Thermal Comfort In Classrooms Research Articles

Comparative Analysis of Indoor Air Quality and Thermal Comfort Standards in School Buildings across New Zealand with Other OECD Countries

COVID-19 has improved awareness of the importance of appropriate indoor air quality (IAQ) in indoor spaces, particularly in classrooms where children are expected to learn. Research has shown that poor IAQ and temperature levels affect the cognitive performance of children. In this paper, we critically compare IAQ standards for New Zealand’s Designing Quality Learning Spaces (DQLS Document) against international benchmarks from the Organization for Economic Co-operation and Development (OECD) countries, including ASHRAE 62.1, CIBSE TM57, EN-15251, WHO AQGs, and Building Bulletins 99 and 101. The aim was to ascertain the robustness of New Zealand’s DQLS document, identify areas of superiority, and recommend the required improvement for appropriate IAQ and thermal comfort in classrooms. This comparison review focuses on IAQ parameters: CO2 levels, temperature, ventilation rates, room size, occupant density, and occupancy rates. The findings illuminate a slight lag in New Zealand’s DQLS standards compared to her international counterparts. For instance, while New Zealand’s standards align closely with WHO standards for IAQ concerning temperature and ventilation rates, the recommended CO2 range appears slightly inadequate (800 to 2000 ppm) along with occupancy and classroom size for effectively controlling classroom pollutant growth. This paper emphasises the need to align New Zealand’s IAQ and thermal comfort standards with optimal OECD benchmarks. The identified disparities present opportunities for improving learning spaces in terms of CO2 concentration, size of classroom, and occupant density in schools in New Zealand to meet globally recognised standards, ultimately creating a healthier and more conducive learning environment.

From perception to prediction: A comparative study of thermal comfort assessment techniques in school facilities

Indoor environmental quality (IEQ) significantly affects learning, health, and productivity in educational buildings, particularly classrooms. Thermal comfort is crucial to IEQ in classrooms, and various approaches have been developed to assess it. This study compares subjective evaluation, fieldwork measurement, and simulation methods in naturally ventilated secondary school classroom environments in Abuja, Nigeria. It evaluates their reliability, validity, advantages, and limitations. In achieving this objective, fieldwork measurements, questionnaire surveys, and building simulations were conducted in 83 classrooms with 2758 respondents. The data were subjected to descriptive and inferential statistical analysis using the analytical software programs SPSS version 23 and Microsoft Excel. The study found that the Actual Mean Vote (AMV) comfort operative temperature for classrooms was 28.7 °C. Findings from the comparative analysis of the methods indicate that the PMV generally overestimates students’ thermal sensation and that the fieldwork measurement Predicted Mean Votes (PMVf) undervalues the neutral temperature by 4.2 °C. In contrast, the computer-simulated Predicted Mean Votes (PMVs) undervalues it by 3.9 °C. The study found that all three methods are valid and reliable, with some advantages and limitations, depending on the assessment’s specific context and goals. The findings provide valuable insights into improving indoor environmental quality and occupant satisfaction in educational buildings, contributing to the discourse on assessing thermal comfort in classrooms and informing the development of more effective assessment methods. The systematic comparison of these methods addresses a notable gap in the literature, providing practical insights to optimize thermal conditions in learning environments.

Comparative Analysis of Productivity Methods to Evaluate Thermal Comfort in Classrooms through Hierarchical Clustering

This research examined the modeling of productivity with thermal comfort using various models in a case study conducted in classrooms at a university in Southern Brazil. A total of thirteen models were selected after performing a literature review to identify the main models. Through the application of hierarchical clustering to separate the models into groups with similarities, the results identified four groupings: the first focused on temperature, the second associated age groups with Thermal Sensation Vote (TSV), the third compared different age groups, and the fourth highlighted “Model 11”, derived from structural equations in air-conditioned classrooms in China, revealing poor performance due to its incompatibility with temperature variations in productivity. Meanwhile, “Model 5”, developed using ordinary regression in air-conditioned offices in Japan, showed the lowest Root Mean Square Error (RMSE), emerging as the most accurate in predicting productivity associated with thermal comfort. The use of objective methods to assess productivity and the application of regression analysis in modeling, as identified in the literature review, is noteworthy. The evaluation of the models’ performance also explored the impact of the independent variables on their scope. Through cluster analysis, reasons behind discrepancies in model performance were identified, providing insights into best practices for representing the relationship between thermal comfort and productivity. These results offer valuable perspectives for developing more effective models in this field and reveal a wide methodological diversity in the approach to the subject.

