Indoor Air Quality in School Classrooms with Mechanical Ventilation ...

SHB2012 - 7th International Symposium on Sustainable Healthy Buildings, Seoul, Korea
18 May 2012
Indoor Air Quality in School Classrooms with Mechanical
Ventilation Systems
Jong Ryeul Sohn 1 , Hyeun Jun Moon 2* , Seung Ho Ryu 2 , Taeyon Hwang 3
1 Department of Environmental Health, Korea University, Seoul 136-703, Korea
2 Department of Architectural Engineering, Dankook University, Yongin, 448-701, Korea
3 Technology Research Center, Samsung C&T Corporation, Seoul 137-857, Korea
* Corresponding author: H.J. Moon (hmoon@dankook.ac.kr)
Abstract
In modern society, people spend more than 90% of their time indoors; good indoor air quality
is very important to us. Poor indoor air quality can cause many adverse health effects such as
respiratory symptoms, asthma, especially for children. Thus, indoor air quality of schools is
important since children are susceptible to indoor pollutants, including airborne particles,
volatile organic compounds, etc. Indoor air problems can increase the chance of long-term
and short-term health problems for students and teachers in terms of comfort and productivity.
One of the strategies to maintain indoor air quality in buildings is to use mechanical
ventilation systems. Investigation of indoor air quality in classrooms helps us to characterize
pollutant levels and effects of ventilation systems.
In this study, three classrooms, two laboratories and one computer classroom at three
different schools in Korea were chosen for investigation of indoor air quality with mechanical
ventilation systems. Measurements were conducted for particulate matter (PM 10 ),
formaldehyde (HCHO), total volatile organic compounds (TVOC), carbon monoxide (CO),
carbon dioxide (CO 2 ), nitrogen dioxide (NO 2 ), ozone (O 3 ), radon, and total bacteria counts.
Differences in indoor pollutants concentrations with and without operation of ventilation
systems in each classroom were analyzed. Operation of ventilation systems could decrease
the levels of indoor pollutants in the classrooms, especially showing the reduction of TVOC
concentrations by 26.3–64.4 %.
Keywords: Indoor air quality, School buildings, Ventilation systems, Field measurement
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SHB2012 - 7th International Symposium on Sustainable Healthy Buildings, Seoul, Korea
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1. Introduction
In modern society, people spend more than 90% of their time indoors; good indoor air quality
is very important to us [1]. Poor indoor air quality can cause many adverse health effects such
as respiratory symptoms, asthma [2-4]. School children spend about 6–8h per weekday in
classrooms, which is the second most time-spent indoor environment after homes [5].
Moreover children are more susceptible to indoor pollutants, including airborne particles,
volatile organic compounds since their organs are in developing stage and they breathe more
air relative to their body size than adults [6, 7]. Thus, good indoor air quality should be
maintained in schools for children’s health. Several studies have reported that the indoor air
problems can increase the chance of long-term and short-term health problems for students
and teachers in terms of comfort and productivity [8-10].
Several studies have been conducted during the past decades to investigate the indoor air
quality in school classrooms. Chitra and Nagendra [5] have investigated indoor air quality
parameters in a naturally ventilated school building located near an urban roadway in India.
This study reported that the mean value of indoor PM 10 , PM 2.5 , PM 1 and CO concentrations
were found to be 149 ± 69, 61 ± 29, 43 ± 24, 0.10 ± 0.18 and 95 ± 61, 32 ± 16, 18 ± 9 µg/m 3 ,
0.11 ± 0.14 ppm, respectively for winter and summer seasons. Norback et al. [11] have
studied the relationship between VOCs, respirable dust, and personal factors to prevalence
and incidence of sick building syndrome in six primary schools. They reported that the
average CO 2 concentrations in all sites were greater than 800 ppm and indicated inadequate
ventilation. Lee and Chang [12] investigated IAQ of five classrooms in Hong Kong. This
study showed that the average respirable suspended particulate matter (RSPM) concentrations
were higher than the Hong Kong air quality objective (annual average, 55 µg/m 3 ) and the
maximum indoor PM 10 level exceeded 1000 µg/m 3 . Yang et al. [13] characterized the
concentrations of different indoor air pollutants within Korean schools and to compare their
indoor levels within schools according to the age of school buildings. The I/O ratio for
HCHO was 6.32 during the autumn, and the indoor HCHO concentrations (mean=0.16 ppm)
in schools constructed within 1 year were significantly higher than the Korean Indoor Air
Standard, indicating that schools have indoor sources of HCHO. Fromme et al. [14] evaluated
indoor air quality in 64 schools in the city of Munich and a neighboring district outside the
city boundary. They reported that the median indoor CO 2 concentration in a classroom was
1603 ppm in winter and 405 ppm in summer. A median PM 2.5 concentrations of 19.8 µg/m 3
and PM 10 =91.5 µg/m 3 were observed during winter period. In summer, a reduced PM
concentrations were reported (median PM 2.5 =12.7 µg/m 3 , median PM 10 =64.9 µg/m 3 ).
