SEASONAL VARIATION OF INDOOR AIR QUALITY ...

SEASONAL VARIATION OF INDOOR AIR QUALITY IN CLASSROOMS OF A 1970s CONVENTIONAL, A PRE-PASSIVHAUS AND A PASSIVHAUS PRIMARY SCHOOL BUILDINGS IN THE UK Chrysoula Thoua Mark Lumley Dr Azadeh Montazami Prof Mark Gaterell

Architype Architype Coventry University Coventry University

Fig: Average CO 2 concentration plotted against average outdoor temperature for the occupied hours, for 3 classrooms

Research summary A number of studies argued that poor indoor air quality (IAQ) in primary school classrooms can have a measurable impact on the concentration and learning ability of pupils (Bakó-Biró et al, 2012). As children’s academic performance is seen to decrease in deprived areas in the UK, the classroom environment needs to be assessed with a focus on its impact on pupils’ learning. The conflict between winter thermal comfort and natural ventilation has been investigated in a number of studies and, while it is understood that the risk of poor IAQ in the classroom is higher in winter, more often than not there is not enough evidence to support a correlation between indoor temperatures and IAQ. This study uses monitoring data to investigate if classrooms in a naturally ventilated and poorly insulated building are more prone to a negative correlation between mean outdoor temperature and indoor CO 2 levels, compared to a naturally ventilated super-insulated and a Passivhaus building. Findings from this study, suggested that in order to eliminate the risk of a negative effect on children’s health and performance due to poor IAQ in colder climates, we need to invest in well-insulated airtight Passivhaus schools equipped with mechanical ventilation with heat recovery, and CO 2 dictated supply rates. Further research shall use thermal dynamic simulation and CFD analysis for classrooms in different building types in the UK, to reveal the ideal strategy and design. Keywords: classroom, indoor air quality, passivhaus primary schools

1. Introduction While the importance of CO 2 concentration levels has been recognised in a number of studies and guidelines, children across the UK continue to spend approximately 1/3 of their time in classrooms that do not comply with the requirements. CO 2 concentration was found to be a good approximation of indoor air quality (IAQ) in learning spaces. High CO 2 levels in the classrooms in primary schools can have an impact on academic performance (Bakó-Biró et al, 2012) and long exposure can impact health and development. A minimum air change rate of 8 l/s per person and an average CO 2 concentration no greater than 1000 ppm is required in classrooms to prevent negative impact on pupil’s performance. Because of the known conflict between maintaining indoor air quality and thermal comfort conditions, CO 2 levels tend to be higher in the heating season. This study investigated whether colder temperatures within the heating season can influence CO 2 concentration profiles? 2. Research objectives The aim of this study is to investigate how indoor air quality in primary school classroom can vary from summer to autumn and from autumn to winter in 3 different types of buildings and whether it is possible to estimate the seasonal change in CO 2 concentration from the outdoor temperature. A number of studies have suggested that there is a conflict between indoor air quality and thermal comfort in winter. This is more evident in naturally ventilated classrooms while mechanical ventilation with heat recovery has proved an effective way to resolve the conflict.

However, a correlation between CO 2 levels and indoor air temperature is not always apparent. It is likely therefore that indoor CO 2 levels are associated with average outdoor temperature rather than with average indoor temperature. Classrooms in UK schools need to comply with the soon-to-be-updated Building Bulletin 101 (DfES, 2006) which requires that, a) CO 2 concentration should never exceed 5000 ppm, b) the average CO 2 concentration during occupied hours should not exceed 1500 ppm, and c) occupants should be able to reduce CO 2 levels to 1000 ppm at any occupied instance. 3. Method 3.1 Monitoring For this study we used monitoring data of air temperature (°C), and CO 2 concentration (ppm) in 3 classrooms over 3 1-week periods: in summer, autumn and winter 2014. The 3 desktop EXTECH CO210 data loggers used to monitor indoor air temperature and CO 2 concentration have an accuracy of ± 0.6 °C and ± (5%+50) ppm, and a resolution of 0.1 °C and 1 ppm. Logging was set at 10-minute intervals. The monitoring weeks were in summer: 23th – 27th June 2014, in autumn: 6th – 10th October 2014 and in winter: 1st -5th December 2014 while outdoor temperature data for the period were provided by the MetOffice for the two locations. 3.2 The classrooms We selected 3 classrooms one from 3 different primary schools located in the West Midlands, UK. These included Classroom A, from a singlestorey 1970s primary school in Herefordshire, which is naturally ventilated with fan heaters operating in heating season. Classroom B from a naturally ventilated pre-Passivhaus school

with underfloor heating and Classroom C, from a Passivhaus primary school with BMS, radiators, mechanical ventilation with heat recovery in winter mode and mixed mode ventilation in summer mode. All classrooms are roughly north facing and have similar occupancy density of 27-30 pupils and 1-2 staff. The effective window opening area in the 1970s classroom was less than the one in the 2 other classrooms (B and C).

concentration exceeded the 1500 ppm threshold only in winter. Classroom A, in the 1970s building, only satisfied the average concentration requirement in summer, and failed all 3 requirements in winter. Also, there was an increase in the maximum recording of each week from summer to autumn and to winter. The seasonal changes are easier to observe in the Figures 4 to 6 where the 3 CO 2 profiles are plotted separately for each classroom.

