Assessment of thermal comfort in the modern lecture theater: Kielce University of Technology, Poland - case study

This paper investigates student’s thermal comfort in the intelligent building called “Energis” of Kielce University of Technology located in Poland, which is equipped with advanced heating, ventilation and air conditioning (HVAC) mechanical systems. One lecture theater is selected for thermal analysis. Analysis was focused on student’s assessment of thermal sensations in the autumn season to determine whether modern intelligent buildings can provide adequate comfort conditions during the European transitional period, which is between summer and winter seasons, when heating system is usually off. This study is based on survey data and experimental measurements of indoor parameters using a microclimate Testo 400 meter. The experimental data indicate that a relatively large proportion of students are not satisfied with indoor environmental air quality prevailing in the intelligent building. The results of this study indicate that only 10% of students reported weak productivity related to indoor environmental conditions in the building. In addition, 52% of students describe their thermal sensations as comfortable and 17% of students are not satisfied with environmental conditions in the lecture room. Therefore, improvements on existing mechanical systems for indoor air quality is recommended. Furthermore, it is recommended to conduct more experimental trials and surveys to confirm the results presented in this paper in different University buildings.


Introduction
A human being spends more and more time indoors in an artificially created climate.Therefore, the issue of thermal comfort and its subjective feelings inside the building is of increasing interest.At educational facilities specifically it is crucial to consider the most favourable indoor environmental conditions to enhance the learning productivity.Therefore, there is a significant demand for an improved design of heating, ventilation and air conditioning (HVAC) mechanical systems.
Thermal comfort is defined a state of not feeling too cold or too warm and is described as satisfaction with the thermal environment [1].It affects the quality of life, therefore, it is important to ensure this comfort through the use of air conditioning, heating, and ventilation systems.There are many variables that effect the thermal comfort including air temperature, air velocity, relative humidity, average radiant temperature, clothing insulation, metabolic rate and physical activity [2].The Fanger model [3] is used to determine thermal comfort which is based on a combination of standards ISO 7730 [4] along with PN-EN 16798-1 standard [5].The PMV is an assessment tool used to measure the thermal sensation of people range between "-3" (which is described as "too cold") to "+3" (described as "too hot").In accordance with the American standard ASHRAE 55 [6] and ISO 7730 standards [4], the acceptable range for the PMV indicator is between -0.5 to +0.5 for educational buildings.
Thermal comfort in educational buildings is directly related to students productivity, well-being, energy conservation, physical and mental health [8].Thermal comfort analyses at educational facilities are not very common compared to offices.Almeida et al. [9] collected measurements in six Portuguese educational buildings, where both questionnaire and experimental tests were conducted.Similar research concept was adopted by Krawczyk et al. [10] where a comparison was made between Polish and Spanish Universities.In Spain , it was reported that the majority of students felt the thermal sensation of cold or too cold in spite of the fact that temperature values were within the recommended range and 2 o C higher compared to Poland.Fang et al. [12] investigated thermal comfort in air conditioned classrooms in Hong Kong where a strong linear relationship between the mean thermal sensation vote and the operative temperature was observed.Aghniaey et al. [15] described experimental studies of thermal comfort that were conducted at the University of Georgia, USA where thermal sensation, acceptability, and preferences corresponding to increased cooling temperature setpoint were investigated.The results showed that the thermal environment conditions were overwhelmingly acceptable and women typically preferred warmer environments.Furthermore, Singh et al. [16] tested thermal comfort of nine hundred students in the summer season in India in naturally ventilated classrooms.It was observed that 81% of the responses were in the comfort zone despite the set mean indoor air temperature of 30.4 o C. On the other hand, for a research conducted in a foyer of a French intelligent educational building [17] indicated a high level of dissatisfaction of thermal conditions in this chosen educational space.It was found that carbon dioxide concentration exceeded the upper limit.In a very recent publication of Izzati et al. [18] who conducted experimental tests in two student activity rooms under various cooling temperature settings in a university building in Malaysia to determine the respondents' characteristics as well as their behavior towards utilizing air conditioning for thermal comfort, also to estimate students' comfort at various indoor temperatures.It was observed that there are many factors that affect thermal comfort including water intake and clothing insulation.The average comfort temperature for respondents was 24.3°C which is within an indoor thermal comfort zone of 23-27°C.
An intelligent building is created with sustainability in mind, so as to reduce eclectic and thermal energy consumption (and thus expenditure) and to provide maximum thermal comfort to the occupants of such buildings by means of modern technology.Mainly, it has a low negative impact on the environment and responds quickly to the changing thermal needs of the occupants with the help of building management systems [19].Thermal comfort depends on large number of parameters, most of them are subjective [20,21], but the rate at which human dissipate heat is key to understand thermal comfort.It is known that heat is being dissipated via convection, conduction and radiation as well as phase change processes which is considered as a very effective way of cooling [22][23][24].
Educational facilities in general are unique due to the fact that many people spend large amount of time both as students and educators.The indoor environment seems to affect the learning productivity to a very large extent.This paper analyses thermal comfort and productivity of students in a lecture theater of a modern intelligent building called "Energis" at Kielce University of Technology, Poland where more such buildings are being built around the world.The main objective in this paper is to determine whether modern intelligent buildings can provide an adequate thermal comfort conditions during the European transitional period, which is between summer and winter seasons when the heating system is off.

