Thermal sensation of Hong Kong people with increased air speed,temperature and humidity in air-conditioned environment

In the warm and humid climate zone, air-conditioning (AC) is usually provided at working places to enhance human thermal comfort and work productivity. From the building sustainability point of view, to achieve acceptable thermal sensation with the minimum use of energy can be desirable. A new AC design tactic is then to increase the air movement so that the summer temperature setting can be raised. A laboratory-based thermal comfort survey was conducted in Hong Kong with around 300 educated Chinese subjects. Their thermal sensation votes were gathered for a range of controlled thermal environment. The result analysis shows that, like in many other Asian cities, the thermal sensation of the Hong Kong people is sensitive to air temperature and speed, but not much to humidity. With bodily air speed at 0.1–0.2 m/s, clothing level 0.55 clo and metabolic rate 1 met, the neutral temperature was found around 25.4 °C for sedentary working environment. Then recommendations are given to the appropriate controlled AC environment in Hong Kong with higher airflow speeds.     

Thermal effect of temperature gradient in a field environment chamber served by displacement ventilation system in the tropics

The effect of vertical air temperature gradient on overall and local thermal comfort at different overall thermal sensations and room air temperatures (at 0.6 m height) was investigated in a room served by displacement ventilation system. Sixty tropically acclimatized subjects performed sedentary office work for a period of 3 h during each session of the experiment. Nominal vertical air temperature gradients between 0.1 and 1.1 m heights were 1, 3 and 5 K/m while nominal room air temperatures at 0.6 m height were 20, 23 and 26 °C. Air velocity in the space near the subjects was kept at below 0.2 m/s. Relative humidity at 0.6 m height was maintained at 50%. It was found that temperature gradient had different influences on thermal comfort at different overall thermal sensations. At overall thermal sensation close to neutral, only when room air temperature was substantially low, such as 20 °C, percentage dissatisfied of overall body increased with the increase of temperature gradient. At overall cold and slightly warm sensations, percentage dissatisfied of overall body was non-significantly affected by temperature gradient. Overall thermal sensation had significant impact on overall thermal comfort. Local thermal comfort of body segment was affected by both overall and local thermal sensations.     

Effect of warm air supplied facially on occupants’ comfort

Human response to air movement supplied locally towards the face was studied in a room with an air temperature of 20 °C and a relative humidity of 30%. Thirty-two human subjects were exposed to three conditions: calm environment and facially supplied airflow at 21 °C and at 26 °C. The air was supplied with a constant velocity of 0.4 m/s by means of personalized ventilation towards the face of the subjects. The airflow at 21 °C decreased the subjects' thermal sensation and increased draught discomfort, but improved slightly the perceived air quality. Heating of the supplied air by 6 K (temperature increase by 4 K at the target area) above the room air temperature decreased the draught discomfort, improved subjects' thermal comfort and only slightly decreased the perceived air quality. Elevated velocity and temperature of the localized airflow caused an increase of nose dryness intensity and number of eye irritation reports. Results suggest that increasing the temperature of the air locally supplied to the breathing zone by only a few degrees above the room air temperature will improve occupants' thermal comfort and will diminish draught discomfort. This strategy will extend the applicability of personalized ventilation aiming to supply clean air for breathing at the lower end of the temperature range recommended in the standards. Providing individual control is essential in order to avoid discomfort for the most sensitive occupants.     

Local thermal sensation and comfort study in a field environment chamber served by displacement ventilation system in the tropics

This paper presents a study of local thermal sensation (LTS) and comfort in a field environmental chamber (FEC) served by displacement ventilation (DV) system. The FEC, 11.12 m (L)×7.53 m (W)×2.60 m (H), simulates a typical office layout. A total of 60 tropically acclimatized subjects, 30 male and 30 female, were engaged in sedentary office work for 3 h. Subjects were exposed to three vertical air temperature gradients, nominally 1, 3 and 5 K/m, between 0.1 and 1.1 m heights and three room air temperatures of 20, 23 and 26 °C at 0.6 m height. The objective of this study is to investigate the mutual effect of local and overall thermal sensation (OTS) and comfort in DV environment. The results show that in a space served by DV system, at OTS close to neutral, local thermal discomfort decreased with the increase of room air temperature. The OTS of occupants was mainly affected by LTS at the arm, calf, foot, back and hand. Local thermal discomfort was affected by both LTS and OTS. At overall cold thermal sensation, all body segments prefer slightly warm sensation. At overall slightly warm thermal sensation, all body segments prefer slightly cool sensation.     

