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Description
Two independent field intervention experiments were carried out in school classrooms in late summer (in 2004 and 2005). The air temperature was manipulated by either operating or idling split cooling units installed for the purpose. In one of these experiments, the outdoor air supply rate was also manipulated. The conditions were established for one week at a time in a blind crossover design with repeated measures on two classes of 10- to 12-year-old children. Six to eight exercises exemplifying different aspects of schoolwork (numerical and language-based) were performed as part of normal lessons. Pupils indicated their environmental perceptions and the intensity of any symptoms on visual analogue scales. Their thermal sensation changed from slightly too warm to neutral, and the performance of two numerical and two language-based tests was significantly improved when the temperature was reduced from 25[degrees]C to 20[degrees]C (77[degrees]F to 68[degrees]F). When the outdoor air supply rate was increased from 5.2 to 9.6 L/s (11.0 to 20.3 cfm) per person, their performance of four numerical exercises improved significantly, confirming the results of previously reported experiments in the same series. The above improvements were mainly in terms of the speed at which tasks were performed, with negligible effects on error rate. Most school classrooms worldwide experience raised air temperatures during increased thermal loads, e.g., in warm weather; these results show that providing some means of avoiding elevated temperatures would improve educational attainment.
INTRODUCTION
Unsuitably high temperatures are common in classrooms, even those in cold countries. For example, a survey of temperatures in a large number of schools in Sweden showed that classroom temperatures were generally 23[degrees]C-25[degrees]C (73.4[degrees]F-77[degrees]F) in the shoulder seasons (April to September), 3[degrees]C-6[degrees]C (5[degrees]F-10[degrees]F) above what teachers and pupils preferred. Some classroom temperatures were as high as 30[degrees]C (86[degrees]F), which is quite remarkable for such a cold country (Eriksson et al. 1967). The most common reason for such high temperatures is that classroom ventilation rates are too low to remove the excess heat load caused by sunshine entering the windows, which until relatively recently were traditionally designed to provide as much daylight as possible, with large glazed areas that faced the sun. This is especially the case in the many schools that have only natural ventilation, as windows must often remain closed to exclude external noise and prevent draft, but it may also be the case in schools with mechanical ventilation and no cooling.
Very few data are available on thermal effects on the performance of schoolwork by children. A recent wide-ranging and authoritative review of research by Mendell and Heath (2005) of the factors that might influence student performance found only one peer-reviewed study of how the air temperature in classrooms affects schoolchildren's performance (Schoer and Shaffran 1973). These authors reported three experiments in which 10- to 12-year-old pupils in matched pairs were assigned either to a classroom without cooling (where the temperature was about 26[degrees]C [78.8[degrees]F]) or to an adjacent air-conditioned classroom (where the temperature was about 22.5[degrees]C [72.5[degrees]F]). The classrooms were especially built for the purpose. Each group then worked in the same classroom every school day for six to eight weeks. Nineteen different tests were applied, ranging from very simple and repetitive tests (such as crossing out certain letters in a text) to school exercises stated to be current at the time (such as coding numbers onto machine-readable punched cards), and the students' performance was significantly better in the classroom that was always cool, on average by 5.7%. However, the subjects knew they were taking part in an experiment (because they were taken by bus each day to the experimental classrooms and instructed by experimenters who were not their normal class teachers) and knew when they were being tested (because each test was performed under maximum effort conditions and timed with a stop-watch), and by talking to each other over six to eight weeks, they must have known that there was a difference in temperature between the two classrooms. This means that the observed difference in performance could have been due to a gradual process of discouragement and growing resentment between two groups of pupils. This interpretation is supported by the original authors' own analysis showing that the difference in performance between the groups increased over time, while the parallel processes of acclimatization, familiarization, and learning would all be expected to reduce over time the negative effects of temperature on performance.
