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Today in addition to the design of structures, layout solutions, and the design of suitable materials, the modern construction industry also addresses meeting the requirements for the energy performance of a building, with which the topic of the quality of the indoor environment is fully intertwined. Comfort in the use of buildings, and especially the provision of thermal comfort, is a fundamental aspect in the design of technical equipment systems, where a properly selected system regulating the indoor environment can affect b oth t he e nergy p erformance o f t he building and the quality of the indoor environment. One of the important factors is the air quality, where the main factor that af-fects the indoor environment is the concentration of CO 2 , whose value affects the biological functions of the human organism. The subject of this research is an evaluation of the indoor air quality in a kindergarten because children are more sensitive to environmental influences.
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1
ANALYSIS OF INDOOR AIR QUALITY IN
AKINDERGARTEN
Petra STIBOROVA1*, Andrea BADUROVA1, Iveta SKOTNICOVA1
Address
1 Dept. of Building Environment and Building Services, Faculty of
Civil Engineering, VSB- Technical University of Ostrava, Ludvika
Podeste 1875/17, 708 00 Ostrava-Poruba, Czech Republic
*Corresponding author: petra.stiborova@vsb.cz
Abstract
Today in addition to the design of structures, layout solutions,
and the design of suitable materials, the modern construction
industry also addresses meeting the requirements for the energy
performance of a building, with which the topic of the quality of
the indoor environment is fully intertwined. Comfort in the use
of buildings, and especially the provision of thermal comfort, is
a fundamental aspect in the design of technical equipment sys-
tems, where a properly selected system regulating the indoor
environment can aect b oth t he e nergy p erformance o f t he
building and the quality of the indoor environment. One of the
important factors is the air quality, where the main factor that
af-fects the indoor environment is the concentration of CO2,
whose value affects the biological functions of the human
organism. The subject of this research is an evaluation of
the indoor air quality in a kindergarten because children are
more sensitive to environmental influences.
Key words
Indoor environment of a building,
Kindergarten,
Thermal comfort,
Carbon dioxide,
Ventilation,
1 INTRODUcTION
People spend most of their time, i.e., up to 90 %, in build-
ings. Therefore, the quality of the indoor environment in
buildings should be one of the most important parameters in
building design. Therefore, when implementing measures to
reduce the energy performance of buildings and when build-
ing new buildings, the quality of the indoor environment
should not be neglected in addition to the energy performance
requirements. Alongside health care facilities, buildings for
the education of children and young people are the most
monitored buildings in this regard. Therefore, in these build-
ings, compliance with CO2 limits is stressed (Bogdanovica
et al., 2020), of course, together with other monitored vari-
ables such as the indoor air temperature and relative humid-
ity (Coggins et al., 2022). The issue of indoor environmen-
tal quality is mainly addressed in primary school buildings,
where air quality measurements are carried out within the
framework of professional publications (Skotnicova et al.,
2019) (Talukdar et al., 2020), including proposed measures
leading to their improvement. However, few measures are
devoted to kindergarten buildings, where it is also important
to monitor compliance with the relevant parameters, given
the sensitive organisms of preschool children.
2 INDOOR ENVIRONMENTAL QUALITY
An optimal indoor microclimate is a prerequisite for the
well-being and health of its inhabitants. It is important to note
that the concept of an optimal microclimate can be a very sub-
jective assessment, unless we talk about it only in terms of
standard requirements (Coggins et al., 2022). Thermal comfort
is closely related to an optimal microclimate. Thermal comfort
in an indoor environment is one of the fundamental factors
that inuence the quality of an indoor environment and make
Vol. 31, 2023, No. 2, 1 – 8
DOI: 10.2478/sjce-2023-0007
© 2023 The Author(s). This is an open access article licensed under the Creative Commons Attribution
4 .0 License (https://creativecommons.org/licenses/by/4.0/)
Heat demand.
