Ventilation rates in schools

ARTICLE IN PRESS Building and Environment 43 (2008) 362–367 www.elsevier.com/locate/buildenv Ventilation rates in schools D.J. Clements-Croomea,, H.B. Awbia, Zs Bakó-Biróa, N. Kochhara, M. Williamsb a School of Construction Management and Engineering, The University of Reading, Whiteknights, P.O. Box 219, Reading RG6 6AW, UK b School of Psychology and Clinical Language Sciences, The University of Reading, Harry Pitt Building, Earley Gate, Whiteknights Road, Reading RG6 6AL, UK Received 15 January 2006; received in revised form 23 March 2006; accepted 23 March 2006 Abstract Research shows that poor indoor air quality (IAQ) in school buildings can cause a reduction in the students’ performance assessed by short-term computer-based tests; whereas good air quality in classrooms can enhance children’s concentration and also teachers’ productivity. Investigation of air quality in classrooms helps us to characterise pollutant levels and implement corrective measures. Outdoor pollution, ventilation equipment, furnishings, and human activities affect IAQ. In school classrooms, the occupancy density is high (1.8–2.4 m2/person) compared to offices (10 m2/person). Ventilation systems expend energy and there is a trend to save energy by reducing ventilation rates. We need to establish the minimum acceptable level of fresh air required for the health of the occupants. This paper describes a project, which will aim to investigate the effect of IAQ and ventilation rates on pupils’ performance and health using psychological tests. The aim is to recommend suitable ventilation rates for classrooms and examine the suitability of the air quality guidelines for classrooms. The air quality, ventilation rates and pupils’ performance in classrooms will be evaluated in parallel measurements. In addition, Visual Analogue Scales will be used to assess subjective perception of the classroom environment and SBS symptoms. Pupil performance will be measured with Computerised Assessment Tests (CAT), and Pen and Paper Performance Tasks while physical parameters of the classroom environment will be recorded using an advanced data logging system. A total number of 20 primary schools in the Reading area are expected to participate in the present investigation, and the pupils participating in this study will be within the age group of 9–11 years. On completion of the project, based on the overall data recommendations for suitable ventilation rates for schools will be formulated. r 2006 Elsevier Ltd. All rights reserved. Keywords: Performance; Schools; Children; Outdoor air supply rate 1. Background A review of over 300 peer-reviewed articles of indoor air quality (IAQ), ventilation and building-related health problems in schools [1] has shown that ventilation is inadequate in many classrooms and was considered to be the main cause of health symptoms. Mendell and Heath [2] review evidence that certain conditions commonly found in US schools have adverse effects on the health and the academic performance of many of the more than 50 million US school children. They propose actions throughout the life of each existing and future school building to include Corresponding author. Tel.: +44 118 378 8197; fax: +44 118 378 3856. E-mail address: d.j.clements-croome@reading.ac.uk (D.J. Clements-Croome). 0360-1323/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2006.03.018 adequate outdoor ventilation, control of moisture, and avoidance of indoor exposures to microbiologic and chemical substances considered likely to have adverse effects. A recent Dutch study [3] carried out in homes and in classrooms also showed that pupils’ health appear to be associated with both the school and domestic exposure. Poor IAQ in schools was indicated; out of the 11 classrooms studied CO2 levels were all above the recommended level of 1000 ppm with only one exception. Scandinavian research has shown that poor IAQ in school buildings can cause a reduction in the students’ performance, whereas good air quality in classrooms can enhance children’s concentration and also teachers’ productivity [4,5]. An International Society for Indoor Air Quality (ISIAQ) Task Force report on Nordic schools [6], has identified the following areas for further research: ARTICLE IN PRESS D.J. Clements-Croome et al. / Building and Environment 43 (2008) 362–367 ventilation requirements in schools; impact of physical indoor environments on learning, behaviour and interaction with social, psychological and organisational environments. The investigation of air quality in classrooms helps us to characterise pollutant levels and implement corrective measures. Outdoor pollution, ventilation equipment, furnishings, and human activities all affect IAQ. In school classrooms the occupancy density is high (1.8–2.4 m2/person) compared to offices (10 m2/person). Ventilation systems expend energy and there is a trend to save energy by reducing ventilation rates. We need to establish the minimum acceptable level of fresh air required for the health of the occupants. In schools, the supply of adequate fresh air, and hence perceived acceptable air quality, should be high on the list of priorities to help ensure healthy working conditions for learning. No pollutant should be present in sufficient quantities to cause adverse health effects or irritation to occupants. Indoor pollutants, such as human body odour, dog