Analysis of determining factors in the thermal comfort of university students. A comparative study between Spain and Portugal

The quality of the indoor thermal environment is essential because of its impact on the energy efficiency of buildings and on the health and well-being of those who occupy them. This is particularly important in educational buildings because of the direct impact on student performance. Various factors, such as natural ventilation, have become particularly relevant since COVID-19. Although this measure is no longer mandatory, its usefulness has been proven, and it is therefore interesting to evaluate it to understand its impact on thermal comfort in classrooms. In addition to ventilation, other aspects such as clothing, gender and habits can also influence the thermal perception of the occupants. Therefore, this study investigates the impact of these factors on thermal comfort in university buildings in Spain and Portugal through a campaign of measurements and questionnaires. The results showed that, according to CO2 concentrations, natural ventilation strategies have been maintained more in Spain than in Portugal. Also, these protocols did not have a negative effect on the thermal comfort of the occupants. On the other hand, there were significant differences between the student's responses in the two countries. In fact, Portuguese students showed warmer preferences (Tn = 26.40 °C) than Spanish students (Tn = 24.70 °C). Finally, clothing habits were a crucial factor in the perception of thermal comfort, with differences by country and by gender.

Optimising Mechanical Ventilation for Indoor Air Quality and Thermal Comfort in a Mediterranean School Building

The growing concern over indoor air quality (IAQ) and thermal comfort in classrooms, especially post-COVID-19, underscores the critical need for optimal ventilation systems to bolster students’ health and academic performance. This study explores the potential for improving indoor air quality and thermal comfort in the most energy- and cost-optimal manner using a demand-controlled ventilation (DCV) system coupled with a carbon dioxide control sensor. This is achieved through precooling via night purging in summer and by introducing warmer corridor air into the classroom in winter. The methodology employs both computer simulation and a real-world case study. The findings reveal that while natural ventilation in winter can achieve IAQ standard (EN 16798-1) thresholds for classrooms under favourable outdoor conditions, it results in uncontrolled and excessive energy loss. The retrofitted DCV system, however, maintained CO2 levels below the recommended thresholds for at least 76% of the year depending on classroom orientation and only exceeded 1000 ppm for a maximum of 6% of the year. This study also indicates that utilising the external corridor as a sunspace can further enhance the system’s efficiency by preheating incoming air. This comprehensive study highlights the significant potential for integrating mechanical and passive solutions in school ventilation systems. This contributes to the attainment of the United Nations Sustainable Development Goal 11 and ensures healthier and more energy-efficient learning environments that benefit both students and the environment.

Design and Development of IoT-based Temperature and Humidity Monitoring System for Thermal Comfort Evaluation in Classrooms

In the learning process in the classroom thermal comfort greatly affects the attitude and performance of students who are doing learning. However, in fact, when students are carrying out the learning process experience some obstacles that make them not feel comfortable in the classroom such as feeling the room temperature is too hot or the room temperature is too cold. Indonesian National Standard sets the air temperature for thermal comfort of the tropics which can be divided into (1) Cool comfort, between the effective temperature of 20.5 ° C - 22.8 ° C, (2) Optimal comfort, between the effective temperature of 22.8° C - 25.8 ° C, (3). Comfortably warm, between an effective temperature of 25.8°C - 27.1°C. While the relative air humidity that is comfortable for humans ranges from 30%60%. The purpose of the temperature and humidity monitoring system is to monitor temperature and humidity conditions that can be used to determine whether the room is in a comfortable condition or not. In this study, the reference used is the 2001 Indonesian National Standard on Procedures for Designing Ventilation and Air Conditioning Systems in Buildings.

Critical Review of the Literature on Thermal Comfort in Educational Buildings: Study of the Influence of the COVID-19 Pandemic

Thermal comfort in educational buildings affects not only the well-being of students but also their academic performance. Over time, various methods have been developed to assess it. However, none of them takes into account the adaptation of students of different ages, which is an important issue. In recent years, the study of thermal comfort has become very important due to energy-saving measures and ventilation protocols to combat the spread of the SARS-CoV-2 coronavirus. Therefore, it is necessary to gather all the information to guide future research. Thus, this paper presents a comprehensive review of field studies on thermal comfort in classrooms at different educational levels. The focus is on those conducted during the global pandemic of COVID-19. It has been observed that students from climates with a higher degree of variation have shown a better adaptation. Children also tended to feel less affected by changing temperatures. High school and university students showed a greater range of dissatisfaction with heat than with cold. The adaptive approach is more suitable for recognising the comfort needs of all age groups. However, by using this approach together with the Fanger method, more reliable results have been reported. In most of the studies, comfort levels were found to be lower than those indicated by the standards, highlighting the need for guidelines adapted to the thermal comfort conditions of all students. Finally, the various natural ventilation measures to avoid COVID-19 infection have led to a decrease in comfort levels, especially in winter.