ANALYSIS OF INDOOR AIR QUALITY IN AKINDERGARTEN2
Slovak Journal of Civil Engineering Vol. 31, 2023, No. 2, 1 – 8
a signicant contribution to the satisfaction of the occupants
(Talukdar et al., 2020). Thermal comfort means that thermal
conditions are achieved where a person is neither too cold nor
too warm and therefore feels comfortable. A person feels best
in a climate range of 20 to 22°C and 40 to 60% relative hu-
midity. Climatic conditions outside this range are perceived by
most people as uncomfortable (McGill et al., 2015). The tem-
perature and humidity are essential factors that inuence the
optimal microclimate. Both variables are inuenced by the pa-
rameters of the external environment and can be controlled in
a targeted manner. The basic prerequisite is the correct design
of the thermal engineering properties of the building structures
that enclose the interior space of the building under consider-
ation and form the envelope of the building. Compliance with
the building envelope level is part of the requirements for the
energy performance of buildings.
In terms of air temperature, it is also necessary that the
heating system is designed to achieve the design indoor tem-
peratures in individual rooms in the winter period, at the same
time, eective regulation is necessary to avoid overheating. In
the summer, there should be no unwanted overheating of the
interior spaces (Cihelka, 1976).
In addition to the standard requirements for the tempera-
ture, humidity, and ventilation, one of the main indicators of
air quality is the concentration of carbon dioxide (CO2), whose
value informs the quality of the ventilation of the indoor space.
It is expressed in ppm units (parts-per-million). The ppm units
means the number of volumetric units of CO2 in one million
volumetric units of air. In an outdoor environment, the CO2
concentration is approximately 0.04 %, that is, 400 ppm. In
terms of hygiene standards, the Czech Decree No. 20/2012
Coll., provides as follows: “Residential rooms must have su-
cient natural or mechanical ventilation and be adequately heat-
ed with the possibility of regulating the internal temperature.
For ventilation of living rooms, a minimum amount of outdoor
air exchange of 25 m3/h per person or a minimum ventilation
rate of 0.5 1/h shall be ensured during the stay of the persons.
Carbon dioxide CO2 shall be used as an indicator of the quality
of the indoor environment and shall not exceed a concentration
of 1500 ppm in the indoor air.” In addition to CO2, indoor air
can also contain other pollutants such as formaldehyde, car-
bon monoxide, VOCs, radon, asbestos, dust particles, odours,
and microorganisms. Proper ventilation of the building will,
of course, ensure that the concentration of these substances is
also reduced.
The requirements for ventilation and microclimatic con-
dition parameters that apply to the premises and operation of
facilities and establishments for the education and training of
children and adolescents are specied in the Czech Decree No.
410/2005 Coll. In the current version of the Czech Decree No.
410/2005 Coll. dated 22th October 2022, the amount of the
fresh air supply in classrooms has been reduced from 30 m3/h
per pupil to 20 m3/h per pupil.
3 EXPERIMENTAL MEASUREMENT
3.1 Subject of the measurement
The subject of the measurement is a single-storey kinder-
garten building. The oor plan is L-shaped with dimensions of
approximately 40 x 20 m, and the built-up area is 598 m2. The
building lacks a basement and has a at roof. It has been in
operation since 2013. In terms of layout, the kindergarten is di-
vided into three separate units consisting of three departments
according to the age of the children and the related facilities
for these departments. The total capacity of the kindergarten is
60 children. Each department has a separate entrance from the
exterior. A separate terrace is adjacent to the day rooms of each
department, which is accessible through French windows. The
heating of the building is handled using a block heat transfer
station located in the technical room of the building, which is
connected to the central heating system. The heating surfaces
in the building are panel heating and underoor heating. There
is an air handling unit installed in the building, which provides
ventilation for areas without any natural ventilation through
windows. The children’s day rooms are ventilated by windows
that open.
Tab. 1 Eect of CO2 concentration on the human body
Concentration CO2 (ppm) Evaluation and eect of CO2 concentration
350-500 normal outdoor concentration
500 - 800 high level of healthy indoor environment
800 – 1,000 acceptable level of healthy indoor environment
1,000 recommended value
1,000 – 1,500 complaints of odours, feeling of heavy (foul) air, slight fatigue
1,500 limit value – Decree no. 268/2009 Coll.
