Ventilation rates in schools and pupils’ performance
Abstract
This paper is a development of our earlier work
[5],
[6] and [11]. The effects of classroom ventilation on pupils’ performance were investigated in 8 primary schools in England. In each school the concentrations of carbon dioxide and other parameters were monitored for three weeks in two selected classrooms. In 16 classrooms interventions were made to improve the ventilation rate and maintain the temperature within an acceptable range using a purpose-built portable mechanical ventilation system. As a result of the interventions the provision of outdoor air to the classrooms was improved from the prevailing levels of about 1 l/s per person to about 8 l/s per person.The pupils and teachers in the classrooms studied were usually exposed to unacceptably poor air quality conditions, with CO2 concentrations of up to 5000 ppm, much higher than the average recommended levels of 1500 ppm and the preferred level of 1000 ppm.The results of computerized performance tasks performed by more than 200 pupils showed significantly faster and more accurate responses for Choice Reaction (by 2.2%), Colour Word Vigilance (by 2.7%), Picture Memory (by 8%) and Word Recognition (by 15%) at the higher ventilation rates compared with the low ventilation conditions.The present investigation provides strong evidence that low ventilation rates in classrooms significantly reduce pupils’ attention and vigilance, and negatively affect memory and concentration. The physical environment therefore affects teaching and learning.Highlights► Level of CO2 affects cognitive performance. ► Test data collected from 8 UK primary schools. ► Recommended ventilation rates are proposed. ► Teachers participated and provided case history evidence for further recommendations for designers.
Ventilation rates in schools and pupils’ performance
Zs. Bakó-Biró
b
, D.J. Clements-Croome
a
,
*
, N. Kochhar
a
, H.B. Awbi
a
, M.J. Williams
c
a
The University of Reading School of Construction Management and Engineering, United Kingdom
b
Monodraught Ltd, United Kingdom
c
The University of Reading Department of Psychology, United Kingdom
article info
Article history:
Received 23 March 2011
Received in revised form
2 August 2011
Accepted 25 August 2011
Keywords:
Schools
Ventilation rates
CO
2
Environmental effects on learning
Pupils’ performance
abstract
This paper is a development of our earlier work [5,6,11]. The effects of classroom ventilation on pupils’
performance were investigated in 8 primary schools in England. In each school the concentrations of
carbon dioxide and other parameters were monitored for three weeks in two selected classrooms. In 16
classrooms interventions were made to improve the ventilation rate and maintain the temperature
within an acceptable range using a purpose-built portable mechanical ventilation system. As a result of
the interventions the provision of outdoor air to the classrooms was improved from the prevailing levels
of about 1 l/s per person to about 8 l/s per person.
The pupils and teachers in the classrooms studied were usually exposed to unacceptably poor air
quality conditions, with CO
2
concentrations of up to 5000 ppm, much higher than the average recom-
mended levels of 1500 ppm and the preferred level of 1000 ppm.
The results of computerized performance tasks performed by more than 200 pupils showed signifi-
cantly faster and more accurate responses for Choice Reaction (by 2.2%), Colour Word Vigilance (by 2.7%),
Picture Memory (by 8%) and Word Recognition (by 15%) at the higher ventilation rates compared with
the low ventilation conditions.
The present investigation provides strong evidence that low ventilation rates in classrooms signifi-
cantly reduce pupils’ attention and vigilance, and negatively affect memory and concen tration. The
physical environment therefore affects teaching and learning.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Background
Schools in the UK house about 10 million pupils [14,15] who
spend almost 30% of their life in schools and about 70% of their time
inside a classroom during school days. As such, classrooms are the
second most important indoor environment for children, after their
homes, where they are exposed to various airborne pollutants to
a much greater extent than outdoors. Compared to adults, children
are more vulnerable to environmental pollutants as they breathe
more, relative to their body weight, and are also less well able to
deal with toxic chemicals [17,32].
Former reviews on the subject of school environments indicated
that ventilation is often inadequate in classrooms, causing an
increased risk for asthma and other health-related symptoms
among school children [13,25]. Actions have been proposed for
existing and future school buildings to include adequate outdoor
ventilation, control of moisture, and avoidance of indoor exposures
to pollutants such as microbiological particles, allergens and
chemical substances which are considered likely to have adverse
effects.
The current ventilation standards and guidelines [2,3,9]
recommend a minimum ventilation rate of 8 l/s per person in all
teaching facilities. Building Bulletin 101 (2006) [8] (the UK Regu-
latory Framework for schools), the European Standard pr EN15251
(not specifically for schools but the monitoring approach here
aligns with its recommendations which are also confirmed in the
work of [7]) and REHVA Guidebook 13 [1], refer to proposed
performance- based standards limiting the level of carbon dioxide
(CO
2
) concentration to 1500 ppm over a full school day from 9:00 to
15:30 and specify a minimum ventilation rate of 3 l/s per person in
all teaching and learning spaces when they are occupied. Further-
more, a ventilation rate of 8 l/s per person should be achievable
under the control of occupants, although it may not be required at
all times if the occupancy density decreases.
A number of studies have also reported that ventilation rates in
schools are often substandard, and it is not unusual to find CO
2
levels above 3000 ppm in classrooms [16,24]. The quality of the
classroom environment not only affects health and comfort
*
Corresponding author.
E-mail address: d.j.clements-croome@reading.ac.uk (D.J. Clements-Croome).
