series of field intervention experiments Thermal and air quality effects on the performance of schoolwork by children

Transcription

1 Thermal and air quality effects on the performance of schoolwork by children David P. Wyon Technical University of Denmark Swegon Air Academy Lisbon Field intervention experiments This lecture reports the findings of a recent series of field intervention experiments that was carried out in schools in Denmark and Sweden on behalf of ASHRAE DTU was awarded the research contract in open competition with bidders from USA, Europe, Australia and the Far East The Final Report has just been accepted The effects of temperature, outdoor air supply rate and airborne particles on children in school classrooms (Final Report of ASHRAE 1257) David P. Wyon and Pawel Wargocki Technical University of Denmark Main RP-1257 Objective To investigate whether improving indoor air quality in classrooms and reducing moderately elevated classroom temperatures can improve the performance of schoolwork by children Window opening behavior was passively recorded during the experiments 1

2 Methods Indoor air quality was modified by increasing the outdoor air supply rate from a mechanical ventilation system Air temperature was reduced in hot weather by operating split cooling units Windows could be opened as usual Window opening behavior was recorded as all windows closed or 1 or more open Door opening was also recorded Selected school in Denmark School at Rungsted DTU Schools Randomly selected elementary school No reported IEQ problems Mechanically ventilated South-facing facades Plan of the selected classrooms Selected classrooms 2

3 Selected classrooms View of classroom Ventilation system Split cooling was unobtrusively installed for the temperature interventions Split cooling Silent electrostatic air cleaners 3

4 4th to 6th grade year old ~3 pupils Pupils Physical measurements Continuous measurements (with pupils): CO 2, Air T, RH, window opening state recorders Effective outdoor air supply rate in L/sp was estimated from CO 2 rate of increase each time children entered the classroom.. Note that this includes air entering through windows as well as supply air Measurements of perceptions and symptoms The children marked Visual-Analogue scales at the end of the week Intensity of symptoms and their perceptions of the classroom environment was indicated How is the classroom right now? Too cold The air is It is draughty humid The air is poor Too dark Too noisy How do I feel right now? Nose is blocked Throat is dry Lips are dry Skin is dry I am very hungry I slept badly last I feel very night tired I slept too little last I do not feel night like I working have a headache Too warm The air is still It is dry The air is fresh Too much light Too dark I can breathe freely Throat is not dry Lips are not dry Skin is not dry I am full I slept well last night I am not at all tired I slept long last night I feel like working today I do not have a headache Measurements of performance Tasks appropriate to children s age, developed in consultation with class teachers 4 language-based based: Acoustic proof-reading reading Reading and comprehension Logical reasoning Proof-reading reading 4 numerical: Subtraction Multiplication Number comparison Addition Tasks performed during mathematics and language lessons 4

5 Sensory assessments of air quality ACCEPTABILITY SCALE Clearly acceptable Just acceptable Just not acceptable Clearly not acceptable Classrooms w/o pupils Permissions obtained Parents School Headmaster School Board Teachers Local Authority Danish Ethics Review Board Swedish Ethics Review Board Design of experiments Interventions always improved IEQ They were applied for 1 week at a time in balanced order of presentation Cross-over over design (one classroom with existing conditions and one with improved conditions) Mechanical ventilation system modified to provide more air to one classroom at a time Split cooling installed and run in one classroom at a time Ventilation rate 2x2 design current high Temperature Current Cool 5

6 Estimated effective L/s p Mean classroom CO2 ppm L/s per person Low L/s High L/s AC No AC Mean CO2 ppm Low L/s High L/s AC No AC Peak classroom CO2 ppm Teaching environment and routines Peak CO2 ppm Low L/s High L/s AC No AC No restrictions on normal daily activities No changes in class schedules Doors and windows could be opened No contact between researchers and children 6