1,500 – 2,500 decrease in concentration, fatigue
2,500 – 5,000 dullness, fatigue, possible health problems
>5,000 nausea, increased heart rate
>15,000 breathing diculties
>40,000 possible loss of consciousness
ANALYSIS OF INDOOR AIR QUALITY IN AKINDERGARTEN 3
Slovak Journal of Civil Engineering Vol. 31, 2023, No. 2, 1 – 8
3.2 Method
A classroom attended by 24 children aged 5 to 6 years was
selected for the measurements. Class occupancy is from Mon-
days to Fridays from 7:30 am to 5:00 pm. It is a rectangular
room with dimensions of 19 x 5.8 m and a oor area of 109 m2.
The room has three outer walls, the longest of which is orient-
ed towards the southwest. The ventilation of the classroom is
provided naturally by opening the windows. The windows are
tted with external blinds. For ventilation in the summer and
also in the winter, the possibility of fully opening the French
window leading to the terrace is used. Heat and humidity sen-
sors and CO2 sensors were placed in the classroom. Given the
shape of the room and the division of the room into two halves,
i.e. a dining and working area with tables, and a play and re-
laxation area, two measuring points were created to measure
the necessary quantities as realistically as possible (see Fig. 2).
The values were recorded every 15 minutes on data loggers.
The data logger is an appliance that allows the connection of up
to four measurement inputs. It is equipped with an LCD display
and a keyboard. The display shows the current values of the
measured parameters, and it is also possible to enable storage
of the data into the memory of the data logger. Sensors and a
data logger from Ahlborn were used for the measurements.
Apart from the actual measurements, the number of chil-
dren present and the activities performed within the schedule
were recorded on a daily basis using the sensors, e.g., rest-
ing activity (drawing, independent play, etc.), physical activ-
ity (exercise, movement games, etc.), and being in the gar-
den (without the presence of children in the measured area).
In addition, the frequency of the ventilation of the space was
also recorded. For completeness, the outdoor environment pa-
rameters were measured using a professional weather station
installed on the roof of the building. Measurements were tak-
en every week from Monday to Sunday in the summer period
(June), the transition period (October), and the winter period
(November), when the heating season had already started, and
expected cooling had occurred.
3.3 Results
Through the experimental measurements, it was found that
the CO2 concentrations in June, i.e., in the summer, were in
the range of 350-500 ppm, i.e., they reached the same level as
the CO2 concentration in the outdoor environment. The mea-
surements carried out in the months of October and November
indicated that CO2 concentrations in the area addressed were
in a range of 400-1400 ppm. Fig. 3 shows the course of the
CO2 concentration for a week in the month of October. It is
obvious that there are significant fluctuations in values, which
are caused by the diverse physical activity of the children and
Fig. 1 Aerial photo of the kindergarten
Fig. 2 Layout of the classroom
ANALYSIS OF INDOOR AIR QUALITY IN AKINDERGARTEN4
Slovak Journal of Civil Engineering Vol. 31, 2023, No. 2, 1 – 8
their presence in the classroom or in the garden. As expected,
the highest concentration values were mainly in the morning
during physical activity.
Fig. 4 shows the course of the internal temperature and rel-
ative air humidity during the period evaluated. It is evident that
the values measured of the internal temperature are outside the
optimal range from the point of view of the assessment of ther-
mal comfort. This graph also records the course of the outdoor
air temperature, which aects the indoor air temperature and
the frequency of ventilation.
Fig. 3 Graph of the CO2 concentration during the week (October)
Fig. 4 Graph of the temperature and humidity during the week (October)
Fig. 5 Graph of the CO2 concentration during the week (November)
ANALYSIS OF INDOOR AIR QUALITY IN AKINDERGARTEN 5
Slovak Journal of Civil Engineering Vol. 31, 2023, No. 2, 1 – 8
The activity record during the measurement shows that
ventilation was provided throughout the day by opening two
hinged windows. In the case of higher outdoor temperatures,
the doors to the terrace were also opened. Fig. 4 shows that
on Thursday and Friday, the outdoor temperatures were lower.
At the same time, it follows from the activity records on these
days that the frequency of ventilation through the door to the
terrace was not the same as on other days in this period. There-
fore, the measured concentrations exceeded the 1000 ppm lim-
it, which is not a limit value, but a recommended value.
