Human perception of local air movement in the tropics

Chapter 1: Introduction 1.1 Background and Motivation This study is about indoor environment and people. Nowadays, people usually spend more than 90% of their time in indoor environment (ASHRAE, 2003), thus indoor environment is very important for human health, comfort, and even productivity (Wargocki et al, 1999; Tham, 2004). Ventilation and air-conditioning is commonly adopted to adjust and control the indoor environment. Being a top energy consumer in buildings, ventilation and air-conditioning system is extremely important for energy conservation and sustainable development. The energy situation especially holds true for the Tropics. A survey of commercial buildings in Singapore (Lee, 2004) has shown that the ventilation and air-conditioning system can consume more than 55% of overall energy in buildings. Mechanical Ventilation and air-conditioning plays a crucial role especially in achieving comfortable conditions for work and living in the Tropics. In Singapore as an example, the diurnal temperature ranges from a minimum 23-26 °C to maximum of 31-34 °C, and the relative humidity from around 90% in the early morning to around 60 % in the mid-afternoon. During prolonged heavy rain, relative humidity often reaches 100 %. (Absoluteastronomy, 2005). This is probably why Lee Kuan Yew, Singapore’s former Prime Minister, and currently Minister Mentor, called air-conditioning “the 20th century’s most important invention”! Mixing ventilation (conventional air-conditioning) is widely adopted in public buildings in the Tropics. However, these buildings are usually operated to create conditions that are overcooled (de Dear et al, 1991). Where such a centralized system is used, end users usually cannot adjust the temperature and control their local environment. In some places, jackets and sweaters become essential officer wear in the Tropics. The overcooling of buildings also means that there is potential for energy conservation with subsequent positive contribution to sustainability. The arguments for the present overcooling situation are usually the need of dehumidification, and that reheat is energy intensive and prohibited in some countries in the Tropics. Under the overcooling situation, designers avoid having to deal with complaints about the place being too warm, and they argue that those who are too cold can just put on a jacket or something (Thestar, 2005). The present overcooling situation of mixing ventilation does not follow human centered buildings design and is not consistent with the comfort, healthy and sustainable life style. The high humidity in the Tropics should be taken care in a proper way, but not be tackled with price of sacrifice of comfort and with energy waste. Meanwhile, indoor air quality as an important issue for human health should be taken into consideration in addition to thermal comfort for indoor environment. However, under mixing ventilation, fresh air is mixed with room air before it reaches occupants’ breathing zone. As a result of the mixing, contaminant concentration is usually same in the whole space, and occupants usually breathe the mediocre quality mixed-air but not the high quality fresh-air. Personalized Ventilation (PV) is recently advocated for indoor environment to cater to the need of a paradigm shift from acceptable to excellent indoor environment (Fanger, 2001). Under a PV system, conditioned fresh air is supplied directly to the occupant’s breathing zone without mixing with recirculated air. Occupants can control the PV air parameters such as air flow rate, i.e., velocity, direction or even temperature of the personalized air. The individual control makes it possible to change from previous passive environmental adaptation (adding clothing) to active environmental control, i.e., the air-conditioning process should not be human adapting to indoor environment but should be indoor environment providing optimal conditions to human. Occupants’ satisfaction of indoor air quality and thermal comfort could then be greatly improved. Personalized ventilation also provides opportunities of energy conservation. In PV, the outdoor air is efficiently dehumidified by cooling coil which needs to deal with the outdoor air only; the conditioned outdoor air is efficiently utilized by presenting it directly into the breathing zones thus minimizing cross contamination and mixing; the quantity of outdoor air needed is reduced as it is able to effectively achieve the desired