Contents lists available at SciVerse ScienceDirect
Building and Environment
journal homepage: www.elsevier.com/locate/buildenv
0360-1323/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.buildenv.2011.08.018
Building and Environment 48 (2011) 1e9
([26,35]; Norbäck and Nordström, 2008), but it may also impair the
learning performance of pupils. Following earlier studies which
indicated such a correlation [27,31], there is growing evidence to
show that impairment of learning performance and increased
absenteeism are partly due to inadequate ventilation and unsuit-
able thermal conditions in classrooms [7,12,18,27,29,30,33,34].
Coley and Greeves (2007) [7] carried out a study on how
ventilation rates affect cognitive performance in a primary school
and reported in their words: "The effects are best characterised by
the power of attention factor which represents the intensity of
concentration at a particular moment with faster responses
reflecting higher levels of focused attention. Increased levels of CO2
from a mean of 690 ppm to a mean of 2909 ppm lead to a detriment
in power of attention of about 5%."
Satish et al. (2011) [29] tested the effects of CO
2
levels on deci-
sion making and concluded that at levels of 2500 ppm and even
lower the performance of decision making becomes marginal and
in some cases dysfunctional. This work is very interesting as it was
carried out by an interdisciplinary team which included people
with environmental, medical and management skills and has
implications for all buildings [29]. The evidence is growing which
suggests that more generally we need to increase public awareness
about limiting CO
2
levels in buildings and also on transport systems
so promoting freshness and so creating less fatiguing air environ-
ments in which we live and work.
On the other hand, achieving adequate ventilation to provide
a healthy and comfortable classroom environment without
impairing the learning performance of children has inevitable
implications for the energy performance of school buildings. It is
a delicate balance for every building designer to ensure that the
design meets both ventilation and energy performance require-
ments. However, apart from achieving the ventilation criteria there
also seems to be a large difference between the intended
(designed) levels of energy performance and the actual perfor-
mance in use. According to LessEn (an initiative of the international
Urban Land Institute), which issued a league table in 2010 showing
the energy efficiency of local authority schools in the UK, of 11,993
schools, only 29 had the top energy rating whilst 1703 had the
lowest.
Whilst recognising the importance of creating a low carbon
economy, this must not be achieved at the expense of neglecting
human needs. Schools are for teaching and learning and if these are
impaired by poor environmental conditions, then these cannot be
considered as sustainable, irrespective of their energy performance.
2. Aims and objectives
The purpose of the research was to establish a direct link
between pupils’ health, well-being and cognitive performance, and
the indoor air quality in a sample of primary school classrooms near
Reading in the UK and to examine the suitability of the air quality
guidelines.
This paper focuses on the indoor air quality in classrooms by
using CO
2
as an indicator of ventilation and shows how it affects the
performance of mental tasks using in-situ direct measurements.
3. Methods
The field surveys were completed over a period, starting in
February, 2006 to 2008. The measurements were carried out in
eight schools (referred as S1-S8 from here-on), during winter (S1,
S7), spring (S2, S8), early summer (S3, S4) and autumn (S5, S6). All
schools were built in the last 20e40 years. Except for one school,
none had a mechanical ventilation system; in most schools staff
had no control over the temperature. At each selected school,
investigations were carried out in two classrooms for at least three
consecutive weeks. The first week was reserved for monitoring the
classroom conditions without modifying any of the indoor climatic
parameters, and to familiarise the children with the performance
tests. During the second and third weeks, a purpose-built mobile
ventilation system was installed in each classroom to control the
ventilation rate and maintain the temperature within certain limits.
The system was set either to provide outdoor air or to re-circulate
the classroom air. Although the ventilation system was visible,
the staff and the children were not informed about whether it was
providing fresh air or re-circulated air. The order of provision of
fresh air/re-circulated air conditions was made in a cross-over
repeated-measures design for the two classrooms; order of
presentation of the two ventilation conditions in the weeks two
and three was balanced within the two classrooms in a school and
across all schools.
The ventilation system consisted of an exterior fan placed
outdoors; a ductwork with a diameter of 200 mm supplied the air
into the building through window openings, which were covered
with Perspex plates and cut to connect to the ducts (Fig. 1).
In the classrooms, the air was distributed using Softflo air
terminal units, which consist of a perforated duct with small
nozzles creating confluent jets flowing into the room [10]. The
temperature of the supply air was controlled by means of a duct
Fig. 1. Exterior fan of the mobile ventilation system (a); testing area with the measuring trolley in the background (b) and air terminal device (c).
Zs. Bakó-Biró et al. / Building and Environment 48 (2011) 1e92
heater (3 kW) and a mobile air conditioning unit of 2.7 kW con-
nected to the ventilation system. The capacity of the supply fan was
selected to provide 200 l/s, matching the prescribed level of 8 l/s
per person in a classroom holding, on average, 25 children. Sound
attenuators were also built into the system upstream and down-
stream of the fan to reduce the soundbreakout from the ductwork
into the classroom. The rating for the AC unit was based on the
thermal performance of a typical classroom; the classrooms were
all similar in size and construction.
The mobile ventilation system was fully developed only after the
measurements in the third school had been completed. Therefore
in the first three schools the ventilation system was used only to
supply the outdoor air to the classrooms in a controlled manner;
the low ventilation condition was obtained with the windows
closed. The maximum concentration of CO
2
in the re-circulated
conditions never exceeded that normally occurring in the class-
rooms prior to the interventions. During experiments, the teachers
and pupils were allowed to open the windows whenever they
needed to, without any encouragement or hindrance by the
investigators. The open/closed state of windows and classroom
doors was monitored by state loggers.