From the point of view of the marginal conditions of the
measurements, the month of October 2022 was above aver-
age in terms of temperature; as shown in Fig. 4, temperatures
reached up to 20 °C at the beginning of the week measured.
The experimental measurements were repeated in the month
of November, when expected cooling had already occurred
and the supply of heat to the building under consideration had
begun. It can be seen in Fig. 5 that the measured values of
CO2 were higher than the previous measurement and that the
recommended level of the CO2 concentration was exceeded 4
times. This was due to a decrease in the frequency of ventila-
tion of the space due to lower outdoor temperatures, as is clear
from Fig. 6.
4 ENSURING INDOOR AIR QUALITY
One of the main indicators of air quality is the concentra-
tion of carbon dioxide (CO2), the value of which indicates the
quality of the indoor ventilation (Wallace et al., 2002). The
most common and simplest method of ventilation is natural
ventilation, in which the indoor air with a higher carbon di-
oxide concentration is exchanged for outdoor air with a lower
carbon dioxide concentration. However, this may not be the
case in locations that are aected by increased trac in the
vicinity. In the past, inltration through leaks in window joints
was sucient to provide the necessary room air exchange,
with an exchange rate of 2 to 4 times the room’s air per hour
(Cardoso et al.,2020). Today, when new buildings are con-
structed or existing window openings are replaced with new
high-leakage window openings, the air exchange rate drops
below 0.5 times the room volume per hour. It is also important
Fig. 6 Graph of the temperature and humidity during the week (November)
to note that with natural ventilation through window openings,
it is not possible to control the air exchange rate according to
the actual state of the indoor environment. In this case, the fre-
quency and length of the ventilation is completely dependent
on the person who can quickly acclimatize in the environment.
Acclimatisation refers to the process by which occupants who
have been in a room for some time become less sensitive to
contamination of the indoor microclimate by odours, so that
the unsatisfactory quality of the indoor environment is always
best assessed by a newly arrived person. Therefore, provid-
ing sucient ventilation through the windows is problematic
unless the space is tted with sensors to measure the indoor
environmental quality.
If a room is designed to be naturally ventilated through
windows, the room should be equipped with sensors to mea-
sure indoor air quality, that is, sensors for the concentration of
CO2 or other pollutants such as volatile organic compounds
(VOC) (Ahn et al., 2022). Temperature and relative humidi-
ty sensors are also suitable for monitoring thermal comfort.
Based on the CO2 concentration value and when a set limit
is exceeded, the measuring instrument will be signalled, e.g.,
by illuminating a light, and the windows should be kept open
for a certain period of time, e.g., 10 minutes. In the case of a
building with intelligent control, the windows (or vents) will
automatically open, and the windows will close when the CO2
concentration falls below the set level. However, the disadvan-
tage of natural ventilation is that heat is removed along with
exhaust air in the winter. The heat loss through this ventilation
must be covered by the heating system, resulting in an increase
in the heating demands and the design of a heat source with a
higher rated capacity. In addition, natural ventilation can cause
thermal discomfort due to cold air entering the room in the
winter.
The second way to maintain the quality of an indoor en-
vironment is to design a forced ventilation system. Ventila-
tion in this case can be designed for a constant air ow rate,
whose value is set by legislation or, even better, based on the
measured CO2 concentration using sensors. Forced ventilation
operates automatically for the duration of a building’s oper-
ation according to the requirements set and, where appropri-
ate, a time schedule. The forced ventilation system should be
supplemented by the installation of heat recovery equipment.
ANALYSIS OF INDOOR AIR QUALITY IN AKINDERGARTEN6
Slovak Journal of Civil Engineering Vol. 31, 2023, No. 2, 1 – 8
This transfers the heat from the exhaust air to the fresh air
supplied to the interior. In this case, the energy consumption
of the ventilation is reduced. Forced ventilation can be de-
signed to be central for a whole building or local for a room
or group of rooms. A local ventilation system is particularly
suitable for existing buildings, e.g., typically for classrooms in
school buildings, where a separate ventilation unit is designed
for each classroom located directly in the space to be designed.
