Air-conditioned Office Research Articles

Machine learning approach for predicting personal thermal comfort in air conditioning offices in Malaysia

The existing machine learning based models for personal thermal comfort have traditionally focused on physiological and psychological variations among occupants, and the spatial parameters have been largely overlooked. Field measurements are conducted to collect data and synthesise the collective findings for optimal spatial positioning based on a 24 °C setpoint. The objective of the present study is to investigate and compare the prediction performance made by the machine learning models for personal indoor thermal comfort in air-conditioned office environments using non-spatial parameters (NSP) and spatial parameters (SP). The data was collected from the respondents at four different occupants. A comprehensive data set of NSP and SP is comprised of machine learning models in predicting different thermal comfort situations are Decision Trees (DT), Random Forests (RF), Support Vector Machines (SVM), K-Nearest Neighbours (KNN), Naive Bayes (NB), and Neural Networks (NN). Results indicate a substantial improvement in the accuracy prediction with the Random Forest algorithm outperforming others, enhancing overall accuracy by 38.6 % with spatial parameters for thermal sensation vote (TSV). However, the SVM algorithm improves 50 % accuracy by considering SP input for thermal comfort (TC). Spatial parameters, including the distance between windows and air conditioning units, emerge as critical factors influencing thermal comfort.

A Sonic Vaccine for a White-Collar Disease

Abstract Members of the Matua religion, a displaced Dalit community from Bengal, believe that the coronavirus can affect only the upper-caste/class layers of society, those who sit in air-conditioned offices and live in the big cities. Matua devotees, on the other hand, are predominantly part of an agriculturist community inhabiting multiple fringes: the borderlands of India and Bangladesh, the peripheries of unorthodox Vaishnavism, and the social margins of untouchability. Conducting remote ethnography with Matua participants based in West Bengal, Bangladesh, and the Andamans, one comes across insistent narratives of immunity and recurrent interpretations of the pandemic that fit into the onto-cosmology and sociocultural imagination of the Matua religious movement. I discuss these as dissident tales of immunity that describe COVID-19 as an urban-based white-collar disease. Matua practitioners successfully prevent it through a sonic vaccine – the practice of kīrtan – and a kind of power (śakti) accumulated through physical agricultural labor.

Development of a rapid assessment tool for integrating thermal comfort in early design stage of energy-efficient office buildings

Comprehending and predicting energy performance of existing buildings and new constructions is crucial towards decarbonization. Instead of utilizing simulation software, multiple regression models are utilized to predict building energy consumption while ensuring indoor thermal comfort to speed up this process. However, previous predictive models prioritize reducing energy demand, with limited focus on thermal comfort. This study aims to support decision-making during retrofitting and new construction planning though developing a prediction model. An air-conditioned office building served as a reference building for simulation. 21 design parameters were analyzed, including aspects of weather, building envelope, internal loads, ventilation, and temperature settings. Stepwise regression results unveiled the crucial variables in the final model, with 8, 9, 13, and 6 variables remaining for peak cooling load, annual cooling load, overheating hours (WE), and Environmental Quality Index for thermal comfort (EQITC) in the perimeter zones, and 5, 6, 8, and 5 variables for the core zones, respectively. Furthermore, insights into the important variables regarding cooling load and thermal comfort were respectively provided. Weather- and envelope-related variables, such as cooling degree-days, global solar radiation, solar heat gain coefficient (SHGC), and U-value, have the highest impacts on cooling load. For thermal comfort, variables including temperature setpoint, occupant activity level, and factors related to window sunlight transmission performance, such as SHGC, window area ratio, and overhang projection ratio, proved to be influential. Overall, this study provided accurate models for assessing optimal strategies for energy efficiency and thermal comfort during the early design phases, advancing building performance practices.