Physical measurements: CO
2
concentration (Vaisala GMP222;
0e5000 ppm 20 ppm and 2% of reading), air temperature,
relative humidity (RH) (Eltek GD-10; þ5e40
C 0.4 K; 10%e
90%, 2%), globe temperature (diam 36 mm, probe thermistor; 50
to þ150
C 0.1 K), air velocity (Accusense AVS, 0e1 m/s, 5% of
range) and light level (Skye Instr. SL15 0e 4000lx 3% of range)
were continuously monitored in each classroom and recorded at
3-min intervals on a central logger (Eltek Squirrel) using a wireless
data transmission technique. These sensors were fixed on a trolley
(Fig. 1b) and placed close to the testing area in the classrooms. In
addition three thermistor type temperature probes were distrib-
uted on a vertical pole fixed to the trolley to record differences in
temperature between the pupils’ head and foot levels. Separate
units were placed outdoors and in the corridors to measure CO
2
concentration, temperature and RH. The corridor units were
providing information about the immediate vicinity of the
measured classes but generally there was little risk of cross
contamination from corridors as doors were closed for most of the
time. The amount of supplied air to the classrooms was measured
with Venturi flow metres built into the duct system downstream of
the fan. The ventilation rate measurements were conducted using
the tracer gas decay method (Brüel&Kjaer Multi-Gas monitor
Innova Type 1302) with SF
6
as tracer gas (photoacustic detection
limit 0.006 ppm SF
6
). This tracer gas was selected due to the
availability of instrumentation. The measurements took place
during school breaks in unoccupied classrooms in schools 5e8. The
monitoring procedures were compatible with ISO-16000-1.
Subjective eval uatio ns: Simultan eous to the physical moni-
toring, measures of self-assessed environmenta l perception,
comfort and health were obtained immediately after the perfor-
mance tests had been carri ed out. The pupils were asked to
complete a simple questionnaire about the classroom environ-
ment, thermal sensation, mood, Sick Building Syndrome (SBS)
symptoms an d life style, such as level of hunger and quality of
sleep during the previous night, factors which are believed to
affect concentration and, hence, task performance. The majority of
the assess ments were made on Visual An alogue s cales consisting
of a continuous horizontal l ine with statements at the two
endpoints [23] and thermal sensation was recorded on a 7-point
PMV scale [4]. With few exceptions, all pu pils partic ipated in the
testing. The targeted age group of the children was between 9 and
10 years attending Year 5. This age group of pupils was selected
because they remain in their classrooms, and are therefore in the
same environment, throughout a school day.
New software - VISCoPe (Ventilation in Schools and Cognitive
Performance) was developed for these tests which uses algorithms
that are based on the work of [19] in order to assess changes in
pupils’ cognitive performance under different air quality conditions
in classrooms. The test was designed using a flexible approach to
allow pupils some control in conducting it. The test battery
included 9 different tests: Simple Reaction Time (RT), Choice RT,
Colour Word Vigilance, Addition RT, Digit Span Memory, Digit
Classification, Digit-Symbol Matching, Picture Memory and Word
recognition.
The VISCoPe tests are described, in their order of presentation in
Table 1. These tests were conducted on laptops set up in the
classroom, using a method similar to that of [7]. The pupils inter-
acted with the software on a standard numerical keypad.
Tests were completed during the lessons at a time arranged with
the teacher (which was often before the lunch break). By the time
the testing commenced, the CO
2
concentrations had reached steady
state level with increased ventilation or the higher end of the
achievable CO
2
level of the teaching session with re-circulated
ventilation. The computer tests lasted for 20 min and were con-
ducted consecutively with 3e4 groups, each including up to 8
Table 1
Description of VISCoPe tests in their order of presentation.
Test Description
Simple Reaction Time A large, red circle appeared on the screen at irregular intervals. Pupils’ task was to press the <ENTER> key as fast as they could when the
circle appeared.
Choice Reaction Time A red pointer was displayed on the screen, indicating towards North, East, South or West. Pupils’ task was to follow the direction
of the pointer on the keyboard by pressing the appropriate arrow key as fast as they could.
Colour Word Vigilance Colour words: RED, YELLOW, BLUE AND WHITE were shown on screen one at a time at constant intervals. Each time any of these words
was presented it could be written in any one of the colours. Pupils were instructed to press the <ENTER> key as fast as possible when there
was a match between the meaning of the word and the colour of the text.
Addition Reaction Time Three digits appeared in the middle of the screen at constant intervals. Pupils were asked to add the digits and indicate the sum as quickly
as possible by pressing the <ENTER>key
Digit Span Memory A series of digits were presented one at a time on the screen. When a series was completed a question mark appeared, after which pupils
were supposed to repeat the digits shown in the series in the correct order. Correct response was followed by the next series which was
one digit longer; if the response was incorrect, the last series was then repeated.
Digit Classification Numbers between 1 and 20 were presented one at a time on the screen. Pupils’ task was to decide whether each digit was either ODD or
EVEN by pressing Number 1 Key if the number was ODD, Number 2 Key if the number was EVEN
Digit-Symbol Matching On the top of the screen there was a row of symbols. The symbols were paired with digits which were shown below each symbol.
At the bottom of the screen the same symbols were presented in a mixed order. Pupils were instructed to match the correct number
(from the top row) for each symbol.
Picture Memory Six pictures were shown on the screen for 2 s. Pupils were asked to memorize the location of each picture shown and recall their correct
location by pressing the appropriate number key using the keypad.
Word recognition Four words were presented on the screen. One of the four words had no meaning (non-word); the task was to indicate the non-word by
pressing the corresponding numeric key.
