Ventilation Rates in Schools and Learning Performance

Abstract

Associations between classroom ventilation and pupils' performance were investigated in primary schools in the United Kingdom. The concentration of carbon dioxide and other parameters were monitored for three weeks in two selected classrooms in each school. A direct air supply system through the windows was used to alter the ventilation rates in the classrooms. The system was set either to provide outdoor air or to re-circulate the classroom air while all other physical parameters were left unchanged. Computerised Assessment Tests and Paper-based Tasks were used to evaluate pupils' performance. Pupils' perceptions about the classroom environment, comfort, general mood and hunger were assessed on subjective scales. The present paper shows preliminary results obtained for one primary school out of eight being studied. Due to the intervention the fresh air supply increased from 0.3-05 to 13- 16 L/s per person that increased pupils' work rate by ~7% in addition (p

Full text

Ventilation Rates in Schools and Learning Performance
Zs. Bakó-Biró
1
, N. Kochhar
1
, D.J. Clements-Croome
1
, H.B. Awbi
1
and M. Williams
2
1
School of Construction Management and Engineering, The University of Reading,
Whiteknights, PO Box 219, RG6 6AW Reading, United Kingdom
2
School of Psychology and Clinical Language Sciences, The University of Reading, Harry
Pitt Building, Earley Gate, RG6 6AL Reading, United Kingdom
Corresponding email: z.bakobiro@reading.ac.uk
SUMMARY
Associations between classroom ventilation and pupils’ performance were investigated in
primary schools in the United Kingdom. The concentration of carbon dioxide and other
parameters were monitored for three weeks in two selected classrooms in each school. A
direct air supply system through the windows was used to alter the ventilation rates in the
classrooms. The system was set either to provide outdoor air or to re-circulate the classroom
air while all other physical parameters were left unchanged. Computerised Assessment Tests
and Paper-based Tasks were used to evaluate pupils’ performance. Pupils’ perceptions about
the classroom environment, comfort, general mood and hunger were assessed on subjective
scales. The present paper shows preliminary results obtained for one primary school out of
eight being studied. Due to the intervention the fresh air supply increased from 0.3-05 to 13-
16 L/s per person that increased pupils’ work rate by ~7% in addition (p<0.036) and
subtraction (p<0.052).
INTRODUCTION
Former reviews on the subject of school environments emphasised that ventilation is often
inadequate in classrooms causing increased risk for asthma and other health-related symptoms
among school children [1], [2]. Mendell & Heath [2] proposed that throughout the life of each
existing and future school building immediate measures should be taken for the provision of
adequate outdoor ventilation, control of moisture, and avoidance of indoor exposures to
microbiologic and chemical substances considered likely to have adverse effects. The current
ventilation standards and guidelines [3], [4] recommend a minimum fresh air supply rate of 8
litres/s per person for occupants in all teaching facilities. The recently published Building
Bulletin 101 refers 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
specifies a minimum supply of external air at least 3 L/s per person in all teaching and
learning spaces when they are occupied. Furthermore, a ventilation rate of 8 L/s per person for
the normal number of occupants should be achievable under the control of occupants,
although it may not be required at all times if occupancy level decreases. However, according
to recent studies the average CO
2
levels in classrooms often exceed the above limit and
ventilation rates are often below the minimum requirement of 3 L/s per person [5], [6].
The negative effects of poor ventilation rates on work performance in office buildings have
been widely investigated [7]. Knowing the outcome of poor ventilation rates for the adult
population it could be expected that not only the comfort and health, but also the learning
performance of school children are affected by the poor environmental conditions in
classrooms [2]. Following the earlier studies suggesting correlation between pupils’ health
Proceedings of Clima 2007 WellBeing Indoors

and work performance, [8], [9] there is growing evidence showing impairment of learning
performance and increased absenteeism due to inadequate ventilation and unsuitable thermal
conditions in classrooms [10], [11], [12], [13]. The main purpose of the present research was
to investigate the relationship between pupils’ health, well-being and performance, and the
indoor air quality in several primary schools in Southern England. Another aim was to
examine the suitability of the air quality guidelines in preventing the reported negative effects
even when the recommended levels of fresh air to the occupants are met.
