ENSURING COMFORT MICROCLIMATE IN THE CLASSROOMS UNDER CONDITION OF THE REQUIRED AIR

Research into the process of ensuring comfortable microclimate is very relevant, since about 20 % of the total population spends a significant part of their day at preschool and school facilities. Papers [1, 2] show that the deterioration of microclimate conditions in classrooms, in particular due to an increase in СО2 concentration, leads to deterioration of the state of health and disability of pupils, as well as insufficient learning of their educational material. This is especially important, since СО2 concentration often exceeds permissible values in the outdoor air of large cities. Thus, room ventilation systems require significant air exchange for СО2 assimilation. Ecologists, doctors, diagnosticians, engineers and designers of ventilation and air conditioning systems pay special attention to the issue of an influence of air quality in premises of buildings on the state of people health. A physical condition of a person depends on a content of pollutants in air. If the air quality is poor, people experience fatigue, loss of concentration, development of diseases, etc. Carbon dioxide, along with nitrogen oxides, carbon monoxide, sulfur dioxide and volatile organic compounds, are typical pollutants. Thus, we should take this into consideration at evaluation of the quality of air when designing ventilation and air conditioning systems. The European standard EN 13779 “Ventilation for-residential buildings ‒ Performance requirements for ventilation and room-conditioning systems” [3] suggests accepting the concentration of carbon dioxide of 350 ppm in outdoor air in countryside, of 400 ppm ‒ in small cities and of 450 ppm ‒ in centers of large cities as a general base reference value. In fact, it can be substantially higher. The problems outlined emerged a long time ago, therefore the USA accepted ASA A53.1: Light and Ventilation standard in 1946. The first version of ASHRAE 62 replaced this standard in 1973. It included minimum and recommended air exchange norms for more than 250 types of building structures. Such requirements were a significant achievement at


Introduction
Research into the process of ensuring comfortable microclimate is very relevant, since about 20 % of the total population spends a significant part of their day at preschool and school facilities.Papers [1,2] show that the deterioration of microclimate conditions in classrooms, in particular due to an increase in СО 2 concentration, leads to deterioration of the state of health and disability of pupils, as well as insufficient learning of their educational material.This is especially important, since СО 2 concentration often exceeds permissible values in the outdoor air of large cities.Thus, room ventilation systems require significant air exchange for СО 2 assimilation.
Ecologists, doctors, diagnosticians, engineers and designers of ventilation and air conditioning systems pay special attention to the issue of an influence of air quality in premises of buildings on the state of people health.A physical condition of a person depends on a content of pollutants in air.If the air quality is poor, people experience fatigue, loss of concentration, development of diseases, etc.
Carbon dioxide, along with nitrogen oxides, carbon monoxide, sulfur dioxide and volatile organic compounds, are typical pollutants.Thus, we should take this into consideration at evaluation of the quality of air when designing ventilation and air conditioning systems.The European standard EN 13779 "Ventilation for-residential buildings -Performance requirements for ventilation and room-conditioning systems" [3] suggests accepting the concentration of carbon dioxide of 350 ppm in outdoor air in countryside, of 400 ppmin small cities and of 450 ppmin centers of large cities as a general base reference value.In fact, it can be substantially higher.
The problems outlined emerged a long time ago, therefore the USA accepted ASA A53.1:Light and Ventilation standard in 1946.The first version of ASHRAE 62 replaced this standard in 1973.It included minimum and recommended air exchange norms for more than 250 types of building structures.Such requirements were a significant achievement at

I . S u k h o l o v a
PhD, Assistant* Е-mail: isukholova@gmail.com*Department of Heat and Gas Supply and Ventilation Lviv Polytechnic National University S. Bandery str., 12, Lviv, Ukraine, 79013
In 1981, there was a revise of ASHRAE 62.In the standard as of 1981, a concentration of pollution determined air exchange and other design parameters.In ASHRAE 62 norms of the year 1989, there was an increase in minimum intensity and it related to other norms.Minimum intensity was increased and related to other norms since of 1973 in ASHRAE norm from 62-1989.This step admitted that limited energy consumption caused an inappropriate reduction in efficiency of a ventilation system.The ASHRAE 62.1-2004a edition marked the first change in requirements for air exchange since the 1989 standard.
The indirect definition approach was accepted in 2000 in ASHRAE 62-2001.Existing and future CEN standards use the specific quantitative determination of individual sources of pollutants in premises.

