Neutral Operative Temperature Research Articles

Experimental evaluation of thermal environment built by decoupled radiant cooling system with low radiant cooling temperature

Decoupled radiant cooling system (DRCS)1, which utilizes an infrared-transparent membrane to isolate the radiant surface from the ambient air, can provide radiant cooling temperature below the dew point to prevent condensation and increase cooling capacity. However, whether the thermal environment built by DRCS with low radiant cooling temperature meets thermal comfort needs further investigation. This includes: 1) Do the environment parameters meet the comfort standard? 2) How do subjects evaluate the environment's comfort? Thus, environmental monitoring and questionnaire surveys were conducted to evaluate the thermal environment of DRCS in summer. Initially, the environment parameters were measured and 32 subjects were recruited to perform subjective and physiological response tests. Further, the environment was evaluated using thermal comfort models and thermal sensation votes. Finally, the applicability of the predicted mean vote (PMV) model was examined by comparing actual and predicted thermal sensations. The results confirmed that thermal environment built by DRCS satisfied the ASHRAE Standard criteria. The neutral operative temperature was around 24.8°C and the comfort environment was achieved between 23.3°C and 26.5°C. Moreover, PMV model has a high accuracy in predicting the thermal sensation of DRCS.

Comparison of thermal comfort between different heating systems and adaptation to different indoor climates in winter.

Individual heating systems, such as the air-source heat pump (ASHP) air-conditioner or floor heating (FH), are usually used by people living in the hot summer and cold winter (HSCW) zone of China to heat indoor climates in the winter. However, little research has been conducted in the HSCW zone on the thermal comfort difference between indoor climates heated by ASHP air-conditioners and those heated by floor heating, as well as how occupants adapt to different indoor climates. We conducted a comparative field experiment in ASHP-heated and FH-heated apartments in Nanjing to investigate how different types of heating systems influence the thermal sensation of occupants, and we conducted a comparative field experiment in ASHP-heated office buildings and naturally ventilated teaching buildings in Shanghai to investigate how occupants adapt to different indoor thermal environments. Indoor environmental parameters and body surface temperatures were measured using instruments, and occupants' thermal sensation, activity level, and clothing were evaluated using the questionnaire. The results show that floor heating improves thermal comfort by raising foot temperature compared to the ASHP air-conditioner, and that occupants become acclimatized to different indoor climates by adjusting neutral operative temperature. According to the findings, there is no need to overheat the indoor environment in the HSCW zone because occupants can adapt to their experienced thermal environment and it is critical to maintain warm foot temperature in the cool/cold indoor environment.

Thermal Comfort in a Tropical Climate: Case Study of the Cafeteria in Student Residential College, UTHM Pagoh Branch Campus

Thermal comfort is important for buildings, especially in tropical climates. The issue of increasing indoor temperature is influenced by various factors that cause occupants to face thermal discomfort in cafeterias that uses both mechanical and natural ventilation systems. This study aims to determine the perception of occupants and evaluate parameter variations of thermal comfort in the cafeteria of Pagoh Campus Residential College, UTHM Pagoh Branch Campus. This study was conducted through the measurements of subjective and physical parameters. Data collection is carried out in two days, which are weekdays and weekends. This study uses some parameters variation which are thermal sensation vote index (TSV), predicted mean vote index (PMV), predicted percentage of dissatisfaction (PPD), operative temperature (To) and neutral operative temperature (Tneutop) to determine the thermal comfort conditions in the cafeteria. The results shows that the average values of air temperature, mean radiation temperature, relative humidity and air velocity from environmental measurements were 30.2 °C, 30.6 °C, 66% and 0.1 m/s respectively. In addition, PMV and PPD values were 2.0 and 76% from environmental measurements, while 1.36 and 43% from questionnaires. For To and Tneutop, the average values obtained are 30.4 °C and 28.6 °C. Furthermore, the findings showed that only the morning session was in the acceptable operative temperature range and complied with ASHRAE Standard 55 for both the 80% and 90% acceptability limits. At the end of the study, it was found that the values from the thermal environment measurements and surveys exceeded those recommended by ASHRAE Standard 55. This concluded that the quality of the occupants’ environment in the cafeteria is outside the satisfactory thermal comfort level. Therefore, the improvement through mechanical ventilation may very helpful in improving a good ventilation system as well as encouraging an increase in thermal comfort in the building.