Effect of preferable wind directions on personal thermal comfort of occupants in the air-conditioned office in hot-humid climate

The utilization of a desk fan in the personal thermal comfort (PTC) method is a thermal adaptation that provides indoor comfort and energy-saving for office applications due to the high energy consumption of ACs in the HVAC sector. Researchers have conducted numerous studies on this utilization. However, the question of which wind direction provides thermal comfort for respondents remains an issue, along with the effect of different wind directions on thermal comfort and its influence on skin temperature. Field measurements were conducted inside an air-conditioned office room at a set point temperature of 29.0 °C, involving 400 questionnaire samples from 20 respondents. There were three stages of desk fan configurations; Stage 1 No-fan, Stage 2 Single fan, and Stage 3 Dual fan configurations. The result showed that most respondents preferred wind direction from front and head. Meanwhile, left and right were least favoured. Different wind directions from fans successfully lowered the heat sensation perceived by respondents up to 53% compared to the no-fan configuration. It improved the overall comfort from slightly uncomfortable to moderately comfortable, on a scale of 3.5 to 2.4, under the indoor temperature of 28.6 °C. Respondents' initial average skin temperature during no-fan configuration, ranging from 33.9 to 35.4 °C, was lowered during fan configurations, recorded at 33.2–34.5 °C. PTC setup used in the study also provides lower energy consumption, ranging from 8-20%, compared to low AC set point temperatures of 20.0 and 24.0°C commonly used in hot and humid tropical countries.

Relationship between Self-Assessed Productivity, Gender and Age in Mixed-Mode and Fully Air-Conditioned Offices in Florianópolis, Brazil

The quality of the indoor environment and anthropometric parameters influence the users’ productivity in a building. This study aims to evaluate the influence of environmental and anthropometric characteristics on the self-assessed productivity of office building users in the humid subtropical climate of Florianópolis, Brazil. Three hybrid buildings equipped with air-conditioning and natural ventilation and one centrally air-conditioned building were considered. Indoor environmental data were obtained by means of measurements. Electronic questionnaires collected anthropometric characteristics and the perception of productivity by the users. The analysis of the users’ performance was performed using box diagrams. The results showed that women and occupants over 50 years old preferred high temperatures during the use of natural ventilation. When air-conditioning was on, the perception of productivity concerning the operative temperature did not show significant differences between anthropometric variables. It was concluded that the use of air-conditioning reduced the influence of anthropometric characteristics on self-assessed productivity and that people maintained their work performance despite the higher internal temperature variations during natural ventilation operation.

Would employees accept curtailments in heating and air conditioning, and why? An empirical investigation of demand response potential in office buildings

Support for demand response has mostly been investigated in the context of private households. We extend the examination of support to organizational contexts. Specifically, we analyze employee support for a scenario in which employees are faced with temporary heating or air conditioning curtailments in their workplace. We also examine the factors underpinning support, including socio-demographic and workplace characteristics and psychological motivations and beliefs. Our empirical results are based on a sample of 551 employees from different organizations who work in air-conditioned offices. Results indicate that employees generally support corporate demand response programs and are willing to accept small deviations from their ideal office temperature, but the level of support is heterogeneous across employees. Subsequent modeling of potential underlying factors shows that socio-demographic or workplace-related characteristics only play a minor role in explaining these variations. In contrast, psychological factors, including environmental motivations and perceived corporate environmental responsibility underpin support, and specific beliefs about the consequences of participation can directly explain support as well. Moreover, personal norms emerged as an important antecedent of program support. Policy makers and organizations can use these insights to design effective demand response programs that address the relevant drivers and barriers of employee support.