Literature review and problem statement
Currently, researchers pay great attention to the issues of energy saving in construction of new school buildings and significant renovation of existing ones.Therefore, increasing of thermal stability and tightness of perimeter structures is of prime importance in reconstruction and construction of new buildings.To achieve this objective, it is necessary to minimize uncontrolled air exchange due to air leakage through building constructions (infiltration).There are recuperators in mechanical ventilation of such systems.Recuperators reduce energy consumption of buildings [4,5].
To determine values of air exchange in classrooms, which would provide optimal parameters of a microclimate, it is necessary to investigate how these parameters were formed in the normative documents of the leading western countries [6].
The European Committee for Standardization (CEN) developed a set of 31 standards to support implementation of the Energy Performance of Buildings Directive (2002/91/EC) accepted on 04.01.2003.There was a revision of the Directive to EU Directive 2010/31 and it was issued by the European Commission in December 2010 [7].Table 1 shows the value of the normative air exchange regulated by this Directive.3 provides an overview of the requirements to efficiency of school and office ventilation systems around the world [8].
EN 13779 and EN 15251: 2007 standards determine the amount of inflow air in the European Union.After analysis of the data presented in the Tables 1-3, we can state that there is no generally accepted approach to determination of a value of standard air exchange in classrooms.The recommended values vary in a significant range: the minimum value is 10.8 m 3 /h per person in accordance with the Bygningsreglement, and the maximum value is 30 m 3 /h per person according to the Order 527/2007 [9].Some documents calculate the amount of ventilation air not per person, but in dependence on an area of a classroom.The analyzed data from documents of certain countries of the European Union indicate specific numerical values of recommended air exchange.But they do not indicate methods of calculation or results of studies used to accept these values.
SNIP II-L.4-62Comprehensive school and boarding schools, Design standards, 1964 regulated the requirements for ventilation of school premises before the national building standards came into force on the territory of Ukraine.Thus, there is a significant number of schools in Ukraine built in accordance with these standards.According to this document, it is necessary to calculate ventilation of educational premises by determination of an amount of air for assimilation of excess of heat emissions, wet releases and СО 2 emissions in order to maintain temperature of internal air within 16-22 °С, humidityfrom 30 to 60 % and СО 2 contentup to 1 l/m 3 .
Since 1998, DBN V.2.2-3-97 "Buildings and facilities of educational institutions", 1997 [10] has been in force in Ukraine.Table 3 presents the requirements for efficiency of ventilation systems.They differ from the above-mentioned European ones.
