Balancing CO2 Enrichment and Air Quality: Performance and Safety of a Propane-Based Greenhouse System

Carbon dioxide (CO2) enrichment using fuel combustion is widely applied in greenhouse production. However, its implications for air quality and occupational safety under real operating conditions remain insufficiently characterized. This study evaluates a propane-based CO2 enrichment system in an advanced greenhouse. The analysis integrates CO2 dynamics, combustion-derived pollutants, and occupational exposure. High-resolution monitoring at 5 min intervals was conducted in an enriched module and a control module over a five-month period. Two operational modes were assessed: continuous and diurnal-only enrichment. The system maintained CO2 concentrations within agronomic targets. Mean values reached 1200 ppm and 940 ppm for continuous and diurnal operation, respectively. However, significant CO2 losses were observed due to ventilation. The maximum enrichment efficiency, expressed as the Combustion Efficiency Index (CEI), was 2.67 × 10−3. Combustion-related pollutants (CO, NO, NO2, SO2, and O3) showed transient peaks during burner activation. However, concentrations remained below occupational exposure limits when evaluated using time-weighted averages. The incomplete combustion ratio (ICR) remained stable at approximately 1.9 × 10−3. This indicates predominantly complete combustion. These results provide field-based evidence on the performance and safety of propane-based CO2 enrichment systems. They also highlight the importance of continuous monitoring and improved CO2 retention strategies in semi-confined greenhouse environments.