Thermal Comfort Assessment in University Classrooms: A Discriminant Analysis for Categorizing Individuals According to Gender and Thermal Preferences

The concern with the well-being of users in buildings has become increasingly essential, covering aspects related to health, energy efficiency, and productivity. The thermal environment evaluation in buildings has become more frequent due to the time people spend inside them. In this context, this study aimed to analyze thermal comfort in classrooms at a Brazilian University. During the autumn, 50 measurements were performed, resulting in 519 valid responses. The results of the linear regression analysis revealed that the thermal comfort range for females was 20.39–22.19 °C, while for males it was 19.47–22.56 °C. Through discriminant analysis, participants were classified based on their thermal sensation vote (TSV), predicted mean vote (PMV), and thermal preference votes (PREF), achieving a success rate of 76.1% for females and 81.6% for males in forming the groups, which demonstrates the effectiveness of discriminant functions in predicting thermal comfort for both groups. These results highlight the importance of considering gender differences in the search for thermal comfort conditions and providing guidelines that promote the well-being of occupants and the conscious use of energy. This implies adjusting the thermal conditions according to the specific needs of males and females in classrooms, always seeking to provide a suitable environment for activities, and considering energy efficiency and users’ productivity.

Improving classroom thermal comfort of educational buildings: Case of Kantipur City College

Well-designed and thermally comfortable learning spaces contribute to better academic performance, enhanced concentration, and improved productivity of students. Thermal comfort is often one of the most overlooked design parameters while constructing educational buildings in Nepal. The Nepalese government has yet to develop design guidelines or regulations which ensures optimum indoor thermal comfort. Due to this, classrooms either lack insulation, have poor ventilation, or have overall poor thermal performance. This study illustrates how the use of passive design measures such as thermal mass, insulation, and glazing can help in improving the thermal comfort of students in such classrooms. Kantipur City College, an engineering college in Kathmandu was selected as a case study to evaluate the thermal environment of the classrooms. The field study also determined the existing comfort levels of students based on their thermal sensations and preferences. Design Builder Software was used to carry out the thermal simulation analysis and evaluate the impacts of passive design strategies when applied to the base classroom model. Field survey showed that the indoor temperatures were in the range of 27-32 °C, and students felt quite uncomfortable during the lesson hours. Results from simulation analysis revealed that providing insulation to the walls and ceilings, applying thermal mass, or changing the window glazing lowered temperatures by 2-4 °C. The study concluded that careful consideration of appropriate passive design measures can help to significantly lower indoor temperature during the summer and maintain thermal comfort in the classrooms.

Examining thermal comfort levels and ASHRAE Standard-55 applicability: A case study of free-running classrooms in Abuja, Nigeria

Most thermal comfort research has traditionally focused on office and commercial buildings as opposed to educational facilities. Due to the high population density in schools and the undesirable impact an unsuitable thermal setting can have on performance, teaching and learning, providing thermal comfort in school facilities is crucial. Considering the above information, this study aims to collect empirical data from secondary schools in Abuja’s hot and dry climate to evaluate thermal comfort settings for students in naturally ventilated classrooms and the applicability of ASHRAE Standard-55 in the area. To achieve this, field investigations were conducted in free-running classrooms from four secondary schools. The study involved 1448 students drawn from 41 classrooms. Data collection involved measuring classroom thermal comfort variables and respondent survey, simultaneously performed while students were learning in the classroom. Findings revealed none of the studied classrooms’ thermal conditions met the ASHRAE Standard-55 comfort range. However, 44% of students felt comfortable. The study indicated a regression-neutral temperature of 28.8°C and a ‘comfort temperature’ range of 26 to 31°C. The findings of this research could form the foundation data for a local thermal comfort standard. However, the prior thermal experiences of respondents were not investigated in this study.