dilution and freshness in the breathing zone. Meanwhile, indoor ambient temperature can be maintained higher, with the thermal comfort requirements achieved via local cooling with localized air movement. Hence energy efficiency may be achieved with better indoor air quality and occupant comfort and health. Most PV research is conducted in temperate climatic zones (Bauman et al, 1993; Tsuzuki et al, 1999; Kaczmarczyk et al, 2002a; Melikov et al, 2002; Zeng et al, 2002). In the studies, some PV air terminal devices were developed and human responses were examined under PV system (The detail is introduced in Chapter 2). PV system should be examined for the tropical context to explore whether the local people will accept it, e.g., the acceptance of thermal comfort and inhaled air quality, and whether it has energy conservation potential in the scenario of tropical climate. Those needs motivated the first study of human response to PV and energy saving in year 2002, which is described in Chapter 4. Due to the short distance supply of PV air, PV air flow may cause occupants’ local thermal discomfort, e.g., draft. The draft guideline (ISO 7730, 1995), however, was developed under whole-body exposure to air movement and isothermal conditions (Fanger et al., 1988), and it may not be applicable to human perception of air movement under local exposure and nonisothermal conditions under PV situation. The situation necessitates further studies to examine human perception of local airflow. Therefore following-up studies were initiated, which are described in Chapter and 6. 1.2 Research Objectives This study aims to expand the knowledge of perception and acceptability of local air movement of people passively acclimatized by day-to-day life in the Tropics. The objectives of this thesis are described as follow: a. Evaluate the acceptability and energy saving potential of personalized ventilation system in the Tropics. b. Study human perception of local air movement created by personalized air terminal device in the Tropics under short-term exposure, with focus on preference for air movement and local thermal conditions. c. Study human perception of local air movement created by personalized air terminal device in the Tropics under long-term exposure, with focus on the influence of time of occupation on people’s perception of air movement and local thermal conditions. 1.3 Scope of Work This study is in the field of human perception of local air movement in air-conditioned environment in the Tropics. The scope of work and the structure of discussion in each chapter are described briefly as follows: ‰ Literature review. This study is not independent to, but based on, previous research on human perception of personalized ventilation (mainly about thermal comfort and indoor air quality) and air movement (mainly about draft). Chapter provides useful information on experimental design and method adopted, and compares the results of those studies. Particular emphasis is given to the studies carried out in the Tropics/hot humid climate, although unfortunately very few were focused on human perception of local air movement. The research gaps are identified. ‰ General methodology. The work comprised a series of three related studies. The general research methodology is described for the series of experiments, which includes experimental design (facility and instrument, and measurement protocol) and data analysis (statistical analysis and analysis of relationship). The discussion of general methodology is presented in Chapter 3. Other methods applied only in a specific study will be introduced in separated chapters. ‰ Human response to PV and energy saving. Human response to PV was studied with a group of 11 subjects in the Tropics, where there was individual control of the air terminal device. Objective measurements of relevant indoor environmental & ventilation parameters in the vicinity of one human subject were conducted. The information from these two parts of the experiment was analyzed to explore human perception when individual control of local air movement is made available. Coil cooling load was estimated to examine the energy saving opportunities of the personalized ventilation system adopted in this study. The detailed data analysis is discussed in Chapter 4. ‰ Human perception (short-term exposure). In Chapter 5, human perception of local air movement under short-term exposure was studied using an intervention study of local air parameters, without subjects’ interference