaviors. Qualitative features of airflows have been analyzed from the viewpoints of turbulence statistics and airflow fluctuations in time and space. Corresponding Author: Tel: , Fax: address: yiu46259@nifty.com

2 This study also aimed to clarify differences between occupants evaluations of thermal environment under cross ventilation and airflows from an air-conditioning system and an electric fan. Experiments were carried out with subjects in a thermal environment with similar ambient temperatures and mean radiant temperatures in summer, 26. METHODS OF EXPERIMENT Measuring methods Nine sedentary subjects evaluated four kinds of sensations under cross ventilation and airflows from an air-conditioning system and an electric fan in an experimental room located in the suburbs of Tokyo, Japan in the summer of 26. Three were seated side by side and wore uniforms (insulation value.6 clo) in each experimental case. They completed questionnaires regarding their sensory responses over the whole body and at individual body sites every 5 minutes for 4 minutes and controlled sensation devices to respond immediately to thermal environment changes for the last 2 minutes during a one-hour experimental period. Ambient temperatures, relative humidity, surface temperatures and air velocity surrounding subjects were measured at the same time. Physiological data such as skin surface temperatures, skin surface hydration and body core temperatures were recorded every 5 minutes during the experimental period. Air velocity was measured instantaneously by ultrasonic anemometers at a 2 Hz sampling rate. Skin temperatures were recorded by thermal infrared cameras at 2 Hz and 3 Hz sampling rates. The experimental room and locations of respective measuring instruments are illustrated in Figure 1. The subjects were 6 male (M1~M6) and 3 female (F1~F3) university students. Details of these subjects are presented in Table 1. The number of experimental cases per subject was 2~4 under cross ventilation, 4 or 5 under flows from the air-conditioning system, and 2 for each swing pattern of the electric fan. The swing patterns were fixed (no-swing), swung vertically (vertical swing), swung horizontally (horizontal swing). The evaluations of thermal environment and the number of scales comprised thermal sensation (7 scales), thermal comfort sensation (6 scales), airflow sensation (4 scales) and humidity sensation (7 scales). The respective sensation scales are shown in Table 2. Entlance :Solarimeter :Thermo-couples :Infrared camera :Glove thermometer :Thermometer :Ultrasonic anemometer Table 1 Details of nine subjects M1 M2 M3 M4 M5 M6 W1 W2 W3 Sex Male Male Male Male Male Male Female Female Female Age Height(cm) Weight(kg) Surface area of body(m 2 ) Subjects Air-conditioning unit Balcony Figure 1 Experimental room and locations of measuring instruments Table 2 Scales for four sensations Thermal Thermal comfort Humidity Airflow Sensation Scales Sensation Sensation Sensation 1 Hot Very uncomfortable No feeling Very humid 2 Warm Uncomfortable Weak feeling Humid 3 Slightly warm Slightly uncomfortable Feeling Slightly humid 4 Neutral Slightly comfortable Strong feeling Neutral 5 Slightly cool Comfortable Slightly dry 6 Cool Very comfortable - Dry 7 Cold - Very dry

3 RESULTS OF ANALYSIS AND DISCUSSION Features of cross ventilation and airflows from air-conditioning system and electric fan Airflow features were defined by the results of turbulence statistics and temporal and spatial fluctuations. The turbulence statistics include the average and standard deviation of air velocity and turbulence intensity. These results and changes in air velocity under cross ventilation and airflows from the air-conditioning system and the electric fan are shown in Figure 2. Airflow fluctuations were described as ratios of power spectra in respective frequency ranges and spatially represented as power spectra in wavenumber under these three airflows, as illustrated in Figure 3. In most cases of cross ventilation, air velocity was momentarily and unsteadily changed over wide ranges. The values of average and standard deviation of air velocity differed from case to case. The turbulence intensity was 6~8%. Wave lengths were long because the major contributions to the energy spectra of cross ventilation were revealed as more than 6% in the frequency range less than.1hz. The cross ventilation consisted of many big eddies because the concentrations of the energy spectra were around 8% in the ranges of 1 rad/m wavenumber. For airflow from the air-conditioning system, mean air velocity was less than.5m/s, mean standard deviation was around.17m/s and turbulence intensity was around 4~6%. The changes in air velocity were stable and uniform. There were many long-length waves in the airflow of the air-conditioning system because the ratios of the energy power spectra in the frequency range of over.1hz were higher than for cross ventilation. The airflow consisted of many small eddies because the concentrations of the energy spectra were in the wavenumber range of over 1 rad/m. Air velocity (m/s) swing Vertical swing Horizontal swing Air velocity (m/s) Average Average Average.5 swing Vertical swing Horizontal swing Cross ventilation Airflows from air-conditioning system Airflows of electric fans (b) Average and standard deviation of air velocity No swing Vertical swing Horizontal swing - Cross ventilation Airflows from air-conditioning system Airflows of electric fans (c) Turbulence intensity Figure 2 Change, average and standard deviation of air velocity and turbulence intensity under three airflows Turbulence intensity (%) Cross ventilation Airflows from air-conditioning system Airflows of electric fans (a) Change of air velocity

