David Peter Wyon

The Effects of Moderately Raised Classroom Temperatures and Classroom Ventilation Rate on the Performance of Schoolwork by Children (RP-1257)

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°C to 20°C (77°F to 68°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.

Effects of thermal discomfort in an office on perceived air quality, SBS symptoms, physiological responses, and human performance

UNLABELLED The effects of thermal discomfort on health and human performance were investigated in an office, in an attempt to elucidate the physiological mechanisms involved. Twelve subjects (six men and six women) performed neurobehavioral tests and tasks typical of office work while thermally neutral (at 22°C) and while warm (at 30°C). Multiple physiological measurements and subjective assessment were made. The results show that when the subjects felt warm, they assessed the air quality to be worse, reported increased intensity of many sick building syndrome symptoms, expressed more negative mood, and were less willing to exert effort. Task performance decreased when the subjects felt warm. Their heart rate, respiratory ventilation, and end-tidal partial pressure of carbon dioxide increased significantly, and their arterial oxygen saturation decreased. Tear film quality was found to be significantly reduced at the higher temperature when they felt warm. No effects were observed on salivary biomarkers (alpha-amylase and cortisol). The present results imply that the negative effects on health and performance that occur when people feel thermally warm at raised temperatures are caused by physiological mechanisms. PRACTICAL IMPLICATIONS This study indicates to what extent elevated temperatures and thermal discomfort because of warmth result in negative effects on health and performance and shows that these could be caused by physiological responses to warmth, not by the distraction of subjective discomfort. This implies that they will occur independently of discomfort, i.e. even if subjects have become adaptively habituated to subjective discomfort. The findings make it possible to estimate the negative economic consequences of reducing energy use in buildings in cases where this results in elevated indoor temperatures. They show clearly that thermal discomfort because of raised temperatures should be avoided in workplaces.

THE EFFECTS OF OUTDOOR AIR SUPPLY RATE AND SUPPLY AIR FILTER CONDITION IN CLASSROOMS ON THE PERFORMANCE OF SCHOOLWORK BY CHILDREN (RP-1257)

Two independent field intervention experiments were carried out in mechanically ventilated classrooms receiving 100% outdoor air. Outdoor air supply rate and filter condition were manipulated to modify indoor air quality, and the performance of schoolwork was measured.The conditions were established for one week at a time in a blind crossover design with repeated measures on 10- to 12-year-old children in two classes. Seven exercises exemplifying different aspects of schoolwork (numerical or language-based) were performed as part of normal lessons by pupils who also marked visual analogue scales to indicate their environmental perceptions and the intensity of any symptoms. The children indicated that the air was fresher but otherwise perceived little difference when the outdoor air supply rate increased from 3.0 to 8.5 L/s (6.4–18 cfm) per person, while the speed at which they performed two numerical and two language-based tasks improved significantly. A significant effect of ventilation rate was observed in 70% of all the statistical tests for an effect on work rate, but there were no significant effects on errors. The effects were probably due to improved air quality in the classrooms as judged by a sensory panel of adults blind to conditions, as perceived by children, and as indicated by the reduction in the average CO2 concentration from 1300 to 900 ppm, taking this as a marker of reduced bioeffluent concentration. It was not possible to test the effect of replacing a soiled filter with a new one because very little dust had been retained by the “used” filter and because of an incompletely balanced design. The unbalanced design also made it impossible to test for an interaction between filter condition and ventilation rate. These results indicate the importance of improving indoor air quality and ventilation in classrooms.

The Acceptable Air Velocity Range for Local Air Movement in The Tropics

The perception of locally applied airflow was studied with tropical subjects who had become passively acclimatized to hot conditions in the course of their day-to-day life. During the experiments, 24 subjects (male and female) performed normal office work in a room equipped with six workstations. They were exposed to local airflow from the front and toward the face at six air velocities (0.15, 0.3, 0.45, 0.6, 0.75, and 0.9 m/s) at ambient temperatures of 26°C, and 23.5°C and local air temperatures of 26°C, 23.5°C, and 21°C. Each combination was maintained for 15 minutes, during which the subjects responded to computer-administered questionnaires on their thermal and draft sensations using visual-analogue scales. The results showed that the subjects preferred air movement within a certain range, i.e., a higher percentage was dissatisfied at both low and high velocity values. Most dissatisfaction with air movement is caused by thermal sensation, with air movement perception accounting for a smaller proportion. The subjects preferred air movement to be between “just right” and “slightly breezy” and preferred their thermal sensation to be between “neutral” and “slightly cool.” The study also identified an acceptable air velocity range from 0.3 up to 0.9 m/s under the experimental conditions. This velocity range is relevant for the design of personalized ventilation in practice. This preferred velocity range is higher than the maximum velocity permissible under ASHRAE Standard 55 (ASHRAE 2004) in situations where subjects have no control over local air movement.

