Published papers

The study analyzes the thermal environment and energy-saving performance of nearly net-zero energy apartments in Japan during winter by measurement and questionnaire. Results show the average indoor temperatures exceeded 18°C even without air conditioning, due to superior insulation performance. Energy consumption for heating was 58.9% to 62.9% of the national average, and residents perceived their homes as warmer, leading to lower temperature settings of air-conditioner. However, there were several challenges, such as the low ratings by residents of non-heated rooms during winter.

Worker performance is affected by environmental stimuli in the office. Therefore, it is important to analyze the relationship between workers and multiple environment elements simultaneously in order to understand the relationship between the office environment and worker performance. In addition, surveying a large sample of offices simultaneously is desirable to obtain more practical insights. Therefore, this study surveyed multiple elements of the physical office environment related to worker performance in a large sample of offices. The elements of the physical office environment surveyed were air temperature, relative humidity, CO2 concentration, and sound pressure level during the summer. Along with measurements from 58 offices across 29 buildings in Tokyo, Japan, 947 responses to a questionnaire survey of workers conducted to evaluate work performance were analyzed to elucidate the relationship between these elements of the physical office environment and perceived work efficiency. The analysis showed that air temperature was more related to worker performance than to the other elements. In addition, 25 °C air temperature group was observed to be associated with high worker performance, with worker performance being lowest in the 27 °C group. This finding is expected to provide insight into indoor environments that can effectively enhance office worker performance.

Well-being is a positive mental state that includes evaluations and affective reactions individuals make about their experiences, including life evaluation, affect, and eudaimonia. The importance of well-being is underscored by its association with productivity, health, and longevity. Despite extensive research on well-being related to demographics, personality traits, and satisfaction in various life domains, it remains unclear how and to what extent the office environment impacts workers' well-being. Therefore, this study explores the impact of the office environment on workers' subjective well-being, using structural equation modeling. Conducted with 1438 white-collar workers working in 61 offices in Tokyo, Japan, the survey assessed perceived office environment and measured subjective well-being based on guidelines from the OECD. The key findings indicate a significant association of the office environment with life domain factors such as satisfaction with one's job, work–life balance, private life, and subjective health, which are positively correlated with overall subjective well-being. In particular, common-area environments within the office such as spaces that promote refreshment and conversation have the most significant impact on well-being. The analysis model also revealed that the perceived quality of the office environment had a positive correlation with subjective well-being even after adjusting for demographic information such as age, gender, and personality traits. This research provides valuable insights for improving the design of office environments to foster workers' well-being.

The residential environment impacts the health and economic status of residents, for example, via medical costs and income loss from absenteeism. However, previous studies often do not consider assessments of the thermal, acoustic, light, hygiene, safety, and security environments in the residence simultaneously, and the age and sex of the residents. Therefore, this study proposed improvements to a previous method and validated the improved method for estimating health economic impact that considers the residential environment conditions and residents comprehensively. The individual scale validation demonstrated that the relationship between the comprehensive assessment of the residential environment and the risk of 10 types of diseases (diabetes mellitus, cerebrovascular diseases, disorders of conjunctiva, hypertensive diseases, heart diseases, upper respiratory tract disorders, chronic obstructive pulmonary disease, asthma, dermatitis and eczema, and inflammatory arthropathies) differs by age and sex. When these disease-related economic losses were aggregated, older males were estimated to suffer the greatest losses from their residential environment in Japan. The economic impact of residential environment by resident attributes was aggregated according to the population distribution as an advanced application of the estimation model. The total economic loss from substandard residential environments across Japan was estimated to be about JPY 725 billion per year. These results should incentivize residents and policymakers to improve the residential environment. The estimation-model development process is universally applicable and may lead to the creation of optimized benchmarks in every region of the world, thereby contributing to improvements in the residential environment aimed at reducing health risks and economic losses.

