Improving the ventilation of a classroom to achieve heating energy savings and better indoor air quality

Indoor air quality and heating energy consumption are closely linked, especially in densely occupied spaces, as classrooms. In a classroom of Rennes University, a transient thermal simulation highlights the impact of ventilation on heating consumptions for different cases: (1) without controlled mechanical ventilation (CMV), (2) with a single flow CMV (SF CMV) of a regulatory flow of 18 m 3 .h −1 . person −1 during periods of occupancy, and (3) a double flow CMV (DF CMV) whose flow is during periods of occupancy either equal to 18 m 3 .h −1 . person −1 or (4) to 35 m 3 .h −1 .person −1 . The infiltration flowrate was evaluated experimentally using CO 2 concentration measurements in the first case, which corresponds to the actual situation. In the normal use of the classroom with 30 persons inside, CO 2 concentration exceeds 5000 ppm and the heating energy consumption is equal to 52 kWh.m −2 .year −1 . In case (2) and (3), CO 2 concentration has a maximum level of 1350 ppm and the energy consumption is equal to 65 and 53 kWh.m −2 .year −1 , respectively. In case (4), the maximum CO 2 concentration stays in the range 800-900 ppm without excessive heating consumption (58 kWh.m −2 .year −1 ). Finally, by limiting the fresh air flowrate to 18 m 3 .h −1 .person −1 in DF CMV and coupling it to a façade insulation (extra Case 5), the heating consumption is reduced to 32 kWh.m −2 .year −1 . These results are valuable within the context of the upcoming energy renovation strategy of the campus. Practical application In most schools, in France and elsewhere, insufficient ventilation flowrates are often observed compared to regulatory requirements. If compliance with ventilation standards and the subsequent revision of CMV installations are necessary to ensure the health of users, it is important to evaluate the energy cost of these renovations, and to identify the best choice to reduce heating consumptions. Our contribution is to compare different renovation choices in terms of two indicators: energy consumption and indoor air quality evaluated using CO2 concentration.