and cat allergens, may cause occupants to become irritated or uncomfortable with their indoor environments; others arise from emissions from materials, badly maintained ventilation systems, dust mites, fungi, and processes within the building. Sources of outdoor air pollution are from traffic, industrial processes, construction activities, and combustion systems [7]. In the 2000 review of the National Air Quality Strategy, the UK Department for Environment, Food & Rural Affairs identified the following pollutants as the most serious threats to people’s health [8]: benzene, 1,3butadiene, CO, NO2, ozone (O3), particulates (PM10) and SO2. A range of guidelines have been in place for a number of years regarding IAQ. The Chartered Institution of Building Services Engineers [9] recommend a minimum fresh air supply rate of 8 l/s per person for non-smoking adults in offices and the same value for occupants in schools. However, the UK Department for Education [10] recommends that the heating system shall be capable of maintaining the required room air temperatures in the range 18–21 1C with the minimum average background ventilation of rate of 3 l/s per person of fresh air for all areas in schools when the external temperature is 1 1C. The DfES guidelines further recommend that ‘all teaching accommodation shall also be capable of being ventilated at a minimum rate of 8 l/s of fresh air per person for each of the usual number of people in those areas when such areas are occupied’. The American Society of Heating, Refrigerating and Air-conditioning Engineers [11] recommend fresh air supply rates of 10 l/s per person and 8 l/s per person for general office accommodation and school classrooms, respectively. The term ‘fresh air’ or ‘outdoor air’ is used within these standards and guidelines as a basis for prescribing ventilation rates. However, caution should be taken with regard to the quality of the outdoor or fresh air, as it may not be as ‘fresh’ as may have been assumed and so replacing indoor air with air from outdoors may not always 363 provide an adequate solution. The study by Gusten and Strindehag [12] revealed that outdoor air pollutants play a major role in affecting the IAQ, but cleaning products and floor polish can temporarily add to the pollution content in classrooms. Other important factors influencing air quality indoors are the intensity of the human activities (number of students, length of lessons, breaks) in the premises and the building design (e.g. window openings and door-ways). There have been numerous studies on sick building syndrome (SBS), but no co-ordinated research, which has meant that the methodology of investigation has varied, making it difficult to compare results. Research by Jones [13], together with the work on a standard questionnaire by Raw et al [14], Burt [15], Wilson et al [16] and Baldry, et al. [17] means future investigations can be carried out in a more consistent manner [18,19]. SBS conditions are such that they are prevalent in the work environment but disappear when people leave it [20,21]. Earlier research [22–25] indicated that ventilating a building with 10% or 100% outdoor air makes little difference and appears to have no effect on SBS symptoms. However, recent independent studies have documented that the quality of indoor air has a significant and positive influence on the productivity of office workers [20,22,26,27] In one study, a well-controlled normal office was used in which two different air qualities were established by including or excluding an extra pollution source, invisible to the occupants [27]. The same subjects worked for 412 h on simulated office work in each of the two conditions. The productivity of the subjects was found to be higher with good air quality; they made fewer errors and experienced fewer SBS symptoms. A related study was performed in the Danish field lab with the same pollution sources present at three different ventilation rates: 3, 10 and 30 l/s. person [28]. The productivity increased significantly by increased ventilation. These findings demonstrate that perceived air quality has a significant influence on productivity in offices. The Danish study has been repeated in Sweden with similar results [29,30]. Research by Clements-Croome [23] and Holcomb et al. [31], has revealed that potential savings in costs can be achieved by improving the working environment. According to this work, the increase in cost associated with improving the environmental conditions can be offset by the gain in productivity resulting from an increase in employee work performance. For instance, Collins [32] reported that 50% of all acute health conditions were caused by respiratory conditions due to poor air quality. Cyfracki [33] reported that a productivity increase of only 0.125% would be sufficient to offset the costs of improved ventilation. Holcomb and Pedelty [31] concluded that although there is some inconsistency in the results, there was sufficient evidence to suggest that there is an association between ventilation rates, IAQ, sick building syndrome symptoms and employee productivity. Good ventilation systems should not only provide thermal comfort but also distribute adequate fresh air to ARTICLE IN PRESS 364 D.J. Clements-Croome et al. / Building and Environment 43 (2008) 362–367 occupants and remove pollutants. Poor outdoor air quality and noise prompted action in schools in Hong Kong to be converted from naturally ventilated to air-conditioned classrooms. However, a study by Koo et al. [34], found that the frequency of symptoms in students learning in airconditioned classrooms were higher than those in naturally ventilated classrooms in Hong Kong. Studies on indoor environments in school buildings, [1,35–37] suggest that there is a correlation between pupils’ health and work performance, and the CO2 concentrations in the classrooms. There is little published information available about the effects of indoor environments on pupils’ health and performance in UK schools. 