Scientific literature and documents pertaining to the effects of inhalation exposure to carbon dioxide (CO2) on human health and psychomotor performance were reviewed. Linear physiological changes in circulatory, cardiovascular, and autonomic systems on exposure to CO2 at concentrations ranging from 500 to 5000 ppm were evident. Human experimental studies have suggested that short-term CO2 exposure beginning at 1000 ppm affects cognitive performances including decision making and problem resolution. Changes in autonomic systems due to low-level exposure to CO2 may involve these effects. Further research on the long-term effects of low-level CO2 exposure on the autonomic system is required. Numerous epidemiological studies indicate an association between low-level exposure to CO2 beginning at 700 ppm and building-related symptoms. Respiratory symptoms have been indicated in children exposed to indoor CO2 concentrations higher than 1000 ppm. However, other indoor comorbid pollutants are possibly involved in such effects. In the context of significant linear increase of globally ambient CO2 concentration caused by anthropogenic activities and sources, reducing indoor CO2 levels by ventilation with ambient air represents an increase in energy consumption in an air-conditioned building. For the efficient energy control of CO2 intruding a building from ambient air, the rise of atmospheric CO2 concentration needs to be urgently suppressed.

Psychosocial and environmental factors at the workplace play a significant role in building-related symptoms (BRSs). Environmental factors change during summer cooling and winter heating using air-conditioning systems. Thus, significant risk factors in each season need to be clarified. A nationwide cross-sectional study was conducted during summer in Japan and seasonal differences between summer and winter were evaluated. Self-administered questionnaires were distributed to 489 offices. Possible risk factors for BRSs associated with the work environment, indoor air quality, and job stressors were examined by multiple regression analyses. Among people having at least one BRS, the prevalence of BRSs in summer (27.8%) was slightly higher than that in winter (24.9%). High prevalence was observed for eye and nasal symptoms related to dryness and general symptoms related to psychological distress in both seasons. Analyses revealed that dryness of air was an important and significant risk factor associated with BRSs, and job stressors were significantly associated with general symptoms in both seasons. Conversely, humidity was a significant risk factor of general symptoms in summer (odds ratio, 1.20; 95% confidence interval, 1.02–1.43). Carpeting, recently painted walls, and unpleasant chemical odors in summer and noise, dust and dirt, and unpleasant odors such as body or food odors in both seasons were significant risk factors for BRSs. Improvements in the physical environmental qualities in an office throughout the year are important along with the reduction in psychological distress related to work.

In this paper, to better understand indoor humidity in cold regions where it is more difficult to maintain indoor humidity in winter and to obtain basic information for improving indoor humidity, we evaluated thermal environments from measurement data in special nursing homes for the elderly of Miyagi and Hokkaido, and estimated the lack of humidification from an analysis of ventilation amount in these cold regions. Measured of indoor temperature, humidity and CO₂ concentration showed the following. 1) Although there were differences in the number of years of construction and the type of facility, it was shown that the indoor temperature was almost the same, the relative humidity was about 20 to 30%, which was a low humidity environment, and the CO₂ concentration was less than 1,000 ppm in the facilities investigated. In addition, it was shown that the average value of the indoor temperature, humidity and CO₂ concentration of the common space and the rooms were the same for the same building and the same floor. 2) The indoor temperature of the common space and rooms in the facilities were controlled relatively stably, and the indoor temperature fluctuation during the three months in winter tends to be smaller in facilities in Hokkaido Prefecture than in facilities in Miyagi Prefecture. 3) The indoor humidity ratio in the common space and rooms in the facilities was low and the indoor humidity ratio also fluctuated up and down following the change in humidity ratio of the outside air, showing that the indoor humidity ratio is strongly affected by outside air. 4) Indoor temperature and humidity (temperature, relative humidity and humidity ratio) and CO₂ concentration showed a tendency to fluctuate with the user's daily rhythm spent in the common space during the day and in the rooms at night. An analysis of the ventilation amount and required humidification amount showed the following. 1) It was shown that there was diversity in ventilation patterns, and ventilation modes in each facility, such as by opening windows, or opening and shutting the living room door, were closely related to building performance. Also, it was shown that the colder the region, the more the ventilation amount tended to increase. 2) It was shown that there was a need to introduce an industrial humidifier at an early stage in examination facility construction specifications so that indoor relative humidity could be more than 40%, because the humidification produced by portable humidifiers was insufficient. 3) It was shown that if CO₂ concentration were controlled to 1,000ppm, the lack of humidification could be reduced by more than 50%.