Educational environments' energy demand optimization based on indoor CO2 concentration and temperature: Together better than separately

Although optimization tools have been widely used to both minimize and control the energy consumption of buildings maintaining thermal comfort, the dramatic impact of the COVID-19 pandemic showed the relevance of considering the indoor air quality to act on the ventilation system. However, CO2 concentrations in closed environments with high occupancy rates, such as classrooms in schools, universities, or other educational environments, increase rapidly without effective ventilation, reaching the safe limits in about 15-30 min. Observing that the natural ventilation guides indicated by governments were insufficient to keep safe and comfortable spaces simultaneously, this study analyzes how mechanical heating, cooling, and ventilation systems would improve these results by using optimized control strategies in the same buildings that now use natural ventilation. Setting the objective function to minimize energy consumption, this study optimizes the use of mechanical systems considering the indoor temperature and CO2 concentration of educational indoor spaces in 4 types of schools and 3 climate zones in winter and summer. Results show that, at full occupancy, the ventilation should activate every 12 min, making slow-frequency control strategies inappropriate to keep the spaces safe. A 1-min step modeling asks for high computation that makes it critical for real-time control strategies, however, it allows a perfect setting of the working limits for legacy conditional equipment for establishing control policies on a one-day horizon.