A field study on thermal acceptability and energy consumption of mixed-mode offices building located in the hot-dry climate of Burkina Faso

To ensure thermal comfort in hot dry climates such as the climate of Burkina Faso, occupants of buildings often rely on air conditioning systems. Defining the appropriate conditions for thermal comfort is crucial to reduce energy consumption. This paper presents the findings of a field study that aimed to assess acceptable temperatures for thermal comfort and analyze the energy consumption related to the use of air conditioning systems in a mixed-mode office building. Surveys were also conducted to gather occupants’ feedback on thermal comfort. The results of the study revealed that the average air temperature was 27.1 °C with standard deviation of 1.7 °C. Fifty-four offices were investigated and all 93 occupants to the survey consider their thermal environment comfortable. The study also identified neutral air temperature and operative temperature which are between 26.2 °C and 26.5 °C, and 26.3 °C and 26.5 °C, respectively. The results show a non-significant gap between the neutral temperature of male and female subjects. It was observed that the energy consumption for comfort is linked to the neutral temperature. These findings can serve as a starting point for establishing thermal comfort parameters for mixed-mode office buildings in Sudano-Sahelian climates having a particular socio-cultural context.

Occupant’s thermal responses to asymmetric radiant thermal environment with warm wall and cool ceiling, Part A: Overall thermal responses

A radiant ceiling cooling (CC) system integrated with a mechanical ventilation system, which can improve human thermal comfort and reduce HVAC system energy consumption simultaneously, has been extensively applied in the modern office building with glass curtain walls. In a ceiling cooling room with a glass curtain wall, the horizontal and vertical asymmetric radiation caused by the warm wall and cool ceiling may result in different thermal responses of human body. Therefore in this paper, occupant’s thermal responses in a simulated ceiling cooling office room with mixing ventilation (MV) or underfloor air distribution (UFAD) were investigated by a combination of subjective and objective experiments. Indoor operative temperature was increased from 23.0 °C to 30.0 °C as the surface temperatures of warm wall and cool ceiling were from 30.0 °C to 40.0 °C and from 14.0 °C to 27.0 °C. The results showed that the indoor thermal environment with CC + MV or CC + UFAD was comfortable and acceptable as the indoor operative temperature was from 25.0 °C to 27.0 °C. The thermal neutral operative temperature in the room was 25.6 °C with CC + MV and 26.4 °C with CC + UFAD, and the corresponding thermal neutral skin temperatures was 33.4 °C and 33.7 °C, respectively. Moreover, the thermal comfort stability of indoor operative temperature was close to 0.30 °C−1 with CC + MV or CC + UFAD, and the corresponding thermal comfort stability of mean skin temperature was 0.90 °C−1–0.94 °C−1. There were clearly linear relationships between thermal sensation or thermal preference and indoor operative temperature or mean skin temperature, and these relationships may be beneficial for the intelligent control of a radiant ceiling cooling system combined with a mechanical ventilation system.

Impact of Pandemic Safety Measures on Students’ Thermal Comfort—Case Study: Romania

The indoor environmental quality of a building has attracted everyone’s attention since a worldwide pandemic was declared and forced people indoors. After several months, people were able to return to their usual activities, but with strict safety measures added due to the circumstances. This paper focuses on the impact of safety measures on students’ thermal comfort, a case study performed in a continental climate zone, during the winter. The methodology used involved the collection of both quantitative and qualitative data. Descriptive statistics and frequencies alongside correlations and cross-tabular methods were used to analyze the collected data. The results indicated that the predicted mean vote (PMV) underestimated students’ thermal perception. A difference of 1.5 °C was found between the operative neutral temperature of the PMV and students’ thermal sensation votes while wearing masks. Likewise, a lower neutral operative temperature was found for students wearing masks than for those without masks. Students wearing masks preferred a slightly cooler environment and a significant difference was found (p = 0.001) between students’ thermal comfort votes. All of these findings indicate that there is a potential for energy savings without affecting students’ thermal comfort.