Indoor CO2 removal: decentralized carbon capture by air conditioning

Growing evidence indicates that an elevated CO2 concentration as low as 1000 ppm could lead to direct human health risks, while the CO2 concentration in a lot of indoor environments may exceed that figure by several times. Employing the latest developed moisture swing sorbent, we here built a CO2 purification module to be incorporated with existing air conditioning units to keep the indoor CO2 concentration at healthy levels. The sorbent binds CO2 spontaneously from ambient air when dry and then releases CO2 in the presence of moisture, thanks to the moisture-driven reversible hydrolysis reaction of carbonate ions at a nano interface. Thus, the indoor dry air circulation and the outdoor air flow (for cooling the condenser) of the air-conditioning system provide a perfect carbon capture platform for the moisture swing sorbent to work. Tests in an acrylic box (mimicking an indoor environment) showed that the CO2 purification module can keep the indoor CO2 level to be close to or even lower than outdoor levels with an initial CO2 concentration of 1000 or 2000 ppm. An enlarged test was further conducted in an air-conditioned office to demonstrate the effectiveness of the purification module. Finally, we discussed the potential of this kind of decentralized carbon capture facility enabled by retrofitted air conditioners to contribute to negative emissions and mitigation of the global warming and climate change crisis.

A Review on Adaptive Thermal Comfort of Office Building for Energy-Saving Building Design

The thermal environment quality of office buildings has an important role because thermal comfort is directly related to human productivity. Thermal comfort conditions are influenced by climate, location, and the built environment; hence, comfort standards are required to assist building designers in creating a comfortable indoor environment for building occupants. In this context, the present study analyzes the adaptive thermal comfort studies conducted in office buildings from various countries. A large number of research articles selected from the Scopus database were considered for this study. Based on the analysis, outdoor climatic conditions have a greater influence on indoor thermal conditions in naturally ventilated than in air-conditioned office buildings. The temperature required for comfort is as low as 17.6 °C and as high as 31.2 °C in naturally ventilated buildings. An adaptive comfort equation for naturally ventilated and air-conditioned office buildings has also been proposed to predict the indoor comfort temperature. Various studies show that a substantial amount of energy can be saved by changing the set point and natural ventilation. Furthermore, this study successfully provides hearty evidence that there is a need for climate-specific standards on thermal comfort for energy-efficient design development because existing comfort standards might not be applicable to all climates.

Numerical study on the thermal performance of water flow window fed with air-conditioning condensate

A water flow window (WFW) fed with potable water is deemed as an effective system for absorbing incoming heat energy through the glazing area of a window. In this study, condensate formed in an air-conditioning (A/C) system is applied in a WFW for reducing heat gain and electricity consumption of a building. There is no need to consume any potable water. Through building energy simulations and numerical computation, this study unveils that a fully air-conditioned office building operating under a subtropical climate can produce condensate of sufficient flow rate to absorb heat energy from the glazing panes of an A/C condensate fed WFW system. The surface temperature of an outer glazing pane in an A/C condensate fed WFW system can be dropped by 16.3 °C when compared to a Low-e glass window. Moreover, an A/C condensate fed WFW can offer better thermal performance than a conventional WFW. When comparing to a Low-e glass case, an A/C condensate fed WFW facing four different orientations (N, E, S & W) can give reduction percentages of transmitted heat gain ranging from 57.2% to 63.5%. This A/C condensate fed WFW system shows a promising performance and has good potential for real application in commercial buildings.

Study on Winter Comfort Temperature in Mixed Mode and HVAC Office Buildings in Japan

Comfort temperature is important to investigate because the chosen office indoor temperatures affect the energy used in a building, and a thermally comfortable environment makes the occupants be more productive. The effects of temperature on comfort are broadly recognized for thermal comfort. Japanese office buildings are well equipped with air-conditioning systems to improve the thermal comfort of the occupants. The main objectives of this research were to compare the winter comfort temperature in mixed mode (MM) and heating, ventilation and air-conditioning (HVAC) office buildings and to investigate the relationship between the comfort temperature and the indoor air temperature. This study measured the thermal environmental conditions of the office buildings and surveyed the thermal comfort of the occupants. The field survey was conducted during winter in seven office buildings located in the Aichi prefecture of Japan. In total, 4466 subjective votes were collected from 46 occupants. The result suggested that the occupants were found to be more satisfied with the thermal environment of MM buildings than that of HVAC office buildings. Overall, 95% of comfort temperatures were in the range 22~28 °C in MM and HVAC buildings, which were higher than the indoor temperature of 20 °C recommended by the Japanese government. The comfort temperature was highly correlated to the indoor air temperature of the MM buildings than to that of HVAC buildings. This indicated that the occupants were more adapted towards the given thermal environment of MM buildings.