A comparison of the dierent ventilation methods in terms
of energy demands and ventilation costs can be shown by the
example of the class that was the subject of the experimental
measurements described in Section 3. The air volume of the
classroom is 327 m3. The capacity of the classroom is for 24
children. According to current legislation in the Czech Repub-
lic (Decree No. 20/2012 Coll.), the amount of the air supply
should be 20 m3/h per pupil. Therefore, the total amount of the
air supply required for the classroom is 520 m3/h. If we want
to evaluate the energy consumption of the ventilation, it is nec-
essary to consider the heat demands for ventilation throughout
the heating period. On site, the design outdoor air temperature
in winter is -15 °C; the average outdoor air temperature in the
heating period is 4 °C; and the number of heating days is 229.
Therefore, for the heating period there are 1554 hours of oper-
ation of the building, corresponding to the number of the oper-
ating hours of the ventilation and a total volume of 808,080m3
of the fresh air supply.
In order to determine the energy demands, it is necessary to
know the heat loss through ventilation. According to CSN EN
12831-1 (2018) and CSN EN ISO 52016-1 (2019), the design
ventilation heat loss for a heated space is calculated by the
following equation:
(W) (1)
where HV, i is the design ventilation loss factor (W/K); is
the design indoor temperature in the heated space (°C); and
is the design outdoor temperature (°C). The design ventilation
loss factor is expressed by the mathematical formula below:
(W/K) (2)
where Vi is the air exchange in the heated space (m3/h); ρ is the
air density by θint,i (kg/m3); and cp is the specic heat capacity
(Wh/kg.K). When natural ventilation is designed in the heating
space, the value of the air exchange in this space is at a maxi-
mum, i.e., the air exchange by inltration or the minimum air
exchange required for hygiene reasons. For a structure with a
very tight building envelope, the air exchange value required
for hygienic reasons, which is given in the Czech Decree No.
410/2005 Coll., is considered. Based on the mathematical re-
lationships mentioned above (1)(2), the heat loss through the
ventilation of the design for the class under consideration is
6.05 kW.
Calculating the heat demands for heating and ventilation
can be performed in several ways with dierent degrees of
accuracy, and the value of the heat demands for heating can
vary depending on the method used and the parameters chosen
(CSN EN ISO 52016-1, 2019). The choice of specic parame-
ters and the calculation method also depends on the purpose of
the calculations. At the conceptual design stage, without any
knowledge of the detailed building design, the grad-day meth-
od can be used, which is based on a single-zone quasi-station-
ary model with an annual time step. The grad-day method is
based on the heat loss of the building and the climatic data of
the building site and considers the factors of limited night-time
operation, building accumulation, and the noncontemporane-
ity of the heat loss by transmission and inltration. If the heat
loss through natural ventilation is covered by the heat source
for heating, then the annual heat demand is calculated using
this method according to the following equation:
(3)
where ΦHL is the heat loss of the structure (kW); ε is the correc-
tion factor for the temperature reduction, shortening the heat-
ing time, and non-simultaneity of heat loss through ventilation
and heat transfer (-); D is the number of grad-days (K.day);
θis is the average calculated internal temperature (°C); and θe
is the external temperature calculated (°C). If only the heat
demand for natural ventilation is calculated, then instead of
the structure’s heat loss ΦHL , the value of the heat loss through
ventilation is substituted for by ΦV,i . A crucial parameter that
signicantly aects the resulting value of the energy demands
for ventilation is the number of grad-days. Unlike heating,
which mostly operates continuously during the heating period,
depending on the type of building operation, the ventilation
system may only operate for a few hours a day, depending
on the presence of the occupants. Therefore, it is important
to correctly determine the number of operating hours of the
ventilation system during the heating period. According to re-
lation (3), the heat demand for ventilation for the class is 3961
kWh/a, i.e., 14.3 GJ/a.
In the Czech Republic, the cost per 1 GJ of heat to cover
the heating needs of the building in 2021 was € 18. With the
current increase in energy prices, the cost may increase to € 83
per 1 GJ in 2023. On this basis, the cost to cover the annual
heating needs for ventilation may be up to € 1,187 in 2023. If a
forced ventilation system with a heat recovery eciency of 60
% (minimum seasonal heat recovery eciency) is installed in
the building, the cost of the annual heat demand for ventilation
would be € 475. This means an annual savings of up to € 712.
