Optimizing ventilation in schools for improved comfort and energy efficiency

Abstract

Thermal comfort (TC) and Indoor Air Quality (IAQ) in classrooms are critical for students to achieve their learning potential in a healthy environment. Ventilation to maintain IAQ is very energy intensive, so it is important that it is carried out in a sustainable manner. This study aims to identify whether the use of natural ventilation, as is the current practice in schools in Malta, is sufficient to satisfy EN 15251 TC and IAQ requirements. The study also aims to identify the best way mechanical ventilation can be applied to optimise IAQ, TC and energy efficiency. Temperature and carbon dioxide (CO2) data from a typical school building in Malta was used to calibrate an EnergyPlus building model. Results showed that for fully occupied classrooms having closed windows in winter, infiltration (alone) was not adequate to provide the required IAQ based on CO2 ppm readings. In contrast, CO2 levels can be controlled within safe limits when demand controlled mechanical exhaust ventilation is applied. This was confirmed via monitoring of CO2 ppm over a one-year period. The same exhaust fan also improved TC by bringing in pre heated corridor air in winter while reducing the temperatures by 1 ° to 1.4 °C during the summer via night purging. Computational Fluid Dynamics (CFD) confirmed that inlets placed close to floor level between classrooms and corridors provide the best IAQ at student working height while inlets placed on top provide the best TC. In addition, initial EnergyPlus analysis showed that continuously running exhaust fixed speed fans provide the lowest financial global costs over a 20-year period versus the more complex demand control ventilation scenarios. The study has primarily concluded that mechanical ventilation in schools is required to ensure IAQ and optimise TC, while also enabling energy savings in space heating and cooling.