A machine learning led investigation to understand individual difference and the human-environment interactive effect on classroom thermal comfort

The availability of the global thermal open database means that machine learning models have been increasingly applied in thermal comfort studies in order to understand the factors and mechanisms that affect human thermal sensation. Previous global database analyses focused less on classroom thermal comfort, however, and more on model accuracy, while model interpretation was usually ignored, and individual differences and interaction effects are particularly poorly explained. This study screened 4527 related records about classrooms from the ASHRAE Global Thermal Comfort Database II, and used the cleaned data to train a hybrid model of extreme gradient boosting (XGBoost) and Bayesian optimisation (BO). SHAP values were used to interpret the machine learning model. The results identified ten key influencing factors that are associated with thermal comfort, although their importance varies among individuals. The effects of the factors can also be divided into main effects (80%) and interactive effects (20%), and some interactive effects are more potent than the main effect. Three typical types of interactive effects are concluded: two-way interaction, one-way interaction, and cross-interaction. This study was based on a comprehensive global database and an innovative machine learning method, and will lead to a more robust personal comfort model (PCM) that guides HVAC design and regulation development in order to meet thermal environment and energy-saving requirements.

Comparison of indoor air quality and thermal comfort standards and variations in exceedance for school buildings

Addressing indoor air quality (IAQ) and thermal comfort issues in school buildings is challenging but relevant. Firstly, their primary occupants are more vulnerable than adults. Secondly, school buildings are often inadequate being too old or designed to prioritise energy-efficiency targets. Thirdly, occupants have often little control over the indoor environmental quality (IEQ). Lastly, the SARS-CoV-2 pandemic highlighted the complexity and vulnerability of existing decision-making processes in relation to making timely and well-informed decisions about IEQ threats. Standards and guidelines vary over time and among similar countries despite targeting similar occupants, evaluate IAQ and thermal comfort independently, and do not include any specific adaptations to children. Thus, the aim of this research is to compare different available standards to evaluate IAQ and thermal comfort in school buildings. By analysing with different standards (EN16798, BB101, and ASHRAE 55 and 62.1) the data collected in schools in northern Italy, this research evaluated the consequences of different limits and approaches, and proposed improvements. The conclusions are that (i) thresholds and methods inconsistency within the same standard should be avoided; (ii) upper- and lower-bounded operative temperature scales are the most appropriate means to design and verify thermal comfort in classrooms; (iii) IAQ metrics that give an upper limit per a certain amount of consecutive time might prevent the build-up of indoor pollutants, even with high emissions from the building fabric; (iv) no standard proposes a combined IAQ and thermal comfort analysis which could enable more informed trade-off decisions considering IAQ, thermal comfort, and energy targets.

The Challenge of Multiple Thermal Comfort Prediction Models: Is TSV Enough?

Classroom thermal comfort has a direct effect on student health and educational outcomes. However, measuring thermal comfort (TC) is a non-trivial task. It is represented by several subjective metrics e.g., Thermal Sensation Vote, Thermal Comfort Vote, Thermal Preference Vote, etc. Since machine learning (ML) is being increasingly used to predict occupant comfort, multiple TC metrics for the same indoor space may yield contradictory results. This poses the challenge of selecting the most suitable single TC metric or the minimal TC metric combination for a given indoor space. Ideally, it will be a metric that can be used to predict all other TC metrics and occupant behavior with high accuracy. This work addresses this problem by using a primary student thermal comfort dataset gathered from 11 schools and over 500 unique students. A comprehensive evaluation is carried out through hundreds of TC prediction models using several ML algorithms. It evaluates the ability of TC metrics to predict (a) other TC metrics, and (b) the adaptive behavior of primary students. An algorithm is proposed to select the most suitable single TC metric or the minimal TC metric input combination. Results show that ML models can accurately predict all TC metrics and occupant-adaptive behavior using a small subset of TC metrics with an average accuracy as high as 79%. This work also found Thermal Sensation Vote to be the most significant single TC predictor, followed by Thermal Satisfaction Level. Interestingly, satisfaction with clothing was found to be as equally relevant as thermal preference. Furthermore, the impact of seasons and choice of ML algorithms on TC metric and occupant behavior prediction is shown.

