Home | Business News | Browse by Publication | H | HVAC & R Research

The effects of electrostatic particle filtration and supply-air filter condition in classrooms on the performance of schoolwork by children (RP-1257).

Article Excerpt
INTRODUCTION

Many studies have reported high concentrations of particles in classrooms (EFA 2001; Dijken et al. 2005; Simoni et al. 2006), but until recently none demonstrated that removing particles in classrooms improves the performance of schoolwork. The only study that directly tested this hypothesis was a recent field experiment in Sweden in which electrostatic air cleaners were operated or disabled in two pair of classrooms (Mattsson and Hygge 2005). The study focused on the possible benefits of air cleaners for children with allergies or hypersensitivity and was, therefore, performed during the pollen season. The air cleaners reduced the concentration of airborne particles and tended to reduce the amount of cat pollen, although the effect was not statistically significant (Mattsson et al. 2004). When the air cleaners were operated, children "stating themselves to be sensitive to airborne particulate contaminants" experienced a significantly greater reduction in eye and airway irritation, and these pupils scored about 25% higher on one of the five performance tests (finding synonyms); however, multiple testing (i.e. chance) could be a possible reason for this isolated result.

It has always been assumed that respirable particles in indoor air must have some negative effects on health and that this may have negative consequences for task performance. The origin of this assumption is that in the absence of additional indoor sources, such as combustion, cooking, or smoking, indoor particles are, to a very large extent, the same particles found in outdoor (ambient) air (Fromme et al. 2005) where, according to reliable epidemiological evidence, they do have negative effects on the health of older people with pre-existing medical problems, on asthmatics of all ages (NRC 2004; Dominici et al. 2006; Hartog et al. 2003; Peters et al. 1997) and on children (Ward and Ayres 2004; Moshammer et al. 2006). In spite of this evidence, a recent major literature review of 1725 relevant publications on the health effects of particles in indoor air (EUROPART) concluded that there was "inadequate scientific evidence that airborne indoor particulate mass or number concentrations can be used as generally applicable risk indicators of health effects in nonindustrial buildings" (Schneider et al. 2003).

The concentration of particles indoors can be reduced by installing electrostatic deposition air cleaners, particulate collection devices that remove particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic air cleaners are able to remove small airborne particles very effectively (Mattsson et al. 2004; Croxford et al. 2000; Skulberg et al. 2005), including allergenic particles (Hacker and Sparrow 2005; Francis et al. 2003; van der Heide et al. 1999), whose concentrations in school classrooms are often as high as they are in the homes of pet owners (Almqvist et el. 1999; Berge et al. 1998). However, operation of electrostatic air cleaners has not reliably been shown to result in a benefit for occupants. Installation of free-standing electrostatic air cleaners with disposable deposition plates in a London office reduced the concentrations of small particle fractions [less than or equal to]2[micro]m (PM2) more than they reduced those of larger fractions (PM10), but they did not reduce surface dust (Croxford et al. 2000) and showed no effect on symptoms reported by occupants of the office (Wyon et al. 2000). In a similar intervention experiment in Norway offices, operation of electrostatic air cleaners reduced dust concentration but again had no significant effect on reported symptoms (Skulberg et al. 2005). Rosen and Richardson (1999) operated ionizers (with no deposition plates) in two day-care centers in Sweden during a three-year study and reported that their intervention reduced the number of small particles by 78% and the number of larger particles by 45% but that absenteeism due to illness was significantly reduced in only one of the two institutions. There were large changes in absenteeism over time in the control condition, which indicated that this apparent effect of the intervention could have been due to external factors.

The present experiments were designed to determine whether reducing the concentration of airborne particles in school classrooms improves the performance of schoolchildren on homework and whether the condition of the bag filter in the ventilation system affects this. The experiments are part of a larger study investigating the effects of improving classroom conditions on the schoolwork performance (Wargocki and Wyon 2007a, 2007b).

METHODS

Experimental Design

The study was designed as a series of field experiments in existing classrooms occupied by children performing their normal schoolwork. These were crossover experiments in pairs of classrooms in which electrostatic air cleaners were operated or disabled in the same week in each adjacent classroom. The operation mode of the electrostatic air cleaners was switched between the classrooms the following week (crossover design) (see Table 1). The main advantage of this design is that any external factors that affect performance, environmental perceptions, and symptoms in a given week equally affect the results obtained under both conditions established during that week, thus avoiding bias. To eliminate any random bias due to individual differences in symptom intensity or the ability to perform schoolwork, the experiments were run as repeated-measures designs. Experiment 1EF, performed in January 2005, was a 2 x 2 design in which each operation mode of the air cleaners was reimposed after exchanging used and new supply-air particle filters. Experiment 2EF was performed in March and April of 2005, and the supply-air filters had been in use for some months. Both experiments were performed outside the pollen season to avoid this additional source of individual difference in sensitivity to particles. During the experiments, teachers and pupils were allowed to open and close the windows and doors as they would normally according to their habits. No changes were made in the schedule of normal school activities so as to maintain the teaching environment and routines as normal as possible. The interventions were approved by parents, teachers, the school board, the responsible local authority, and the ethics review board. Children were not asked for their consent so that they would remain blind to experimental conditions.

Table 1. The Partially Balanced Design of Experiments 1EF and 2EF Experiment 1EF, Winter Week Classroom 1 Classroom 2 1 Used filters Electrostatic air Placebo units (a) cleaners 2 New filters Electrostatic air Placebo units (a) cleaners 3 New filters Placebo units (a) Electrostatic air cleaners 4 Used filters Placebo units (a) Electrostatic air cleaners Experiment 2EF, Spring Week Classroom 1 Classroom 2 1 Used filters Electrostatic air cleaners Placebo units (b) 2 Used filters Placebo units (b) Electrostatic air cleaners 3 4 (a) Cabinets without electrostatic air cleaner and top-mounted fans in operation. (b) Cabinets with electrostatic air cleaner, corona charge disabled and top-mounted fans in operation.

Schools, Classrooms, and Ventilation

Experiments were carried out in five elementary public schools, all run by the local authorities, for children aged 6-16 years (see Table 2). The school buildings were made of bricks and the classrooms had floor coverings and typical school furniture; outdoor clothing used by pupils was left outside the classrooms, and smoking was not allowed. All classrooms were ventilated with mechanical ventilation systems that supplied 100% outdoor air filtered and preheated in central air-handling units (AHUs) with or without heat recovery; no cooling or humidification was provided (see Table 2). The AHUs were operated intermittently (the system was on 9-10 hours...

View this article FREE - Now for a Limited Time, try Goliath Business News
Free for 3 Days!