Thermal comfort for naturally ventilated residential buildings in Harbin

This field study was conducted during summer 2009 in Harbin, northeast of China in order to investigate human responses to the thermal conditions in naturally ventilated residential buildings in cold climate. We visited 257 families in six residential communities and collected 423 sets of physical data and subjective questionnaires. The neutral temperature is 23.7 °C, with the clothing insulation of 0.54 clo. The neutral temperature in Harbin is lower than neutral temperatures in warm climates by others, which is in accordance with the thermal adaptive model. 80% of the occupants can accept the air temperature range of 21.5-31.0 °C, which is wider than the summer comfort temperature limits by the adaptive model. The preferred temperature range fell between 24.0 °C and 28.0 °C. About 57.9% of the subjects voted “no change” with the humid range of 40% and 70%. 61.5% of the occupants voted “no change” with the air velocity within the range of 0.05-0.30 m/s. In summer, occupants preferred air velocity of lower than 0.25 m/s even at higher indoor temperature, which is different from the other field studies. The Harbin occupants in naturally ventilated dwellings can achieve thermal comfort by operable windows instead of running air-conditioners.     

Combined thermal acceptability and air movement assessments in a hot humid climate

In the ASHRAE comfort database [1], underpinning the North American naturally ventilated adaptive comfort standard [2], the mean indoor air velocity associated with 90% thermal acceptability was relatively low, rarely exceeding 0.3 m/s. Post hoc studies of this database showed that the main complaint related to air movement was a preference for ‘more air movement’ 3 and 4. These observations suggest the potential to shift thermal acceptability to even higher operative temperature values, if higher air speeds are available. If that were the case, would it be reasonable to expect temperature and air movement acceptability levels at 90%? This paper focuses on this question and combines thermal and air movement acceptability percentages in order to assess occupants. Two field experiments took place in naturally ventilated buildings located on Brazil’s North-East. The fundamental feature of this research design is the proximity of the indoor climate observations with corresponding comfort questionnaire responses from the occupants. Almost 90% thermal acceptability was found within the predictions of the ASHRAE adaptive comfort standard and yet occupants required ‘more air velocity’. Minimum air velocity values were found in order to achieve 90% of thermal and air movement acceptability. From 24 to 27 °C the minimum air velocity for thermal and air movement acceptability is 0.4 m/s; from 27 to 29 °C is 0.41–0.8 m/s, and from 29 to 31 °C is >0.81 m/s. These results highlight the necessity of combining thermal and air movement acceptability in order to assess occupants’ perception of their indoor thermal environment in hot humid climates.     

Thermal evaluation of a chair with fans as an individually controlled system

It is difficult for a total air-conditioning system to satisfy the thermal comfort of all workers in an office. Therefore, an individually controlled system that can create a comfortable thermal environment for each worker is needed. In the present study, two chairs incorporating two fans each, one under the seat and one behind the backrest, were developed to provide isothermal forced airflow to the chair occupant. The chairs differed in the size of the fans. Experiments were conducted in a climate chamber during the summer. Seven subjects, who were healthy male college students, were allowed to freely control the two built-in fans by adjusting dials on the accompanying desk. The room air temperatures were set at 26 °C, 28 °C, 30 °C and 32 °C. The following findings were obtained. At a room air temperature of 28 °C, the whole-body thermal sensations were almost thermally neutral, regardless of the type of chair. At a room air temperature of 30 °C, the occupants were able to create acceptable thermal environments from the viewpoints of whole-body thermal sensation and comfort by using the chairs with fans. Their local discomfort rates at the back and lower back, which were affected by the isothermal airflows, were greatly improved at this room air temperature. However, at a room air temperature of 32 °C, the chairs tested in the present study were not able to provide acceptable thermal environments. In order to provide a more comfortable environment to the chair occupants, additional local systems to cool the head, arms, and hands are needed.     