Energy-Use and Indoor Thermal Performance in Junior High School Building after Air-Conditioning Installation with the Private Finance Initiative

Japan’s government has adopted the “Private Finance Initiative (PFI)” as a project method for monitoring “air-conditioning (AC)” performance after AC installation projects to overcome heatstroke increase in schools during the summer. However, this project was conducted long after schools were built, which raises the question: what is the AC “energy-use (EU)” and how comfortable will the classroom be when it is installed without going through the planning stage? Minimizing AC EU while keeping indoor thermal comfort is the main concern for low-carbon building design technology development. This research aims to evaluate the AC EU and summer indoor thermal comfort in classrooms by position and zone. This research method analyzes PFI monitoring data, field measurement data, and questionnaires with sensitivity analysis. It found that AC EU in the summer was higher than in the winter. In addition, the AC setting temperatures in the summer (cooling) were below the government-recommended value of 28 °C. Although the indoor thermal comfort percentage in the summer had reached 75.3%, there was a seating position with a smaller comfort percentage than others. The result further shows that most students felt “neutral”. However, the number of students who felt “slightly cool” and “cool” were more than those who felt “slightly warm” and “warm”.

A Review Paper on Thermal Comfort and Ventilation Systems in Educational Buildings: Nano-Mechanical and Mathematical Aspects

Thermal comfort has always been an essential factor that affects students’ productivity and success. Students spend considerable time at their schools or universities more than any other building type except their homes. Thus, indicating the importance of providing thermal comfort in educational buildings. Many studies worldwide are conducted to assess and optimize thermal comfort inside classrooms. However, the results have not been accurate even for similar study conditions due to the differences in the studies’ conditions. This paper focuses on thermal comfort studies in educational buildings (classrooms). The studies are divided into two sections, the first covering field studies methodologies, objective, and subjective questionnaires, and the second reviewing thermal comfort results based on the climatic zone, educational level, and analysis approach. It is recommended that thermal comfort studies be carried out using rational and adaptive models as they provide more accurate, reliable results. Also, it is found that thermal comfort standards are generally inadequate to assess thermal comfort in classrooms. Thus, other international standards should be created and considered for classroom assessment. Over the past few years, the combination between nanotechnology and architecture engineering has been widely used in several disciplines because of its crucial significance in finding new nanodevices to contribute in reducing of energy consumption, particularly on construction materials. Filling functionalized tools with nanoparticles plays a critical role in improving the thermal and optical properties, particularly with respect to nanofluids applications, i.e., buildings applications of thermal comfort. The experimental results of long-term studies show that the calculation values of optimization have a consistent agreement with the experimental transmission of nanofluids models.

Early design evaluation of low-rise school building morphology on energy performance: Climatic contexts of Southeast Europe

Contemporary societies have shifted their focus towards sustainable and resilient public buildings, transcending the institutional and functional role of the physical structures. School buildings remain the second highest expenditure of municipalities' total running costs. The impact on well-being and improved knowledge, and the average lifespan of school buildings, imply the necessity to pay special attention to its expected performance from the early design phase.The present research aims to estimate the impact of early design evaluation of open-school building morphology on energy performance in four climatic contexts of Southeast Europe. Design variables, including building shape and orientation, are selected for a comprehensive whole-building energy performance analysis. The results highlight the method's efficiency in reducing a maximum of 35.4% of the annual energy demand and increasing a maximum of 1.21 °C the thermal comfort in classrooms through geometry optimization. Suggestions are made on the appropriateness level of each typology for each studied climatic context. A fundamental framework for early design decision-making stages is generated through the performed simulation results.

Preliminary Study on Student’s Performance and Thermal Comfort in Classroom

In Malaysia, students spend up to 33% of their day in classrooms and school buildings. Previous research had shown that thermal comfort conditions in educational buildings can stimulate student productivity. This study aimed to preliminary investigate the relationship between thermal sensation and student performance in the classroom. Data collection was conducted in a selected classroom at a secondary school in Segamat, Johor. All data were collected for three days. Physical measurement data were taken using thermal comfort equipment, KIMO AMI 310 for indoor measurement (air temperature, mean radiant temperature, air velocity, relative humidity), and TSI VelociCalc for outdoor measurement (air temperature, relative humidity). The thermal comfort satisfaction questionnaire was distributed to 36 students in the classroom. The learning performance was assessed through a simple reaction test and digit span test based on the WHO Neurobehavioral Core Test Battery (NCTB) method. The results of the thermal comfort satisfaction questionnaire clearly showed that the lower the fan speed, the more students preferred the cooler option. Furthermore, students performed better when the fan speed was increased. Based on the correlation analysis, it can be concluded that the learning performance and thermal preference vote (TPV) are positively correlated. As a result, students tend to get higher scores when they feel cooler. This study provides important preliminary information on classroom conditions in secondary schools in Malaysia and provides a better understanding of the relationship between thermal perception and student learning performance in the classroom.