Thermal adaptation of different set point temperature modes and energy saving potential in split air-conditioned office buildings during summer

The Chinese government issued a regulation that the cooling set point temperature (SPT) in office buildings cannot be lower than 26 °C. Therefore, SPTs were divided into different modes: SPT≥26 °C and SPT<26 °C. To study the human thermal adaptation of different SPT modes and determine the comfort and energy saving of the policy, a field test and subjective questionnaires were conducted in 21 split air-conditioned (SAC) office buildings during the warm season in the cold zone of China. We measured the environmental parameters and subjects' skin temperatures, and the subjective thermal responses were also investigated. The results showed that 45% of the air conditioner SPTs were less than 26 °C. In the high SPT mode, people's physiological adaptability to the warm environment was stronger, and subjects were more active in reducing clothes and increasing air velocity to improve thermal discomfort. Because the two modes had similar thermal histories and the same perceptual control, in the same SET ranges, no significant differences were found in thermal sensation, acceptability and comfort between the two SPT modes. The effects of long-term indoor thermal history on human thermal adaptation varied with the thermal exposure type, mode and intensity. From the analysis of thermal adaptation, the rationality of the policy was fully proved, and it was determined that SAC office buildings could save 26.4–35.2% of power energy consumption by reasonably increasing SPT in the cold zone. The results can enrich the thermal adaptation theory and provide a theoretical basis for the government's energy-saving policies in SAC office buildings.

Respiratory Symptoms and Skin Sick Building Syndrome among Office Workers at University Hospital, Chiang Mai, Thailand: Associations with Indoor Air Quality, AIRMED Project.

Sick building syndrome (SBS) is the term used to describe the medical condition in which people in a building suffer from symptoms of illnesses for no apparent reason. SBS was found to be associated with indoor air quality (IAQ) but there are a variety of determinants (buildings, in particular). Identifying and controlling factors related to SBS is crucial for improving worker health and efficiency. A cross-sectional study was conducted to investigate (1) the prevalence of respiratory symptoms and skin SBS and (2) their associations with IAQ among office workers in administrative offices in an academic medical institute. A self-reporting questionnaire assessing the worker’s characteristics, working conditions, and perception of working environments was used. The building assessment was via a walk-through survey and IAQ measurement. Of 290 office workers, 261 (90%) in 25 offices of 11 buildings took part in the survey. The highest prevalence of SBS was nasal symptoms (25.3%). We found that to reduce the risk of SBS, optimal air temperature levels in air-conditioned offices should be lower than 23 °C, with relative humidity between 60% and 70%. Lowering indoor CO2 levels below 700 ppm may be indicative of adequate ventilation to prevent SBS by reducing worker discomfort and indoor contaminants (e.g., formaldehyde).

Influence of Gender on Thermal, Air-Movement, Humidity and Air-Quality Perception in Mixed-Mode and Fully Air-Conditioned Offices

As gender may influence thermal and air quality perception in indoor environments, the aim of this study was to analyse gender influence on air movement, air humidity, air quality and thermal perception in office buildings in Southern Brazil. Statistical descriptions, regression analyses and hypothesis tests were performed using data collected from field studies conducted in a fully air-conditioned building and in three mixed-mode buildings. In addition, comfort temperatures were estimated through the Griffiths method. Results showed that females tend to feel colder compared to males. Men and women tended to present higher thermal acceptability and thermal comfort in mixed-mode buildings and in fully air-conditioned buildings, respectively. Weak but significant correlations were obtained between some environmental and subjective variables. In general, comfort temperatures were statistically higher for females (24.2 °C) than for males (23.5 °C). Significant gender differences for thermal perceptions of indoor environments were detected.