The State sanitary rules and regulations on establishment and maintenance of general educational institutions and organization of educational process state necessity for laboratory studies.It is necessary to measure air temperature, relative humidity, air velocity, radiation temperature, CO 2 concentration, CO concentration, formaldehyde concentration and concentrations of other substances in premises during the studies.It is necessary to perform laboratory studies and instrumental measurements in dynamics of a school day, namelybefore the first lesson and at the end of the last lesson.However, the State sanitary rules and regulations do not provide specific values of permissible concentrations of CO 2 and CO.Some modern publications apply to formation of microclimate in premises of educational institutions [11,12], but the emphasis is on energy efficiency of ventilation systems in most cases [12], they determine air exchange based on already existing normative documents.They also consider natural ventilation systems, but such systems can not always provide calculated air exchange during a cold season [13].Also, researchers studied natural ventilation potential for maintenance of an acceptable air quality in premises of US educational institutions during periodic operation of mechanical ventilation systems [14].There are similar studies carried out for educational and sports facilities, in particular for water sports [15].There researchers investigated the situation by simulation analysis and they established that forced ventilation is required to ensure adequate ventilation in a water center.
Authors of paper [1] noted that ventilation of classrooms goes through windows in almost all schools in Germany.In this regard, parameters of microclimate, especially in winter, are unsatisfactory.In addition, there are results of field studies of microclimate in a classroom (internal air temperature and СО 2 concentration) presented at various geometric characteristics of open windows and different wind speeds.Paper [2] presents results of studies on microclimate parameters in classroom premises of the gymnasium in the city of Misbach (Germany) conducted throughout a year.It shows the dependence of a change in СО 2 concentration during the entire educational period at different areas of open windows, but there is no amount of inflow ventilating air.
Since the methods of theoretical determination of air exchange do not take into consideration a subjective evaluation of microclimate, it is necessary to conduct experimental research.It will make it possible to substantiate objectively and clearly an amount of air exchange for formation of optimal parameters of microclimate in classrooms.
Oxygen enters a body, and a body emits carbon dioxide when breathing.Table 4 shows components of air inhaled and exhaled by healthy people measured in health facilities [16].A healthy person inhales about 250 ml of oxygen and releases about 200 ml of carbon dioxide per minute in a state of rest.The inhaled air composition differs from the composition of exhaled air, which in turn contains less oxygen, but more carbon dioxide and water vapor.During breathing, a body releases also energy, so temperature of exhaled air is higher.
Literary sources [4,6,17] do not indicate an amount of CO 2 released.Most often, the proportion of carbon dioxide in exhaled air is 4 %.The volume of air in human lungs when inhaling and exhaling in a state of rest is about 0.5 liters of air.It is possible to inhale about 2.5 liters of air more at quiet breathing.Due to the fact that there is a reserve in lungs, about 4 liters of air can be released from lungs after maximum breathing.About 0.5 l of air remains in lungs and bronchi after maximal exhalation.A healthy adult inhales and exhales from 7.5 to 8 l/min of air approximately at a frequency of about 15 inhales/exhales per minute.
There are difficulties in design of school ventilation systems due to the lack of data on emission of СО 2 by pupils, that would take into consideration such additional factors as age (for junior pupils and senior pupils), a ratio of girls and boys and intensity of physical activity.

