Can Indoor Air Quality In Victorian Classrooms Satisfy Government Stipulated Requirements?
Nafsika Drosou, Loughborough University
Research indicates that high carbon dioxide (CO2) levels in classrooms adversely affect the health and productivity of students. To address this, the government stipulates indoor air quality (IAQ) requirements in Building Bulletin 101 (BB101) as maximum CO2 concentrations and minimum ventilation rates for classrooms. Due to recent budget cuts, school refurbishments are attracting more attention than new-build.
This work, involving a naturally ventilated Victorian classroom, uses computational fluid dynamics (CFD) simulations to predict the IAQ performance of six refurbishment interventions in order to investigate compliance with BB101 requirements. Furthermore, focusing on the BB101 compliant interventions, it explores their thermal comfort impact in terms of draught and vertical temperature difference, and determines their energy consumption impact by combining output from a parallel dynamic modelling (DTM) study.
Three interventions (parallel windows, plenum, roof-window) satisfy BB101 IAQ requirements. Of these, the parallel window emerges as the intervention achieving the greatest energy savings and causing thermal discomfort to the least number of occupants.
AIM AND OBJECTIVES
The aim of the study was to determine the most appropriate intervention for the classroom of the case study, with respect to heating energy consumption and thermal comfort parameters, in order for BB101 requirements to be met throughout the year.
In reaching the above aim the following objectives were pursued:
1. Select the most appropriate IAQ standards and thermal comfort requirements that will be used throughout the study to appraise predictions of CO2 concentration, ventilation rates, draught and vertical temperature difference.
2. Obtain data on dimensions, location and surroundings, heat gains, occupancy schedules, as well as window opening strategy.
3. Monitor external temperature and indoor CO2 concentration and temperature, for characterising current IAQ levels and calibrating the base case CFD model.
4. Compile a list of interventions suited to the specific case study, based on: safety, acoustics, maintenance and ease of use, and model them as parametric CFD studies.
5. Using CFD predicted CO2 concentrations and ventilation rates for each intervention assess compliance with BB101 requirements.
For interventions whose IAQ performance satisfies BB101 requirements:
6. Assess the CFD predicted thermal comfort impact on the occupants in terms of draught and vertical temperature difference.
Compare the CFD predicted CO2 level reductions with the corresponding DTM reductions and obtain the DTM predicted energy savings associated with each intervention.
The parallel windows intervention results to the largest energy savings and causes thermal discomfort to the least number of people while meeting BB101
requirements for IAQ. Compared to the modelled base case it is predicted to:
• reduce CO2 concentration at seated head height by up to 21.0%
• increase ventilation rate per person by up to 43.3% and purge capacity by up to 47.1%
• reduce heating energy consumption by 21%
• cause discomfort due to vertical temperature difference only for the minimum openable window area
• cause discomfort due to draught only during the heating season, to a maximum of 16% of occupants, and discomfort due to temperatures less than 16°C to a maximum of 13% of occupants.
Running additional simulations for peak recorded winter and summer external temperatures would be useful in determining a range in values of IAQ and thermal comfort parameters for each intervention.
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