Indoor thermal conditions and thermal comfort in air-conditioned domestic buildings in the dry-desert climate of Kuwait

The summer season in the state of Kuwait is long with a mean daily maximum temperature of 45 °C. Domestic air conditioning is generally deployed from the beginning of April to the end of October. This accounts for around 75% of Kuwaiti electrical power consumption. In terms of energy conservation, increasing the thermostat temperature by 1 °C could save about 10% of space cooling energy 1 and 2. However, knowledge of indoor domestic temperatures and thermal comfort sensations is important to aid future advice formulation and policy-making related to domestic energy consumption. A field study was therefore conducted during the summers of 2006 and 2007 to investigate the indoor climate and occupants' thermal comfort in 25 air-conditioned domestic buildings in Kuwait. The paper presents statistical data about the indoor environmental conditions in Kuwait domestic residences, together with an analysis of domestic-occupant thermal comfort sensations. With respect to the latter, a total of 111 participants provided 111 sets of physical measurements together with subjective information via questionnaires that were used to collect the data. By using linear regression analysis of responses on the ASHRAE-seven-point thermal sensation scale, the neutral operative temperatures based on Actual Mean Vote (AMV) and Predicted Mean Vote (PMV) were found to be 25.2 °C and 23.3 °C, respectively, in the summer season. Findings from this study provide information about the indoor domestic thermal environment in Kuwait, together with occupant thermal comfort sensations. This knowledge can contribute towards the development of future energy-related design codes for Kuwait.     

Behavioural adaptation and the use of environmental controls in summer for thermal comfort in apartments in India

Building energy use in India is rising phenomenally. Indian codes prescribe a very narrow comfort temperature range (23-26 °C) for summer. Ventilation controls alone consume 47% of total energy in residences. Thermal comfort field studies in Indian residences were not attempted. The author conducted a field study in apartments in Hyderabad, in summer and monsoon seasons in 2008. This paper presents the occupants’ methods of environmental and behavioural adaptation and impediments in using controls.Only about 40% of the occupants were comfortable in summer due to inadequate adaptive opportunities. The comfort range obtained in this study (26.0-32.5 °C), was way above the standard. Fanger's PMV always overestimated the actual sensation.The occupants used many adaptation methods: the environmental controls, clothing, metabolism and many behavioural actions. Use of fans, air coolers and A/cs increased with temperature, and was impeded by their poor efficacy and noise, occupant's attitudes and economic affordability. A/c and air cooler usage was higher in top floors. Behavioural adaptation was better in summer and was restricted in higher economic groups always. Thermal tolerance was limited in subjects using A/cs and resulted in “thermal indulgence”. This study calls for special adaptation methods for top-floor flats.     

Comfort,perceived air quality,and work performance in a low-power task–ambient conditioning system

Zhang's thermal comfort model [Zhang H. Human thermal sensation and comfort in transient and non-uniform thermal environments, Ph.D. thesis, UC Berkeley; 2003. 415 pp.] predicts that the local comfort of feet, hands, and face predominates in determining a person's overall comfort in warm and cool conditions. We took advantage of this in designing a task–ambient conditioning (TAC) system that heats only the feet and hands, and cools only the hands and face, to provide comfort in a wide range of ambient environments. Per workstation, the TAC system uses less than 41 W for cooling and 59 W for heating. We tested the TAC system on 18 subjects in our environmental chamber, at temperatures representing a wide range of practical winter and summer conditions (18–30 °C). A total of 90 tests were done. We measured subjects' skin and core temperatures, obtained their subjective responses about thermal comfort, perceived air quality, and air movement preference. The subjects performed three different types of tasks to evaluate their productivity during the testing. The TAC system maintains good comfort levels across the entire temperature range tested. TAC did not significantly affect the task performance of the occupants compared to a neutral ambient condition. Whenever air motion was provided, perceived air quality was significantly improved, even if the air movement was re-circulated room air. In our tests, subjects found thermal environments acceptable even if they were judged slightly uncomfortable (−0.5). By reducing the amount of control normally needed in the overall building, the TAC system saves energy. Simulated annual heating and cooling energy savings with the TAC system are as much as 40%.     