4 Ratio of power spectra in respective ranges of frequency(%) Ranges: % 9% 8% 7% 6% 5% 4% 3% 2% 1% % East side Center West side East side Center West side swing Vertical swing Horizontal swing Cross ventilation Airflows from air-conditioning system Airflows from electric fans (a) Ratios of power spectra in respective frequency ranges 1 East side 9 East side 9 swing 8 Center Center 8 Vertical swing 7 West side West side Horizontal swing Wave number(rad/m) Wave number(rad/m) Wave number(rad/m) Cross ventilation Airflows from air-conditioning system Airflows from electric fans (b) Accumulative power spectra in respective wavenumbers Figure 3 Ratios of power spectra in frequency ranges and accumulative power spectra in wavenumbers under three airflows Accumulative power spectra in respective wave numbers(%) For airflow from the electric fan, mean air velocity was about.6m/s and mean standard deviation was around.65m/s. The turbulence intensity was 2~4% for no-swing, 11~14% for vertical swing and 8~12% for horizontal swing. The swinging fan was assumed to increase turbulent flow. The ratios of energy power spectra varied according to the swing patterns. The frequency range of over 1Hz for no-swing was higher than those of other swing patterns. The contributions to the energy power spectra were distinguished in the fan swing wavenumber ranges around 9 rad/m for vertical swing and about 1 rad/m for horizontal swing. Thus, short-length waves and a lot of smaller eddies were created by vertical and horizontal swings. Agreements of sensations between whole body and at individual body sites The ratios of agreements between sensation scales over the whole body and those at the 11 individual body sites under airflows from the air-conditioning system are shown in Figure 4. The agreement ratios for most sensations other than thermal sensation were around 4% at naked body sites under airflows from the air-conditioning system, which was higher than for those under cross ventilation. It was assumed that the airflow environment was different in respective surrounding sites under cross ventilation. The agreement ratios of thermal sensation under both airflows showed the lowest values in comparison with other sensations. The agreement ratios at the chest and back sites covered by uniforms were lower than those at naked sites. Change of sensation scales The average changing frequencies and the range ratios of changing scales using the sensation device under both airflows for the last 2 minutes during experimental period are illustrated in Figure 5 and Figure 6. The average changing frequency of the airflow sensation was more than 15 times under cross ventilation compared with 5 times under airflows from the air-conditioning system. The change in one or two scale ranges under cross ventilation was more than no change or change in one scale range under airflows from the air-conditioning system. The average frequencies and the range ratios of changing scales for sensations other than humidity sensation under cross ventilation were more and higher than those under airflows from the air-conditioning system because the mean air velocity of cross ventilation

5 6 Cross- ventilation:thermal sensations Cross-ventilation:Comfort sensations Cross-ventilation:Airflow sensations Cross-ventilation:humidity sensations Air-conditioning:Thermal sensations Air-conditioning:Comfort sensations Air-conditioning:Airflow sensations Air-conditioning::humidity sensations Agreement ratio of sensation in the whole body and sensations at individual Average changing frequencies of scales body site (%) Feet Right leg Left leg Right thigh Left thighchest Waist Back Right arm Left arm Neck Face Head Body sites Figure 4 Ratios of sensation scale agreements between whole body and at individual body sites M1 M2 M3 M4 M6 W1 W2 W3 all Subjects Cross ventilaion cases Thermal sensation Comfort sensation Airflow sensation Humidity sensation M1 M3 M4 M6 W1 W2 W3 all Figure 5 Average changing frequencies of scales for four sensations under cross ventilation and airflows from air-conditioning system Changing ranges1% Changing range ratios of scales Thermal Comfort Airflow Humidity Thermal environmental evaluations Figure 6 Range ratios of changing scales for four sensations under cross ventilation and airflows from air-conditioning system was variously and widely changeable in comparison with the constantly changing airflows from the air-conditioning system. Evaluations of thermal environment under cross ventilation and airflows from air-conditioning system The ratios of respective scales for all subjects four sensations under classification in air velocity or relative humidity are illustrated in Figure 7 under cross ventilation and airflows from the air-conditioning system. The ratios are shown as the width of bar. Mean air temperature and relative humidity during the experimental period were approximately 28~32 and 55~8% under cross ventilation and about 27 ~29 and 57~72% under airflows from the air-conditioning system. 8% 6% 4% 2% % Stable 1 scale 2 scales 3 scales CV AC CV AC CV AC CV AC Regarding the thermal sensation, when the air velocity was more than.5m/s, neutral scale or cool side scales (slightly cool, cool and cold) were shown under both airflows. The scale of cold was occasionally given under airflows from the air-conditioning system because the ambient temperature was lower than that under cross ventilation. When the air velocity was less than.5m/s, the ratios of slightly warm scale and neutral scale under cross ventilation was more than those under airflows from the air-conditioning system because the cooling effects of cross ventilation for subjects were insufficient at points of air velocity and flow fluctuations.