7 Reduced classroom temperature 2 independent experiments in August/September 24 and 25: 1st experiment: temperature reduced from 23.5 to 2 o C at two ventilation rates 2nd experiment: temperature reduced from 25 to 21 o C with no mechanical ventilation Other parameters of classroom IEQ were unchanged Typical time-course of classroom temperature in the two classrooms T [ C ] :3 9: 1:3 12: 13:3 15: 16:3 Time Children s perception of temperature Too warm (P<.1) Performance of schoolwork as a function of classroom temperature 1,4 Performance 1,2 1,8 R 2 =.68 Too cold Low temp High temp, Temperature Estimated PMV PMV= PMV=.7 1 o C lower temperature ~3.5% higher performance 7

8 Cf. experiments performed by DP Wyon in Malmö in 1967 Raising classroom temperature from 2 C to 3 C reduced most types of schoolwork performance by up to 3% For 4 years this was widely believed to be an overestimate The present results support the magnitude of the thermal effect first reported in 1967: +1 C would lead to 35% slower work! Increased outdoor air supply rate Three independent field intervention experiments with 1% outdoor air supplied through new filters: was increased to 9.5 L/sp was increased to 6.5 L/sp was increased to 9.5 L/sp (with and without cooling ppm Time-course of classroom CO 2 concentration, example 15:59 15:3 15:2 14:33 14:4 13:35 13:6 12:38 12:9 11:4 11:11 1:42 1:14 9:45 9:16 8:47 8:18 7:5 Children s perception of IAQ Fresh air Poor air Low vent (P<.1) High vent 8

9 Sensory assessments of air quality made by an untrained panel after children had left the classroom Dissatisfied % (P<.1) Low vent High vent Effect of increasing ventilation rate on performance: increase in speed % Experiment 1 Experiment 2 Experiment 3 * * * * * * * * Subtraction Multiplication Number comparison Addition Logical reasoning Reading and comprehension * Performance of schoolwork as a function of classroom ventilation Performance 1,4 1,2 1 R 2 =.59,8 Results Condition of supply air filter Two studies in January 25 No consistent effects on perceptions, symptoms or perceived air quality when a used filter was replaced with a new one, Ventilation (L/sp) Doubling ventilation rate ~14.5% higher performance 9

10 % Effect of installing new filter on performance: increase in speed * (*) * * * Effect of installing new filter on performance: decrease in % errors % Subtraction Multiplication Number comparison Logical reasoning Reading and comprehension -15 Subtraction Multiplication Number comparison Logical reasoning Acoustic proof-reading Acoustic proof-reading (errors) (false positives) Reading and comprehension Performance Installing a new filter had no effect on children s performance % Used filter Speed (P<.92) New filter % Used filter % errors (P<.37) New filter Interpretation Inconsistent results Incompletely balanced design Very little dust was retained in the used supply air filter Supply was 1% outdoor air, so all the dust originated outdoors 1

11 Results Operation of electrostatic air cleaners 2 independent experiments in January and March/April 25 in 1 Danish and 4 Swedish schools Concentration of particles in classrooms was considerably reduced when electrostatic air cleaners were in operation Number of particles per cm Placebo units Air cleaners >.75 >1. >2. >3.5 >5. >7.5 >1 >15 Concentration of particles per cm3 (with/without without electrostatic deposition) Reduction greater in the 2 poorly ventilated classrooms Operating electrostatic air cleaners had no effects on performance Performance % Speed (P<.59) % % errors (P<.36) 1 7 Placebo units Air cleaners 7 Placebo units Air cleaners 11