of the local air movement. Subjective study is the key approach to reveal human perception to local air movement. A group of 24 subjects took part in the experiments. Each experimental intervention lasted 15 minutes to study the first impression of human perception. Human preference of local air movement and local thermal environment was the focus of data analysis. A model to predict percentage of dissatisfied people was developed in this study as well. ‰ Human perception (long-term exposure). Using the same experimental protocols of the short-term exposure study, the human perception of a group of 24 subjects in the Tropics were studied under prolonged-stay of 90-minutes exposed to local air movement. The impact of time of occupation on human perception is the focus of the study of long-term exposure. It is observed from this study that thermal sensation, subjects’ preferred local air velocity and importance of reasons for air movement preference changed when time elapsed. The influence of time of occupation is discussed and summarized in Chapter 6. ‰ Conclusion and Recommendation. The objectives are reviewed and a summary of significant findings is presented. In particular, the contributions of the new understanding of human perception are briefly discussed. Lastly, some suggestions for further research and the development of personalized ventilation system in the Tropics are given in Chapter 7. Chapter 2: Literature Review Three topics relevant to this study are discussed in detail in this literature review – personalized ventilation, human perception study of air movement and human perception study in the Tropics/hot humid climate. The knowledge gaps are then summarized and hypotheses are proposed at the end of this chapter. 2.1 Tropical Climate and Mechanical Ventilation The tropical zone is defined as the zone between the Tropic of Cancer (latitude 23.5 °North) and the Tropic of Capricorn (latitude 23.5 ° South). Occupying approximately forty percent of the land surface of the earth, the Tropics are the home to almost half of the world’s population. The characteristics of tropical climate are abundant rainfall and high humidity associated with a low diurnal temperature range and relatively high air temperature throughout the year. Singapore, for example, is an island state in Southeast Asia, at latitude 1°17'35"N longitude 103°51'20"E, situated on the southern tip of the Malay Peninsula, south of the state of Johore in Peninsular Malaysia and north of the Indonesian islands of Riau (Absoluteastronomy, 2005). Singapore's climate is tropical (“tropical rainforest climate”), with no distinct seasons. Because of its geographical location and maritime exposure, its climate is characterized by uniform temperature and pressure, high humidity and abundant rainfall. Temperature has a diurnal range of a minimum 23-26 °C and a maximum of 31-34 °C and relative humidity has a diurnal range in the high 90% in the early morning to around 60 % in the mid-afternoon. During prolonged heavy rain, relative humidity often reaches 100 %. Singapore is influenced by Northeast monsoon (wetter season) which lasts from October to March and Southwest monsoon (drier season) from May to September (Dutt and de Dear, 1991). In general, tropical climate is characterised with uniformly high relative humidity and air temperature throughout the year. Given the feature of the high relative humidity and air temperature, it is natural that mechanical ventilation and air conditioning play a key role for the control of the indoor environment in the Tropics. Commercial office buildings usually adopt total-volume mechanical ventilation for airconditioning in the Tropics. The total-volume ventilation includes mixing ventilation and displacement ventilation. Mixing ventilation aims to maintain uniform and constant indoor environments while displacement ventilation aims to maintain a temperature and contaminant gradient with the most acceptable region occurring in occupant zones. However, such environments may not meet every individual’s thermal requirement due to the variations of the individual’s thermal preferences, clothing and heat load in the different places of the room. Moreover, occupants usually cannot adjust local environments to meet their unique thermal requirement. On the other hand, it is obvious that under circumstances of both mixing ventilation and displacement ventilation, air inhaled by occupants is the mixture of fresh and ambient air (although fresh air at different