*Article* **Assessment of Indoor Climate for Infants in Nursery School Classrooms in Mild Climatic Areas in Japan**

**Kahori Genjo**

Graduate School of Engineering, Nagasaki University, Nagasaki 852-8521, Japan; genjo@nagasaki-u.ac.jp; Tel.: +81-95-819-2598

**Abstract:** In Japan, the standard of indoor climate in nursery school classrooms has not been established, and the control and maintenance of indoor climate in the classrooms are entrusted to individual childminders. Therefore, indoor climate in nursery school classrooms was measured to prepare fundamental information for proper environmental design and environmental control, considering infants' comfort and health. The climate of 0-year-old and 1-year-old children's rooms in 15 nursery schools located in mild climatic areas in Japan were measured in the summer and winter over four years. Consequently, a lower average temperature was found during winter at lower heights at which infants spend time and indoor air quality was found to be poor in both summer and winter due to a lower ventilation rate in some classrooms with a smaller area per infant compared to the minimum standards for child welfare institutions. One classroom with an average CO2 concentration of over 1500 ppm was found in both summer and winter due to less ventilation. Illumination less than 300 lx in one-third of the studied classrooms and high equivalent noise level in most classrooms were measured. The need for indoor environmental standards was indicated in terms of infants' comfort and health.

**Keywords:** nursery; classrooms; vertical temperature difference; humidity; CO2; air stuffiness index; particle matter; illumination; noise level

#### **1. Introduction**

In Japan, with the advancement of women in society, the number of children who use nursery schools is increasing, and the proportion of young children is increasing [1]. Infants exhibit less thermoregulatory function than adults and are more affected by the surrounding thermal environment. Childcare time increases up to 11 h, and children who go to the nursery spend most time in nursery schools' indoor environments. Therefore, the environmental improvement of the nursery school classrooms is becoming increasingly important in maintaining children's mental and physical health. Guidelines for the indoor environment have been defined by the school environmental health standard for kindergartens, which is under the jurisdiction of the Ministry of Education, Culture, Sports, Science and Technology [2]. However, no specific guidelines have been developed for the classrooms in nursery schools, which fall under the jurisdiction of the Ministry of Health, Labor and Welfare. Consequently, control and maintenance of the indoor environment in nursery schools are entrusted to individual childminders. The indoor environments in nursery schools are controlled based on the sense of comfort for adults, and the comfort and health of infants who spend time at lower heights tend to be overlooked. If an indoor environment standard for the nursery school classrooms is prepared, childminders could adjust indoor environment appropriately to make the indoor climate in the classrooms more conducive to comfort and health. Infants are particularly susceptible to infectious diseases such as influenza; hence, controlling indoor temperature and humidity in nursery classrooms is necessary for infants' wellbeing. Additionally, ventilation is important to prevent the spread of coronavirus disease 2019 (COVID-19)—not only in office and school buildings but also in nursery schools. The infectious disease control

**Citation:** Genjo, K. Assessment of Indoor Climate for Infants in Nursery School Classrooms in Mild Climatic Areas in Japan. *Buildings* **2022**, *12*, 1054. https://doi.org/10.3390/ buildings12071054

Academic Editors: Yue Wu, Zheming Liu and Zhe Kong

Received: 24 June 2022 Accepted: 18 July 2022 Published: 20 July 2022

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**Copyright:** © 2022 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