The aim and objectives of the study
The objective of the study is to determine a value of a multiplication factor of air exchange in classrooms, which would provide optimal sanitary and hygienic conditions in premises.
It is necessary to solve the following tasks to achieve the objective: determination of actual values of СО 2 emissions from pupils in classrooms under different parameters of internal air by conduction of field studies in classrooms; microclimate monitoring in a class by the method of subjective assessment of air quality; -obtaining of graphical and analytical dependences of СО 2 concentrations in classrooms on a value of air exchange and parameters of internal air; determination of an amount of air exchange for formation of optimal microclimate parameters in classrooms.

1. Measurement of CO 2 in indoor and outdoor air
It is interesting to compare results of field studies of air conducted at existing schools in Slovakia and Ukraine.In both cases, researchers performed experimental carbon dioxide concentration measurements to study air in classrooms.They also recorded temperature of indoor air and relative humidity of indoor air simultaneously with measurement of carbon dioxide concentration.They recorded a concentration of carbon dioxide, temperature and relative humidity of air during measurement of outdoor air parameters.
Measurements took place in the heating period: January, February and March.During the measurement, researchers carried out also a subjective assessment in the form of questionnaires.Pupils assessed the air quality in a premise in the questionnaires.
The results of experimental studies determined the selection of a method for determination of ventilation efficiency in school buildings.
Experimental studies in Slovakia took place in selected lecture rooms located in the city of Kosice in the Street Vysokoshkilskaya in a five-story building on the fifth floor, and in Ukrainein Lviv in the Street Khotinskaya in a four-storey building on the fourth floor.Researchers recorded a concentration of carbon dioxide, air temperature, air velocity and relative humidity in a premise during experimental measurements.
During tests on Testo 435-4 device (Germany), they measured the following parameters of air in the selected premises: indoor air temperature, relative humidity and a carbon dioxide concentration.
Parameters of the device were as follows: measurement of CO 2 concentration in the range from 0 to 10000 ppm, accuracy of measurement of CO 2 concentration was ±3 ppm [18][19][20][21].
CO 2 concentration depends on human activity and differs in different areas in the external environment.Fig. 1 illustrates documented carbon dioxide concentration measurements made in Kosice this year, at an altitude of 20 meters above the ground approximately.Researchers measured also the concentration of carbon dioxide in the external environment during experimental measurements of the concentration of carbon dioxide in the premises under consideration.
As we can see on the graph presented in Fig. 1, the average concentration of carbon dioxide in the air of Kosice was between 420 and 430 ppm, which was consistent with the standard [3], although peak values exceeded 500 ppm.
Experimental measurements in classes of Lviv and Koshitsky schools also took place at fixed time.5 measurements took place at the same time.Beginning of stay in a classroom was always from 8.00 in the morning.From 8.00 to 9.00 (until 9.38) a written part of the experiment lasted, when pupils responded to the questions asked in writing.All pupils left the premise after the written test.The room re-mained empty with closed windows to carry out further calculations to determine the efficiency of ventilation through infiltration and exfiltration.The concentration of carbon dioxide dropped indoors due to air leakage through building constructions.All people who participated in the written part of the test entered the room after 1 hour.Oral part of the test took place in the room.Duration of the oral part of the test was different.Fig. 2 shows the results on the changes in the concentration of carbon dioxide recorded.
After the oral test, all people left the room, which remained empty, and windows and doors were closed.With a decrease in CO 2 concentration, room ventilation may occur through infiltration, which differs for each measurement day.
The results of the experimental measurements in the class showed that CO 2 concentration ranged from 876 to 1,582 ppm at staying in the room from 7 to 17 persons and the time of stay from 76 to 98 minutes.

2. Subjective assessment of the indoor environment in the classroom
Individual participants in the measurement documented the subjective perception of the internal environment in the class during the experimental measurement.At the end of their stay in the class, pupils completed a questionnaire for subjective assessment of the indoor environment parameters, which included an assessment of thermal comfort and intensity of odors.Table 5 shows the results of the measurements given in dependence on the number of persons in the class during the measurement.Subjective assessment by individuals in the classroom during the measurement determined air quality values.From a subjective point of view, we can note that the presence of high concentration of carbon dioxide in the room also increased a number of people who were dissatisfied with the air quality in the classroom.With the largest number of pupils and the highest concentration of carbon dioxide, one can assume that the subjective perception of respondents does not correspond to the objective definition of the observed factors of the internal environment.We should note that 12 % of respondents described the state of microclimate almost unacceptable at СО 2 concentration lower than the maximum according to the results of measurements conducted on 05.02.This is due to the longest duration of stay in the premise.