levels of the two types of ventilation). Just as stated by Fanger (2001), in the supplied fresh air, say 10 L/s for a person, only 0.1 L/s, or 1% is eventually inhaled, and even the 1% being inhaled is polluted by bioeffluents from occupants or emissions from building materials etc. Therefore, Fanger (2001) recommended that a small quantity of high-quality air be supplied directly to each individual rather than serving plenty of mediocre air in the whole room. Such “personalized air” should be clean, cool and dry (according to the findings of Fang et al, 1998a; 1998b), and supplied directly to the breathing zone. Personalized Ventilation (PV), also known as Task/Ambient Conditioning (Bauman et al, 1998), is such a ventilation method that provides the “personalized air”. Under a PV system, conditioned fresh air is supplied directly to the occupant’s breathing zone without mixing with contaminated recirculated air. The concept of PV has tremendous potential for enhancing the acceptability of ventilation, indoor air quality and thermal comfort in air-conditioned buildings. Occupants can control the PV air parameters such as air flow rate/velocity, direction or even temperature. In Chapter 2.2, personalized ventilation is reviewed in detail. 2.2 2.2.1 Personalized Ventilation Air Terminal Device and Air Flow ™ Air Terminal Device Fundamentally, the present personalized ventilation differentiates from other ventilation approaches through its air supply parameters (usually fresh, clean, dry and cool air with low turbulence intensity) and supply position (close to breathing zones of occupants). The air terminal device plays key role in creating ‘high quality’ personalized air, and thus the design of terminal device is important and some air terminal devices are reviewed. Localized ventilation has been applied in vehicle cabin (bus, car and aircraft) and theatre buildings for many years. The localized ventilation usually only addresses thermal comfort, and air quality is usually not a concerned issue and therefore recirculated air is used in localized ventilation. Fanger (2001) advocated a paradigm shift to excellent indoor environment, and air terminal devices of PV have since been developed and studied for their contribution towards this goal. Different to previous air terminal device used for localized ventilation, only fresh air is supplied by the PV air terminal devices. Figure 2.2.1 shows a, the original prototype of PV air terminal device in Fanger (2001), and some air terminal devices, in which b, is called round moveable panel (Bolashikov et al, 2003); c, five types of air terminal device- Movable Panel (MP), Computer Monitor Panel (CMP), Vertical Desk Grill (VDG), Horizontal Desk Grill (HDG), and Personal Environments Module (PEM) (Melikov et al, 2002); d, desk-edgemounted task ventilation system (Faulkner et al, 2004); e, Headset-Incorporated Supply (Bolashikov et al, 2003) and f, microphone-like air supply nozzle (Zuo et al, 2002). Other PV air terminal devices, e.g., those of Akimoto et al. (2003) and Levy (2002), are similar as those in Figure 2.2.1c. Hence, they are not included in the figure. Although the air terminal devices are of different appearances, shapes or positions relative to the occupants, the designs have some similar considerations, i.e., achieving high inhaled air quality by minimizing mixing between personalized air and ambient/exhaled air without causing much discomfort or inconvenience to occupants; with user-friendly control; being compatible with occupants’ movement; and being harmony with the surrounding environment. 10 term study in Chapter 5.6, although the human perception scale is relative, the observation of the preference of a certain air movement is still meaningful at near steady state since all the experiments were conducted under subjective neutral thermal condition. The observation is in agreement with the previous observation of the preference of air velocity to a certain extent in Chapter 6.4 under specified temperature combinations, which is observed from the relation between air movement acceptability and local air velocity. 6.6 Dissatisfaction due to Air Movement Following the study of subjective mean vote in the last two sections, percentage dissatisfied and preference of air movement are explored in this section. 