Based on numerous cross-sectional analyses, the residential environment has been identified to have an impact on residents’ health status. However, there has been little study of whether these impacts persist in the long term or diminish over time. Accordingly, the present study used data tracking of more than 15,000 residents for nearly 10 years to examine the long-term relationships between the residential environment and residents’ health status using the Kaplan–Meier method and discrete time logit models. The results revealed that higher comprehensive assessment of the thermal, acoustic, light, hygiene, safety, and security environment in the residence is likely to extend the period until health deteriorates. Specifically, the period until low subjective health perception was about 2 years longer for residents in the top 16% of assessments of the residential environment compared with the national average assessment. This trend was also supported by supplementary analyses using the incidence of 10 types of non-communicable diseases: diabetes mellitus, cerebrovascular diseases, disorders of conjunctiva, hypertensive diseases, heart diseases, upper respiratory tract disorders, chronic obstructive pulmonary disease, asthma, dermatitis and eczema, and inflammatory arthropathies. These findings are relevant for a wide range of stakeholders, from individual residents to policymakers, and highlight that a good residential environment effectively promotes healthy longevity. This study will serve as a starting point for further long-term studies.

An Indoor measurement survey was conducted to investigate the effects of whole-house air conditioning using floor chamber systems in a highly insulated apartment building on the indoor thermal environment, sleep quality in summer, and blood pressure in winter. The survey was conducted in the summers and winters of 2022 and 2023, both before and after moving into an apartment building equipped with high insulation and whole house air conditioning using floor chamber systems. The room temperatures in each room improved and stabilized in both summer and winter after moving in, due to the insulation performance and the whole-house air conditioning using floor chamber systems. The temperature difference between 1 meter above the floor and near the floor in the living room decreased in winter but increased in summer. Furthermore, the relative humidity in the living room and bedroom decreased in both summer and winter, and the CO2 concentration in the bedroom improved. The results suggested a potential for improvement and stabilization of summer sleep efficiency and winter blood pressure.

Despite the recognition of housing as a determinant of health, most prior studies relied on cross-sectional data, limiting their ability to infer causal effects of residential environments on residents’ health. This study addresses these gaps by conducting a two-wave, 7-year prospective cohort survey, utilizing a cross-lagged panel model, a method also used in public health research, to rigorously analyse causal paths from residential environment quality to health status. Data were collected from 2153 residents on personal attributes, residential environments, and the presence of physician-diagnosed disease among 10 major non-communicable diseases. The analysis identified significant causal effects of residential environment quality on the onset of hypertension, heart disease, and asthma. Odds ratios indicated that better residential environments significantly reduced the likelihood of developing these conditions, particularly hypertension (0.791), heart disease (0.554), and asthma (0.593). Given the high proportion of time people spend indoors, these results underscore the importance of residential design. However, for other diseases where significant causality could not be confirmed in this study, the prevalence samples or the survey intervals may have influenced the results. Addressing these challenges could potentially expand insights, and it is premature to conclude that there is no causal relationship for the remaining diseases. In conclusion, this study expands knowledge in the field of housing and health and highlights the importance of the residential environment in influencing individual health status.

The quality of the office environment has a substantial impact on workers’ comfort, health, and productivity. Assessing these environments and identifying key elements that influence occupant satisfaction is the starting point for designing better offices. This study uses item response theory (IRT) to analyze post-occupancy evaluation (POE) data and identify key elements of the office environment. The use of POE to analyze the built environment has been limited, making this study an innovative approach. A survey of 3552 workers was conducted to subjectively evaluate various office elements in addition to personal attributes, and data-driven methods were used to identify key office environment items. The results show that the factors with the greatest effect on the occupants’ assessment of the overall office environment include comfortable interiors and furnishings in individual workspaces. Spaces that encourage conversation were the next most important, with many of the most important items related to the common-area environment in the building. The analysis also reveals differences based on gender and occupation, with women valuing aspects of the building operation and maintenance environment more than men do, and clerical workers valuing the common-area environment more than technical workers do. The study underscores the need for an office space design that considers the varying needs of the personal attributes of different workers.