3. Calculation of the efficiency of a ventilation system based on measured CO 2 concentrations
We used the methodology, which determines air exchange in dependence on an amount of carbonic acid gas for determination of the required ventilation efficiency.We determined the mass flow rate of СО 2 from the concentration of carbonic acid gas obtained by experimental measurements of the carbon dioxide concentration.Experimental measurements took place in winter in several selected premises.We determined the required air flow, which meets hygiene requirements, based on the measured data on carbon dioxide.
It was very important to provide the most stable boundary conditions of measurement to be able to determine a change in carbonic acid gas concentration quantitatively according to the measured data.In addition to the measured indoor air parameters, we also fixed hourly information on outdoor air temperature and wind speed.These data influence intensity of ventilation through infiltration.
Fig. 3 shows the measured parameters of external air.It is evident from the measured values that the relative humidity of air also increases as the concentration of carbon dioxide increases.
It is necessary to divide the graph into two main parts (Fig. 3) in the analysis of the process, namely: an increase in the concentration of carbon dioxide, when a source of pollutants is indoors -A-B part; ventilation of the premise through infiltration, when there is no source of pollutants in the premise -B-C part.
There is an increase in the concentration of carbonic acid gas in A-B part, where the main source of pollutants is a person.We can express the change in the concentration of carbon dioxide mathematically by the relations [22,23]: where C IDA is the СО 2 concentration in air at t time (mg/m 3 ); C SUP is the СО 2 concentration in inflow air at t time (mg/m 3 ); q ms is the mass flow of СО 2 in a premise from a source of a pollutant (mg/s); q V is the volume flow of air required for premise ventilation (m 3 /s); V M is the room volume (m 3 ); t is time (s).The known variables were a volume of premises, СО 2 concentration and time of its change.Unknown values weremass flow of СО 2 and of outdoor air, which penetrates into a premise due to infiltration.
We obtained the concentration of carbon dioxide in ppm by multiplication of the concentration of carbon dioxide in mg/m 3 by k=0.556.
We used the method of indirect chemical mixing to determine the intensity of air exchange by means of air infiltration in the premise.This method controlled reduction of СО 2 concentration.The method implied monitoring of time of reducing of СО 2 concentration during its emission.And measurement stopped when its indoor concentration decreased to the concentration in the outside air.For this case, we used the following differential equation [24]: where n is the multiplication factor of ventilation through infiltration (1/s); C IDA,Z and C IDA,K are the CO 2 concentrations in a premise at the beginning of a concentration decrease (mg/m 3 ) and at the end of its reduction (mg/m 3 ); t is the time of reduction of CO 2 concentration (s).The increase in CO 2 concentration occurred due to the presence of people (A-B part).Ventilation in the room occurred due to infiltration.
There are no people in B-C part, so there is no CO 2 either.In B-C part, there is a gradual decrease in CO 2 concentration through infiltration (uncontrolled ventilation).Since CO 2 concentration at the end of the measurement differed from its concentration in the exhaust where n is the multiplication factor of ventilation through infiltration (1/s); C IDA,B and C IDA,C are the indoor CO 2 concentrations at the beginning and at the end of concentration reduction, respectively (mg/m 3 ); C SUP is the CO 2 concentration in inflow air (mg/m 3 ); t is the time of reduction of CO 2 concentration (s).
We compared the equations and the multiplication factor of ventilation through infiltration: .
(1/s).( 4) Since the boundary conditions (external air temperature and wind speed) influenced a change in the amount of infiltration, we determined a multiplication factor of ventilation by CO 2 assimilation at different values of air exchange [21].
We used the calculation volume of air flow supplied into a premise with uncontrolled infiltration of fresh air in the expression (1) for determination of the concentration of carbon dioxide.

Calculation of theoretical emission of carbonic acid gas by a person
When calculating the efficiency of ventilation systems, it is necessary to know an amount of CO 2 , which gets into a room from people.We can determine a volume and mass flow of CO 2 from humans based on previously reported values of lung volume, inhalation/exhalation volume and CO 2 percentage content as components of a gaseous mixture.
When calculating volume and mass flow of СО 2 , we assumed that the average value of one inhalation/exhalation was 0.5 liters.We took the intensity of respiration, which depends on a physical activity and temperature of air indoors, within 12-20 times per minute.In this case, the volume inhalation/exhalation flow will vary within the range of 0.10-0.17l/s or 0.36-0.60m 3 /h.In order to determine the mass flow of СО 2 , which accompanies the process of breathing, it was necessary to multiply СО 2 volume flow by its density.According-ly, СО 2 density at room temperature was ρ СО2 =1.82 kg/m 3 .Taking into consideration СО 2 percentage content in the air, we determined СО 2 mass (by hours and seconds) flow.Table 6 shows the results of the calculation.