The purchase cost of an air handling unit with heat recovery
for the class to be addressed ranges from € 4,149 to € 7,469.
The simple return on the investment is 6-11 years. If we were
to consider the realistically achievable eciency of the heat
recovery to be around 80%, then it is possible to achieve a
payback of up to 4 years.
In this context, it should also be mentioned that, in addition
to the proven energy savings in ventilation, a forced ventila-
tion system is comfortable and requires minimal maintenance,
which means regular replacement of the air lters, the frequen-
cy of which depends on the level of outdoor pollution and the
type of operation of the building. This is also related to a pos-
sible need to clean the air ducts.
5 DIScUSSION
Our research shows that the limit value of the CO2 con-
centration, which is the main indicator in the assessment of
ANALYSIS OF INDOOR AIR QUALITY IN AKINDERGARTEN 7
Slovak Journal of Civil Engineering Vol. 31, 2023, No. 2, 1 – 8
indoor air quality, is not exceeded in the class evaluated. The
measured values exceed the recommended concentration lev-
el only exceptionally. However, it should be mentioned that
although the measurements took place during the heating sea-
son, they were performed during the period when the outdoor
temperatures had not yet fallen below freezing. From the point
of view of thermal comfort, it could be said that the internal
temperature of the interior is outside the optimal range. This
can be caused by the improper regulation of the heating sys-
tem or an inappropriate overheating of the space being treated
above the design value of the indoor air temperature given by
the relevant regulations. As already mentioned, the assessment
of thermal comfort is very subjective. However, it was found
that precisely based on higher values of internal air tempera-
tures and the feeling of the air exhaled, targeted ventilation
of a window takes place, which subsequently contributes to
reducing the concentration of CO2 and ensuring the good air
quality of the internal environment. For this reason, the mea-
sured CO2 values are above any low expectation. Natural ven-
tilation is uneconomical from the point of view of an energy
building in the winter and leads to an increase in the heat de-
mand for heating.
We must not forget, however, the eect of natural ventila-
tion on the human mind. Natural ventilation is a daily repetitive
activity in which our sensory experiences, smells coming from
outside, the feeling of comfort, and the pleasure of a breeze play
a major role. On the other hand, we remove odours from the in-
terior that are unpleasant to us. According to (Hauge, 2012), it
is known that natural ventilation is a part of practical, aesthet-
ic, and social needs, in the sense of caring for other occupants
of a building. Furthermore, natural ventilation is especially
important in the so-called transition period when people adapt
to a change of season. Natural ventilation in this period induc-
es a feeling of freedom. Moreover, in the transition period, the
outdoor air temperatures are high enough, and there is no lon-
ger a signicant increase in the building’s energy eciency.
If we would like to combine the advantages of both systems,
we can recommend the use of forced ventilation with heat
recovery in the winter and natural ventilation in the interim
period, which could support the good mental state of the oc-
cupants.
6 cONcLUSION
The purpose of this article was to point out the importance
of monitoring and maintaining the quality of the indoor en-
vironment in buildings, as it has a direct impact on human
health. The basis for the evaluation of the internal environment
of the selected kindergarten was the measured values, which
did not signicantly exceed the recommended values. Howev-
er, they demonstrated how important ventilation is to ensure
high indoor air quality. Furthermore, the article proved that
by using forced ventilation with heat recovery, it is possible
to reduce the energy demand of the building, especially within
the framework of the need of ventilation for heat.
Acknowledgment
The work was supported by funds by Student Grant
Competition of the Technical University of Ostrava, Grant
No. SP2022/117, allocated to VSB–Technical University of
Ostrava by the Ministry of Education, Youth and Sports of the
Czech Republic.
ANALYSIS OF INDOOR AIR QUALITY IN AKINDERGARTEN8
Slovak Journal of Civil Engineering Vol. 31, 2023, No. 2, 1 – 8
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Slovak Journal of Civil Engineering
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