6 Concerning thermal comfort sensations, when the air velocity was over.5m/s, comfort side scales (slightly comfortable, comfortable and very comfortable) were mostly shown under both airflows. The scale of very comfortable was presented only under cross ventilation. It is assumed that airflow fluctuation and flows from various directions made subjects more comfortable under cross ventilation. When the air velocity was less than.5m/s, the ratio of very uncomfortable scale under airflows from the air-conditioning system was more than that under cross ventilation because there were some subjects who felt cold. Regarding airflow sensation, when the air velocity was more than.5m/s, all scales were revealed under cross ventilation because the air velocity was momentarily and unsteadily changed over wide ranges and differed from case to case. On the other hand, the scales of weak feeling and feeling were mostly revealed under airflows from the air-conditioning system. The subjects were exposed under flows of constant air velocity from the same direction. When the air velocity was less than.5m/s, the ratio of no feeling scale was higher under cross ventilation than under airflows from the air-conditioning system because cross ventilation could not make subjects sensitive to airflow fluctuation when air temperature was high. Concerning humidity sensations, when the relative humidity was more than 7%, most scales were neutral under airflows from the air-conditioning system whereas humid side scales (very humid, humid and slightly humid) were mostly kept under cross ventilation. When the relative humidity was less than 7%, neutral scale and dry scale were mainly presented under airflows from the air-conditioning system. On the other hand, neutral scale and slightly humid, slightly dry and dry scales were revealed under cross ventilation. Mean air velocity Less than.5m/s More than.5m/s Thermal Sensation Thermal comfort Sensation Airflow Sensation The width of bar shows ratios of respective scales Mean relative humidity Less than 7% More than 7% Humidity Sensation Hot Thermal sensation 7 Cold, 1 Very uncomfortable Thermal comfort sensation 6 Very comfortable, 1 No feeling Airflow sensation 4 Strong feeling, 1 Very humid Humidity sensation 7 Very dry Figure 7 Ratios of respective scales for four sensations under cross ventilation and airflows from air-conditioning system CONCLUSIONS This study aimed to characterize qualitative features of cross ventilation as compared with airflows from air-conditioning systems and electric fans and to clarify differences in subjects evaluations of thermal environment under these airflows. Experiments were carried out with nine subjects. The following results were obtained: 1) The flow features of three airflows were clarified in regard to turbulence statistics and fluctuations in time and space. 2) The agreement ratios of sensation scales between the whole body and at respective body sites under airflows from the air-conditioning system were higher for the naked body sites than those under cross ventilation for most sensations other than thermal sensation. 3) The average changing frequencies and range ratios of changing scales under cross ventilation were much more and higher than those under airflows from the air-conditioning system for thermal sensation, thermal comfort sensation and airflow sensation. 4) From the results for four

7 sensations under cross ventilation and airflows from the air-conditioning system, when the air velocity was less than.5m/s, the cooling effects of cross ventilation for subjects were insufficient at points of air velocity and flow fluctuations. When the air velocity was more than.5m/s, various changes of air velocity and temporal and spatial fluctuation made subjects feel more comfortable under cross ventilation than under airflows from the air-conditioning system. ACKNOWLEDGEMENTS We express our sincere gratitude to Dr. Tomonobu Goto, Mitushiro Ishida, Kouei Shimoji and other students of the Tokyo Polytechnic University, Toshiaki Ono of Niigata Institute of Technology and Shizuo Iwamoto of Kanagawa University for their kind assistance and cooperation with the authors in carrying out the experiment. This study was funded by the Ministry of Education, Culture, Sports, Science and Technology, Japan through the 21 st Century Center of Excellence Program, This study was partially supported by Grand-in-Aid for Scientific Research (No , Prof. M. Ohba). REFERENCES 1. Y. Iino, T. Kurabuchi, et al (25) Study on characteristics of wind over the building and airflows in cross-ventilated and air conditioned rooms based on measurement, Journal of Environment Engineering (Transactions of AIJ), No. 589, Y. Iino, T. Kurabuchi, et al (24) Measurement errors of ultrasonic anemometer and its correction methods, AIJ journal of technology and design, No. 19, Q. Ouyang, W. Dai and Y. Zhu (24) Study on the Fluctuant Characteristics of Natural Wind in Built Environment, Book of Abstracts, 9 th International conference on ROOMVENT,