1. Determination of the actual mass flow of carbonic acid gas
The direct measurement of СО 2 mass flow, which goes from pupils to a classroom, is a technically challenging task.This value depends on a number of factors such as a physiological state of pupils, room temperature, age and gender of pupils.Therefore, we used the indirect measurement method to determine СО 2 mass flow from pupils.We measured СО 2 concentration at the known number of pupils in a premise (20 people) and the known initial СО 2 concentration in a premise with an interval of 15 minutes in indoor air.Fig. 4 presents the obtained results as the graphical dependence of changes in СО 2 concentration during 95 minutes of measurements.The same graph also shows the curves of the dependence of the change in СО 2 concentration in a room during a specified time at different values of СО 2 mass flow in the range from 6.55 to 9.8 mg/s obtained on based on the dependence (1).The curve constructed based on experimental data coincides with the calculated curve corresponding to СО 2 mass flow -7.86 mg/s.We compared the curves, which reflect actual and theoretical changes in the concentration of carbonic acid gas, and we can state that the actual averaged value of CO 2 emissions by pupils in a class corresponded to the calculated value of 7.86 mg/s per person.

2. Determination of a multiplication factor of air exchange
We determined a multiplication factor of air exchange in dependence on CO 2 concentration.We used the formulas ( 1)-( 4) for determination of its concentration taking into consideration CO 2 mass flow (7.86 mg/s per person), a volume of a room and a measured initial concentration of carbon dioxide.We made calculations for various multiplication factors of air exchange (from 0.3 1/h to 1.4 1/h).Fig. 5 shows the results of calculations.
We can see on Fig. 5 that there is an increase in CO 2 concentration at different multiplication factors of air exchange.We observe the highest CO 2 concentration of 3,360 ppm at closed windows, when ventilation in a classroom occurs only through infiltration and exfiltration through building constructions.
It is necessary to change air in a classroom three times in one hour to achieve the maximum acceptable concentration of carbonic acid gas of 1,000 ppm.
The method of finding of the required multiplication factor of air exchange is quite accurate, but very labor-intensive.We compared the defined multiplication factor with the multiplication factor obtained from other sources: norms and standards active in Slovakia and Ukraine.

3. Theoretical determination of a multiplication factor of air exchange
We compared the determined multiplication factor of indoor air exchange, which base is the experimentally measured CO 2 concentration of 3.0 l/h, with the calculated values of the multiplication factor of air exchange in accordance with standards and legislation active in Slovakia and Ukraine.
We compared the multiplication factor of air exchange, which is based on the experimentally measured concentration of carbon dioxide: in accordance with pressure caused by the simultaneous action of temperature and wind; measured reduction of carbonic acid gas concentration.
We determined the multiplication factors of air exchange listed in Table 7 by infiltration, which, in turn, was determined by measurement of reduction of CO 2 concentration.We obtained the data on a concentration drop during the measurement after a\the written test, when no one was in a closed premise, and the CO 2 concentration decreased due to leakage through structures.We should note that in a class where there was 7 people and the multiplicity factor of air exchange through infiltration through building structures was 0.54 1/h, the CO 2 concentration increased to 1,500 ppm over 8 hours of stay.
We determined CO 2 mass flow based on the data on CO 2 concentrations measured during the stay of persons in a premise during the written part of the test and the calculation value of the multiplication factor of air exchange through infiltration.
We determined the amount of CO 2 using the measured CO 2 concentration, and then we determined the multiplication factor of air exchange in the selected lecture room.We also calculated the required multiplication factor of air exchange for this lecture room in accordance with the Order of the Ministry of Health of the Slovak Republic No. 527/2007 [9] and according to EN 13779 [3].Table 8 shows the values obtained.
Comparing different methods for calculation of efficiency of ventilation systems, the classroom examined in accordance with STN EN 15251: 2007 belonged to category II.According to EN 13779 [3] the classroom belonged to IDA 2 category, which required an average air quality in a premise.
We calculated air flow by the established multiplication factor of air exchange, taking into consideration the infiltration and the volume of the premise.Table 9 shows the values obtained.We compared the obtained results with the current European standards presented in Table 3 and analyzed them in the form of the diagram (Fig. 6).We presented the received volume air flow (m 3 /h for 1 person) in the form of the multiplication factor of air exchange for the particular selected lecture room where measurements and calculations took place.Consequently, we should perform calculation of the multiplication factor of air exchange in accordance with Order 527/2007 [9], which considers the required volume of inflow air of 30 m 3 /h per person, for the best result.We can state this in accordance with the measured data on CO 2 concentration in the chosen room and the calculated multiplication factor of air exchange according to different calculation methods.