METHODS
Field surveys were carried out at primary school buildings located in the proximity of
Reading during years 2006-2007. Up till now measurements have been done in eight different
schools. The sample included schools that were built in the last 20-40 years. Except for one
school, none of them had mechanical ventilation system and in most schools no control over
the temperature was available to the staff. At each selected school investigations were carried
out in two classrooms for at least three consecutive weeks. The first week was reserved to
monitor 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 week a
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 of the ventilation conditions, i.e. whether it was providing
fresh air or re-circulated air. The order of presentation of the fresh air/re-circulated conditions
were made in a cross over repeated design for the two classrooms.
The ventilation system consisted of an exterior fan placed outdoors and simple ducting of
diameter 200 mm led the air into the building through window openings, which were closed
with Perspex plates (Figure 1, a). In the classrooms the air was distributed using Softflo air
terminal units, which consist of a perforated duct with small nozzles creating confluent jets
flow into the room [14]. The temperature of the supplied air was controlled by means of a
duct heater (3kW) and a mobile air conditioning unit of 2.7kW built into the ventilation
system. The capacity of the supply fan was selected to provide 200 L/s, matching the
prescribed level of 8L/s per person in a classroom having on average 25 children. Silencers
were also built into the system upstream and downstream of the fan to reduce the noise level
propagating through the duct work into the classroom.
a)
b)
Figure 1. a) Exterior fan of the mobile ventilation system, b) Testing area with laptops and
measuring trolley with the air terminal device in the background; the trolley was placed close
to the testing area during performance tests.
Proceedings of Clima 2007 WellBeing Indoors

Physical measurements: CO
2
concentration (0-5000 ppm), air temperature, globe
temperature, relative humidity (RH), air velocity and light level were continuously monitored
in each classroom and recorded with 3 minutes interval on a central logger using a wireless
data transmission technique. These sensors were fixed on a trolley (Figure 1. b) and placed
close to the testing area in the classrooms. In addition three thermistor type temperature
probes were distributed on a vertical pole fixed to the trolley to record the temperature
differences between pupils’ head and feet levels. Separate units were placed outdoors and in
the corridors to measure CO
2
concentration, temperature and RH. Mass concentration of
airborne particles (PM2.5) and noise level were measured during the performance tests on
pupils over a few hours. The amount of supplied air to the classrooms was measured with
Venturi flow meters built into the duct system downstream of the fan.
Subjective evaluations: Simultaneous to the physical monitoring, measures of self-assessed
environmental perception, comfort and health were obtained immediately after the
performance tests were carried out. With some exceptions all pupils participated in the
testing. The targeted age group of the children was between 9-10 years attending Year 5. This
age group of pupils was selected because they remain in their classrooms most of the day and
are therefore in the same environment throughout a school day. The pupils were asked to
complete a simple questionnaire about the classroom environment, thermal sensation, mood,
Sick Building Syndrome (SBS) symptoms and life style, such as hunger and quality of sleep
over the previous night believed to affect their performance. The questionnaire about the
classroom environment included questions about air stuffiness, dryness, perception of light
and noise. The SBS questionnaire focused on symptoms of the mucous membrane and in
upper respiratory tract, such as nose congestion, nose, mouth, throat and eye dryness, and
neurobehavioral symptoms including headache, attention, dizziness, tiredness, sleepiness.
Pupils were asked to rate the intensity of each symptom on Visual Analogue (VA) scales [15].
Thermal sensation was recorded using a 7-point PMV scale [16]. Furthermore, pupils were
asked to rate the air movement around their body and inform whether it was acceptable or not.
Pupil’s Performance Tests: Two different performance tests were administered to the pupils
in each school. Traditional tests were carried out on paper for 40 minutes, including simple
addition and subtraction of numbers (15 minutes each) and reading comprehension [17] (10
minutes) similar to that performed in a normal school day. New software (VISCOPE –
Ventilation in Schools and Cognitive Performance) was developed that uses algorithms based
on the work of Iregren et al. [18] to study changes of pupils’ cognitive performance under
different air quality conditions in classrooms. These tests were conducted on laptop
computers set up in the classroom, similar to the method used by Coley and Beisteiner [19].
Both the traditional tests and the computer tests were given to pupils during their lessons
preferably before the lunch break when the CO
2
concentrations had reached the maximum
level of the morning’s teaching session. The computer tests lasted for 20 minutes and were
conducted in 3-4 consecutive groups, each group including 7-8 children. The tests, whether
they were conducted on paper or computers, were carried out on each testing week on the
same weekday and time period for each group of children.