6.6.1 Percentage Dissatisfied and PD Model Same as the short-term study, the percentage dissatisfied is divided into two parts according to the preference of local air movement, i.e., preference for less or more air movement. Similar trends are observed in this long-term study, i.e., more subjects prefer less air movement and fewer subjects prefer more air movement when local air velocity increases, throughout the entire time duration from 15 to 90 minutes’ exposure. In other words, the two-way perception of air movement also exists at prolonged stay with local air movement. The two parts of percentage dissatisfied at the 90th minute is depicted in Figure 6.6.1. The twoway perception of air movement suggests that some air movement is favorable and preferred by the subjects even after prolonged exposure to local air movement. 156 PD%-prefer less air movement Percentage of dissatisfied Percentage of dissatisfied PD%-prefer more air movement 40% 23.5-21,R2=0.66 26-21,R2=0.66 26-23.5,R2=0.88 30% 20% 10% 0% 0.15 0.3 0.45 0.6 0.75 40% 23.5-21,R2=0.76 26-21,R2=0.31 26-23.5,R2=0.22 30% 20% 10% 0% 0.9 Local air velocity (m/s) 0.15 0.3 0.45 0.6 0.75 0.9 Local air velocity (m/s) Figure 6.6.1 Logarithmic regression of percentage dissatisfied – Prefer more (left)/ less (right) air movement at the 90th minute The percentage dissatisfied derived from the long-term study is further used to test the robustness of the PD model (preferring of less air movement), which was developed in short-term study. The measured percentage dissatisfied is compared to the prediction and the results are presented in Figure 6.6.2. The dataset comprises the percentage dissatisfied derived from the three experimental conditions within the velocity range from 0.15 to 0.75 m/s (low turbulence), respectively at the 15th and 90th minute of the long-term study. Predicted values has demonstrated a moderate correlation (R=0.82) with the 15th minute data. Nevertheless, some discrepancies are observed which may be due to the fact of relatively small sample size of 24 people. The model needs to be substantiated in further studies. The reliability for the prediction at the 90th minute is decreased (R=0.74). The situation suggest that that the model derived from 15 minutes’ exposure may not be applicable to the percentage dissatisfied after prolonged exposure to local air movement. 157 35% 30% 30% Dissatisfied (Measured) Dissatisfied (Measured) 35% 25% the 15th minute, R = 0.82 20% 15% 10% 5% 0% 25% the 90th minute, R = 0.74 20% 15% 10% 5% 0% 0% 2% 4% 6% 8% 10% 12% 14% 0% 2% Dissatisfied (Predicted) 4% 6% 8% 10% 12% 14% Dissatisfied (Predicted) Figure 6.6.2 Validation of PD Model (prefer less air movement) using the 15th minute (left) / 90th minute (right) data in long-term study 6.6.2 Optimum Air Velocity The percentage dissatisfied and optimum air velocities are studied during the 90 minutes time of occupation in this part. The percentage dissatisfied including both preference for more and less air movement are plotted against time of occupation at each air velocity and temperature in Figure 6.6.3. The percentage dissatisfied fluctuates and no clear trend is observed. 26-21-overall Percentage of dissatisfied Percentage of dissatisfied 23.5-21-overall 40% 30% 20% 10% 0% 0.15 15 0.3 30 45 60 75 0.45 0.6 0.75 Time of occupation (min) 90 0.9 40% 30% 20% 10% 0% 0.15 15 0.3 30 45 60 75 0.45 0.6 0.75 Time of occupation (min) 90 0.9 158 Percentage of dissatisfied 26-23.5-overall 40% 30% 20% 10% 0% 0.15 15 0.3 30 45 60 75 0.45 0.6 0.75 Time of occupation (min) 90 0.9 Figure 6.6.3 Overall Percentage dissatisfied throughout 90 minutes The percentage dissatisfied is then plotted with air velocities at different time from Figure 6.6.4 to Figure 6.6.9 to examine optimum velocities. Quadratic regression is applied in the figures. The curves have similar shape, in which percentage dissatisfied initially decreases with the increasing air velocity and beyond a certain velocity (optimum velocity) percentage dissatisfied begins to increase. This scenario illustrates that to a certain extent, air movement may be considered pleasant by the subjects during the 90-minutes time of occupation. 