4. Results and design potential 4.1 Results The average outdoor temperature during occupied hours in each of the selected weeks decreased by approximately 6 °C from summer to autumn and another 6 °C to winter. Fig. 1 shows how average air temperature varied during these 3 weeks in the 3 different classrooms. The indoor air temperature during occupied time in the pre-PH and PH classrooms, varied very little from the cooling to the heating season, but in the 1970s classroom it was the same in the autumn and winter weeks and approximately 4 °C higher in summer. However, in Fig. 2, the average CO 2 concentration during occupied hours decreased almost from autumn to winter as much as from summer to autumn in the 2 naturally ventilated classrooms. Although the 1970s average concentration was constantly higher. As shown in Figure 3, Classroom C, from the Passivhaus building outperformed all requirements of the BB101, in all seasons. Classroom B, in the pre-PH building satisfied all the requirements only in summer, and 1 out of 3 in the other seasons, without ever exceeding the absolute maximum limit. The average

Fig. 1 Average indoor air temperature plotted against average outdoor operative temperature for the occupied hours, for 3 classrooms.

Fig. 2 Average CO 2 concentration plotted against average outdoor temperature for the occupied hours, for 3 classrooms.

4.2 Discussion The results indicate that CO 2 concentration during occupied hours in a naturally ventilated primary school classroom is likely to increase as the average outdoor temperature reduces. There was a similar increase in the average CO 2 concentration levels in the 2 naturally ventilated classrooms. This was not the case in the Passivhaus classroom that was mixed mode ventilated during the cooling season and with mechanical ventilation with heat recovery in the heating season. In this case, the average summer CO 2 concentration was only marginally lower compared to the other seasons.

Classroom A, in the 1970s school has a higher CO 2 concentration in general potentially because of the insufficient window opening area. It is not clear whether the lower indoor temperatures in autumn and winter (averaging at 19°C) or the type of heating system used was a factor that relates to occupants not opening the windows enough. Findings show that window opening behaviour in naturally ventilated buildings is likely to be influenced by outdoor temperature rather than indoor temperature in autumn and winter. The colder the outdoor temperature, the more reluctant the occupants to open the windows for fresh air.

Fig 3: CO 2 ranges, quartiles and averages in a box plots for 3 classrooms and 3 weeks, one in each

season: summer, autumn and winter. The red lines indicate the upper limits of guidelines (BB101).

Fig 4: CO 2 concentration profile in Class A, a classroom from a naturally ventilated 1970s primary school, for 3 different weeks, in summer, autumn and winter. The yellow stripes indicate the occupied hours 9:00-16:00.

Fig 5: CO 2 concentration profile in Class B, a classroom from the naturally ventilated pre-Passivhaus school, for 3 different weeks, in summer, autumn and winter. The yellow stripes indicate the occupied hours 9:00-16:00.

Fig 6: CO 2 concentration profile in Class C, a classroom from the Passivhaus school, for 3 different weeks, in summer, autumn and winter. The yellow stripes indicate the occupied hours 9:00-16:00.

5. Future implementation It is suggested that more data are investigated in order to produce statistically significant results, including data from longer monitoring periods as well as a larger classroom sample from more primary schools in the UK. Confirming the above findings can have a number of implications in: a) dynamic modelling for predicting indoor air quality and concentration of particles in classrooms as it introduces a variable that affects window opening behaviour, b) improving ventilation systems design to reduce cold draught dissatisfaction. Recommendations from the findings of this study include: a) To provide education to pupils and teaching staff, as part of post-occupancy Soft Landings services in order to raise awareness on

acceptable CO 2 levels in the classrooms and how to achieve them. b) In terms of design, the ventilation system, whether natural of mechanical should ensure fresh outdoor air is provided above a certain temperature threshold, by means of heat recovery. 6. Conclusions In this study CO 2 concentration and indoor air temperature in classrooms from 3 primary schools in the UK were monitored for the duration of a week in summer, autumn and winter, as part of a collaborative research project that involved longer term monitoring. Findings indicated that, higher CO 2 concentration in naturally ventilated classrooms increased from summer to autumn and autumn to winter, but this was not the case in a passivhaus classroom, with MVHR.

This could mean that naturally ventilated classrooms are likely to be more susceptible to a deterioration of indoor air quality due to cold outdoor temperature and this could be severe during a cold winter or in different climates. Designing and delivering a classroom that is resilient to future climate change in the UK is influenced by the uncertainty of future projections. Designers of primary schools, can benefit from an understanding of how external temperatures can impact on indoor air quality which is considered one of the most important factors that affect learning and in the UK can be more problematic in cold weather. 7. Acknowledgments This study is part of the Knowledge Exchange and Enterprise Network (KEEN) project between Architype and Coventry University, led by the University of Wolverhampton and funded by the ERDF and Architype. We are grateful for the assistance from the headteachers and staff of the case study Primary Schools. External weather information was kindly provided by the Met Office.

8. References Bakó-Biró, Z., Clements-Croome, D. J., Kochhar, N., Awbi, H. B., & Williams, M. J. (2012). Ventilation rates in schools and pupils’ performance. Building and Environment, 48, 215-223. Mumovic, D., Palmer, J., Davies, M., Orme, M., Ridley, I., Oreszczyn, T., ... & Way, P. (2009). Winter indoor air quality, thermal comfort and acoustic performance of newly built secondary schools in England. Building and Environment, 44(7), 1466-1477. CIBSE, TM 57 - (2015). DfES, Building Bulletin 101 – Ventilation of school buildings. Department for Education and Skills; (2006). Mumovic, D., Davies, M., Pearson, C., Pilmoor, G., Ridley, I., Altamirano-Medina, H., & Oreszczyn, T. (2007). A comparative analysis of the indoor air quality and thermal comfort in schools with natural, hybrid and mechanical ventilation strategies. Proceedings of Clima WellBeing Indoors, 23.