One of the strategies to maintain good indoor air quality in buildings is to use mechanical
ventilation systems. Adequate ventilation systems should not only provide thermal comfort
but also distribute fresh air to occupants and remove pollutants. This study aims to investigate
the indoor pollutant levels in school classrooms according to the operation of mechanical
ventilation system. Differences in indoor pollutants concentrations with and without
operation of mechanical ventilation systems in each classroom are analyzed. Investigation of
indoor air quality in classrooms helps us to characterize pollutant levels and effects of
ventilation systems.
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SHB2012 - 7th International Symposium on Sustainable Healthy Buildings, Seoul, Korea
18 May 2012
2. Methodology
2.1 Description of the selected school buildings
A field study was conducted in three classrooms, two laboratories and one computer room
with mechanical ventilation systems in three different schools located in Seoul, Korea. Two
schools of selected buildings were newly constructed and the other school was constructed
seven years ago. Detailed description of the selected school buildings is shown in Table 1.
Encased energy recovery ventilation systems were installed in all selected classrooms, as
shown Figure 1. The measurements were taken in two different ventilation operation modes
(before and after operation of ventilation system), with the aim of investing the effect of
ventilation system on the indoor air pollutants concentrations.
Table 1. Description of the selected school buildings and classrooms
Target buildings Construction years Selected classrooms
School A 7 years Classroom (AC1), Laboratory (AL1)
School B
Under 2 years
Classroom (BC1), Classroom (BC2),
Laboratory (BL1)
School C Under 2 years Computer room (CP1)
Fig 1. Ventilation systems in selected classrooms
2.2 Measurement of the indoor air pollutants
One-day indoor air quality investigations at each school were performed. The indoor
pollutants were monitored for particle matter (PM 10 ), Carbon monoxide (CO), Carbon
dioxide (CO 2 ), Nitrogen dioxide (NO 2 ), Ozone (O 3 ), Radon (Rn), total bacteria count,
Formaldehyde (HCHO) and Volatile Organic Compounds (VOCs). Indoor air temperature
and relative humidity were also monitored during the field measurement. Sampling
equipment was placed at 1.5 m above floor level. The measuring equipment and
experimentation are presented in Figure 2.
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SHB2012 - 7th International Symposium on Sustainable Healthy Buildings, Seoul, Korea
18 May 2012
Fig 2. Indoor air pollutants measurement in the selected school
Measurement methods for each indoor pollutant were referred to the indoor air quality
control in public use facilities, an act provided by the Ministry of Environment, Korea [15],
as shown in Table 2. PM 10 samples were collected on a pall flex membrane filter using Mini
Volume air sampler. CO and CO 2 were measured by means of a non-dispersive infrared
(NDIR) analyzer (CO Analyzer 300E and CD 98 Plus). NO 2 was measured by means of a
chemiluminescence analyzer (NO 2 Analyzer 200E). O 3 was measured by means of an
ultraviolet photometric analyzer (O 3 Analyzer 400E). Radon was measured based on
continuous radon monitoring method using the RAD7. The sampling method employed for
the total bacteria count was a MAS impactor, which used the centrifugal impaction principle.
HCHO was collected by pulling air through a 2,4-DNPH cartridge (MP-∑100). The DNPH-
HCHO derivative eluted with acetonitrile was determined by a reverse-phase highperformance
liquid chromatography (HPLC). TVOCs’ samples were collected using Tenax-
TA tubes, which were analyzed by gas chromatography with flame ionization detection and a
modified thermal desorption cold trap injector.
