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 Stockholm

2 Field intervention experiments This lecture reports the findings of a 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 project was known as ASHRAE 1257

3 Final Report of ASHRAE 1257 The effects of temperature, outdoor air supply rate and airborne particles on children in school classrooms David P. Wyon and Pawel Wargocki Technical University of Denmark

4 Main ASHRAE 1257 Objective To determine whether improving classroom air quality and ensuring classrooms do not become warm can improve the performance of schoolwork by children Window opening behavior was passively recorded during the experiments

5 Methods Indoor air quality was modified by increasing the outdoor air supply rate from an existing mechanical ventilation system Air temperature was reduced in hot weather by installing & 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

6 Selected school in Denmark School at Rungsted DTU

7 Schools Elementary school with no IEQ problems South-facing facades Mechanically ventilated Energy conservation measures in place

8 Plan of the selected classrooms Selected classrooms Fig. 4 Plan of selected classrooms

9 Selected classrooms

10 View of classroom

11 Ventilation system Split cooling Electrostatic air cleaners

12 Split cooling was installed and either operated or idled in summer

13 Silent electrostatic air cleaners were installed and operated or idled

14 4th to 6th grade year old ~300 pupils Pupils

15 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 or doors as well as supply air from the ventilation system

16 Measurements of perceptions and symptoms The children marked Visual-Analogue scales at the end of the week They reported the: Classroom environment Intensity of the symptoms they experienced How is the classroom right now? Too cold The air is draughty It is 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 night I feel very tired I slept too little last night I do not feel like working I 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

17 Measurements of performance Tasks appropriate to children s age were developed in consultation with class teachers 4 language-based: Acoustic proof-reading Reading and comprehension Logical reasoning Proof-reading 4 numerical: Subtraction Multiplication Number comparison Addition Tasks were performed in mathematics or language lessons

18 Sensory assessments of air quality by visiting adult panel ACCEPTABILITY SCALE Clearly acceptable Just acceptable Just not acceptable Clearly not acceptable After classes ended

19 Permission was obtained from: Parents School Headmaster School Board Teachers Local Authority Danish Ethics Review Board Swedish Ethics Review Board

20 Design of experiments Interventions always improved conditions Interventions were for 1 week at a time in balanced order of presentation Cross-over design (one classroom with existing conditions and one with improved conditions) The ventilation system was modified to provide more air to one classroom at a time Split cooling was installed in both but operated in one classroom at a time

21 2x2 design Temperature Current Cool Ventilation rate current high

22 Estimated effective L/s p 10 8 L/s per person AC No AC 0 Low L/s High L/s

23 Mean classroom CO2 ppm Mean CO2 ppm AC No AC 0 Low L/s High L/s

24 Peak classroom CO2 ppm Peak CO2 ppm AC No AC 0 Low L/s High L/s

25 Teaching environment and routines No restrictions on normal daily activities No changes in class schedules Doors and windows could be opened No contact between researchers and children (no white coats or stop-watches)

26 Reduced classroom temperature 2 independent experiments in August/September : 1st experiment: temperature reduced from 23.5 to 20 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

27 Typical time-course of classroom temperature in the two classrooms

28 Children s perception of temperature Too warm (P<0.001) Too cold Low temp High temp Estimated PMV PMV=0 PMV=0.7

29 Performance of schoolwork as a function of classroom temperature 1,4 Performance 1,2 1 0,8 R 2 = , Temperature 1 o C lower temperature ~3.5% higher performance

30 Earlier experiments by DP Wyon in Sweden in 1967 Raising classroom temperature from 20 C to 30 C reduced most types of schoolwork performance by up to 30% For 40 years this was widely believed to be an overestimate The present results confirm the size of the thermal effect first reported in 1967: +10 C would lead to 35% less schoolwork

31 Increased outdoor air supply rate Three independent field intervention experiments with 100% 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

32 Time-course of classroom CO 2 concentration, example

33 Children s perception of IAQ Fresh air (P<0.001) Poor air Low vent High vent

34 Sensory assessments of air quality made by an untrained panel after children had left the classroom % 40 (P<0.001) Dissatisfied Low vent High vent

35 Effect of increasing ventilation rate on performance: increase in speed % Experiment 1 Experiment 2 Experiment 3 * 25 * * * * 15 * * * * 5-5 Subtraction Multiplication Number comparison Addition Logical reasoning Reading and comprehension

36 Performance of schoolwork as a function of classroom ventilation 1,4 Performance 1,2 1 0,8 R 2 = , Ventilation (L/sp) Doubling ventilation rate ~14.5% higher performance

37 Classroom air quality matters Windows are often not opened Outdoor air supply rates are often low CO2 levels are often above 1000 ppm Increasing the air supply rate from 2.5 to 5 to 10 L/sp would improve the performance of schoolwork by 29% Poor air quality is a major disadvantage for children, and especially for slow workers