The Mental Performance of Subjects Clothed for Comfort at Two Different Air Temperatures

Thirty-two subjects (16 male and 10 female students aged (8-25 yr) performed sedentary work in a climate chamber under two different conditions. The subject wore a light standard clothing (0.6 clo) on one occasion and a heavy clothing ensemble (1.5 clo) on the other. Each subject was exposed singly, for 2-5 hr on each occasion. During the exposures the air temperature was continuously adjusted up or down at the subjects request, as indicated on a dial voting apparatus, so that he remained in thermal comfort. Skin temperatures were measured throughout. Performance measures were obtained on a numerical addition task, a recognition memory task, and on a test of cue-utilization. Subjects rated their effort, arousal and fatigue, and the freshness of the air on semantic differential scales. No significant differences in performance could be shown between the two conditions. Subjective effort, arousal and fatigue did not differ, but subjects considered that the air was fresher in the cool air/heavy clothing con...

The combined effects of many different indoor environmental factors on acceptability and office work performance

Ninety-nine young-adult subjects of both genders were randomly assigned to four groups. One group performed simulated office work for two hours in a set of poor environmental conditions, with overhead fluorescent lighting, recorded traffic noise from a busy street, 27°C (80.6°F) operative temperature, supply air polluted by emissions from linoleum, recorded open office noise, and almost no daylight. The realistic annual cost of improving each of the six conditions was estimated and expressed as a percentage of the total sum of the cost of improving conditions. The modifications included improved lighting, barely audible traffic noise, operative temperature of 22°C (71.6°F), clean air, quiet, and a daylit view out. A second group briefly experienced all 12 conditions and individually selected the improvements they preferred, up to a 50% budget. A third group of subjects was randomly paired with each of the subjects from the second group, and each pair was exposed to the conditions selected by the second-group subjects. A fourth group was exposed to fully-improved (100% budget) conditions. Significant improvements in subjective assessment occurred at higher budget/individual choice levels, and the self-reported performance of office tasks improved, although measured performance could not be shown to differ significantly between treatment groups.

The influence of heated or cooled seats on the acceptable ambient temperature range

In 11 climate chamber experiments at air temperatures ranging from 15 to 45°C, a total of 24 subjects, dressed in appropriate clothing for entering a vehicle at these temperatures, were each exposed to four different seat temperatures, ranging from cool to warm. In one simulated summer series, subjects were preconditioned to be too hot, while in other series they were preconditioned to be thermally neutral. They reported their thermal sensations, overall thermal acceptability and comfort on visual analogue scales at regular intervals. Instantaneous heat flow to the seat was measured continuously. At each ambient room temperature, the percentage dissatisfied was found to be a second-order polynomial function of local heat flow. Zero heat flow was preferred at an air temperature of 22°C and the heat flow that minimized the percentage dissatisfied was found to be a single linear function of air temperature in all conditions. The analysis indicates that providing optimal seat temperature would extend the conventional 80% acceptable range of air temperature for drivers and passengers in vehicle cabins by 9.3°C downwards and by 6.4°C upwards.

Experimental determination of the limiting criteria for human exposure to low winter humidity indoors (RP-1160)

Thirty subjects (17 female) were exposed for five hours in a climate chamber at 22°C (71.6°F) to clean air at 5%, 15%, 25%, and 35% RH. A comparable group was similarly exposed to air polluted by carpet and linoleum to the 35% RH condition and to 18°C, 22°C, and 26°C (64.4°F, 71.6°F, and 78.8°F) at an absolute humidity equal to 15% RH at 22°C (71.6°F). They performed simulated office work to ensure that they kept their eyes open and reported sick building syndrome (SBS) symptom intensity on visual-analogue scales. Nine objective tests of eye, nose, and skin function were applied. Subjective discomfort, though significantly increased by low humidity, was slight even at 5% RH. More rapid blink rates were observed at 5% than at 35% RH (P < 0.05), and tear film quality as indicated by the Mucous Ferning Test deteriorated (P < 0.05) at low humidity (5%, 15%) and at the highest air temperature 18°C, 22°C > 26°C (78.8°F). Low humidity was found to have reduced the rate of performance of three office tasks by 3%–7%.