This study applies image sensors and machine learning for the development and validation of an automatic optimal control technology to enhance energy efficiency in air conditioning systems within manufacturing factories. Through the implementation of variable air volume (VAV) control based on occupant detection via image sensors, the power consumption of industrial air handling unit fans is reduced by up to 41%. Additionally, optimization of the temperature of chilled water supply to modular chillers via machine learning resulted in an improvement in the coefficient of performance from 0.51 to 0.67. Such energy-saving measures were achieved while simultaneously minimizing the impact on temperature and humidity in production areas. This research highlights the effectiveness of automated optimal control via the application of image sensors and machine learning to improve energy efficiency across entire manufacturing factories.

This study developed and validated ZEF (net Zero Energy Factory) as a new energy performance evaluation framework for manufacturing facilities. ZEF overcomes the limitations of conventional ZEB (net Zero Energy Building) by enabling comprehensive evaluations that include air conditioning, ventilation, and lighting in production areas. In a manufacturing facility designed based on this concept, the ZEF baseline value was set at 1,389 MJ/m², approximately 4.4 times higher than the ZEB baseline value of 313 MJ/m². Operational performance data confirmed that the facility achieved Nearly ZEF (BEI=0.06). This study demonstrates the validity of using ZEF as a universal evaluation framework for visualizing total energy consumption and enabling comparisons across manufacturing facilities.

The rapid adoption of remote working has increased the importance of indoor environmental quality (IEQ) in residential environments. However, the relationship between residential environments and remote working productivity remains under discussion. Exposure to cold indoor environments during winter may contribute to decreased productivity because discomfort and thermal stress can impair cognitive performance. Many previous studies have examined the direct relationship between IEQ and productivity in thermal comfort research, overlooking the stepwise influence of physiological and psychological responses. However, IEQ probably affects productivity through the physiological and psychological responses of workers. Therefore, this study examines the effects of residential floor-level thermal environment on task performance through psychophysiological responses using multilevel SEM. A controlled experiment was conducted with participants performing work tasks in either a convective air-conditioned room or a radiant floor-heated room. Physiological (foot skin temperature), psychological (thermal comfort and concentration), and task performance measures were collected and analyzed. Multilevel SEM revealed that radiant floor heating significantly increases foot skin temperature, which improves thermal comfort and perceived concentration. In addition, no differences were observed among conditions for simple tasks, such as typing, whereas improved physiological and psychological states positively affected performance on cognitively demanding creative tasks. The results underscore the critical role of floor-level thermal environments in supporting work-from-home productivity. By integrating multilevel SEM, this study advances the understanding of hierarchical human–environment interactions. The results suggest that incorporating radiant floor heating into residential design can improve both comfort and cognitive performance, contributing to home workspaces that are more comfortable and productive.

High sleep quality is essential for people’s health. Numerous studies have investigated the relationship between indoor environmental quality and sleep quality, and the thermal environment, in particular, has been shown to have a significant effect on sleep quality. However, most of these studies measured the thermal environment of the bedroom for only short periods of time. Although seasonal variations and individual differences in sleep quality have been reported, most studies on the thermal environment and sleep quality have not adequately taken these factors into account. Therefore, the present study measured bedroom temperature and sleep quality objectively without intervention for 1 year and mathematically modeled the annual variation in bedroom temperature and sleep efficiency using a simplified sine function. This mathematical model was able to quantitatively characterize individual differences in the annual variation of bedroom temperature and sleep efficiency. The amplitude and phase of the sine function indicate the annual variation range of sleep efficiency and the degree to which sleep efficiency decreases in summer or winter. The mathematical model was also able to identify bedroom temperatures that optimize sleep efficiency. Analysis of each participant’s annual bedroom temperature and sleep efficiency revealed that sleep efficiency was high in the spring and fall when temperatures were moderate for all participants, while sleep efficiency decreased during the summer and winter and that there were individual differences in terms of whether sleep efficiency decreased more during the summer or winter. Furthermore, there were differences in the bedroom temperature that optimized sleep efficiency for each individual, and the vulnerability of sleep efficiency to fluctuations in bedroom temperature also differed for each individual. By utilizing the developed mathematical model, the bedroom temperature could be individually controlled to enhance sleep efficiency, thereby impacting health and performance.