38 CO2 in 1663 Scandinavian classrooms October 2009

39 Natural Ventilation only Classrooms in: CO2 >1000 ppm Denmark 69 % Sweden 47 % Norway 48 %

40 Taking all 1663 Scandinavian classrooms together:

41 CO2 was then measured in 100 classrooms in Denmark Random selection Structured representative sample CO2 recorded throughout school hours 2 weeks in November Outdoor temperature was 0-15 C Proportion with mean CO2 > 1000 ppm : 66%

42 ASHARE 1257 Results Condition of supply air filter Two studies in January No consistent effects on perceptions, symptoms or perceived air quality when a used filter was replaced with a new one

43 Installing a new filter had no effect on children s performance

44 Interpretation Results differ from our office findings, but: Very little dust was retained in the used supply air filter Supply air was 100% outdoor air, so all the dust originated outdoors

45 Operation of electrostatic air cleaners 2 independent experiments in January and March/April in 1 Danish and 4 Swedish schools Concentration of particles in classrooms was considerably reduced when electrostatic air cleaners were in operation

46 Number of particles per cm Placebo units Air cleaners >0.75 >1.0 >2.0 >3.5 >5.0 >7.5 >10 >15

47 Concentration of particles per cm3 (with/without electrostatic deposition) Reduction greater in the 2 poorly ventilated classrooms

48 Operating electrostatic air cleaners had no effects on performance

49 Conclusions on filters and airborne particles Electrostatic air cleaners reduced the concentration of airborne particles but had no effects on schoolwork Installing a new filter in the outdoor air supply flow had no effects on schoolwork However, reducing airborne particle concentration may reduce the long-term effects of IAQ on health

50 Main 1257-RP conclusions Reducing even slightly warm classroom temperatures eliminated thermal discomfort and improved children s performance Increasing outdoor air supply rate improved classroom air quality and children s performance Schoolwork was performed faster, with no increase in errors, in both cases

51 Field experiments in the UK Bakó-Biró et al. (2012) Building & Environment 48, Air supply 1 or 8 l/sp in 16 classrooms Air T changed very little (0.6 o C) Diagnostic tests, not schoolwork Significant improvement at 8 l/sp Test performance improved by 2-15%

52 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

53 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

54 Window opening In the DK experiments, the opening of windows and doors was recorded Teachers and children opened windows and doors as usual This is the first intervention experiment on window-opening behaviour in response to raised temperature or decreased outdoor air supply rate in school classrooms

55 Summertime classroom T in C (NB: Different classes with natural/mechanical ventilation) No AC AC 15 Off Low High Mechanical ventilation

56 Observations Split cooling reduced air T by only 1.7 C at the highest ventilation rate, but by 5.4 C at the lower rate) With natural ventilation, cooling reduced T by only 3.3 C (NB: this could be due to poor mixing, as T was recorded at 2.2m height)

57 Outdoor air supply rate (L/sp) (NB: Different classes with natural/mechanical ventilation) 10 5 No AC AC 0 Off Low High Mechanical ventilation

58 Hours/week with windows open (NB: Different classes with natural/mechanical ventilation) No AC AC 0 Off Low High Mechanical ventilation

59 Observations Windows were opened much more when it was warm in the classroom Even at 10 L/sp, a 1.7 C increase in T increased window opening by 75% With no cooling, opening windows provided only 3.7 L/sp Split cooling reduced window opening by 65%, reducing the outdoor air supply rate to only 2.7 L/sp

60 Classroom T (NB: different classes in winter & summer) 25 C 20 Summer Winter 15 Low High Ventilation (with no AC)

61 Outdoor air supply rate (L/sp) 10 (NB: different classes in winter & summer) Summer Winter 2 0 Low High Ventilation (with no cooling)

62 Hours/week with windows open 10 (NB: different classes in winter & summer) Summer Winter 2 0 Low High Ventilation (with no cooling)

63 Hours/week with windows open and with cross ventilation 10 (2 classes in winter, 2 other classes in summer) Windows open Cross ventilation 2 0 Winter Summer (With mechanical ventilation set to low in both seasons)

64 Hours per week with windows open and with cross ventilation 15 (Summer, same 2 classes in all 4 conditions) 10 5 Windows open Cross ventilation 0 T low (A/C) T high (No A/C) (With mechanical ventilation set to low throughout)

65 Observations Windows were open 4x as long in summer (when classroom T was 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

66 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 Both slightly raised T and poor IAQ decreased children s performance

67 SOLUTIONS (In order of first cost and sophistication) CO2 sensor signals windows open/close Computer operates windows optimally CO2 controlled by variable exhaust flow Balanced 100% fresh air supply + exhaust Pre-heat supply air and remove ozone Recover heat from exhaust airflow Remove pollutants from return air using a desiccant wheel purged with outdoor air

68 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

69 Further reading ASHRAE Journal, October 2006 (Summary of T, IAQ effects) ASHRAE HVAC&R Research J, March 2007 (2 papers: T, IAQ effects) ASHRAE HVAC&R Research J, May 2008 (e-filters) Indoor Air 2008, September 2008 (Observations of window opening)