Discussion of results of studying the optimal air exchange in classrooms
СО 2 concentration is not only an indicator of cleanliness of indoor air.Carbon dioxide is a toxic substance even at relatively low concentrations, and therefore we should consider its concentration as an initial value for calculation of efficiency of ventilation systems for long-term stay of people.
The proposed methodology makes it possible to increase accuracy and reliability of air quality control in classrooms due to the direct measurement of СО 2 concentration in a service area of a premise.
Nowadays, high-precision tools for measurement of СО 2 concentration for scientific purposes and household appliances, which make possible continuous monitoring of СО 2 concentrations in classrooms, are available.Deterioration of the environmental situation, especially in large cities, which causes an increase in СО 2 concentration in outdoor air, leads to a significant increase in efficiency of ventilation systems.
The above research results make possible to design ventilation systems for classrooms efficiency, which will provide optimal sanitary and hygienic conditions.The advantage of the study is that the results obtained experimentally are in good agreement with the results obtained by the analytical method.This suggests that we can use the dependences (1) to (4) for determination of СО 2 concentration of at an arbitrary time in premises of different purposes with a long stay of people.In addition, in comparison with researches of other authors, it proposes a combination of the analytical method with experimental research in the field conditions.The disadvantage of the study is that it is not universal, since it concerns only classrooms.Therefore, there is a need for further similar studies for other school premises -specialized offices, gymnasium, assembly hall, etc.In particular, we performed the study with pupils of senior classes.It would be advisable to conduct similar studies with stay of pupils of 1-4 grades in premises and to compare results.The total air exchange of a classroom determined by the estimated volume of inflow air of 30 m 3 /h per person can reach significant values.Therefore, in view of this, school premises require equipment with energy-efficient ventilation systems with the maximum degree of utilization of heat of exhaust ventilation air.
In this case, it is necessary to pay special attention to the method of provision of inflow air to a classroom to provide a normalized difference between temperature of internal air and inflow air.We can realize this with a use of modern air distributors, for example [25][26][27], and when creating dynamic microclimate [28].

Conclusions
1. Comparison of the results of experimental studies and estimated values make us state that the actual mass flow of CО 2 in a classroom corresponds to the estimated value of 7.86 mg/s per person.
2. According to the results of field studies, we established that if the multiplication factor of air exchange is 1.0 1/h, СО 2 concentration is less than 1,000 ppm.Further increase in the multiplication factor of air exchange results in a slight decrease in СО 2 concentration.
3. Subjective monitoring of microclimate in classrooms made possible to assess a state of air environment at different air parameters and different duration of stay in a classroom.
4. We established that air exchange in the amount of 30 m 3 /h per person provides parameters of the microclimate close to the optimal ones in a classroom.The calculation methodology and the required volume of inflow air in the amount of 30 m 3 /h per person can serve as the basis for improvement of ventilation systems of school buildings.It will also be a prerequisite for obtaining a social effect in improvement of efficiency of learning for future generations.

Fig. 1 .Fig. 2 .
Fig. 1.Concentration of carbon dioxide measured in outside air in the central part of the city of Kosice (Slovakia)

Fig. 4 .
Fig. 4. Dependence of СО 2 concentration on СО 2 mass flow and time of measurements ("x" and "o" are the results of experimental measurements in Kosice and Lviv respectively)

Fig. 5 .
Fig. 5. Dependence of CO 2 concentration on time for various multiplication factors of air exchange

Table 4
Composition of air inhaled and exhaled by a healthy person

Table 5
Assessment of air quality in the class

Table 6
Calculated values of mass flow of carbon dioxide from one adult person

Table 7
Multiplication factor of air exchange due to leakage through building constructions

Table 8
Required multiplication factor of ventilation in a classroom

Table 9
Mandatory volume flow of inflow air in a class