Material and method
The measurements used in this study have been conducted in the "Energis" intelligent building of Kielce University of Technology, South -Eastern Poland.The building was built in 2012 and is considered as one of the most modern educational buildings in Poland.Figure 1 presents a photo of the building (Western facede).The lecture theater where this study was conducted is presented in Figure 1.One lecture theater was chosen for the study, which is marked with the red rectangle in Figure 1.The lecture theatre is located on the first floor and is one of the two largest theatres where most of the lectures take place during the term.Students usually spend an average of 1.5 hours in the lecture theatre.The usable area is 157 [m] which can accommodate up to 120 students.The intelligent building chosen in this study was put into public use in 2012.
Experimental tests were conducted using two methods -questionnaire and measurements of indoor parameters such as: relative humidity, air and globe temperatures, air velocity, light intensity and carbon dioxide concentration.During the research phase, students filled in questionnaires concerning the characteristics of their thermal sensations.54 students took part in this study, including 15 women and 39 men.This allowed them to express their subjective assessment of thermal comfort as well as their preferences concerning the prevailing indoor conditions in the lecture room.Students also indicated the types of clothes they wore and the activities they performed before answering the survey.
In addition, the experimental measurements were conducted in October 2020 over two days.The outside air temperature at the time of measurements was around 7-8 o C. Figure 2 shows the microclimate meter Testo 400 and students filling the questionnaires.The microclimate meter took measurements of indoor environmental parameters every 1 second.

