Indoor temperature, relative humidity and CO2 monitoring and air exchange rates simulation utilizing system dynamics tools for naturally ventilated classrooms

Abstract

This study reports the results of two-season (summer and winter) monitoring of indoor CO2, temperature (T) and relative humidity (RH) levels conducted in naturally ventilated classrooms of a primary school. Parameters were recorded at 1-min interval for one week including occupancy and non-occupancy hours. CO2, T and RH exceeded ASHRAE recommended limits for significant fraction of occupancy period. Minute-by-minute ventilation (VRs) and air exchange rates (AERs) were calculated for occupancy hours. Results showed significant variation (p < 0.05) of indoor parameters between occupancy and non-occupancy hours. Though Indoor CO2 levels did not vary between two seasons, thermal comfort parameters showed significant variation. Average AERs and VRs were found in range of 1.4–10.6 h-1 and 1.1–6.3 l/s/person respectively which were well below recommended ASHRAE standards. Second part of study includes development of a system dynamics (SD) based model which was used to estimate indoor CO2 concentrations utilizing calculated VRs (minute-by-minute and averaged) using VENSIM software. The developed SD based model results showed high correlation (>0.98 for all classrooms, using minute-by-minute VRs) with monitored CO2 concentration and low root mean square error. Similarly, minute-by-minute VRs input to models showed more accurate simulation as compared to VRs averaged for a session (Correlation coefficient <70 for all classrooms). Finally, ASHRAE and REHVA recommended VRs (8 and 3 l/s/person respectively) were input to SD based model to simulate CO2 concentration, in which the former successfully kept CO2 levels below 1000 ppm and later failed to maintain claimed limits of 1500 ppm.