guidelines for nursery schools were established in 2018, which was before the COVID-19 pandemic; thus, the standards for thermal environment were demonstrated specifically for the first time [3]. According to the guidelines, the temperature should be set at 26–28 ◦C in the summer and at 20–23 ◦C in the winter, and relative humidity should be set to 60%. Although the basics of air infection control clearly include the isolation of the affected person and management of room ventilation, the guideline for indoor air environment is not clearly indicated. The aforementioned school environmental health standard provides the following guidelines: carbon dioxide concentration should be set to less than 1500 ppm as an index of ventilation; temperature should be set to more than 18 ◦C and less than 28 ◦C (the lower limit of the temperature standard was 17 ◦C until the end of March 2022) [2]; relative humidity should be set to more than 30% and less than 80%, illumination should be set to more than 300 lx; noise level should be set to less than 50 dBA when the window is closed and 55 dBA when the window is open. The humidity ratio (HR) is not specified in Japan; the current ASHRAE Standard 55-2017 [4] only specifies the upper limit of HR as 0.012 kg/kg (DA) and does not specify the lower limit. By contrast, recently, noise has been acknowledged as a social problem in nursery schools in Japan. Kawai et al. [5] investigated the conditions of the acoustic environment of six nursery schools of the Kanto area that were opened during 2005–2012 and conducted a review of overseas standards and guidelines. They revealed the problems of acoustic environment specific to nursery schools, such as the possibility of health effects by indoor high sound pressure level, securing quietness during nap time, and the importance of speech intelligibility for children in the developmental stage. On the contrary, in the United Kingdom, Building Bulletin 93 [6], published by the Institute of Acoustics and the Association of Noise Consultants in 2015, provided design criteria for acoustics and lighting design and guidance on fulfilling these criteria. The guidelines on ventilation, thermal comfort, and indoor air quality in schools have been updated in Building Bulletin 101 (BB101) in 2018 [7], wherein thermal comfort criteria are classified into four categories, and a higher level of expectation for thermal comfort may be needed for very young pupils. For example, the normal maintained operative temperature during the heating season is set at 25 ◦C, and the strictest draught criteria to provide thermal comfort are applied to the space utilized by young children less than 5 years of age. The control of the ventilation rate in nursery school classrooms is as important as that of the indoor thermal environment. In the case of natural and hybrid ventilation systems, the control set points on carbon dioxide concentration for the ventilation system in teaching spaces, which include opening windows, should be set to achieve less than 1000 ppm whenever possible; however, although carbon dioxide concentration in school classrooms should be kept below 1500 ppm according to the school environmental hygiene standards in Ministry of Education, Culture, Sports, Science and Technology, Japan (as mentioned earlier), no standards for carbon dioxide concentration have been established in Japanese nursery classrooms. The recommended illumination in nursery schools is 300 lx in BB101 [7], but no standards for illumination have been established in Japanese nursery classrooms.

Thus far, compared to the numerous studies on the indoor environment in school classrooms [8–21], few studies have been conducted on the indoor environment in nursery schools [22–26]. Particularly in Japan, research focusing on the environmental humidity in the winter has been conducted for kindergartens from the perspective of influenza prevention by Aoki et al. [27]; however, recently, Taneichi et al. [28] investigated the indoor environment of nursery schools. To date, however, few survey cases on indoor environment in nursery schools have been conducted. Therefore, for the present study, we have conducted questionnaire and measurement surveys focusing on the indoor environment of nursery schools since before the onset of the COVID-19 pandemic [29,30].

As mentioned earlier, except for the infectious disease control guidelines, there have not been any indoor environmental standards—particularly indoor air environmental standards in nursery schools in Japan, until now [3]. Therefore, indoor climate in nursery school classrooms was measured to prepare fundamental information for proper environmental design and environmental control considering infants' comfort and health. Indoor environments

were measured and questionnaire surveys were administered in 15 different nursery schools in mild climatic areas in Japan during the summer and winter from 2016 to 2019. This paper summarizes the results of the measurements thus far and, further, proposes the indoor environmental standards that should be established for nursery school classrooms.

#### **2. Materials and Methods**

The survey was administered in 15 different nursery schools located in Nagasaki City, which has a population of around 400,000 inhabitants in 406 km2 and is located in western Kyushu Island, with mild climate in Japan (32◦45- N, 129◦53- E). Tables 1 and 2 present the description of the investigated nursery school buildings. The investigated nursery schools included 14 authorized nursery schools—comprising four public schools (Nursery A, B, C, and D), 10 private nursery schools, and one unlicensed in-house nursery school (Nursery O). Thirteen nursery schools, excluding Nursery K and Nursery L, correspond to Certified Childcare Centers, which fall under the jurisdiction of the Cabinet Office and are supervised by the Ministry of Health, Labor and Welfare together with the Ministry of Education, Culture, Sports, Science and Technology. Nurseries K and L fall under the jurisdiction of the Ministry of Health, Labor and Welfare. The newest nursery is Nursery O, which was constructed in 2017, while Nursery A is an extremely old building, with a completion date in 1949. Three public nursery schools, excluding Nursery A, were completed around 1970. The airtightness values of observed buildings were unknown because the measurement of airtightness itself is not obligatory in Japan, although the value influences draught, CO2 concentrations, and noise level. Air conditioners were installed in all the nurseries for space cooling and space heating. Along with air conditioners, floor heating was installed in Nursery I, J, and N. Ventilation systems were installed in 11 nursery schools, excluding three public schools and one private school. Humidifiers were used in 13 nursery schools, excluding Nurseries L and O, and air cleaners were used in 13 nursery schools, excluding Nurseries B and E. In the two nursery schools, Nurseries J and M, the floor area did not meet the standard of 1.65 m2 per child, which was defined by the standards on facilities and operation of child welfare institutions [31], because, due to a shortage of nursery schools in Nagasaki City at the time of this research, it was supposed to accept children up to 120% of its capacity.