Thermal Comfort in the Design Classroom for Architecture in the Cold Area of China

A field study of thermal comfort in a design classroom for teaching architecture and dormitory rooms in a cold area of China was conducted to provide a better understanding of the thermal comfort of students, and to clarify the energy saving potential of such building spaces. Respondents were the same for both the classroom and dormitories field survey, with a total of 89 students majoring in architecture. The students’ subjective thermal responses and their environmental parameters for two months before and after heating were collected and compared, and the results showed that when respondents adjusted their clothing it was not necessarily to adapt to the thermal environment but may have been due to habituation. The thermal neutral operative temperature was determined to be 23.1 °C in the design classroom and the thermal sensation was maintained at neutral-cool in the dormitory rooms. Although there were significant differences between the thermal environments in the classroom and dormitories, thermal acceptability was close to 100%. In the design classroom, the PMV (Predicted Mean Vote) predicted the indoor thermal environment relatively accurately, while in dormitory rooms, the PMV underestimated the thermal sensations. Students can tolerate lower temperatures, showing adaptability to the environment.

Experimental investigation of the effects of personal protective equipment on thermal comfort in hot environments

Since the outbreak of COVID-19, wearing personal protective equipment (PPE) has become increasingly common, especially for healthcare workers performing nucleic acid sample collection. A field experiment and questionnaire survey were conducted in a semi-open transition space of a university building in Guangzhou, southern China. Thirty-two subjects wore PPE to simulate nucleic acid sample collection, during which thermal parameters were recorded and subjective questionnaires were completed. The relationship between thermal sensation and thermal index was analyzed to determine the neutral temperature and comfort temperature zones. Subjects had higher requirements for thermal environment parameters when wearing PPE than when not wearing PPE, and were found to have statistically significant differences in thermal perception when wearing and not wearing PPE. Wearing PPE significantly raised the subjects' thermal and humidity sensations and restricted their airflow. Wearing PPE resulted in thermal discomfort for the subjects and a high unacceptability rate for environmental thermal parameters. The subjects wore PPE for an acceptable duration of approximately 1.5 h. The neutral operative temperatures were significantly lower when wearing PPE than when not wearing PPE, and the deviation from the neutral temperature was 9.7 °C. The neutral operative temperature was 19.5 °C and the comfort temperature zone was 17.4–21.5 °C when subjects wore PPE, demonstrating that subjects who wore PPE preferred lower temperatures. These results suggest that people who wear PPE for work, especially outdoors, should receive more attention to ensure thermal comfort and safety.

Comparison of the thermal comfort of pregnant women at different stages of pregnancy in a subtropical region

During pregnancy, owing to several physiological and psychological changes, the perception of heat by pregnant women changes, leading to them having different heat requirements. In this study, our objective was to determine the differences in the thermal perceptions of pregnant women at different stages of pregnancy (i.e., first, second, and third trimesters). Thus, we conducted an environmental parameter test on the obstetrics waiting rooms of four hospitals in Guangzhou and also administered a questionnaire survey to the waiting pregnant women. A total of 1043 questionnaires were collected during the survey (723 and 302 in summer and winter, respectively), after which the collected data was processed and statistically analyzed. Our results showed that with pregnancy development, the clothing resistance of pregnant women decreased, while their thermal sensation vote increased. Further, the mean neutral operative temperature values for the pregnant women in summer were 26.8, 25.2, and 24.1 °C, and in winter were 20.9, 19.6, and 18.9 °C during the first, second, and third trimesters, respectively. Furthermore, their preferred operative temperature values in summer were 25.8, 24.6, and 23.1 °C and in winter were 24.3, 24.0, and 22.8 °C during the first, second, and third trimesters, respectively. Thus, our results indicated that the perception of heat by pregnant women is dynamic, and increases with the development of pregnancy. These findings have guiding significance with respect to controlling the environment of the obstetrics waiting environments.