Table 2. Main measurement method for indoor pollutants in Korea standard [15]
Pollutants
Particle matter
Carbon monoxide
Carbon dioxide
Nitrogen dioxide
Ozone
Radon
Total bacteria count
Formaldehyde
Volatile organic compounds
Measurement method
Mini volume air sampling method
Non-dispersive infrared method
Non-dispersive infrared method
Chemiluminescence method
Ultraviolet photometric method
Continuous monitoring method
Centrifugal impaction method
2,4-DNPH cartridge method
Solid phase adsorption thermal desorption method
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SHB2012 - 7th International Symposium on Sustainable Healthy Buildings, Seoul, Korea
18 May 2012
3. Results and discussions
3.1 Indoor air quality in school A according to ventilation mode
A field study in school A was conducted in a class room (AC1) and a laboratory (AL1).
Indoor air pollutants levels in AC1 were monitored while the classroom was unoccupied.
Indoor air pollutants levels in AL1 were monitored while the 30 students were sitting in AL1.
The measurements were conducted before and after the operation of ventilation system while
an air-conditioner system was not operated. Table 3 shows the level of indoor air pollutants
measured at school A according to operation of mechanical ventilation system.
T
(°C)
RH
(%)
PM 10
(µg/m 3 )
CO
(ppm)
CO 2
(ppm)
NO 2
(ppb)
O 3
Table 3. Concentrations of indoor air pollutants measured in AC1 and AL1
AC1 AL1
Standard * Before the After the Before the After the
operation of vent. operation of vent. operation of vent. operation of vent.
– 23.2 22.5 25.0 24.6
– 34.5 31.1 36.8 35.3
100 33.3 16.7 88.0 41.7
10 0.03 0.03 0.10 0.10
1000 519 467 527 475
50 26.5 23.7 26.9 24.0
(ppb)
60 N.D. ** N.D. N.D. N.D.
Rn
(pCi/l)
4.0 0.5 0.3 0.1 0.2
TBC
(CFU/m 3 )
800 150 40 200 170
HCHO
(µg/m 3 )
100 52.8 19.9 80.2 30.2
TVOC
(µg/m 3 )
400 189.4 101.4 831.7 295.7
*
Korean Indoor Air Standard (KIAS) [15]
**
Not detected
3.2 Indoor air quality in school B according to ventilation mode
A field study in school B was conducted in two classrooms (BC1 and BC2) and a laboratory
(BL1). Indoor air pollutants levels in BC1, BC2 and BL1 were monitored while the
classroom was unoccupied. The measurements in BC1 and BC2 were conducted before and
after the operation of ventilation system while air-conditioner system was turned on. The
measurements in BL1 were conducted before and after the operation of ventilation system
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SHB2012 - 7th International Symposium on Sustainable Healthy Buildings, Seoul, Korea
18 May 2012
while air-conditioner system did not operated. In case of the school B, measurement of the
indoor pollutants were focused on particle matter (PM 10 ), carbon dioxide (CO 2 ),
formaldehyde (HCHO) and volatile organic compounds (VOCs) excluding other pollutants
since other pollutants were measured significantly lower from pre-test. Table 4–6 show the
level of indoor air pollutants measured at school B according to operation of mechanical
ventilation system.
Table 4. Concentrations of indoor air pollutants measured in BC1
Standard
BC1
Before the operation of vent. After the operation of vent.
T (°C) – 21.7 21.8
RH (%) – 30.9 26.3
PM 10 (µg/m 3 ) 100 75.7 65.2
CO 2 (ppm) 1000 470 350
HCHO (µg/m 3 ) 100 43.0 34.0
TVOC (µg/m 3 ) 400 360.0 205.5
Table 5. Concentrations of indoor air pollutants measured in BC2
Standard
BC2
Before the operation of vent. After the operation of vent.
T (°C) – 23.2 22.3
RH (%) – 24.1 15.7
PM 10 (µg/m 3 ) 100 87.5 25.0
CO 2 (ppm) 1000 510 360
HCHO (µg/m 3 ) 100 32.7 27.7
TVOC (µg/m 3 ) 400 259.4 191.3
Table 6. Concentrations of indoor air pollutants measured in BL1
Standard
BL1
Before the operation of vent. After the operation of vent.