Thirteen nursery schools excluding A and F were evaluated in both summer and winter. Nursery A was evaluated during winter and nursery F was evaluated during summer. Each school was studied during one full school week—from Monday to Friday.

Table 3 shows the description of measurement items and measuring equipment used. We administered a survey on indoor thermal environment, indoor air environment, illumination environment, and acoustic environment for 0-year-old and 1-year-old children's rooms used by infants, and the outdoors. The vertical temperature was measured at the following four points: 0.1 m from the floor, which is the height at which infants crawl; 0.3 m from the floor surface, which is the height at which they sit on the floor; 0.6 m, which is the height of their head when they stand; and 1.1 m, which is the height of a head when adults sit in a chair. In Nurseries H and L, no partition exists between the 0-year-old and the 1-year-old children's rooms; hence, measurements were conducted at one point, considering the two spaces as one room. The measurement survey was administered for about two weeks in Nurseries A, B, C, E, F, and J and for about one week in the other nine nursery schools. The sensors continuously collected data while they were installed in the classroom. Additionally, measurements on the acoustic environment were conducted since the winter of 2016. PM2.5 concentration and equivalent noise level were evaluated once by a 10 min measurement per classroom. Outdoor air temperature and relative humidity were obtained from the nearest meteorological station [32]. In addition to the measurement survey, a questionnaire survey on activities in the nursery classroom was also administered for each nursery classroom. In the questionnaire survey, investigated items included the following: the number of infants and nursery teachers in each nursery room, usage of cooling and heating equipment, usage of ventilation equipment, window opening, and the weekday and Saturday timeline.



KH, kerosene fan heater. EC, electric heating carpet. FL, fluorescent light. IL, incandescent

lamp. 8 '-', 'not measured'.


**Table 2.** Description of the investigated nursery schools.

fluorescent light. 9 IL, incandescent

 lamp. \* 0- and 1-year-old room.


**Table 3.** Description of measurement items and measurement equipment

 used.

An index called ICONE [22] was calculated from the measurement results of CO2 concentration and used to evaluate indoor air quality (IAQ). The ICONE is an air stuffiness index used in the air quality evaluation of the classroom environment in France. Occupancy periods of less than 5 h are discarded. CO2 values are classified according to their levels: *n*0—values < 1000 ppm, *n*1—values between 1000 and 1700 ppm, and *n*2—values > 1700 ppm. The ICONE air stuffiness index is then calculated by applying Equation (1), where *f* <sup>1</sup> is the proportion of CO2 values between 1000 and 1700 ppm (*f* <sup>1</sup> = *n*1/(*n*<sup>0</sup> + *n*<sup>1</sup> + *n*2) and *f* <sup>2</sup> is the proportion of CO2 values above 1700 ppm (*f* <sup>2</sup> = *n*2/(*n*<sup>0</sup> + *n*<sup>1</sup> + *n*2)).

$$\text{ICONE} = \left(\frac{2.5}{\log\_{10}(2)}\right) \log\_{10}(1 + f\_1 + 3f\_2),\tag{1}$$

The final results are rounded to the nearest integer. The air stuffiness level of the room is then expressed by a score ranging from 0–5. ICONE scores from 0–5 correspond to an air stuffiness gradient: 0, none; 1, low; 2, average; 3, high; 4, very high; and 5, extreme stuffiness [22].

#### **3. Results and Discussion**

The median outdoor temperatures and relative humidity (RH) during the measuring period for the summer and winter were 27.8 ◦C and 80%, and 8.5 ◦C and 69%, respectively. The results are evaluated with reference to the infectious disease control guidelines for nursery schools established in 2018 [3]. Further, the school environmental health standard [2] and ASHRAE Standard 55-2017 [4] are referenced as needed.

