Evaluation of air purifier and fan installation heights for enhancing indoor air quality in a plastic greenhouse

Plastic greenhouses, widely adopted due to low cost and flexibility, often rely on natural ventilation, which can cause heat accumulation and the buildup of airborne pathogens and harmful gases. This study evaluated the influence of installation height of air purifiers and circulation fans on indoor air quality (IAQ) in a plastic greenhouse using CFD simulations. Device heights and operating conditions were varied, and IAQ was assessed through age of air. The CFD model was validated against measured indoor temperature data, yielding a mean absolute percentage error of 3.9%. A sensitivity analysis confirmed robustness, as variations in outdoor air temperature (±1°C), ground temperature (±1°C) and solar radiation (±10%) caused prediction variations of about ±1.6%, ±1.5% and ±1.0%, respectively. During daytime, placing air purifiers at 2.6 m and circulation fans at 4.0 m minimized the age of air and suppressed thermal stratification, while at nighttime favourable IAQ was maintained even without fan operation. Compared with less effective setups, the recommended configuration reduced the age of air by approximately 21%. These results suggest an energy-efficient strategy in which both devices are operated during the day and only the purifiers at night, providing practical guidance for low-cost IAQ management in plastic greenhouses.