Zs. Bakó-Biró et al. / Building and Environment 48 (2011) 1e9 3
children. Overall, 53 groups of children were tested in the 8 schools,
and valid data was obtained from 332 children, participating in
both test conditions. During the two testing weeks the performance
tasks were carried out on the same weekday and during the same
time period for each group of children. A Performance Index (PI)
was computed to reflect the error-free reaction time, i.e. the mean
processing/reaction time of valid answers divided by the accuracy
of responses within a task. Thus a high error rate would increase PI
value, the time needed to provide accurate answers.
Since the absolute measures of the individual tasks are at
different levels it was convenient to show the performance data on
a relative scale, where the performance indicator for each task is
averaged across the conditions. Consequently, the performance
result of the two experimental conditions can be expressed relative
to this average, denoted as 1.
4. Data analysis
The focus of this study is on the general level of main physical
parameters describing the classroom environment during test
periods. To evaluate the effect of the two levels of ventilation rates
on pupils’ performance using the computerized assessment tests,
statistical analysis was carried out using a mixed design analysis of
variance (ANOVA) with ventilation rate (low or high) as a within-
participants factor, and order of presentation and class as
between-participant factors (with class nested within order of
presentation). Simple comparisons were also made using t-test or
Wilcoxon matched-pairs for related samples. All values reported in
this paper represent p-values that are 1-tailed tests because we
were interested only in results showing improvement in perfor-
mance with more favourable ventilation conditions. The rejection
region for significance was set to be p < 0.05.
5. Results
5.1. Classroom conditions prior to interventions
The monitoring week was important to provide ba ckground
data and guidance for the conditions established during recircu-
lat ion week. The mean values of environmental parameters d uring
school hours for the monitoring week are s hown in Table 2.
Further details are provided for the concentration of CO
2
and
parameters of the thermal environment including standard
deviation (SD), and the maximum and upper quartile (75th
percentile) values. The air temperature reflects the mean values of
the records received from the temperat ure probes distributed on
the vertical pole at the measuring trol ley. Other parameters
derived from the measured data, such as the operative tempera-
ture, vertical temperature difference between head and feet
levels, predic ted draught rating, predicted mean vote (PMV) and
predicted percentage of dissatisfied due to thermal environment
are also included. The PMV calculations were made for e ach data
point (3-min intervals during occupied period) assuming 1.2 met
(school activity) and 0.9 clo (clothing insulation) for a typical
pupils’ clothing. Although the assumption of 1. 2 met activity may
not always be a representative val ue for t he whole duration of
these tests, it is a value that is often used for children under
sedentary activity (ISO 7730) [21]. Unfortunately the outdoor
measurements at some schools were not available due to technical
failures.
5.2. Classroom conditions during performance tests
Fig. 2 and Fig. 3 show the records of the mean CO
2
concentration
and globe temperature in 16 classrooms of 8 schoolsmeasured during
completion of the performance tests. The classrooms with mean
volume of 154 15 m
3
and floor area of 58 5m
2
were occupied by
25 4 children. The carbon dioxide production (12.4 0.6 l/h per
person) in the occupied class was calculated according ISO standard
8996 based [20]] on the measured body parameters of children
(A
DuBois
¼ 1.15 0.05 m
2
) at normal activity levels of 1.2 met and the
number of children (and adults) present in the classroom.
Using the CO
2
mass balance model the calculated outdoor air
exchange rates corresponding to the CO
2
conditions in Fig. 2 were
slightly over 4 per hour with the high ventilation condition.
Excluding Schools 1 and 2 where no significant change in the
CO
2
level was obtained, the air exchange rates in the rest of the
schools were between 0.3 and 1.7 per hour at low ventilation
condition.
According to tracer gas measurements, air exchange rates of
4.0 0.3 h
1
and 0.6 0.1 h
1
were obtained when the ventilation
system was providing fresh and re-circulated air respectively. The
mean fresh air supply for every school as measured by a flow metre
built into the duct system during improved ventilation was at
166 12 l/s, (4.0 0.4 h
1
air change rates), matching well the
levels calculated with the other two methods. Assuming the
classroom occupancy and the reported air change rates, the air
supply rates per person ranged between 0.6 and 4.0 l/s.pp and
5.1e9.6 l/s.pp at low and high ventilation conditions respectively.
Deviations of the globe temperature (Fig. 3) between low and
high ventilation rate conditions were on average 0.6 1.6 K.
To evaluate the main effect of ventilation on the performance
indicators of the computerized tests, data from Schools 1 and 2
were excluded from the statistical analysis due to the very small
variation of the CO
2
concentrations between the tests. The results of
the ANOVAs are summarized in Table 3 for 215 pupils who were
present in both experimental conditions, out of 250 participants.
The PI which denotes the accurate reaction time for a given test was
significantly reduced for Choice RT (F(1,215) ¼ 5.35), Colour Word
Vigilance (F(1,204) ¼ 4.54) and Word Recognition (F(1,215) ¼ 8.30)
when the ventilation rate was increased from low to high levels. For
the Picture Memory task a similar trend was observed in the vari-
ation of PI F(1, 174) ¼ 2.58, and a significant increase was noted in
task accuracy F(1,174) ¼ 4.62 due to the intervention of increasing
the ventilation rate. Because multiple tests are reported here, there
is the possibility of inflated Type I errors, so these results should be
treated with a little caution. Whenever the effect of practice (order
of presentation) was large, this counteracted the effect of ventila-
tion. This happened especially in the case of the addition and digit
classification tests. Fig. 4a summarises the results expressed in
relative performance, which clearly shows the decrement in
performance with re-circulated air contrasting with the improve-
ment when fresh air is supplied.