#### *3.1. Temperature and Humidity*

Results of temperature at 1.1 m above the floor during opening hours in the summer and winter are presented in Figure 1. Figures 2 and 3 present a part of the vertical temperature distributions during the summer and winter opening hours. The temperature difference between 1.1 m above the floor and 0.1 m above the floor is termed the vertical temperature difference, and whether the temperature difference is above or below the comfortable range of 3 ◦C is evaluated [4]. Results of RH, HR, and globe temperature during opening hours in the summer and winter are presented in Figures 4–6, respectively. The mean values of temperature, globe temperature, RH, and HR during the measuring period were 27.4 ◦C, 26.5 ◦C, 62%, and 0.014 kg/kg (DA) in the summer; and 19.2 ◦C, 18.6 ◦C, 46%, and 0.006 kg/kg (DA) in the winter, respectively. Compared to the infectious disease control guideline mentioned above [3], the summer mean temperature was between 26 and 28 ◦C, but the winter mean temperature was lower than the lower limit of 20–23 ◦C. Mean RH was close to 60% of the standard in the summer, but lower than the standard in the winter.

**Figure 1.** *Cont*.

**Figure 1.** Temperature at 1.1 m from floor surface during opening hours in (**a**) summer and (**b**) winter.

**Figure 2.** *Cont*.

**Figure 2.** Vertical temperature distributions during opening hours in summer: (**a**) 0-year-old room in Nursery B; (**b**) 1-year-old room in Nursery B; (**c**) 0-year-old room in Nursery C; (**d**) 1-year-old room in Nursery C; (**e**) 0-year-old room in Nursery F; (**f**) 1-year-old room in Nursery F; (**g**) 0-year-old room in Nursery N; (**h**) 1-year-old room in Nursery N.

**Figure 3.** *Cont*.

**Figure 3.** Vertical temperature distributions during opening hours in winter: (**a**) 0-year-old room in Nursery A; (**b**) 1-year-old room in Nursery A; (**c**) 0-year-old room in Nursery B; (**d**) 1-year-old room in Nursery B; (**e**) 0-year-old room in Nursery C; (**f**) 1-year-old room in Nursery C; (**g**) 0-year-old room in Nursery N; (**h**) 1-year-old room in Nursery N.

**Figure 4.** Relative humidity at 1.1 m from floor surface during opening hours in (**a**) summer and (**b**) winter.

**Figure 5.** Humidity ratio at 1.1 m from floor surface during opening hours in (**a**) summer and (**b**) winter.

**Figure 6.** Globe temperature at 1.1 m from floor surface during opening hours in (**a**) summer and (**b**) winter.

In the summer, the temperatures of the following nursery classrooms nearly satisfied the above guideline [3]: both classrooms in nursery B, 0-year-old room in nursery E, both rooms in nursery G, 0-year-old room in nursery K, 1-year-old room in nursery M, and 0-year-old room in nursery O. In most other nursery rooms, the temperature was below the lower limit of the guideline and met the requirement except in Nursery F, where the temperature was too high and failed to fulfill the guidelines. Nursery F refrained from using an air conditioner in accordance with the policy of childcare regarding sweating, and thus, the temperature in the 1-year-old room at any height except at 12:00 was higher than 30 ◦C, as illustrated in Figure 2f [30]. From the perspective of preventing heat stroke, using air conditioning is necessary in this nursery school. Overall, the temperature was lower at a height of 0.1 m above the floor than that at 1.1 m above the floor in most nursery rooms, for example, in the 0- and 1-year-old room in nursery H, where cold air was circulated by a ceiling fan.

As shown in Table A2, in the winter, the temperature at 1.1 m above the floor generally meets the aforementioned standard [3] of 20–23 ◦C, except for some nursery schools, such as those that are older; however, the lower the height above the floor, the lower the temperature tended to be (Figure 3b–d) [29,30]. Therefore, the temperature at 0.1 m above the floor did not meet the standards in any nursery room. This may be due to poor insulation performance or poor air circulation, even in recently constructed nursery schools. In nursery schools I, J, and N, where floor heating was installed, the temperature at 0.1 m above the floor was kept relatively high; hence, the vertical temperature difference was within 3 ◦C, as is shown in Figure 3g,h. Since infants spend their time at a lower height than adults, raising the temperature at 0.1, 0.3, and 0.6 m above the floor in the winter is necessary to ensure infants' comfort and health.