Data analysis: Outdoor air supply rate was calculated based on the mass balance model of
CO
2
on each testing day. The subjective and performance data were analysed using Wilcoxon
matched-pairs test, using each subject as their own control. All p-values are 1-tailed of an
effect in the expected direction.
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RESULTS
The current project is still in the phase of data collection hence preliminary results of the
physical environment and performance tests conducted on paper from only one school are
presented. Detailed analysis of the performance results including those conducted on the
computers will be published on the completion of the current investigations.
Figure 2 shows a typical CO
2
pattern in one of the classrooms during a weekday when
performance tests were completed. The classroom of 156 m
3
was occupied by 23 children and
a teacher at normal activity levels. The teaching schedule including lessons and break time
can be clearly followed by looking at the changes in the CO
2
concentrations. The uncontrolled
condition on Figure 2 shows the CO
2
level prior to any intervention in the classrooms. The
CO
2
concentrations obtained during the week with the re-circulation ventilation are matching
closely the uncontrolled levels seen during a normal school day. When the ventilation system
was switched on to provide outdoor air the CO
2
concentrations were dramatically reduced and
remained below 1000 ppm throughout the school day.
Figure 2. Typical pattern of the CO
2
level inside a classroom at different ventilation
conditions on a testing day. The uncontrolled condition reflects CO
2
concentration during a
normal school day without any intervention measures.
The average levels of the main physical parameters in the classrooms during the performance
tests are presented in Table 1. At low ventilation rates the CO
2
concentrations during the
performance tasks at a given day and classroom varied from 1600 ppm up to 4000 ppm
depending on the occupancy level prior to testing. Temperature deviations between low and
high ventilation rate conditions were within 1.7°C with one exception in classroom B where
the difference in the operative temperature reached 2.7
°C due to exceptional hot outdoor
conditions during the tests conducted on paper. Relative humidity was generally higher at low
ventilation rates due to moisture generation from people that is also reflected in the enthalpy
of the classroom air. The air exchange rates in the re-circulation mode were not higher than
0.3 h
-1
in both classrooms, showing an effective building tightness with closed windows that
is responsible for the high levels of CO
2
and the extremely low outdoor air infiltration of not
more than 0.55 L/s per person. The measured amount of fresh air supplied during improved
ventilation was at180 - 190 L/s corresponding to 4.2 - 4.4 h
-1
air exchange rates. The
calculated air exchange based on the CO
2
mass balance model showed higher rates of up to 8
h
-1
(12 - 16 L/h per person) which is most likely due to some windows being opened that
enhanced cross ventilation. The average particle (PM 2.5) concentration during testing was in
the range of 0.05 - 0.1 mg/m
3
and did not show major changes due to ventilation
improvement. Classroom noise levels during testing were typically between 50 - 70 db(A)
Proceedings of Clima 2007 WellBeing Indoors

depending on the classroom activities. The background noise level originating from the
ventilation system installed was less than 48 - 49 db(A).
Table 1. Average levels (± standard deviation) of main environmental parameters inside the
classrooms and outdoors during performance testing; the ventilation rate calculation is based on
the CO
2
mass balance model for each classroom; outdoor CO
2
level was at 380-420 ppm.
Testing on Computer Pen & Paper testing
class
room
Re-circulated
Air
Oudoor Air
Supply
Re-circulated
Air
Oudoor Air
Supply
A 2876 ± 446 735 ± 58 1638 ± 364 709 ± 30
CO
2
level [ppm]
B 4093 ± 509 783 ± 35 2086 ± 171 593 ± 7
A 20.5 ± 0.3 18.9 ± 0.2 20.9 ± 0.3 20.1 ± 0.2
Air temperature [°C]
B 18.7 ± 0.4 20.3 ± 0.7 18.4 ± 0.4 21.5 ± 0.5
A 67 ± 1 56 ± 2 69 ± 1 52 ± 1
Relative Humidity [%]
B 66 ± 1 55 ± 3 61 ± 1 64 ± 2
A 20.5 ± 0.4 18.8 ± 0.3 21.1 ± 0.4 20.2 ± 0.2
Operative temperature [°C]
B 19.0 ± 0.5 20.2 ± 0.7 18.9 ± 0.4 21.6 ± 0.5
A 16.9 ± 0.5 17.7 ± 0.5 24.9 ± 0.5 17.9 ± 0.1
Outdoor temperature [°C]
B 16.7 ± 4.5 21.2 ± 0.9 17.8 ± 0.2 25.0 ± 0.5
A 46.41 38.41 48.28 39.64
Enthalpy [kJ/kg]
B 41.45 41.24 39.00 47.85
A 0.55 16.0 0.51 14.8
Ventilation Rate
[L/s.person] B 0.36 13.9 0.20 12.2
Table 2. Results of a selection of subjective votes recorded following the performance tests;
significance of statistical tests also appear next to each question; n.s.= not significant.