Additionally, the analysis was extended for school no 2, where
temperatures were lower than the existing slightly elevated levels
of 25.3 0.4
C to 23.1 0.8
C as a result of the interventions. The
CO
2
level in this school was controlled by an existing mechanical
ventilation system below 1000 ppm; however, the provision of air
was made at a constant temperature of 28
C due to system failure.
The temperature reduction was obtained by mixing preheated but
slightly cool outdoor air through the mobile ventilation equipment
to bring the thermal environment to an acceptable level.
Based on the analysis of cognitive performance of 36 pupils in
school no 2, the PI significantly improved by about 6% for simple RT
(p < 0.03), choice RT (p < 0.04) and by 8% for Colour Word Vigilance
(p < 0.001).
The analysis of subjective voting from 330 pupils indicated
relatively small alterations between the experimental conditions.
Most of the beneficial effects of the higher ventilation were related
to air freshness, sensation of dryness in the mucous membrane, eye
Zs. Bakó-Biró et al. / Building and Environment 48 (2011) 1e94
Table 2
Mean values of the main environmental parameters in 8 schools (16 classrooms) based on one week’s measurements reflecting existing classroom conditions before any intervention was established.
Classroom S1A S1B S2A S2B S3A S3B S4A S4B S5A S5B S6A S6B S7A S7B S8A S8B
CO
2
[ppm]
Mean 1190 1400 710 791 1049 1071 745 644 1751 1462 1630 1452 2417 2833 2024 1653
SD 448 498 182 178 550 291 233 158 1220 753 613 560 1066 1160 1068 881
Max 2844 2890 1115 1245 2716 2011 1495 1263 5000 4890 2950 2808 5000 5000 4946 3944
Q3 1418 1709 838 918 1262 1260 872 726 2516 1861 2084 1809 3115 3666 2671 2319
Air temperature [
C]
Mean 21.8 22.3 22.0 22.5 18.8 18.5 24.2 23.0 19.3 19.9 22.0 20.3 21.1 20.1 21.2 20.7
SD 1.5 1.9 1.7 0.9 0.9 1.3 2.0 1.9 1.8 1.8 0.9 1.0 0.9 0.9 1.6 1.6
Max 25.8 25.8 24.6 24.4 21.3 22.1 28.6 26.6 22.7 23.7 24.2 22.3 22.6 22.1 24.1 23.7
Min 17.7 15.2 16.2 20.0 16.6 15.8 20.3 20.4 15.9 15.9 19.0 17.5 18.8 17.7 16.6 16.0
Q3 22.6 24.0 23.4 23.1 19.3 19.1 26.0 24.1 20.6 21.3 22.6 21.1 21.7 20.7 22.6 21.9
RH [%] 35 35 38 37 64 63 53 52 73 68 59 64 62 64 51 50
Air velocity [m/s] 0.07 0.09 0.08 0.08 0.06 0.06 0.14 0.08 0.06 0.07 0.08 0.06 0.09 0.06 0.06 0.06
Light [lux] 315 414 359 410 273 232 256 300 211 236 317 291 352 393 186 235
Outdoor termp. [
C] n/a 10.7 17.7 23.3 16.3 12.5 n/a n/a
RH outdoors [%] n/a 65.8 70.6 59.6 79.3 86.3 n/a n/a
CO
2
outdoors [ppm] n/a 472 441 424 440 445 n/a n/a
Operative temp.[
C] 22.5 22.8 23.6 23.2 19.1 18.8 24.5 23.3 19.5 20.4 22.6 20.9 21.5 20.3 22.1 21.5
D
t vertical [
C] 2.5 2.4 3.9 1.9 1.1 0.9 0.3 0.8 0.7 0.9 1.7 1.2 2.2 1.0 3.6 3.2
DR[%] 610772217748849444
PMV
Mean 0.0 0.0 0.2 0.1 0.6 0.7 0.1 0.3 0.5 0.3 0.1 0.2 0.1 0.4 0.0 0.2
SD 0.4 0.4 0.3 0.2 0.2 0.3 0.6 0.6 0.5 0.5 0.3 0.3 0.2 0.2 0.4 0.4
Max 0.9 1.0 0.8 0.6 0.1 0.2 1.5 0.8 0.4 0.5 1.3 0.2 0.4 0.2 0.8 0.6
Min 1.1 1.6 1.7 0.7 1.1 1.5 1.3 1.5 1.5 1.9 0.9 0.9 0.9 1.1 1.4 1.5
Q3 0.2 0.4 0.5 0.3 0.5 0.6 0.4 0.0 0.1 0.0 0.3 0.1 0.1 0.2 0.3 0.2
PPD
Mean 8 9 8 6141812151412 7 7 7 9 9 9
SD 464258891211342456
Max 30556315305050524872412122314648
Q3 9 10 10 7 17 23 15 22 19 12 7 8 7 11 10 10
Zs. Bakó-Biró et al. / Building and Environment 48 (2011) 1e9 5
dryness and alertness. However, the level of significance was ach-
ieved for a minority of classrooms, which do not permit general-
isation of the negative sensory and health-related symptoms
associated with low ventilation rates to the whole sample.
Significant alterations in thermal voting of subjects occurred
only in two classrooms (S3-A & S4-A), where the temperature
difference between the conditions also justified this outcome. In
the other classrooms the pupils could not detect any significant
variations in the thermal environment, whether it was ventilated at
high or low outdoor supply rates. However, it is worth noting that,
with one exception, all thermal votes were distributed on the warm
side of the scale, even though the classroom temperatures were at
the lower end of the comfort range. Most interestingly, the calcu-
lated PMV index according to ISO 7730 was always under-
estimating subjective ratings which could have been due to
uncertainties in the value of the parameters used in the PMV
calculations, such us changes in activity and clothing ensembles.