Thermal Comfort Performance of Naturally Ventilated Royal Malaysian Police (RMP) Lockup in Hot and Humid Climate of Malaysia

Thermal comfort performance of three vacant naturally ventilated Royal Malaysia Police (RMP) case study lockups (LK1 in Penang, LK2 in Melaka & LK3 in Kuala Lumpur) was measured during monsoon change period from Northeast Monsoon to Southeast Monsoon. According to NGO’s report and previous studies, the lockups condition is very poor and hot which contribute to discomfort among detainees. The objectives of the study are to investigate thermal comfort performance of the lockups based on four environmental parameters (Ta, Tr, Va, & RH) through physical measurement, to predict thermal comfort performance based on operative temperature (To) and neutral operative temperature (Tneutop), and to compare the results with thermal comfort criteria recommended by ASHRAE 55 standard and previous thermal comfort studies in hot and humid climate. The results show that To and Tneutop reading of LK1 is exceeding the maximum range recommended by ASHRAE 55 and previous studies by 2% to 8% (To) and 1% (Tneutop) which categorizing LK1 condition as hot. This is mostly due to high hot airflow brought through an ineffective window opening. The results will be used as reference for improvement towards some aspects such as window opening, building finishes materials, space volume and building orientation in future lockup design.

Establishing Indoor Thermal Comfort Range for Office Buildings in Jos Nigeria Using the Adaptive Psychrometric Chart

A psychrometric chart is a web-based graphical user interface that allows for the prediction of thermal comfort and the visualization of comfort boundaries within predefined atmospheric qualities. Based on ASHRAE 55 adaptive method, this chart was used to analyse 10 administrative office buildings, with occupant-controlled natural conditioned spaces, located within Jos urban conurbation in Nigeria. This tool revealed that with an outdoor temperature of 32.0°C, indoor thermal comfort range for 80% and 90% acceptability corresponds to 24.2°C to 31.2°C and 25.2°C to 30.2°C respectively. It also established a neutral operative temperature of 29.0°C on the Adaptive Psychrometric Chart. The neutral operative temperature of 29.0°C is at slight variance with other research indicating a Neutral Temperature of 29.4°C. However, this established neutral temperatures fall within 80% and 90% of acceptability thermal comfort range. This authenticates the validity of Psychometric Chart and the Neutral Temperature Analysis techniques as viable tools in thermal comfort studies in this research environment and conditions. This also indicates that most of the office buildings examined can operate fairly effectively without mechanical ventilation thereby providing savings in energy use and ensuring environmental sustainability.

A field investigation on the winter thermal comfort of residents in rural houses at different latitudes of northeast severe cold regions, China

The severely cold regions of Northeast have a colder climate and large latitude span in China. Scholars should pay more attention to the creation of a comfortable indoor thermal environment in winter. In order to understand indoor thermal environments and residents’ thermal comfort statuses in areas at different latitudes, a field survey was conducted in three areas: Harbin (45°N), Changchun (43°N) and Shenyang (41°N). On-site environmental parameter measurements and a subjective questionnaire were conducted simultaneously. Then, the relation between operative temperature and building energy consumption was explored. The results showed that the neutral operative temperature is the highest in Harbin (16.8 °C), followed by Changchun (16.4 °C) and Shenyang (16.0 °C), which are all higher than the measured temperatures. For these regions, 90% of the acceptable temperature ranges are 14.6–19.1 °C, 14.4–18.6 °C and 13.9–18.2 °C, respectively. The expected operative temperatures are 18.6 °C, 17.8 °C and 17.3 °C higher than the neutral temperature, respectively. This reveals that as the latitude increases, the neutral temperature, the upper and lower limits of the acceptable range and the expected temperature are all increased. For different ages, the youth have a higher requirement in terms of thermal comfort, followed by the middle-aged and elderly groups. Compare to males, females feel colder under the same operative temperature. Due to the independent heating system in rural houses, adjusting the heat supply, instead of clothing, is the main adaptive behavior. Regarding building energy consumption, as the latitude declines, the influence of changes in operative temperature increases. If both the regional neutral temperature and zoning heating mode are adopted, energy consumption further decreases. These findings provide a reference for the development of an evaluation standard for indoor thermal environments and an energy-saving design for rural houses in the northeast severe cold regions of China.