2. Case studies (1) Studies in UK schools by Coley and Beisteiner [38], have indicated levels of CO2 in excess of 4000 ppm and ventilation rates of less than 0.5 l/s per person. Using standardised, computerised tests of cognitive function, Coley [39] has demonstrated that the attentional process of 18 primary school children aged 10/11 were significantly slower when the level of CO2 in classrooms was high. 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 focussed attention. Increased levels of CO2 led to a decrement in Power of Attention of approximately 5%. Thus, in a classroom where CO2 levels are high, students are likely to be less attentive and concentrate less well on what the teacher is saying, which over time may possibly lead to detrimental effects on learning and educational attainment. The size of this decrement is of a similar magnitude to that observed over the course of a morning when students skip breakfast. (2) Research carried out by Awbi and Pay [19] in the university classrooms of different capacities at the University of Reading showed that these rooms had very poor IAQ during occupancy periods; the measured CO2 levels in this study far exceed the recommended value of 1000 ppm, in some cases by a factor of 5. The reason for poor IAQ was attributed to the low ‘‘fresh air’’ rate entering the rooms by natural ventilation. Awbi and Pay [19] made a study of the IAQ in four naturally ventilated classrooms with adult occupancy in which measurements were carried out of CO2 concentrations and relative humidity as well as estimation of formaldehyde (HCHO) emissions from furnishings and odour from the occupants. The classrooms were studied under controlled and uncontrolled conditions. Natural air infiltration measurements were also carried in each classroom three times a day under different window opening conditions using the tracer gas concentration decay method. The nature of the occupancy in the classrooms was transient and as a result concentration of indoor air pollutants were not Fig. 1. CO2 concentration in a classroom with windows and doors shut (S1). (A) and (B) represent duration of occupancy [19]. constant. Although four common pollutants were considered, the CO2 concentration and odour intensity were found to be the dominant pollutants when considering outdoor air supply rates. A typical CO2 concentration profile in one classroom (S1) is shown in Fig. 1. It is clear from Fig. 1 and data for the other classrooms investigated, that the occupancy is transient. Most ventilation standards (e.g. [11]) specify ventilation rates based on continuous occupancy. This may lead to specifying higher flow rates, which increase energy consumption unnecessarily. To determine the minimum ventilation rates for transient occupancy in the classrooms investigated, transient occupancy analysis was carried out using Eq. (1). It has been assumed that each classroom will have 70% of maximum occupancy between 9.00 and 17.00 h with 50 min occupancy in each hour and zero occupancy during lunch break. C ¼ C i en:t þ ðC o þ 106vp =Qo Þð1  en:t Þ, (1) where C (ppm) is the concentration indoors at time t (s), Ci (ppm) is the initial indoor concentration at t ¼ 0, Co (ppm) is the outdoor concentration, vp (m3/s) is the pollutant generation rate inside, Qo (m3/s) is the outdoor air supply rate, n (s), is the air change rate, n ¼ Qo =V where V is the room volume (m3). In order to determine the outdoor air supply rate (Qo) from Eq. (1), a maximum indoor concentration (C) must be assumed. The limit for body odour intensity according to Yaglou’s scale was taken as 1.8 (slightly below the moderate intensity of 2), which according to Yaglou measurements correspond to an outdoor air supply of 8 l/s/person for adult population [20]. The maximum CO2 concentration was taken as 1000 ppm and the CO2 production rate of the occupants to be 18 l/h. Results show that CO2 is the most significant pollutant to consider when calculating outdoor air supply rates with ARTICLE IN PRESS D.J. Clements-Croome et al. / Building and Environment 43 (2008) 362–367 365 odour as the second important pollutant source. Depending on the volume of classroom and average occupancy density the required outdoor air flow rates was about 7.0 l/s person for keeping CO2 at or below 1000 ppm and an average of about 5.0 l/s person for keeping odour concentrations at moderate levels as defined above. flow into the room (Karimipanah et al., 2005). To prevent overheating of classrooms in summer season mobile air conditioning units will be used to maintain the classroom temperatures at 23–24 1C. The amount of outdoor air will be adjusted by varying the fan speed and with airflow control units placed in the duct system. 