Indoor environments play an important role in children’s health and behavior, yet the impact of thermal environments on physical activity remains insufficiently understood. This study investigated the association between indoor thermal environments and children’s physical activity in summer and winter in Japan. Detailed indoor thermal measurements and objective accelerometer data were collected from 26 children aged 4–12 years, each measured in both seasons under parental supervision to ensure data quality. Significant associations were found between temperatures in living areas and physical activity intensity. Warmer indoor environments in winter were associated with higher activity intensity, whereas cooler indoor environments in summer were associated with lower activity intensity. A new indicator, the seasonal activity ratio (SAR), defined as the ratio of winter to summer activity intensity, was developed to assess the degree of seasonal variation. The SAR showed an overall seasonal decline (mean SAR: 0.96 ± 0.06). Children living in homes where non-living areas maintained cooler environments in summer and warmer environments in winter exhibited significantly smaller seasonal declines in activity compared with those in other environments. These findings demonstrate that even in modern, high-performance homes, a thermal design strategy is required that addresses both living and non-living areas in order to promote children’s physical activity year-round and to mitigate typical winter declines. The results of this study provide objective evidence to inform residential design and policies aimed at fostering healthier indoor environmental quality for children.

This study developed a model for estimating energy consumption and CO2 emissions up to 2050 in the household sector in Japan. The total national energy consumption of the BAU case would be 1,136 PJ, a 53.4 % reduction compared to 2013. The total national CO2 emissions would be 10.18 Mt-CO2, a 94.1 % reduction compared to 2013. In addition, energy consumption and CO2 emissions will not reach zero even if Japan achieves current policy targets, suggesting that further efforts will be needed to reduce CO2 emissions to zero.

The purpose of this study was to estimate healthy life expectancy at the small-area level and to examine the association between neighborhood environments and healthy life expectancy, both directly and indirectly through social capital (SC), using community facility indicators as proxy measures of SC. Multiple regression and path analyses were conducted to explore the relationships among neighborhood environment, proxy SC indicators, and healthy life expectancy. The results suggested that neighborhood environment was indirectly associated with healthy life expectancy through SC, with differences observed by age group and gender.

Hybrid work has been widely adopted, but thermal comfort in home workspaces has received less attention than that in laboratories and offices. The adaptability of home workspaces may be associated with individual differences, including those related to personality traits. Thus, the analysis focused on two issues: (i) the relationships among temperature, humidity, and thermal sensation at home, and what neutral temperatures arise in summer and winter; and (ii) how these relationships vary with personality traits. A field survey was conducted in the Tokyo metropolitan area. In situ physical measurements of indoor air temperature and relative humidity were obtained simultaneously in 60 homes in summer and 190 in winter, and these measurements were paired with concurrent occupant evaluations while working from home. Ordinal logistic regression estimated neutral temperatures of 28.1 °C in summer and 21.0 °C in winter, which is a wider seasonal gap than is commonly reported for offices. The associations between personality traits and neutral temperature differed by season. In summer, higher levels of extraversion and neuroticism were associated with a higher neutral temperature. For neuroticism, shifting from −1 to +1 standard deviation moved the neutral temperature from 27.4 to 28.8 °C (Δ 1.4 °C). In winter, the neutral temperature increased with extraversion and decreased with openness. These results highlight season- and personality-related variation in estimated neutral temperatures and provide empirical benchmarks for thermal comfort in home workspaces.