Mendell and Heath (2005) did not review the comprehensive set of experiments on the effects of classroom temperature on the performance of schoolwork that was carried out in the 1960s and 1970s in Sweden, probably because the only report of them in an archival peer-reviewed journal (Wyon 1970) was a brief summary of their findings. In these experiments, three parallel classes of 9- to 10-year-old children were exposed for two hours to each of three classroom temperatures-20[degrees]C, 27[degrees]C, and 30[degrees]C (68[degrees]F, 80.6[degrees]F, and 86[degrees]F), encountered in balanced order, and four classes of 11- to 12-year-old children were similarly exposed to 20[degrees]C and 30[degrees]C (68[degrees]F and 86[degrees]F) in the morning and the afternoon in a 2 x 2 design, again in balanced order of presentation of conditions (Holmberg and Wyon 1969). The temperatures were artificially raised in these experiments, while in the study by Schoer and Shaffran (1973) they were artificially reduced. The children performed a number of school exercises, including numerical tasks (addition, multiplication, number-checking) and language-based tasks (reading and comprehension, supplying synonyms and antonyms) so that their rate of working and the number of errors they made could be quantified. The children's performance of both types of task was significantly lower at 27[degrees]C and 30[degrees]C (80.6[degrees]F and 86[degrees]F), in comparison to 20[degrees]C (68[degrees]F). In the numerical tasks, the effect was on rate of working, but reading comprehension as well as reading speed were reduced by raised temperatures. Performance tended to be lower, though not significantly lower, at 27[degrees]C (80.6[degrees]F) than at 30[degrees]C (86[degrees]), and the negative effects of raised classroom temperatures were significant in the afternoon, when the children were fatigued, but not in the morning. The magnitude of the negative effect of temperature on performance was much larger in this study than was found in the study by Schoer and Shaffran (1973), often as great as 30%. The appearance and behavior of the children were systematically observed in these studies from behind one-way glass, and both were significantly affected by raised classroom temperature (Holmberg and Wyon 1972): the children became visibly hot but were very slow to adjust their clothing; girls became restless but continued to work, while boys began to behave in an undisciplined way and could be seen to concentrate less well. In another experiment in the same series, carried out in a language laboratory rather than a classroom, significant and negative effects of artificially raising the temperature from 20[degrees]C to 27[degrees]C (68[degrees]F to 80.6[degrees]F) could be shown when the children had to listen and speak a word, though not when they were listening and writing (Ryd and Wyon 1970). In a fourth experiment, performed this time in a climate chamber in England, in which groups of four 12-year-old boys were exposed to 20[degrees]C, 23.5[degrees]C, and 27[degrees]C (68[degrees]F, 74.3[degrees]F, and 80.6[degrees]F) in balanced order, no effects of the intermediate temperature could be shown (Wyon 1969), while the highest temperature caused children to perform schoolwork more slowly and to complete a diagnostic test of cue-utilization (the Tsai-Partington test) more rapidly, indicating that raised temperatures reduce arousal or alertness.
The results of the studies summarized above suggest that increased classroom temperatures can have negative effects on the performance of schoolwork by children. However, they were all obtained nearly four decades ago, and the results differ in terms of the magnitude of the effects and yield little information on how far below 27[degrees]C (80.6[degrees]F) it is possible to extrapolate the findings. Mendell and Heath (2005) concluded that no other studies on this issue have been carried out since then, probably because the main focus of indoor environmental research has been on thermal effects on the performance of office work by adults. This research was recently reviewed by Wyon and Wargocki (2006a), who concluded that thermal discomfort distracts attention and generates complaints, while warmth lowers arousal, exacerbates sick building syndrome (SBS) symptoms, and has a negative effect on mental work. The same effects may also be expected to occur for children and their performance of schoolwork, and children may be more affected by environmental effects even though they typically complain less about them. The present experiments were therefore designed to determine whether avoiding elevated temperatures in classrooms can improve the performance of schoolwork by children, and if so, by how much. In addition, the present experiments investigated the effects of increased outdoor air supply rate on the performance of schoolwork by children as a continuation of two other experiments in the same series, reported in a separate paper by Wargocki and Wyon (2007).