3. Current research 3.3. Physical measurements 3.1. Objectives Carbon dioxide (CO2) concentration (0–5000 ppm), total concentration of volatile organic compounds (TVOC) (0–200 mg/m3), air temperature, globe temperature, relative humidity and light level will be continuously monitored. These parameters will be recorded with 3 minutes interval on a central logger using wireless data transmission technique. Mass concentration of airborne particles (including PM1, PM2.5, PM4 and PM10 size ranges) and noise level will be daily measured over a few hours, during the performance tests of pupils. Spot check of selected VOCs (sampled in Tenax-TA) and ozone concentrations will be also completed at some sites when such measurements are justified due to unusual conditions indicated by the regular monitoring.     To determine the effect of IAQ (in terms of the concentrations of particulates and CO2 as indicators) on pupils performance. To investigate the effects of ventilation rates and thermal comfort on pupils performance and health. To recommend suitable ventilation rates for classrooms. To examine the suitability of the air quality guidelines for classrooms. 3.2. Methods This research focuses on the relationship between pupils’ health, well-being and performance, and the IAQ in classrooms of Southern England. Field surveys will be carried out at twenty different primary school buildings located near (Reading), during 2–4 weeks in the Autumn, Winter, Spring and Summer. The sample will include a selection of old and new school buildings to provide comparison. The surveys will be carried out over 2 years and efforts will be made to carry out the tests in clusters of school buildings with different ventilation styles, occupancy profiles and densities, within close geographical proximity but with different background (external) pollution levels. To gather data on the physical environment of classrooms, sampling will be carried out indoors and outdoors at times before, during and after school hours. It is not realistic to contemplate parallel studies in twenty school buildings, but tests in each school will be carried out under similar outdoor climatic conditions and with the existing and increased ventilation rates that can be achieved under ‘as found’ and ‘intervention’ conditions. In each school, two classrooms will be selected for monitoring with either the existing or increased ventilation rates in each day. A portable ventilation system will be used to increase the ventilation rates in classrooms. An exterior fan placed outdoors and simple ducting will be used to increase the outdoor air supply rate to at least the prescribed level of 8 l/s per person in a classroom. Flexible air ducts will lead the outdoor air into the building through window openings, which are closed with Perspex plates. If necessary a duct heater will control the temperature of supply air in the winter season. In the classrooms the air will be distributed using Softflo air terminal units, which consist of a perforated duct with small nozzles creating confluent jets 3.4. Subjective evaluations Simultaneous to the physical monitoring, measures of self-assessed environmental perception, comfort and health will be obtained for a sample of pupils in the morning and immediately after the performance tests are carried out. Two groups of pupils (one group in each classroom) will be selected in each school. The targeted age group of the children will be between 9 and 11 years attending years 5 and 6. This age group of pupils will be selected because they remain in their classrooms most of the day and are therefore in the same environment throughout a school day. The pupils will be 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 that are believed to affect their performance. The subjective questionnaire will provide information on air stuffiness, dryness, perception of light and noise. The SBS questionnaire will focus on symptoms of the mucous membrane and in upper respiratory tract, such as nose congestion, nose, mouth, throat and eye dryness, and neurobehavioural symptoms including headache, attention, dizziness, tiredness, sleepiness. Pupils will be asked to rate the intensity of each symptom on Visual Analogue (VA) scales [29]. The scale is 100 mm long horizontal line without gradation with two vertical lines marking the extreme points of the scale. The pupils will mark the scale, more to the left or right side of the line, depending to what extent they agree with the statement of the symptom in question, labelled on the left and right end of the scale. Thermal sensation will be recorded using a 7-point PMV scale [40]. Furthermore, people will be asked to vote ARTICLE IN PRESS 366 D.J. Clements-Croome et al. / Building and Environment 43 (2008) 362–367 whether the air movement around their body is acceptable or not. 3.5. Pupil’s performance tests Since there have been few methodologically strong studies of the effects of IAQ on children’s performance in schools [2], piloting of performance measures is essential. Measures of reaction time (Swedish Performance Evaluation System, [41]) have been found sensitive to pollutants. The CDR Ltd. tests (from the same family as SPES, of measures designed to assess neurotoxic effects) used by Coley [39], the reaction time measures were also sensitive to CO2. For the study outlined here, the requirements for performance measures are quite stringent—they need to be sensitive to IAQ effects, suitable for use