Effect of local exposure on human responses

At room temperatures ranging from 28 to 35 °C, the three sensitive body parts face, chest and back were exposed to local cooling airflow, whose temperatures ranged from 22 to 28 °C. Dressed in shorts, 30 randomly selected male subjects were exposed to each condition for 30 min and reported their local thermal sensations of all body parts, overall thermal sensation and thermal acceptability on voting scales at regular intervals. It was shown that local exposure affected local thermal sensations of the unexposed body parts significantly, based on which a new influencing factor method was proposed. Influencing factor and weighting factor for each body part are unaffected by room or cooling air temperatures under steady state and the predictive model of overall thermal sensation was obtained using influencing and weighting factors. Taking the maximum thermal sensation difference between body parts to represent non-uniformity of thermal sensation, a new assessment model for non-uniform thermal environment was proposed. The model shows that the upper boundary of the acceptable room temperature range can be shifted from 26 to 30.5 °C while face cooling is provided.     

Evaluation of thermal comfort in a rail terminal location in India

The recent Indian Railway budget proposes upgrading and development of fifty railway stations to world class standards. These stations act as crucial transport nodes for effective operation of the railway network and passenger well being. One of the important aspects regarding passenger satisfaction in these places is an acceptable thermal environment. This article studies the thermal comfort of passengers in a large and significant railway station in South India in the summer month of June. The study entails field measurements and questionnaire responses from 402 individuals over a period of fifteen days. The thermal comfort is estimated using the air temperature and the PET (Physiological Equivalent Temperature) scale. The neutral temperature obtained through questionnaire surveys is 31.93 °C. In presence of fair air movement, there is some relaxation to neutral temperature, although the range of relaxation is much narrower than the models presented by other researchers. Comparing the Thermal sensation votes (ASHRAE 7-point scale) with comfort votes (Bedford 7-point scale), it is observed that the passengers exhibit high tolerance and adaptivity. Further, some observations are made on the relationship between the nature of waiting areas and their spatial influence on passenger thermal comfort.     

Thermal comfort assessment and application of radiant cooling: A case study

A field assessment of thermal comfort was conducted at Mehran University of Engineering and Technology, situated in the subtropical region of Pakistan. The results show that people of the area were feeling thermally comfortable at effective temperature of 29.85 °C (operative temperature 29.3 °C). A comparison of this neutral effective temperature was made with the neutral effective temperature determined from adaptive models. It is found that the neutral effective temperature determined during this study closely match that of the adaptive model based on either indoor temperature or both indoor and outdoor temperatures. The results of thermal acceptability assessment show that more than 80% of occupants were satisfied at an effective temperature of 32.5 °C, which is 6.5 °C above the upper boundary of ASHRAE thermal comfort zone. Naturally ventilated classrooms and air-conditioned offices of the University were simulated using TRNSYS system simulation program for two cases, once when conventional air-conditioning is used for providing thermal comfort, and when comfort is achieved through radiant cooling. In the simulation, cooling tower was used to regenerate cooling water for the radiant cooling system. Energy consumption was estimated from simulation of both cases. The results show that it is possible to achieve thermal comfort for most of the time of the year through the use of radiant cooling without a risk of condensation of moisture from air on the radiant cooling surfaces. A comparison of the energy consumption estimates show that savings of 80% is possible in case thermal comfort is achieved through radiant cooling instead of conventional air-conditioning.     