6. Discussion
For the present sample of schools interesting data was obtained
during the monitoring week when only physical measurements
were made. Considering the average values of CO
2
levels in the
classrooms, only three classes significantly exceeded the recom-
mended level of 1500 ppm given by BB 101 [1,7];. However, the
maximum level reached was as much as 5000 ppm (exceeding the
measuring range of the CO
2
sensor), which is at the limit of the
occupational health values. The upper percentile concentrations
also indicated that a considerable amount of time is spent in much
higher concentrations than the average for about half of the
classrooms.
The thermal conditions found in the classrooms were satisfac-
tory, but occasionally unpleasant warm conditions were recorded
and although only one school was assessed during summer-time,
no particularly hot environments were observed. Vertical distri-
bution of the temperatures rarely exceeded 3 K to cause local
discomfort for the occupants, and the air movement was generally
too low to cause any draught discomfort. Specific complaints of
being too hot were registered from staff in Schools 1 & 2, which was
primarily due to the uncontrollability of the existing HVAC system.
This was largely overcome by keeping the windows or fire-doors
open, which inevitably contributed to unnecessary energy loss
and increase in space heating demand.
The high concentration of CO
2
, resulting from extremely low
outdoor air exchange rates in the classrooms in which the perfor-
mance testing, as well as normal teaching activity, was carried out,
is striking evidence of efficient building tightness successfully
realized to save energy. Double-glazed windows, installed at each
of the schools studied, allowed very little air infiltration, indicating
a need for an effective means for providing fresh air. Historically,
classrooms have relied on air leakage to provide fresh air. In some
classrooms, even though the windows were opened (eg. School 1,
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
S1-A S1-B S2-A S2-B S3-A S3-B S4-A S4-B S5-A S5-B S6-A S6-B S7-A S7-B S8-A S8-B
CO
2
(ppm)
Fresh Air Supply Re-circulated Air Supply
Fig. 2. Mean CO
2
concentrations (SD) during the computerized performance tests in 16 classrooms at 8 schools. Note: For Schools S1 to S3 no recirculation was carried out; the
low ventilation condition was obtained by not changing the windows openings unless the teachers decided so.
Fig. 3. Globe temperature measurements (SD) during the computerized performance tests in 16 classrooms at 8 schools (3e4 groups of pupils were tested in each school).
Zs. Bakó-Biró et al. / Building and Environment 48 (2011) 1e96
Class A, Low ventilation condition), the ventilation rate did not
exceed 3 l/s per person. It should be noted that in all classrooms
studied, window openings were limited to 20e25 cm (representing
the distance between the movable and fixed frame) to satisfy
security requirements demanded by the UK Health and Safety
Regulations. Many professionals, such as those from the CIBSE
Schools Teachers Groups and others, complain about this restric-
tion in hospitals as well as schools as this constraint often prevents
adequate ventilation being achieved.
In situations when the windows were left closed, in the absence
of other means of providing outdoor air (e.g. when recirculation
mode was set), CO
2
levels rose quickly to 3000e 4500 ppm within
a teaching session. Under such conditions the length of school
breaks were often too short to restore CO
2
concentrations to the
outdoor levels before the next teaching session commenced. On
some occasions, the morning teaching sessions even began with
residual CO
2
concentration from the previous day. Similar high
levels in naturally ventilated classrooms have often been reported
in schools in the UK [12,24] and abroad [7,16].
In the current study, the pupils provided their own controls in
a repeated-measures design so that the observed differences in
performance between conditions are unlikely to have been due to
differences between particular groups of children. When calcu-
lating the main effect of the ventilation, the present analysis did
not assess interactions due to other factors, such as temperature,
that may also have contributed in some of the classrooms to the
performance outcomes [34]. In this experiment, an effort was
made to try to avoid thermal effects due to temperature changes
by conditioning the supplied air to maintain the classroom
temperature within the comfortable range and also by using
a balanced order of presentation of the experimental conditions.
In such cases if an external factor, such as change in weather
during one of the exposure weeks had affected the study, the
effect should have influenced both experimental conditions. The
cooling capacity of the portable air conditioning unit, however,
was not always sufficient to handle large variations in heat loads.
Consequently, a large temperature difference between the test
conditions was observed for Class A, School 4, which was not
counteracted to the same extent in the other classroom. The
observed difference in the thermal environment for this class
actually strengthened the influence of ventilation on performance,
if we consider that lower temperatures have a positive impact on
the performance measures. Indeed such an effect could be
demonstrated in School 2, where the air quality conditions were
equally good with and without interventions, and the pupils were
significantly quicker in performing three different reaction tasks
at lower, more comfortable temperatures. In particular, the test
session was repeated in Class A in School 4 for the fresh air supply
condition at a temperature comparable with that for the re-
circulated air condition. However, the results from these
repeated tests did not show a signifi cant alteration to the original
results of the ANOVA.
Fig. 4. Relative effects of Ventil ation (a) and Thermal environment (b) on Pupil performance and learning.
Table 3
Performance measures using the computerized assessment tests for Schools 3e8.