Investigation on typical occupant behavior in air-conditioned office buildings for South China’s Pearl River Delta

The excessive simplification of occupant behavior is considered as the most important factor that affects the uncertainty of building performance simulation, thus affects the reliability and generalizability of simulation-based design and forecast. In this paper, occupant behavior in air-conditioned office buildings of the Pearl River Delta (PRD) region was investigated and defined. Copies of 873 questionnaires about the occupant behavior in air-conditioned office buildings in the PRD region were collected to study the relationship between indoor environment quality and adaptive behaviors. Eight typical office occupant schedules were defined via K-means clustering method. A probability prediction model of cooling temperature set-point was established by using the Ordinal Logistic Regression method. According to the different control modes of air conditioning, window, blind and lighting equipment, four types of typical behavior patterns were proposed using the K-prototype clustering method, which could be developed into 20 typical occupant behavior styles of office buildings in the PRD region.

Effectiveness of phase change material in improving the summer thermal performance of an office building under future climate conditions: An investigation study for the Moroccan Mediterranean climate zone

The rise in global temperature due to the climate change phenomenon would increase the severity of summer season in the future. The integration of phase change materials (PCM) into the building envelope has been considered as one of the most promising measures to improve the thermal performance of buildings. This paper aims at investigating the effectiveness of the PCM in improving summer thermal performance of buildings under the climate conditions of the next three decades. The moderate scenario RCP4.5 of the Intergovernmental Panel on Climate Change was used to simulate future climate conditions. The present study was conducted for two building case studies: free-running and air-conditioned office buildings located in the north of Morocco (Mediterranean climate with hot summer). The findings have disclosed that an appropriate selection of the PCM melting temperature could enhance the thermal performance by 9.87 % for the free-running building and by 20.5 % for the air-conditioned building case over the whole building lifespan (30 years). A decade-by-decade analysis showed that the effectiveness of the optimum selected PCM would slightly decline over time. The research involved an economic analysis of the air-conditioned building case study. The latter led to calculating the maximum allowable cost of the PCM installation to achieve a payback period within the lifespan of the building. The findings of the present work can be used as guidelines to design office buildings integrated with PCM in the Mediterranean region.

Associating thermal comfort and preference in Malaysian universities’ air-conditioned office rooms under various set-point temperatures

Overcooling indoor spaces in hot-and-humid regions indicate excessive usage of air conditioner (AC). Understanding the occupants' thermal perception in AC settings helps navigate the cooling energy required. This study investigated thermal comfort in biased and non-biased environments and examined the occupants’ preferences. Four set-point temperature conditions (Original, Original ±2 °C, and MS Standard) were implemented in a semi-controlled field study done in 19 offices. 628 samples were taken from 42 occupants via thermal measurements and questionnaire surveys. The indoor air temperature in the typical AC settings (Original set-point) was 23.1 °C, denoting non-compliance to the local guideline. The results showed that occupants generally felt more comfortable when the indoor air temperature was increased. The mean comfort temperature was 24.6 °C, and the proportion of comfort votes depletes when the operative temperature reaches 26 °C. The preferred temperature was estimated at 23.9 °C, and the linear relationship with comfort temperatures revealed that occupants preferred a cooler environment despite being thermally comfortable. The findings suggest that occupants could tolerate higher AC settings well, but thermal preference may be a critical factor in estimating the comfort temperature limits.