12 Conclusions on filters and airborne particles Operating the electrostatic air cleaners to reduce the concentration of airborne particles had no effects on the performance of schoolwork No clear effects of installing a new filter in the outdoor air supply flow However, reducing airborne particle concentration may still reduce the long- term effects of IAQ on health Main 1257-RP conclusions Reducing moderately raised classroom temperatures eliminated thermal discomfort and improved children s performance Increasing outdoor air supply rate improved classroom air quality and improved children s performance Schoolwork was performed faster, with no increase in errors, in both cases Implications Removing airborne particles had no effect, so the IAQ effects were due to gas-phase pollutants in classroom air Replacing supply air filters had no effect but increasing the outdoor air supply rate did, so pollutants must originate indoors The active pollutants could be bioeffluents or emissions from materials, or both IAQ effects on adults Emissions: : performance of office work was reduced when office materials were present behind a screen in a clean room Bioeffluents: : performance of office work was reduced when the outdoor air supply was reduced in a clean room Conclusion: both classroom emissions and bioeffluents are likely to affect the performance of schoolwork by children 12

13 Window opening Throughout the DK experiments,, state loggers fitted to windows and doors recorded when they were open Teachers and children were able to open windows and doors as usual This is the first intervention experiment on window-opening opening behaviour in response to raised temperature or decreased outdoor air supply rate in school classrooms Summertime classroom T in C (NB: Different classes with natural/mechanical ventilation) Off Low High Mechanical ventilation No AC AC Observations Split cooling could only reduce the air T by 1.7 C C at the highest ventilation rate (T was reduced by 5.4 C C at the lower rate) With natural ventilation, cooling was not very effective, reducing T by only 3.3 C (NB: this could be due to poor mixing, as T was recorded at 2.2m height) Outdoor air supply rate (L/sp) (NB: Different classes with natural/mechanical ventilation) 1 5 Off Low High Mechanical ventilation No AC AC 13

14 Hours/week with windows open (NB: Different classes with natural/mechanical ventilation) Off Low High Mechanical ventilation No AC AC Observations Windows were open much less when cooling was in operation Even with 1 L/sp, a 1.7 C C increase in T increased window opening by 75% With no cooling, opening windows provided only 3.7 L/sp With open windows,, split cooling reduced window opening by 65%, reducing the outdoor air supply rate to 2.7 L/sp 25 Classroom T (NB: different classes in winter & summer) 1 Outdoor air supply rate (L/sp) (NB: different classes in winter & summer) C 2 Summer Winter Summer Winter 2 15 Low High Ventilation (with no AC) Low High Ventilation (with no cooling) 14

15 Hours/week with windows open (NB: different classes in winter & summer) Low High Ventilation (with no cooling) Summer Winter Hours/week with windows open and with cross ventilation (2 classes in winter,, 2 other classes in summer) Winter Summer Windows open Cross ventilation (With mechanical ventilation set to low in both seasons) Hours per week with windows open and with cross ventilation (Summer, same 2 classes in all 4 conditions) T low (A/C) T high (No A/C) Windows open Cross ventilation Observations Windows were open 4x as long in summer (when classroom T was 5 C 5 C warmer) This raised the total outdoor air supply rate from 6.5 to 9.5 L/sp Both windows and doors were used adaptively to achieve cross-ventilation Window opening was triggered by warmth but not by poor air quality (With mechanical ventilation set to low throughout) 15

16 Conclusions on window opening Windows were opened to reduce classroom temperatures, not to improve IAQ Natural ventilation did not ensure adequate ventilation, even with cross-ventilation Split cooling, by eliminating the perceived need to open windows, decreased the air quality still further In this study, both slightly raised T and poor IAQ decreased children s performance Our thanks are due to ASHRAE, STVF, Asthma and Allergifond and Formas for funding Sophie Irgens (mid-term project student) Bartlomiej Matysiak,, Line Jark,, Maria Schaub- Hansen, Kasper Lynge Jensen, Mateusz Komenda (M.Sc. students) Cristina Pirvu,, Henry Willem (Ph.D. students) Pupils, teachers, schools, municipalities School Technical Services in Rungsted, Lund Further reading ASHRAE Journal, October 26 (Summary of T, IAQ effects) ASHRAE HVAC&R Research J, March 27 (2 papers: : T, IAQ effects) ASHRAE HVAC&R Research J, May 28 (e-filters) Indoor Air 28, September 28 (Observations of window opening) 16