T (°C) – 12.9 10.2
RH (%) – 39.6 32.1
PM 10 (µg/m 3 ) 100 90.1 59.7
CO 2 (ppm) 1000 600 410
HCHO (µg/m 3 ) 100 60.4 42.1
TVOC (µg/m 3 ) 400 320.0 203.9
3.3 Indoor air quality in school C according to ventilation mode
A field study in school C was conducted in a computer room (CP1). Indoor air pollutants
levels in CP1 were calculated using data obtained while the 20 students were sitting in the
CP1. The measurements were conducted before and after the operation of ventilation system
while air-conditioner system was turned on. In case of the CP1, measurement of the indoor
pollutants were focused on particle matter (PM 10 ), carbon dioxide (CO 2 ), formaldehyde
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SHB2012 - 7th International Symposium on Sustainable Healthy Buildings, Seoul, Korea
18 May 2012
(HCHO) and volatile organic compounds (VOCs). Table 7 shows the level of indoor air
pollutants measured at school C according to operation of mechanical ventilation system.
Table 7. Concentrations of indoor air pollutants measured in CP1
Standard
CP1
Before the operation of vent. After the operation of vent.
T (°C) – 23.6 23.4
RH (%) – 23.9 20.7
PM 10 (µg/m 3 ) 100 85.9 59.2
CO 2 (ppm) 1000 660 450
HCHO (µg/m 3 ) 100 48.3 40.7
TVOC (µg/m 3 ) 400 123.5 56.0
3.4 Indoor air pollutants levels by operation of the mechanical ventilation system
Our results clearly showed that indoor air pollutants’ level after operation of the ventilation
system were lower than before operation of the ventilation system, as shown in Figure 3. These
results could be explained by the adequate ventilation by means of a mechanical ventilation
system. The mean of decreasing rates of indoor PM 10 concentrations were 51.2 %, 39.7 % and
31.1 % in the school A, school B and school C, respectively.
Fig 3. PM 10 , CO 2 , HCHO and TVOC concentrations in classrooms according to operation of
the mechanical ventilation system
The mean of decreasing rates of indoor CO 2 concentrations were 9.9 %, 28.9 % and 31.8 % in
the school A, school B and school C, respectively. The mean of decreasing rates of indoor
HCHO concentrations were 62.3 %, 22.2 % and 15.7 % in the school A, school B and school C,
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SHB2012 - 7th International Symposium on Sustainable Healthy Buildings, Seoul, Korea
18 May 2012
respectively. The mean of decreasing rates of indoor TVOC concentrations were 55.5 %, 35.2 %
and 54.7 % in the school A, school B and school C, respectively. There were slight differences
between the decreasing rates of each school buildings. An explanation might be the difference of
mechanical system in each school buildings, number of occupants, operation of air-conditioners
and location of diffusers. The efficiencies of the ventilation systems in the classrooms are
discussed a separate paper.
The indoor air concentrations of all measured pollutants after operation of ventilation system
in the selected school buildings complied with the Korean Indoor Air Standard, although
measurements were conducted for one-day only. The mean of the PM 10 were 51.2, 39.7 and
31.1 µg/m 3 in the school A, B and C, respectively. The mean of the CO 2 were 417, 373 and
450 ppm in the school A, B and C, respectively. The mean of the HCHO were 25.1, 34.6 and
40.7 µg/m 3 in the school A, B and C, respectively. The mean of the TVOC were 198.6, 200.2
and 56.0 µg/m 3 in the school A, B and C, respectively.
4. Conclusions
The indoor air quality parameters (PM 10 , CO, CO 2 , NO 2 , O 3 , Rn, TBC, HCHO and TVOC)
were measured in three different schools with mechanical ventilation system. The results had
shown remarkable difference in indoor air pollutants’ level according to the operation of
mechanical ventilation system. Operation of ventilation systems could decrease the levels of
indoor pollutants in the all selected classrooms. The mean of concentrations and decreasing
rates of indoor PM 10 were 44.6 µg/m 3 and 41.2 % in the selected schools, respectively. The
mean of concentrations and decreasing rates of indoor CO 2 were 418.7 ppm and 23.1 % in the
selected schools, respectively. The mean of concentrations and decreasing rates of indoor
HCHO were 32.4 µg/m 3 and 34.5 % in selected schools, respectively. The mean of
concentrations and decreasing rates of indoor TVOC was 175.6 µg/m 3 and 45.2 % in the
selected schools, respectively. Therefore, increasing the ventilation rate by means of a
mechanical ventilation system can play key roles in improving the indoor air quality within
schools.
Acknowledgements
This work was supported by the National Research Foundation of Korea (NRF) grant funded
by the Korea government (MEST) (No. 2012-0000609).
This research was supported by the Converging Research Center Program funded by the
Ministry of Education, Science and Technology (2011K000761).
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