with children of this age and for small group administration, and to exist in a number of parallel forms. Further, administration needs to be maximally standardised, so that uncontrollable effects of contextual factors such as teacher expectations can be precluded as far as possible, and the duration of testing must be short enough to minimise disruption to school routine and to maintain pupil motivation. While reaction time is important, measures of other facets of cognitive activity (such as speed of processing), will be used in this study, and the use of complex span tasks explored, as potential indicators that classroom learning as customarily understood, might be affected by IAQ. Two different performance tests will be administered to the pupils in each school. Traditional tests will be executed on paper, which include simple math-based (addition, subtraction and multiplication of numbers) and languagebased tests (reading comprehension, word substitution, logical reasoning) similar to that performed in a normal school day. Furthermore, new software (VISCOPE— Ventilation in Schools and Cognitive Performance) has been developed based on earlier works [41] to study changes (improvement and impairment) of pupils’ cognitive performance under different air quality conditions in classrooms. These tests will be executed on laptops installed in the classroom, similar to the method used by Coley and Beisteiner [38]. Both the traditional tests and the computer tests will be given to pupils during their lessons preferably before the lunch break when the CO2 concentrations reach the maximum level of the morning’s teaching session. For the assessment with the VISCOPE software two aspects of cognitive functioning are included: attention and working memory. Attention is a cognitive process selecting, evaluating and responding to appropriate environmental information in a timely and appropriate manner. Three tasks: Simple Reaction Time (SRT), Choice Reaction Time (CRT) and Colour Word Vigilance (CWV), have been included to measure the core aspects of attention. SRT will give assessments of alertness and the ability to sustain a readiness to respond rapidly, CRT will provide stimulus discrimination and response selection and execution, whilst sustained attention, intensive vigilance and ability to ignore distraction will be assessed by CWV. For all these three tasks speed and accuracy will be recorded to give a complete assessment of attention. Working memory is the system for temporarily storing, actively processing and manipulating information needed for carrying out everyday tasks. Two mechanisms for storing information in working memory are the phonological loop and the visuo-spatial sketchpad. These mechanisms will be assessed by the Numeric Working Memory Task and the Spatial Working Memory Task. The speed and accuracy of both tasks will provide two important measures but independent aspects of working memory. The first is the ability to hold information in memory without forgetting which will be reflected by the accuracy scores. The second is the time taken to retrieve information from the working memory, which will be obtained from the speed scores. Numeric working memory task: will test cognitive processes of sub-vocal rehearsal of digit sequences via the articulatory control of the phonological loop of the working memory system. Spatial working memory task: will test both the ability to temporarily retain spatial information and visuo-spatial sketchpad of working memory. Reaction Time Addition and Digit Span Memory are also included in the test battery to assess the numeric working memory whilst Picture Recall Memory is a spatial working memory task. 4. Conclusions Reduction of energy consumption is a major part of sustainable building design. There is a tendency to reduce ventilation rates and natural or hybrid ventilation systems are common in the design of UK schools. The evidence reviewed, including the works of Awbi and Pay [19], and Coley [39], indicates that CO2 levels can rise to very high levels (about 4000 ppm) in classroom occupancy periods. Further, these levels may be detrimental to concentration hence adversely affect learning. A methodology is proposed for a 3-year research programme to investigate if there is a significant relationship between ventilation rates and learning. Acknowledgements 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 and David Warburton for providing the free use of their test systems; Lindab Ltd for the free provision of the duct work; all teachers of year 5 and 6 for their collaborative work in developing the pupil’s performance tests. ARTICLE IN PRESS D.J. Clements-Croome et al. / Building and Environment 43 (2008) 362–367 References [1] Daisey JM, Angell WJ, Apte MG. Indoor air quality, ventilation and health symptoms: an analysis of existing information. Indoor Air 2003;13:53–64. [2] Mendell MJ, Heath GA. Do indoor pollutants and thermal conditions in schools influence student performance? A critical review of the literature. Indoor Air 2005;15:27–52. [3] Dijken FV, Bronswijk JV, Sundell J. Indoor environment in Dutch primary schools and health of the pupils. In: Proceedings of indoor air 2005, Beijing, the 10th international conference on indoor air quality and climate, vol. I (1), 2005, p. 623–27. [4] Myhrvold AN, Olsen E, Lauridsen O. 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