159 Time 10th to 30th mins Percentage of dissatisfied Percentage of dissatisfied Time 5th to 15th mins 40% 23.5-21,R2=0.76 26-21,R2=0.77 26-23.5,R2=0.28 30% 20% 10% 0% 0.15 0.3 0.45 0.6 0.75 40% 23.5-21,R2=0.85 26-21,R2=0.79 26-23.5,R2=0.50 30% 20% 10% 0% 0.9 Local air velocity (m/s) 0.15 0.3 0.45 0.6 0.75 0.9 Local air velocity (m/s) Figure 6.6.4 Percentage dissatisfied from time Figure 6.6.5 Percentage dissatisfied from time 5th to 15th minutes 10th to 30th minutes Time 30th to 60th mins Percentage of dissatisfied Percentage of dissatisfied Time 15th to 45th mins 40% 23.5-21,R2=0.59 26-21,R2=0.52 26-23.5,R2=0.50 30% 20% 10% 0% 0.15 0.3 0.45 0.6 0.75 40% 23.5-21,R2=0.61 26-21,R2=0.53 26-23.5,R2=0.60 30% 20% 10% 0% 0.9 Local air velocity (m/s) 0.15 0.3 0.45 0.6 0.75 0.9 Local air velocity (m/s) Figure 6.6.6 Percentage dissatisfied from time Figure 6.6.7 Percentage dissatisfied from time 15th to 45th minutes 30th to 60th minutes Time 60th to 90th mins Percentage of dissatisfied Percentage of dissatisfied Time 45th to 75th mins 40% 23.5-21,R2=0.71 26-21,R2=0.55 26-23.5,R2=0.69 30% 20% 10% 0% 0.15 0.3 0.45 0.6 0.75 40% 23.5-21,R2=0.83 26-21,R2=0.62 26-23.5,R2=0.70 30% 20% 10% 0% 0.9 Local air velocity (m/s) 0.15 0.3 0.45 0.6 0.75 0.9 Local air velocity (m/s) Figure 6.6.8 Percentage dissatisfied from time Figure 6.6.9 Percentage dissatisfied from time 45th to 75th minutes 60th to 90th minutes Table 6.6.1. Optimum velocities during 90 minutes exposure (m/s) Time (min) 23.5-21 26-21 26-23.5 15 0.056 0.491 0.575 30 0.120 0.479 0.622 45 0.315 0.365 0.552 60 0.370 0.398 0.547 75 0.216 0.454 0.498 90 0.329 0.421 0.511 160 Same as the short-term study, the optimum velocity is defined here as the velocity value associated with the lowest percentage of dissatisfied. By using the first derivative with percentage dissatisfied, the velocities with minimum percentage dissatisfied are calculated at each time point Optimum air velocity (m/s) and are tabulated in Table 6.6.1 and depicted in Figure 6.6.9. The optimum velocities at the 15th minute are 0.7 0.6 compared to those derived from the 15- 0.5 minutes short-term study. It is found that the 0.4 0.3 optimum velocities are comparable for 23.5-21 0.2 26-21 0.1 conditions 26-21 (long-term study of 0.49 26-23.5 0.0 15 30 45 60 75 90 m/s versus short-term study of 0.50 m/s ) and Time of occupation (min) Figure 6.6.10 Optimum air velocity during 90 minutes for conditions 26-23.5 (long-term 0.58 m/s versus short-term 0.52 m/s ). However, it is found for the condition 23.5-21 that the first two values of optimum velocity derived from the long-term study are incomparable to the optimum velocity of 0.38 m/s derived in the short-term study. A close examination of the velocity values in Table 6.6.1 reveals that the air velocities for the 15th and 30th minute are unreasonable low comparing remaining values of the same condition. The two values are thus not shown in Figure 6.6.10. Figure 6.6.10 shows that the optimal velocities decreased as time passed and relatively stabilized towards the end of the 90 minutes. The figure also shows that higher air velocity was preferred at higher air temperature. 6.6.3 Reasons of Dissatisfaction The reasons of dissatisfaction are explored for the long-term exposure. Same as the short-term study, reasons of dissatisfaction are explored on the aspects of thermal discomfort, air quality 161 problem, local physiological discomfort and air pressure. Same evaluation criteria are adopted, and the reasons are explored separately for the preference for more and less air movement. Figure 6.6.11 shows the results of reasons for percentage dissatisfied with the preference for more and less air movement. The percentage of dissatisfied is based on all 24 subjects. Observed from Figure 6.6.11 (left), five reasons contribute to the percentage dissatisfied with the preference for more air movement, i.e., freshness of air (stuffy), dissatisfied of inhaled air quality, air movement perception (air still), thermal sensation (warm) and unexplainable reasons. Thermal sensation (warm) as a main reason accounts for preference for more air movement (2.3% at 15th minute, 1.4% at 30th minute, 1.2% at 45th minute, 0.7% at 60th minute, 0.9% at 75th minute, and 0.9% at 90th minute). During the prolonged occupation time thermal sensation decreased, which is discussed in Chapter 6.4, and the percentage associated with “warm” also decreased. The percentages dissatisfied due to air movement perception (air still) and the unexplainable reason 3.5% 3.0% Percentage dissatisfied prefer more air movement Percentage dissatisfied Percentage dissatisfied fluctuate. Freshness of air (stuffy) and dissatisfied of inhaled air quality are usually trivia. 2.5% 2.0% 1.5% 1.0% 0.5% 0.0% 15 thermal sensation>0 unexplainable air stuff 30 45 60 75 90 air movement perception0 thermal sensation[...]