The Effects of Electrostatic Particle Filtration and Supply-Air Filter Condition in Classrooms on the Performance of Schoolwork by Children (RP-1257)

Two independent field intervention experiments involving a total of about 190 pupils were carried out in winter and early spring of 2005 in five pairs of mechanically ventilated classrooms that received 100% outdoor air. Each pair of classrooms was located in a different school. Electrostatic air cleaners were installed in classrooms and either operated or disabled to modify particle concentrations while the performance of schoolwork was measured. In one school, the used supply-air filters in a ventilation system without recirculation were also replaced with new ones to modify classroom air quality, while the filters in use in other schools were not changed. The conditions were established for one week at a time in a blind crossover design with repeated measures on ten-to-twelve-year-old children. Pupils performed six exercises exemplifying different aspects of schoolwork as part of normal lessons and indicated their environmental perceptions and the intensity of any symptoms. A sensory panel of adults judged the air quality in the classrooms soon after the pupils left. Operating the electrostatic air cleaners considerably reduced the concentration of particles in the classrooms. The effect was greater the lower the outdoor air supply rate. There were no consistent effects of this reduction on the performance of schoolwork, on the childrens perception of the classroom environment, on symptom intensity, or on air quality as perceived by the sensory panel. This suggests there are no short-term (acute) effects of particle removal outside the pollen season. When new filters were installed, the effects were inconsistent, although this is believed to be due to sequential and unbalanced presentation of filter conditions and to the fact that the used filters retained very little dust.

Warmth and performance: reply to the letter from Leyten and Kurvers (2013)

Thank you for giving us an opportunity to reply to the letter from Leyten and Kurvers (2013) concerning our recent paper on the effects of thermal discomfort in an office (Lan et al., 2011). Our experiment does not show which of several possibly driving factors caused our subjects to perform simulated office work about 10% more slowly when they felt too hot at 30°C. It could indeed have been the fact that they felt too hot, in which case the effect would not occur if they did not feel too hot at that temperature. Leyten and Kurvers point out that if office workers can increase the local air velocity and reduce their clothing insulation sufficiently, they may be able to achieve thermal neutrality at 30°C. This is not in dispute—both Predicted Mean Vote (PMV) and the Adaptive Comfort Theory (ACT) predict that this may occur, although ACT does go further by claiming that it will occur at certain outdoor temperatures: ACT uses outdoor temperature as an empirical predictor of this kind of ‘objective’ adaptation to raised indoor temperatures, while PMV simply predicts how thermal comfort would be affected by any changes in clothing insulation, air velocity, and/or metabolic rate that do occur. However, Leyten and Kurvers also claim that subjective adaptation will sometimes occur, namely the ‘acceptance’ that indoor temperatures in naturally ventilated buildings (and more generally in buildings with no mechanical cooling) will inevitably rise when it is hot outside, a state of mind that they claim is further facilitated because in such a building, they ‘subjectively experience that they have control over their thermal condition’ even if that control is insufficient to prevent it becoming undesirably hot. They ask us to believe that the performance of office work will remain unaffected if the occupants of such buildings achieve this state of acceptance even though the objective adaptation predicted by PMV is not sufficient for them to remain in thermal neutrality. Acceptance of undesirably warm thermal conditions is thus equated with achieving thermal comfort, and because they believe that it is the absence of thermal comfort that reduces the performance of office work, they believe that performance will be unaffected. This is where we part company: Our experiment provides detailed evidence of the physiological and mental changes (headache, fatigue, difficulty in thinking clearly, dry eyes, reduced oxygen saturation and increased CO2 levels in blood, and decreased tear film quality) that occur in response to warmth, changes that seem to us not only very likely to be directly responsible for the observed reduction in performance, but also very unlikely to be reduced by subjective ‘acceptance’ of the conditions that cause them. We should perhaps state categorically here that we do of course accept that these physiological changes will not occur if the objective adaptation defined above does occur and does result in thermal neutrality, and that no effects on performance are then to be expected. However, objective adaptation does not always occur, even if it is theoretically possible, for example it does not occur when raised air velocity would be inconvenient and when reduced clothing insulation would be socially unacceptable, and in such cases, PMV will predict reduced performance, whereas ATC will not. When thermal comfort depends on ‘acceptance’, PMV will predict reduced performance, whereas ATC will not, although one of the most frequently reported behavioral adjustments to warm or hot conditions is to ‘take a break’ or to otherwise reduce the rate of working, adjustments that by definition reduce performance at high temperatures. One problem with our laboratory experiment is that warmth and thermal discomfort were confounded, as they so often are, so the observed reduction in performance could have been caused directly by thermal discomfort, acting perhaps as a distraction, or it could have been caused by the physiological changes we describe. Our subjects were not ‘habituated’ to 30°C, by which we mean they were not used to having to work at this temperature, and they had no control over the exposure conditions, so they had not achieved ‘acceptance’ of them. To determine whether the acceptance postulated by ATC can be exploited as a means of achieving energy conservation without the considerable penalty of reduced performance would require a field experiment in a naturally ventilated building (or a building with no mechanical cooling) in which the performance of office work is assessed under conditions in which the predictions of ATC and PMV differ. Until that experiment is performed, we are content to have