A Comparison of Students’ Thermal Comfort and Perceived Learning Performance between Two Types of University Halls: Architecture Design Studios and Ordinary Lecture Rooms during the Heating Season

In classrooms, several variables may affect students’ thermal comfort, and hence health, well-being, and learning performance. In particular, the type of learning activity may play a role in students’ thermal comfort. However, most of the previous research has mainly investigated the thermal comfort of students in ordinary classrooms, while less attention has been paid to students’ thermal comfort in classrooms with particular learning activities, such as architecture design studios, where students spend a long time and perform learning activities with high metabolic rates. For this purpose, we compared the thermal comfort and perceived learning performance of students majoring in architecture (n = 173) between two types of university halls, namely, design studios and typical lecture rooms (N = 15). We applied the classroom–comfort–data method, which included collecting physical, physiological, and psychological data from students and classrooms. Data were collected during the heating season (November 2021–January 2022) in a university building in Jordan. We conducted continuous monitoring combined with periodic measures for indoor temperature, relative humidity, mean radiant temperature, and air speed. Questionnaires, focus groups, and observations were also used to collect subjective data from students. The results showed statistically significant differences (Δμ = 3.1 °C, p < 0.01, d = 0.61) in indoor temperature between design studios and lecture rooms. Only 58% of students’ votes were within the ASHRAE 55-2107 recommended comfort zone. In design studios, 53% of students felt warm compared to 58.8% of students who had a cold sensation in lecture rooms. Students perceived themselves as more productive when they felt cooler. Our research’s significance lies in its injunction that there must be a special thermal comfort guide for educational buildings that are adapted to the local environment and functions of the spaces, cooperatively.

An Investigation of Thermal Comfort in Classrooms in the Tropical Savanna Climate

Studying the thermal environment in classrooms is essential due to its impact on students' health, teaching, learning, and productivity. In the Nigerian context, there is a general lack of thermal comfort studies, and none specifically relate to secondary school settings. This study aims to investigate students' perceptions of the indoor thermal environment and to determine the optimum temperature in naturally ventilated classrooms in the tropical savanna climate. Field investigations were conducted in free-running classrooms in Abuja to evaluate occupants' thermal comfort and perceptions. The study involves 901 pupils from 21 classrooms. Data were obtained through physical measurements of thermal comfort variables and a questionnaire survey on occupants' perceptions of the indoor thermal environment. The objective assessment indicated that 86% of the classrooms were inconsistent with the ASHRAE standard–55. Although 60% of the pupils were satisfied with their thermal environment, 78% preferred a cooler than neutral temperature. The result revealed a comfort temperature of 28.9 oC. The results extend the literature on thermal comfort in classrooms to the tropical savannah climate of the west African sub-region, which has received little attention in earlier research. The findings provide foundation data for developing a comfort standard for classrooms in the zone.

Ventilation and thermal conditions in secondary schools in the Netherlands: Effects of COVID-19 pandemic control and prevention measures

During the COVID-19 pandemic, the importance of ventilation was widely stressed and new protocols of ventilation were implemented in school buildings worldwide. In the Netherlands, schools were recommended to keep the windows and doors open, and after a national lockdown more stringent measures such as reduction of occupancy were introduced. In this study, the actual effects of such measures on ventilation and thermal conditions were investigated in 31 classrooms of 11 Dutch secondary schools, by monitoring the indoor and outdoor CO2 concentration and air temperature, both before and after the lockdown. Ventilation rates were calculated using the steady-state method. Pre-lockdown, with an average occupancy of 17 students, in 42% of the classrooms the CO2 concentration exceeded the upper limit of the Dutch national guidelines (800 ppm above outdoors), while 13% had a ventilation rate per person (VRp) lower than the minimum requirement (6 l/s/p). Post-lockdown, the indoor CO2 concentration decreased significantly while for ventilation rates significant increase was only found in VRp, mainly caused by the decrease in occupancy (average 10 students). The total ventilation rate per classrooms, mainly induced by opening windows and doors, did not change significantly. Meanwhile, according to the Dutch national guidelines, thermal conditions in the classrooms were not satisfying, both pre- and post-lockdown. While opening windows and doors cannot achieve the required indoor environmental quality at all times, reducing occupancy might not be feasible for immediate implementation. Hence, more controllable and flexible ways for improving indoor air quality and thermal comfort in classrooms are needed.