Figures 2 and 3 show that the vertical temperature difference was over 3 ◦C in two (8% of the total) out of 26 rooms in the summer and 11 (42% of the total) out of 26 rooms in the winter. Reportedly, the vertical temperature difference was larger in the winter than in the summer. Except for the 1-year-old room in nursery E and 0-year-old room in nursery F in the summer, temperature was evaluated to be comfortable in terms of the vertical temperature difference because it was less than 1.0 ◦C. On the contrary, most nursery rooms studied in the winter were evaluated to be less comfortable. Figure 3b,c show that the largest and second largest vertical temperature differences were found to be 6.8 ◦C in the 0 year-old room in nursery B and 5.9 ◦C in the 1-year-old room in nursery A, respectively. As illustrated in Figure 3, compared to the vertical temperature distribution at 9:00, 12:00, 15:00, and 18:00 in each studied room, the largest vertical temperature difference was found at 9:00 in the morning in most nursery rooms. In the winter, the room temperature was under 17 ◦C in addition to the large vertical temperature difference; hence, numerous nursery rooms were evaluated to be less comfortable for both infants and childminders. The reason for this is the low insulation performance of the older buildings; thus, the temperature at 0.1 m above the floor did not rise easily even if the temperature at 1.1 m above the floor rose when heated. Most nursery schools heat the rooms only with air conditioners, but when nursery rooms are heated only with air conditioners, especially in old buildings, the temperature near the floor does not increase enough; hence, devising ways to ensure comfort is necessary, for example, through the use of auxiliary heating. Additionally, since the insulation performance in mild climatic areas in Japan is lower than that of Europe or the United States, efforts such as raising the insulation performance of buildings and repairing the insulation of existing buildings can also be considered necessary.

Figure 4 demonstrates that according to the infectious disease control guideline [3], mean RH did not satisfy the value of 60% in any nursery classrooms through the summer and winter measurements. However, according to the school environmental health standard [2], mean RH satisfied the value of 30–80% in all studied nursery classrooms. The mean RH ranged 49–72% in the summer and 36–62% in the winter, respectively. According to Tables A3 and A4, the 95th percentile RH exceeded the upper limit of 80% in three classrooms in the summer, and the 5th percentile RH was below the lower limit of 30% in six

rooms in the winter. Figure 5 shows that the mean HR in most studied nursery classrooms except one classroom (1-year-old room in nursery K) ranged from 0.012 to 0.017 kg/kg (DA) and did not satisfy the upper limit of 0.012 kg/kg (DA) specified by ASHRAE Standard 55-2017 [4] in the summer, though the mean HR in all studied nursery classrooms, which ranged from 0.005 to 0.009 kg/kg (DA), satisfied the standard value in the winter. Since it is hot and humid during the summer in Japan, humidity control from the viewpoint of microbial contamination is vital. On the contrary, the mean HR across eight classrooms (31% of the total) of 26 nursery classrooms in the winter was less than 0.006 kg/kg (DA), which was proposed by Shoji [33] as the index of influenza epidemic warning level despite using humidifiers. HR measured in the winter in this study was higher than that measured in the winter in Aoki et al.'s survey [27] for kindergartens in Gifu prefecture in the Tokai area, which is located in central Japan, with the range 0.004–0.005 kg/kg (DA). Indoor HR values studied in this survey in the winter were similar to the abovementioned survey [27].

From Figures 1 and 6, globe temperature difference obtained by subtracting the temperature at 1.1 m above the floor from the globe temperature of the same height in each nursery room ranged from −2.6 to 0.0 ◦C in the summer and −5.1 to 0.4 ◦C in the winter. Although the globe temperature differences were negative in all nursery classrooms except one classroom (0-year-old room in nursery B) in the summer, it was negative in the studied nursery classrooms in the winter except for some nursery classrooms (0-year-old room in nursery A, 1-year-old room in nursery D, 0-year-old-room in nursery K, and 0-year-old room in nursery M). The globe temperature differences were negative in most classrooms both in the summer and winter, and nursery classrooms were affected by cold radiation.