Testing on Computer Pen & Paper testing
Perception / Symptom /
Comfort
classr
oom
Re-circulated
Air
Oudoor Air
Supply
p <
Re-circulated
Air
Oudoor
Air Supply
p <
A 48 81 0.01 34 72 0.01 Air Stuffy (0) -
Fresh (100)
B 71 66 n.s. 66 52 n.s.
A 62 91 0.01 66 87 0.01
classroom Noisy (0) -
Quiet (100) B 51 59 0.05 81 80 n.s.
A 57 61 n.s. 52 63 0.08
Dreamy (0) -
Attentive (100) B 70 72 n.s.
59 61 n.s.
A 57 59 n.s.
39 50 0.10 Tired (0) -
Not Tired (100) B 57 58 n.s.
61 57 n.s.
A 57 61 n.s.
40 63 0.01 Sleepy (0) -
Alert (100) B 68 69 n.s.
63 60 n.s.
A 46 56 n.s. 27 41 0.01
Feel like Working (0) - Do
not feel like working (100) B 68 68 n.s. 62 60 n.s.
A 1.1 0.3 0.02 1.8 0.2 0.01
Thermal Comfort (-3 =
Cold, +3 = Hot) B 0.4 0.9 n.s. 0.1 0.9 0.01
A 60 77 0.04 56 69 0.03
classroom environment
Bad (0) – Good (100) B 80 83 n.s. 78 81 n.s.
Selected results of subjective responses to the classroom environment immediately after testing
are included in Table 2. The pupils in classroom A perceived the air as being fresher, the
classroom less noisy and their general feeling about the classroom environment was significantly
better in the condition with increased ventilation compared to that with re-circulation. There was a
trend approaching significance towards higher alertness, better work mood and tendency for
less tiredness and increased attention following the performance tests conducted on paper at the
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higher ventilation rates. The pupils’ thermal sensation was in accordance with the existing
temperature differences shown between the conditions. They were closer to neutral at operative
temperatures between 18.8 and 20.2 °C and felt slightly warm at 20.5-21.6 °C.
Evaluation of the reading comprehension task was made according to the marking sheet
provided with the tasks. Compared to a maximum mark of 16, the children in classroom A
obtained an average mark of 9.4 in the condition with improved ventilation that showed a
tendency of a higher rating (p<0.09) than 8.1 achieved in the other condition with low outdoor
air supply rate. No significant change was found in the reading comprehension marks of
children from classroom B between the two experimental conditions. Details of the maths
based performance measures for all (40) children who completed the performance tasks in both
experimental condition are shown in Table 3.
Table 3. Average speed, accuracy and overall performance (i.e. number of error-free units) of
subjects achieved in the addition and subtraction tasks.
Addition task Subtraction task
Class-
room
Condition
Speed
(units/h)
Error Rate
(%)
Performance
(units/h)
Speed
(units/h)
Error Rate
(%)
Performance
(units/h)
Re-circulated Air 142.3 23% 111.2 149.1 43% 90.1
A
Outdoor Air Supply 143.0 19% 118.7 142.7 37% 90.9
Re-circulated Air 139.2 15% 121.3 144.4 28% 103.4
B
Outdoor Air Supply 144.4 13% 125.5 143.4 21% 114.3
Re-circulated Air 140.8 19% 116.0 146.9 36% 96.4
A + B
Outdoor Air Supply 143.7 16% 121.9 143.0 30% 102.0
The children in classroom A tended to work more accurately in both addition (p<0.07) and
subtraction (p<0.07) tasks and slight improvement in the overall performance of addition
(p<0.068) was noticed at the higher ventilation rate compared to low ventilation. Similarly,
the pupils in classroom B made significantly less errors (p<0.01) and achieved better
performance (p<0.029) during subtraction at the higher ventilation rate. For classroom B the
changes in the performance measures of addition did not reach significance levels. However,
when the data for classroom A and B were pooled under the common hypothesis that the
children work better under improved ventilation, significant or close to significant
improvement was obtained in the overall performance of both addition (p<0.036) and
subtraction (p<0.052). Separate analysis was carried out for children with higher math skills
(25 pupils for both classrooms), i.e. excluding those who had a higher than 50% error rate in
these tasks. This analysis resulted in similar but more significant effects than those for
individual classrooms above. The children with higher math skills increased the number of
error-free units in both addition (p<0.02) and subtraction (p<0.007) tasks when working under
the improved ventilation conditions.