... acclimatization, clothing, behaviour, habituation and expectation Since there are very few PV studies in the Tropics, a study of PV systems under tropical conditions has significant implications in the application of PV systems in the Tropics Furthermore, in typical buildings in the Tropics, the air- conditioning systems maintain the indoor volume at relatively low temperatures in the vicinity of 23 °C (de Dear... local air temperature, velocity and turbulence intensity 3 for the study of human perception under long-term exposure of local air movement in the Tropics 28 - Time of occupation as a factor may affect human perception during prolonged exposure of local air movement and a steady state of perception may be reached; and - At steady state, the people may still prefer some local air movement However, the. .. comfort and perceived air quality in tropical buildings; - PV system has a potential to save cooling energy consumption in tropical building designs 2 for the study of human perception under short-term exposure of local air movement in the Tropics - The people in the Tropics may prefer some local air movement; - Percentage dissatisfied due to local air movement may be related to multiple air parameters,... PV system can be envisaged as a system capable of achieving significant energy conservation due to the inherent possibility of maintaining the ambient space temperature higher while supplying the PV air at a preferred lower temperature This would be one of the hypotheses investigated in this study Furthermore, the understanding of human perception of air movement under PV scenario is urgently needed... in the facial region This necessitates an exploration of human perception of local air movement to facilitate the application of PV system The exploration may construct the relation between human perception and local air movement for both isothermal and especially non-isotherm conditions as the human perception under non-isotherm conditions is still relatively little known to date The draft guideline... air through the PV air terminal device The secondary system consists of an Air Handling Unit (AHU), which provides supplementary ambient cooling to the chamber The fresh air supplied by the FCU is brought into the space through a main duct that terminates into a plenum box Six branch ducts originating from the plenum box enter the 30 chamber through openings in the wall at about 1.2 m height from the. .. Zhou et al (2002) The effects of direction of air movement on human perception were studied by Zhou (1999) The study revealed that air flow direction has a significant impact on human perception of air movement Airflow from below results in the highest percentage of dissatisfied, whereas airflow from ceiling to floor results in the least percentage of dissatisfied Airflow from behind, front and side... importance of individual control of the air velocity has been demonstrated in the study of Toftum et al (2002) Meanwhile, various studies explored the relation between human preference and air parameters in warmer environments Fountain et al (1994) investigated human preference to locally controlled air movement in warm isothermal condition The experiment included three different air supply terminal device:... position It is found that the air movement with a frequency of 0.2 Hz was the most preferred out of the three fluctuating air movements The subjects selected a lower mean air velocity and felt more distracted when the air was fluctuating than when it was constant” (Yang et al 2002) As individual control of personalized air may affect subjects’ perception of air movement, the individual control and optimum... guideline in ISO 7730 may be inappropriate for the Tropics/ hot humid climatic zones, and therefore needs to be re-examined The human perception may be examined under short-term and long-term exposure to air movement The following hypotheses are therefore proposed: 1 for the study under PV scenario in the Tropics - PV system in conjunction with ceiling supply air distribution system enhances occupants' thermal . implications in the application of PV systems in the Tropics. Furthermore, in typical buildings in the Tropics, the air- conditioning systems maintain the indoor volume at relatively low temperatures in. Work This study is in the field of human perception of local air movement in air- conditioned environment in the Tropics. The scope of work and the structure of discussion in each chapter are. perception of a group of 24 subjects in the Tropics were studied under prolonged-stay of 90-minutes exposed to local air movement. The impact of time of occupation on human perception is the focus of