Performance Test Vent. Rate Performance index Accuracy Reaction time
(sec) Change p
vent
p
order
(%) Change p
vent
(sec) Change p
vent
Simple RT Low 0.383 3.0% 0.119 0.001 95% 1.1% 0.099 0.360 3.0% 0.33
High 0.372 96% 0.355
Choice RT Low 0.816 2.2% 0.011 0.084 95% 0.5% 0.121 0.771 2.2% 0.05
High 0.798 95% 0.759
Colour Word Vigilance Low 0.859 2.7% 0.017 0.040 88% 1.0% 0.048 0.742 2.7% 0.06
High 0.837 89% 0.733
Digit Classification Low 1.094 1.6% 0.308 0.025 89% 0.3% 0.459 0.956 1.6% 0.25
High 1.112 88% 0.966
Addition RT Low 7.8 2.7% 0.123 0.000 94% 0.4% 0.158 0.007 2.7% 0.25
High 8.0 93% 0.007
Digit Span Low 5.0 0.9% 0.484 0.467 87% 0.9% 0.472 4.747 0.9% 0.18
High 5.0 88% 4.601
Digit-Symbol Match Low 65.6 1.5% 0.346 0.411 81% 0.1% 0.441 47.2 1.5% 0.02
High 66.5 81% 49.4
Picture memory Low 37.1 8.0% 0.055 0.435 55% 7.2% 0.016 16.3 8.0% 0.25
High 34.4 60% 16.4
Word recognition Low 4.6 14.8% 0.002 0.195 95% 0.4% 0.271 4.3 14.8% 0.001
High 4.0 95% 3.8
Note: A positive relative change in the performance measures (
D
) indicates improvement between the conditions; p
vent
denotes the effect of ventilation, p
order
indicates the
effect of presentation order of the experimental conditions.
Zs. Bakó-Biró et al. / Building and Environment 48 (2011) 1e9 7
Contrary to expectation, the improved interventions only
moderately improved pupils’ subjective voting. These interventions
were made on a relatively short time scale in order to generate
strong effects on health and other symptoms. We should also note
that, due to regular school breaks, pupils have more time in each
class hour to get away from their classroom and participate in
outdoor activities that can compensate for negative health effects
due to poor ventilation in the classrooms.
7. Conclusions and recommendations
The present study strengthens the evidence reported by [12],
but for a larger sample of schools and for over 200 children, that
poor ventilation rates in classrooms significantly impair children’s
attention and vigilance. The faster and more accurate responses in
Choice RT and Colour Word Vigilance tasks reflect higher level of
focused attention at higher ventilation rates compared to low rates
with natural ventilation. In poorly ventilated classrooms, students
are likely to be less attentive and to concentrate less well on
instructions given by teachers. The magnitude of the negative
effects with inadequate ventilation was even higher for tasks that
require more complex skills such as spatial working memory and
verbal ability to recognize words and non-words. Ventilation rates
in the order of 8 l/s per person are recommended in all teaching
facilities to prevent any impairment of pupils’ performance due to
inadequate ventilation. Additionally, it was demonstrated in one of
the schools which had good ventilation background that pupils
reacted significantly faster in a number of simple tasks when the
classroom temperatures were reduced from existing slightly
elevated levels to a more comfortable range. The present findings
are in good agreement with the results reported by a number of
other independent studies investigating the effects of classroom
environmental quality on pupils’ learning performance [7,31,34].
Based on the outcomes and observations made during the
investigations in the 8 UK schools which involved feedback from
teachers, the present study proposes the following suggested
recommendations to school managers, designers and related
personnel involved in school design and maintenance:
suggested recommendations for UK schools managers include
equipping classrooms with a device to monitor CO
2
, tempera-
ture & relative humidity in classrooms; providing additional
ventilation if CO
2
concentration exceeds 1000 ppm; keeping
temperatures within comfortable range of 20e22
C (winter)
and 22e24
C (summer); avoiding moisture build up in class-
rooms and keeping humidity levels below 60% during winter
time but preferably above 40%; creating daily windows
opening routines for the school; using odourless cleaning
agents and remembering that dirty carpets can pollute the
indoor environment.
suggested recommendations for school building designers,
facilities managers and other stake holders include: providing
ventilation to limit the concentration of carbon dioxide in all
teaching and learning spaces an average of 1000 parts per
million (ppm) between the start and finish of teaching on any
day, which is lower than the 1500 ppm recommended in the
UK’s Building Bulletin 101; providing a minimum fresh air
supply rate or ventilation rate in all teaching and learning
spaces in the order of 8 l/s per person which falls within the
recommendations of [2,3] and other international standards;
dedicated ventilation systems may be necessary to achieve the
above targets; limiting classroom temperatures to those spec-
ified earlier; avoiding overheating by limiting solar gain using
utilising passive means such as thermal mass, orientation,
fenestration and external/internal shading devices; choice of
opening windows and their location are both important in the
design of the school façade as this affects the effectiveness of
natural ventilation; the high use of computers contributes to an
additional heat load but using slim computers with cloud
computing, as used by some schools, could radically reduce
internal load.
The physical environment affects people’s well-being in terms
of mind and body. This work shows that elevated level of indoor air
pollutants including CO
2
due to inadequate ventilation encoun-
tered in classrooms can affect learning. We know that the air we
breathe can affect the brain via the blood oxygenation in about 4 s.
CO
2
is seen as a harmless gas and so is often accorded little
significance, other than as an indicator of ventilation, but if it
contributes directly to increased tiredness and a loss of concen-
tration [22] then it might be regarded as a very significant air
pollutant. Air quality is just as important as temperature so needs to
be monitored so as to guide teachers when to open windows or
switch on fans [28].