An optimised window control strategy for naturally ventilated residential buildings in warm climates

The adopted window control strategy within an indoor environment affects ventilation performance and occupant comfort. A natural ventilation strategy with optimised window control is proposed and evaluated on a typical Australian residential building. The three main steps of window control are: 1) prediction of outdoor air temperature through rolling forecast; 2) determination of ventilation mode through the decision tree method and; 3) optimisation of window opening percentage through heuristic control. Three control strategies are investigated and compared throughout the hot season. The results suggest that introducing prediction of outdoor temperature into the natural ventilation control process minimises the negative impact of control hysteresis. By using flexible degrees of window opening, the proposed strategy shows improved performance for maintaining an indoor operative temperature compared to the original open-closed control. The mean absolute deviations of indoor operative temperature from the neutral operative temperature are reduced by more than 30 %. In addition, the presented feedback and predictive control logic results in greater stability of indoor thermal operative temperature by avoiding over-ventilation.

Perceptual and physiological responses of elderly subjects to moderate temperatures

Aging populations pose significant social challenges for many countries including China. The elderly spends most of their time inside built environments, so a better understanding of their thermal comfort indoors is important. This study investigated the perceptual and physiological responses of elderly subjects to different operative temperatures (21 °C, 25 °C, 28 °C and 31 °C). Their indoor thermal requirements were investigated, and results compared with those of young people. Sixteen healthy subjects aged 70+, including both males and females, participated in this experiment. In addition to thermal comfort perceptions, two physiological parameters, including skin temperature (local and mean) and electrocardiograph (ECG) were also monitored. Results showed that skin temperature and the ratio of LFnorm to HFnorm of ECG were sensitive to the ambient temperature. For comparative purposes, we refer to the previously published climate chamber experimental results of young college-age subjects also in Shanghai [1]. Neutral operative temperature (26 °C for a mean thermal sensation of “neutral”) and neutral skin temperature (32.2 °C for a mean thermal sensation of “neutral”) of the elderly sample in the present study was not different from that of young people. However, the elderly subjects were not as sensitive as the young college-age counterparts when it came to changes in operative temperature.

Adaptive thermal comfort in naturally ventilated dormitory buildings in Changsha, China

This research focused on investigating thermal comfort in naturally ventilated (NV) dormitory buildings in hot summer and cold winter (HSCW) climate zone in China. A field study was conducted during the summer of 2016 in Changsha, located in HSCW climate zone. The occupants reported subjective thermal perception using questionnaires and ambient environmental variables were measured simultaneously. A total of 11 NV dormitory buildings were investigated. 467 valid sets of measurement data and subjective questionnaires were obtained. Both Griffiths and linear regression analysis showed that the neutral operative temperature (To) was 26.2 °C. The upper limit for 80% acceptability was determined as 28.5 °C. The most acceptable operative temperature was 26.6 °C. 80% of occupants were comfortable at the temperature range between 25 °C and 28.7 °C. Based on this study, the adaptive model was developed and verified. The adaptive behaviors of clothing adjustment and air velocity adjustment were closely correlated to indoor To. The functions of adaptive thermal behaviors can be used for building simulation. The results can be used to assess indoor thermal comfort in buildings, and help to build a more rigorous database for building designing.

A comparative study of thermal comfort in learning spaces using three different ventilation strategies on a tropical university campus

In this study, the thermal comfort of the occupants of learning spaces using three different ventilation strategies (i.e. air-conditioning [AC], hybrid [HB], and natural ventilations [NV]) was investigated at a tropical university campus. Data were collected from 1043 survey questionnaires; concurrently, on-site measurements in three consecutive years were analysed. Findings indicated that HB spaces have significant advantages over AC and NV spaces in terms of a higher rate of neutral thermal sensation votes, temperature satisfaction levels, and overall thermal comfort levels. It was also found that, as compared to those in AC spaces, occupants in HB and NV spaces maintained higher comfort temperature and they could tolerate a wider range of acceptable temperatures. They were also less sensitive to changes in temperature. A significant correlation between the neutral operative temperature and latitude, as identified in existing studies, supports the observation regarding acclimatisation of occupants in warmer climates. The PMV/PPD thermal comfort model predicted warmer thermal sensations than those actually felt by the occupants. The comfort rate estimated according to the PMV/PPD model was consistently lower than that according to the adaptive comfort model in HB and NV spaces, raising concerns about the effectiveness of the PMV/PPD model in predicting thermal comfort in NV spaces in a warm environment. The findings provide convincing evidence to promote the design of HB and NV learning spaces in hot and humid climates. Such ventilation strategies can provide comfortable thermal conditions and, potentially, reduce energy use for cooling and associated CO2 emissions significantly.