METHODS
Experimental Design
This study was designed as a series of field experiments in existing classrooms occupied by children performing their normal schoolwork. This was more natural for children than transporting them to a laboratory where they might behave abnormally, e.g., exert extra effort to perform well. Two experiments in which the air temperature in classrooms was manipulated were performed in the present series, all of them in the same school in Denmark, which is situated in the cool temperate area of Northern Europe; two experiments in which the outdoor air supply rate to classrooms and filter condition were manipulated are reported in another paper (Wargocki and Wyon 2007). The two experiments reported here were both crossover experiments in pairs of classrooms, in which two air temperatures were imposed in the same week, one in each adjacent classroom. The temperature conditions were switched between the classrooms the following week (crossover design). One experiment (Experiment 1T) was a 2 x 2 design in which each air temperature was re-imposed but with a different outdoor air supply rate. In Experiment 2T, the air temperature was changed but the outdoor air supply rate remained constant. Both experiments were performed in late summer in two successive school years, and the supply air filters were always new. Both experiments were performed as repeated-measures designs, i.e., the comparisons between conditions were always within-subject comparisons, to eliminate any bias due to individual differences in the ability to perform schoolwork. The sequence of exposures is shown in Table 1. During the experiments, the teachers and pupils were allowed to open the windows and doors as usual, and no changes in the schedule of normal school activities were made, so as to maintain the teaching environment and routines as normal as possible. The interventions were all improvements to existing conditions and were approved by parents, teachers, the School Board, the responsible local authority, and the Danish Ethics Review Board once this had been satisfactorily explained. Children were not asked for their consent so that they would remain unaware that they were taking part in an experiment in which classroom temperature and ventilation rate were being manipulated.
School, Classrooms, and Ventilation
The school is located in Denmark. It is an elementary public school for children aged 6 to 16 years and is run by the local authority. The school was selected for the experiment partly because it had six identical classrooms, partly also because energy conservation had led to fan speeds being reduced to well below their design level, and partly because large fenestration facing south led to large solar heat gains that considerably increase classroom temperatures (Figure 1). The school buildings were constructed in the 1950s and are made of bricks and concrete with large glazed areas; smoking is not allowed. Mechanical ventilation was installed in 1997. The two classrooms used in the present experiments were part of a row of six identical wings opening off the same straight north-south corridor, all with cathedral-height ceilings and large glazed south-facing facades with five openable windows. Each classroom had a floor area of 65 [m.sup.2] (699.7 [ft.sup.2]) and a volume of 187.5 [m.sup.3] (6621.5 [ft.sup.3]). The classrooms have typical school furniture and floors covered with linoleum; outdoor clothing is left on hooks in the corridor, just outside the classrooms. No cooling was available in the classrooms. They are supplied with 100% outdoor air, filtered (F7 class bag filters) and pre-heated from a central air-handling unit (AHU) situated in the basement; there is a cross-flow plate heat exchanger in the AHU for heat recovery. The intermittent operation of the AHU (the system was on nine hours per day and off during weekends and school holidays) is controlled by a computer. Each pair of classrooms in a given experiment was supplied with outdoor air from the same AHU. Pre-existing vertical brick shafts are used to transport the air from the basement, where the AHU is situated, to the classrooms. Supply air entered each classroom through supply grilles located in the wall above the openable windows and left through exhaust grilles close to the floor in the west wall adjacent to the corridor (Figure 1). Further details of the school, classrooms, and ventilation are given by Wargocki and Wyon (2007).
Interventions
To reduce the classroom temperature, wall-mounted split-unit air conditioning was installed in each classroom, consisting of an outdoor unit, situated on the roof, connected to two low-noise indoor units installed on the walls perpendicular to the south facade, above the height of the ventilation inlet grilles. Two indoor units were installed to keep the noise level as low as possible. The maximum capacity of the cooling system was 6 kW, but the units were always operated at low speed to reduce noise (about 25-30 dB(A) per unit according to their specifications), thus the actual capacity was only 5 kW. The cooling capacity required was estimated by calculating the heat loads from occupants and the sun for the period of the year for which the experiments were scheduled (August-September). The capacity installed was estimated to be sufficient to... |
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