Thermal comfort in residential buildings – Failure to predict by Standard model

A field study, conducted in 189 dwellings in winter and 205 dwellings in summer, included measurement of hygro-thermal conditions and documentation of occupant responses and behavior patterns. Both samples included both passive and actively space-conditioned dwellings. Predicted mean votes (PMV) computed using Fanger's model yielded significantly lower-than-reported thermal sensation (TS) values, especially for the winter heated and summer air-conditioned groups. The basic model assumption of a proportional relationship between thermal response and thermal load proved to be inadequate, with actual thermal comfort achieved at substantially lower loads than predicted. Survey results also refuted the model's second assumption that symmetrical responses in the negative and positive directions of the scale represent similar comfort levels. Results showed that the model's curve of predicted percentage of dissatisfied (PPD) substantially overestimated the actual percentage of dissatisfied within the partial group of respondents who voted TS > 0 in winter as well as within the partial group of respondents who voted TS < 0 in summer. Analyses of sensitivity to possible survey-related inaccuracy factors (metabolic rate, clothing thermal resistance) did not explain the systematic discrepancies. These discrepancies highlight the role of contextual variables (local climate, expectations, available control) in thermal adaptation in actual settings. Collected data was analyzed statistically to establish baseline data for local standardized thermal and energy calculations. A 90% satisfaction criterion yielded 19.5 °C and 26 °C as limit values for passive winter and summer design conditions, respectively, while during active conditioning periods, set-point temperatures of 21.5 °C and 23 °C should be assumed for winter and summer, respectively.     

Effect of age, gender, economic group and tenure on thermal comfort: A field study in residential buildings in hot and dry climate with seasonal variations

Energy consumption in Indian residential buildings is one of the highest and is increasing phenomenally. Indian standards specify comfort temperatures between 23 and 26 °C for all types of buildings across the nation. However, thermal comfort research in India is very limited. A field study in naturally ventilated apartments was done in 2008, during the summer and monsoon seasons in Hyderabad in composite climate. This survey involved over 100 subjects, giving 3962 datasets. They were analysed under different groups: age, gender, economic group and tenure. Age, gender and tenure correlated weakly with thermal comfort. However, thermal acceptance of women, older subjects and owner-subjects was higher. Economic level of the subjects showed significant effect on the thermal sensation, preference, acceptance and neutrality. The comfort band for lowest economic group was found to be 27.3-33.1 °C with the neutral temperature at 30.2 °C. This is way above the standard. This finding has far reaching energy implications on building and HVAC systems design and practice. Occupants’ responses for other environmental parameters often depended on their thermal sensation, often resulting in a near normal distribution. The subjects displayed acoustic and olfactory obliviousness due to habituation, resulting in higher satisfaction and acceptance.     

Thermal comfort in outdoor urban spaces: Analysis across different European countries

This paper presents some of the findings of the European project, RUROS, primarily concerned with the environmental and comfort conditions of open spaces in cities. The results of the microclimatic and human monitoring, in relation to the thermal environment and comfort conditions in open spaces, are presented. The database consists of nearly 10,000 questionnaire guided interviews from field surveys in 14 different case study sites, across five different countries in Europe. The findings confirm a strong relationship between microclimatic and comfort conditions, with air temperature and solar radiation being important determinants of comfort, although one parameter alone is not sufficient for the assessment of thermal comfort conditions. Overall comfort levels are over 75% for all cities on a yearly basis. There is also strong evidence for adaptation taking place, both physically, with the seasonal variation in clothing and changes to the metabolic rate, as well as psychologically. Recent experience and expectations play a major role and are responsible for a variation over 10 °C of neutral temperatures, largely following the profile of the respective climatic temperatures on a seasonal basis, across Europe. In this context, perceived choice over a source of discomfort is another important parameter for people in open spaces.     