Hybrid Ventilation in an Air-Conditioned Office Building with a Multistory Atrium for Thermal Comfort: A Practical Case Study

This study involved a series of computational fluid dynamics simulations to evaluate the effectiveness of stack and displacement ventilation in providing better thermal comfort in an air-conditioned office building. To reduce energy consumption, the public area of the studied building is cooled by air from air-conditioned rooms with lower temperatures. The air, which is driven by buoyancy, then, flows outside through the multistory atrium. The simulation results indicated that displacement ventilation provides superior thermal comfort performance relative to stack ventilation. A design with a higher ceiling, a higher heat source and a lower inlet with cold air can substantially enhance the efficiency of displacement ventilation. Furthermore, handrails near the atrium play a crucial role because they help to retain cold air in the public space for a longer period, thereby contributing to a better predicted mean vote value.

Overcooling of offices reveals gender inequity in thermal comfort

Growth in energy use for indoor cooling tripled between 1990 and 2016 to outpace any other end use in buildings. Part of this energy demand is wasted on excessive cooling of offices, a practice known as overcooling. Overcooling has been attributed to poorly designed or managed air-conditioning systems with thermostats that are often set below recommended comfort temperatures. Prior research has reported lower thermal comfort for women in office buildings, but there is insufficient evidence to explain the reasons for this disparity. We use two large and independent datasets from US buildings to show that office temperatures are less comfortable for women largely due to overcooling. Survey responses show that uncomfortable temperatures are more likely to be cold than hot regardless of season. Crowdsourced data suggests that overcooling is a common problem in warm weather in offices across the US. The associated impacts of this pervasive overcooling on well-being and performance are borne predominantly by women. The problem is likely to increase in the future due to growing demand for cooling in increasingly extreme climates. There is a need to rethink the approach to air-conditioning office buildings in light of this gender inequity caused by overcooling.

Effect of spring grass fires on indoor air quality in air-conditioned office building

Open biomass burning (OBB) is a significant air pollution source, but it is still not clear to what extent OBB events affect indoor air quality [1]. Outdoor and indoor measurements of submicron particulate matter (PM1) were conducted on 25–29 April (2019) in the capital city Vilnius (Lithuania). Fires from neighbouring countries (Belarus, Ukraine and Russia) and in the vicinity of Vilnius broke out during the measurement campaign. The temporal evolution and transport of OBB plume were investigated by combining the air mass backward trajectory analysis and fire satellite observation (MODIS) database. Measurements of the PM1 chemical composition in real-time were performed using an aerosol chemical speciation monitor (ACSM) and an aethalometer. Organic matter was the clearly dominant component, accounting for &gt;70%, in both indoor and outdoor PM1. The air filtering system of the office building removed approximately up to 55% of PM1. Despite a significantly lower PM1 pollution level in the office, highly acidic indoor PM1 could have harmful effects on the human health. Source apportionment of particulate carbonaceous matter revealed a significant importance of OBB-related particles (average 56%) to indoor air.

A comparative study of gender differences in thermal comfort and environmental satisfaction in air-conditioned offices in Qatar, India, and Japan

Gender differences in the assessment of thermal comfort and indoor environmental quality (IEQ) in the Gulf Cooperation Countries (GCC) have not previously been investigated, despite the prevalence of the overcooling of indoor spaces. This study investigated the effect of sex, age and body mass index on subjective thermal comfort perceptions, comfort temperature and IEQ satisfaction in offices using our thermal comfort surveys in Qatar, India, and Japan. Data from the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) databases were used for comparison. We found that females were twice as likely to feel dissatisfied with thermal sensation than males in Doha. Overall, females felt colder than men, and were less satisfied with all IEQ parameters. In Doha, females, younger subjects, and high-BMI subjects had lower comfort temperatures than their counterparts.Increased indoor air speeds and the provision of personal environmental controls could effectively reduce female dissatisfaction and save energy in Qatar. Women's more stringent thermal comfort preferences could be used to evaluate occupant control provisions and IEQ standards. A robust IEQ complaint redressal system may also be required in offices. This study highlights the need to consider female perspectives and thermal expectations in the environmental design of workplaces as well, not merely privacy concerns.