DISCUSSION
The CO
2
patterns over a school day are closely linked to the daily activities performed within
or away from the classrooms and whether windows and doors are left open or not. The levels
presented in Figure 2 reflect a situation when the classroom was occupied throughout a full
school day and no windows were opened due to cool outdoor conditions without sunshine.
Double glazed windows, installed at the majority of the schools studied, allow very little air
infiltration. If windows are left closed in the absence of other means of providing a minimum
amount of outdoor air CO
2
levels rise quickly (typically within 15-20 minutes) to 3000-4000
ppm under normal occupancy. Similar high levels in naturally ventilated classrooms have
often been reported in UK schools [6], [10]. Adverse health effects associated with CO
2
Proceedings of Clima 2007 WellBeing Indoors

exposure below 5000 ppm are difficult to evaluate since there are a number of other factors
such as high pollution level from off gassing of building materials and elevated allergen
concentration, appearing at low ventilation rates that also affect human wellbeing [20].
However, possible alteration in breathing and heart rate as well as loss of concentration and
wellbeing due to CO
2
exposures in the range between 3000-5000 ppm may be expected [21].
Other adverse health effects due to CO
2
exposure such as dyspnea, headache, dizziness and
lethargy were found mainly in medical investigations and short term exposures to CO
2
concentrations above 1% (10000 ppm) [22].
The thermal conditions during the first testing week were generally cooler both indoors and
outdoors compared to the second week of testing. Therefore the average temperatures were
somewhat higher under the re-circulated condition in classroom A and under improved
ventilation in classroom B. Considering that the thermal environment may also affect work
performance [11] the thermal conditions in classroom A would be in favour, and in classroom B
would counteract the expected changes in performance due to improved ventilation. However,
the alterations in temperature between the present experimental conditions were relatively small
compared to those in which such effect were shown [11] and therefore these may be considered
not to affect the present performance results. On the other hand the thermal conditions in
classroom B have to some extent affected the pupils’ perception in air freshness. Although the
air quality conditions were improved the pupils did not perceive significant improvement in air
freshness mostly due to the increased enthalpy of inhaled air at high ventilation [23]. The
children in classroom A who effectively perceived a change in air freshness under improved
ventilation also reported more positive effects in neurobehavioral symptoms (alertness,
attention, tiredness) and work mood in contrast with children in classroom B.
A significant impact of the ventilation rate on the school work performance of pupils was
observed in both classrooms. Summarizing the effects the overall performance of all children
increased under improved ventilation by 5.1% and 5.8% for both addition and subtraction
respectively. These effects were even stronger for the pupils with higher math skills. They
increased their math performance by ~7% when working under the improved ventilation
conditions. The magnitude of such effect is in the expected range that was seen in earlier
studies investigating work performance due to improved ventilation rates [7], [11].
The present results strengthen the evidence of earlier findings that improved ventilation has
beneficial effect on pupils’ learning performance. Without intervention the existing ventilation
rates in naturally ventilated school buildings remain below the minimum recommended levels if
thermal conditions do not influence people to open windows. Measures that allow a minimum
supply of fresh air to the classrooms of naturally ventilated buildings are needed particularly if
windows are not operated adequately to control ventilation.
ACKNOWLEDGEMENT
The present research project is supported by The Engineering and Physical Sciences Research
Council (EPSRC) and carried out in collaboration with the Department for Education and Skills
(DfES). Special thanks to Professors Anders Iregren (Nat. Inst. for Working Life, Sweden) and
David M. Warburton (Sch. of Psychology, The University of Reading) for providing the free
use of their test systems for further development; Lindab Ltd for the free provision of the
ventilation components and ducting; Heads of schools and Year 5 teachers from the
participating schools for their collaborative work in developing the pupil’s performance tests.
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