Thermal comfort requirements in the summer season in subtropical urban spaces

This article presents some of the findings from a thermal comfort study performed in subtropical China. This study was carried out in 17 different urban spaces during the summer of 2010. Thermal environmental measurements were taken and questionnaire surveys were used to assess the thermal comfort of subjects. Thermal comfort requirements and the effect of gender on thermal comfort were analysed. Neutral operative temperature was found to be 28.6°C and preferred temperature occurred at 24.7°C. By using the direct thermal acceptability assessment method, this article also demonstrated a new correlation between percentage of thermal dissatisfaction (PD) and thermal sensation vote (TSV) which is different from the predicted mean vote–predicted percentage dissatisfied model. The acceptable temperature range was 25.3–32.3°C in summer. Besides, the results show significant gender differences in urban spaces in terms of neutral temperature, preferred temperature and optimum wind speed.

Thermal comfort in outdoor urban spaces in Singapore

A thermal comfort study has been carried out in outdoor urban spaces in Singapore. The field study was carried out from August 2010 to May 2011. There were 2059 respondents from 13 different outdoor spaces participated in this study and 2036 effective questionnaire responses were collected. Thermal comfort perceptions and preferences were analyzed in this study. The neutral operative temperature occurred at 28.7 °C and preferred temperature was found to be 26.5 °C. Thermal acceptability analysis shows the acceptable operative temperature range was 26.3–31.7 °C in outdoor urban spaces in Singapore. Correlation analysis indicates that sun sensation/solar radiation has the most significant influence on human thermal sensation in outdoor spaces. This study also explores the impact of thermal adaptation on human thermal sensation in outdoor spaces, which could be useful for future researchers. Comparative analysis shows that people may expect a higher temperature in outdoor conditions than in semi-outdoor or indoor conditions in Singapore, suggesting that people in outdoor conditions could be more tolerant with the heat stress than people in indoor conditions in tropical climate.

A Field Study on Thermal Comfort of Occupants and Acceptable Neutral Temperature at the National Museum in Malaysia

A field study was conducted to investigate the thermal environment and occupants’ comfort in the National Museum of Malaysia. The occupants’ thermal perceptions in the museum were measured and characterised. The response of the occupants has indicated that the thermal conditions inside the museum did not satisfactorily fulfil the ASHRAE Standard 55, because only 78% of the occupants were satisfied with their environment. Besides, actual mean vote (AMV) and predicted mean vote (PMV) were compared. The Fanger’s model gave a neutral operative temperature of 22.2°C from the PMV, whereas the questionnaire data used in the mean thermal sensation vote (MTSV) of the present study gave a higher value (22.5°C) for the neutral operative temperature. The preferred operative temperature was found to be 22.3°C. The minimum air temperature in three galleries was below the lower limit of the temperature range of 18–22°C as recommended by Museums Australia Victoria. The mean indoor humidity was too high compared to the optimal range of 55 ± 5% relative humidity (RH). The mean air velocity, ≤0.15 m·s−1, in each gallery was satisfactory. Findings of this study are very useful for designing heating, ventilating and air-conditioning (HVAC) systems with energy-saving methodology for museum buildings in tropical regions.

Adaptive comfort model for tree-shaded outdoors in Taiwan

Tree-shaded outdoors can reduce the heat effect by ameliorating the microclimate and enhancing the human thermal comfort outdoors; for this reason, they are main places for rest, recreation and social activity in Taiwan's cities. Field comfort surveys of 3839 interviewees were conducted in tree-shaded spaces throughout a year. The aims were to obtain a better understanding of human thermal comfort response outdoors and to propose an adaptive comfort model for tree-shaded spaces. A comfort zone, centering on neutral operative temperature which is an empirically derived linear function of mean monthly outdoor temperature, of 6 °C for 90% acceptability and 8 °C for 80% acceptability was suggested for tree-shaded spaces from surveyed data, adding that a non-linear function of the temperature difference between actual operative temperature and neutral operative temperature was established that aims to predict the percentage of heat or cold discomfort at a particular outdoor thermal condition. An application of the established adaptive comfort model on an actual tree-shaded space was demonstrated to show its practicality in long-term evaluation of a particular thermal environment.