Design considerations with ventilation-radiators: Comparisons to traditional two-panel radiators

Performance of heat emitters in a room is affected by their interaction with the ventilation system. A radiator gives more heat output with increased air flow along its heat transferring surface, and with increased thermal difference to surrounding air. Radiator heat output and comfort temperatures in a small one-person office were studied using different positions for the ventilation air inlet. In two of the four test cases the air inlet was placed between radiator panels to form ventilation-radiator systems. Investigations were made by CFD (Computational Fluid Dynamics) simulations, and included visualisation of thermal comfort conditions, as well as radiator heat output comparisons. The room model was exhaust-ventilated, with an air exchange rate equal to what is recommended for Swedish offices (7 l s⁻¹ per person) and cold infiltration air (−5 °C) typical of a winter day in Stockholm.Results showed that under these conditions ventilation-radiators were able to create a more stable thermal climate than the traditional radiator ventilation arrangements. In addition, when using ventilation-radiators the desired thermal climate could be achieved with a radiator surface temperature as much as 7.8 °C lower. It was concluded that in exhaust-ventilated office rooms, ventilation-radiators can provide energy and environmental savings.     

Numerical Method for a Full Assessment of Indoor Thermal Comfort

Heat, mass and momentum transfer takes place simultaneously in ventilated rooms. For accurate predictions of the indoor environment, all the environmental parameters that influence these transport phenomena should be taken into consideration. This paper introduces a method for a full assessment of indoor thermal comfort using computational fluid dynamics in conjunction with comfort models. A computer program has been developed which can be used for predicting thermal comfort indices such as thermal sensation and draught risk. The sensitivity of predicted comfort indices to environmental parameters is analysed for a mechanically ventilated office. It was found that when the mean radiant temperature was considered uniform in the office, the error in the predicted percentage of dissatisfied (PPD) could be as high as 7.5%. The prediction became worse when the mean radiant temperature was taken to be the same as air temperature point by point in the space. Moreover, disregarding the variation of vapour pressure in the space resulted in an error in PPD of abour 4% near the source of moisture generation. The importance of evaluating both thermal sensation and draught risk is also examined. It is concluded that in spaces with little air movement only the thermal sensation is needed for evaluation of indoor thermal comfort whereas in spaces with air movement induced by mechanical vantilation or air-conditioning systems both thermal sensation and draught risk should be evaluated.     

Air movement acceptability limits and thermal comfort in Brazil's hot humid climate zone

In hot humid climates, natural ventilation is an essential passive strategy in order to maintain thermal comfort inside buildings and it can be also used as an energy-conserving design strategy to reduce building cooling loads by removing heat stored in the buildings thermal mass. In this context, many previous studies have focused on thermal comfort and air velocity ranges. However, whether this air movement is desirable or not remains an open area. This paper aims to identify air movement acceptability levels inside naturally ventilated buildings in Brazil. Minimal air velocity values corresponding to 80% and 90% (V80 and V90) air movement acceptability inside these buildings. Field experiments were performed during hot and cool seasons when 2075 questionnaires were filled for the subjects while simultaneous microclimatic observations were made with laboratory precision. Main results indicated that the minimal air velocity required were at least 0.4 m/s for 26 °C reaching 0.9 m/s for operative temperatures up to 30 °C. Subjects are not only preferring more air speed but also demanding air velocities closer or higher than 0.8 m/s ASHRAE limit. This dispels the notion of draft in hot humid climates and reinforce the broader theory of alliesthesia and the physiological role of pleasure due to air movement increment.     

A relation between calculated human body exergy consumption rate and subjectively assessed thermal sensation

Application of the exergy concept to research on the built environment is a relatively new approach. It helps to optimize climate conditioning systems so that they meet the requirements of sustainable building design. As the building should provide a healthy and comfortable environment for its occupants, it is reasonable to consider both the exergy flows in building and those within the human body.Until now, no data have been available on the relation between human-body exergy consumption rates and subjectively assessed thermal sensation. The objective of the present work was to relate thermal sensation data, from earlier thermal comfort studies, to calculated human-body exergy consumption rates.The results show that the minimum human body exergy consumption rate is associated with thermal sensation votes close to thermal neutrality, tending to the slightly cool side of thermal sensation.Generally, the relationship between air temperature and the exergy consumption rate, as a first approximation, shows an increasing trend. Taking account of both convective and radiative heat exchange between the human body and the surrounding environment by using the calculated operative temperature, exergy consumption rates increase as the operative temperature increases above 24 °C or decreases below 22 °C. With the data available so far, a second-order polynomial relationship between thermal sensation and the exergy consumption rate was established.