Acknowledgements
The project was financed by The Engineering and Physicals
Sciences Council (EPSRC), the Department for Communities,
Schools and Families (DCSF). Professor P Wargocki at the Technical
University of Denmark made a valuable contribution to the project.
Professors Anders Iregren (Nat. Inst. for Working Life, Sweden) and
David M. Warburton (Department of Psychology, The University of
Reading) kindly provided the free use of their test systems for
further development. Thanks are also due to Lindab Ltd. for
providing free of charge ventilation equipment. The project team is
grateful to the Heads of the primary schools for opening their doors
to this study and the teachers who participated and liaised with
pupils and their parents. Last but not least a special thanks to all the
pupils for taking part in the study and providing their comments
and suggestions.
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- "Children spend the majority of their weekdays in classrooms that often have low indoor air quality (IAQ) due to insufficient outdoor airflow [1,2]. There are several studies that link low IAQ to reduced effectiveness of schoolwork and learning outcomes [3][4][5][6][7]. In response to this problem current classroom ventilation standards and guidelines recommend a minimum fresh air amount of 7–8 l/s per occupant [8,9] and an indoor-outdoor CO 2 concentration differential of less than 700 ppm [9,10]. "
[Show abstract] [Hide abstract] ABSTRACT: Children spend the majority of their weekdays in classrooms that often have low indoor air quality and limited financial resources for the initial and running costs of mechanical ventilation systems. Designing effective natural ventilation (NV) systems in schools is difficult due to the intense use of the classroom spaces and the dependence of NV on building geometry and outdoor conditions. Building thermal and airflow simulation tools are fundamental to predict NV system performance in the design phase. These predictions of these tools must be validated (preferably with data from real buildings). This paper presents a set of detailed measurements of buoyancy driven natural DV systems of three classrooms located in two buildings in Lisbon (Portugal). The rooms are located in two educational buildings, a kindergarten and a university, and have different buoyancy driven natural DV systems (with and without chimneys). The experimental measurements are used to validate a three-node DV model implemented on the open-source thermal building simulation software EnergyPlus. The validation results show that the building thermal simulation model tested is able to predict bulk airflow rate with an average error of 16%. In addition, a good agreement is also obtained for the vertical temperature prediction: an average error of 4% corresponding (average deviation of 0.7 °C). Analysis of the kindergarten rooms results revealed, that as expected, increasing chimney height from 1 to 4 m has a significant positive impact in NV system performance. The performance of natural DV systems depends on the number of thermal plumes in the room. For the same sensible heat load, increasing the number of plumes lowers the average occupied zone air temperature and increases the bulk airflow rate. In light of the complexity of the cases tested, NV with uncontrolled boundary conditions, the results of the comparisons performed between measurements and simulations should contribute to increase confidence in the use of EnergyPlus to simulate buoyancy driven natural DV systems.- "However, when designing for natural ventilation its suitability during the winter should be considered [3]. Low ventilation rates in classrooms have been shown to present a significant influence on students' performance with regard to attention, vigilance, memory and concentration [4]. Pupil learning can be affected by increased temperatures, humidity levels, poor air movement [5,6] and by indoor pollutants [7], all resultant of sub optimal ventilation. "
[Show abstract] [Hide abstract] ABSTRACT: Natural ventilation solutions can provide sufficient outside air to maintain adequate indoor air quality (IAQ), which can improve occupants’ performance in classrooms and provide reductions in energy consumption for space conditioning. In this study, the effect of cool outside air and the vent opening configurations on IAQ and occupant thermal comfort in naturally ventilated classrooms during the heating season was examined. Dynamic and steady state computer simulations were performed to investigate the internal conditions of a naturally ventilated classroom, designed to meet the requirements of the Priority Schools Building Programme (PSBP) Output Specification. The modelled designs considered natural cross ventilation airflow through high-level top hung-out or bottom hung-in openings, and a stack (atrium). Dynamic thermal modelling results indicate that adequate IAQ and occupant thermal comfort could be achieved using natural ventilation. However, the CFD simulation results predicted occupant discomfort due to draughts in the regions close to the openings. Bottom hung-in vents reduced draught impact and the study also suggests moving occupants away from the draught zones to minimise the effect of discomfort draughts on occupant comfort. The air velocity and airflow patterns in the classrooms were influenced by the shape, size, location of internal openings, and the flowrate through the openings. This could be controlled by introduction of new openings with lower airflow rates through each opening- "Cornaro et al. (2013analyzed the CO 2 concentration development in a middle school in Rome, Italy that used natural ventilation ( " trickle vent " ) and found that the indoor concentration exceeded 1500 ppm for a consistent period of time during the school year. In an intervention study, Biró et al. (2012) observed in one classroom a mean CO 2 concentration of 2833 ppm while the maximum values ranged between 1115 ppm and 5000 ppm (16 classrooms) before the intervention. "
[Show abstract] [Hide abstract] ABSTRACT: Human civilization is currently facing two particular challenges: population growth with a strong trend towards urbanization and climate change. The latter is now no longer seriously questioned. The primary concern is to limit anthropogenic climate change and to adapt our societies to its effects. Schools are a key part of the structure of our societies. If future generations are to take control of the manifold global problems, we have to offer our children the best possible infrastructure for their education: not only in terms of the didactic concepts, but also with regard to the climatic conditions in the school environment. Between the ages of 6 and 19, children spend up to 8 h a day in classrooms. The conditions are, however, often inacceptable and regardless of the geographic situation, all the current studies report similar problems: classrooms being too small for the high number of school children, poor ventilation concepts, considerable outdoor air pollution and strong sources of indoor air pollution.
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