Analysis of Energy Performance According to Changes in CO2 Setpoint Conditions in Ventilation Systems of Office Buildings

Purpose: This study aims to quantify the impacts of CO₂ concentration setpoint selection in demand-controlled ventilation (DCV) systems on indoor air quality (IAQ) and energy performance in office buildings. Although CO₂ -based DCV has been widely applied to reduce ventilation energy, the effects of different setpoints and deadband ranges on pollutant reduction capability and overall HVAC energy consumption have not been sufficiently clarified. Method: A coupled simulation approach integrating CONTAM and EnergyPlus was employed to analyze CO₂ concentration behavior, ventilation demand, and HVAC energy consumption. A medium office reference building consisting of four perimeter zones and one core zone was modeled under Seoul climate conditions. Four ventilation control scenarios were evaluated: a baseline constant ventilation case, a fixed CO₂ setpoint of 1000ppm, and two deadband-based DCV strategies of 900~1000ppm and 800~1000ppm. Zone-level CO₂ concentrations, ventilation airflow rates, and annual cooling, heating, and fan energy consumption were assessed. Result: The results indicate that all CO₂-based DCV strategies maintained indoor CO₂ concentrations within acceptable limits. Lower CO₂ setpoints resulted in improved air quality, with the 800~1000ppm strategy achieving the best IAQ performance. From an energy perspective, the fixed 1000ppm control achieved the largest reduction in total HVAC electricity, saving approximately 5.9% compared to the baseline. This was primarily driven by a 46.7% decrease in fan energy, while heating energy was reduced by 2.7~4.1%. In contrast, cooling energy exhibited only marginal changes within ±1%. This study highlights the need to select CO₂ control criteria based on building operation.