Results and discussion
This research is based on the use of a microclimate meter Testo 400 and questionnaires.The parameter readings were taken at the exact moment of filling in questionnaires by students.The average air temperature was 19.63 ± 0.33 o C. The illuminance of the lecture rooms ranged from 288 to 429 lx,.The average humidity was between ca.46 to ca. 50%.The air speed differed only in one room where the speed was 0.11 m/s, while in the other rooms it ranged from 0.07 and 0.08 m/s.The content of CO2 was from 664 to 822 ppm, i.e. no significant fluctuations between measurements were observed.The variation in ambient temperature, relative humidity and carbon dioxide levels is presented in Figure 3. Figure 4 presents frequency of the results for the questionnaire answers on thermal impressions experienced by students during microclimate meter measurements.Possible responses to choose from were as follows: -3 -too cold; -2 -too cool; -1 pleasantly cool; 0comfortable; 1 -pleasantly warm, 2 -too warm, 3 -too hot.
It is observed that the answer "too warm" occurs the same number of times as the answer "too cold", which has a percent of 3.70% each.Otherwise, a "comfortable" response was repeated 28 times, which is 51.85% compared to other thermal sensation expressions.Answers of "pleasantly warm" and "pleasantly cool" accounted for 16.67% and 14.81% respectively."Too cool" answer was repeated 5 times, which is 9.26%.A percent of 16.67% of students were dissatisfied with environmental conditions in the lecture room  Figure 5 shows the frequency of questionnaire answers given regarding the acceptance of air temperatures experienced by the students as Thermal Acceptability Vote (TAV).The possible answers in the questionnaire were: 2 -indicated comfortable level, 1 -indicated acceptable level, -1indicated unpleasant level, -2 -indicated definitely unpleasant level.
Students responses show that the "comfortable level" was selected 21 times, which is 38.89% of the total answers.The "acceptable" was repeated 29 times, which is 53.70% of the total reported responses.And the answer "unpleasant" was repeated 4 times, which is 7.41% of all responses.When comparing the results of the conducted study, it can be conducted that students were generally satisfied with the prevailing conditions in the lecture room and only 7.41% of students did not correspond to air temperature in which they were located.
Figure 6 shows the frequency of students answers regarding thermal preferences vote.It is observed that students answered "definitely warmer" twice with regard to thermal preferences vote (TPV) indicator, which is of 1.85% obtained from all responses.Otherwise, the answer "warmer" was repeated 21 times, which is 38.89% of the total responses.For "cooler" answer the frequency is 3.70%.As a summary from the results shown in Figure 6, students felt well in the lecture room.It was observed that the most frequently answer was "no change", which is 55.56% of total responses completed by students.Only 3.70% believed that the conditions in the lecture room are not satisfactory.
Figure 7 presents the frequency of student's responses given in relation to general thermal sensations vote (GSV) by the respondents, which describe their general feelings in the lecture room, describing as: +2 -very well, +1, good, 0 -normal, -1 -bad, -2 -very bad.It was observed that students felt generally comfortable in the lecture room while only 5.56% of them expressed a negative feeling on general thermal sensations vote indicator.
At educational facilities, it is very important to provide conditions that will facilitate fast learning process (knowledge acquisition ability), like +1 -strong, 0 -normal, -1 -weak.
It was found that students, assessing their ability to acquire knowledge as normal, showed that prevailing internal conditions of the environment did not have any positive nor negative impact on their overall educational productivity, which means that the intelligent building provided neither good nor bad conditions for learning and development as presented in Figure 8.The created internal environment turned out to be indifferent to the participants of the study.
The conditions of the internal environment in the lecture room for 4 groups of students showed that the learning productivity did not change to a higher nor lower level, on the contrary, it remained at a normal level of 87.04% of students.The Predicted Mean Vote (PMV) and Thermal Sensation Vote (TSV) indices play a huge role in the assessment of thermal comfort.The range in both cases should be from -0.5 to +0.5.Exceeding this limit will prove the thermal discomfort of the examined social group.It is these indicators that inform about the thermal sensations in a given room in the case of TSV, while the PMV whether the conditions provided in the room comply with the ISO 7730 standard.The average TSV values from each test are presented below, and the PMV that was calculated on the basis of the standard in Figure 9.It is not noticeable in Figure 11 that in as many as q three studies, students felt thermal comfort because the averages were in the range from -0.5 to +0.5.Only the fourth measurement was -0.58.However, look at the internal conditions and the PMV calculation values for four measurements prove that the thermal comfort was not ensured in accordance with the assumptions standardized by law.Taking this into account, only one fourth measurement confirms the lack of comfort according to people and the standard, while in the other three measurements it turns out that human thermal sensations significantly differ from the recommendations in the standard.So a thought arises to create such a modification that it would become closer to the real thermal sensations and the strict range of internal parameters

Conclusions
As a conclusion, it is observed that 52% of students described their thermal sensations as comfortable and 17% were dissatisfied with the indoor environmental conditions in the lecture room, which is above the acceptable value of 10%.When assessing the well-being of students in the lecture room, almost 54% of students described it as a good productive learning environment and only 2% described the general learning environment as very good learning environment.In addition, from the collected data it is found that the thermal conditions in the room are not sufficient to create a thermal comfort condition for all students.In order to avoid such situations in the autumn -spring transition period, where people do not feel thermal comfort, more attention should be given to the use of controllers that maintain the temperature in rooms at constant level.It is neither too cold nor too warm when there is no heating.In addition, one cannot forget about the difference between the real TSV impressions and those calculated from the PMV standard.Three of the examined groups really experienced thermal comfort, while 4 slightly, but still, exceeded the threshold of -0.5.Looking at the PMV, the values exceeded -1.4 for all 4 groups.This proves the discrepancy between Fanger's model and the feelings of the subjects.The only solution that can bring the current thermal sensations closer to the model calculations would be to change the Fanger model.

Figure 2 .
Figure 2. Microclimate meter Testo 400 with probes (in the center) and students filling the questionnaire in the lecture room.

Figure 3 .
Figure 3. Variations in air temperature, relative humidity and carbon dioxide levels with time in the lecture room.

Figure 4 .
Figure 4. Frequency of questionnaire answers on thermal sensations.

Figure 5 .
Figure 5. Frequency of questionnaire answers on temperature acceptability using the TAV indicator.

Figure 6 .
Figure 6.Frequency of student's responses on thermal preferences vote.

Figure 7 .
Figure 7. Frequency of student's responses on general sensations vote.

Figure 8 .
Figure 8. Results for the learning productivity of students.