A solar water column system for greenhouses: Thermal Performance, Dehumidification capacity and Economic analysis

Solar greenhouse nighttime temperatures combined with high humidity readily induce crop diseases. Existing active heating systems consume excessive amounts of energy, while passive systems are limited in functionality and lack cost-effective solutions. To improve solar energy utilization and enhance the adaptability in cold regions, this study proposes a passive heating system that utilizes only surplus air thermal energy and solar radiation, which consists of high-density polyethylene water columns and operates without consuming electricity. It simultaneously addresses heating and dehumidification challenges in cold region greenhouses. Using trigonometric calculations to determine the system optimal width. Response surface methodology was applied to optimize parameters including water column position, film thickness, and control timing, with economic and environmental analyses conducted on system performance. Field tests demonstrated that this novel system achieved a heat collection efficiency of 34.08% and a heat release efficiency of 95.7%. The minimum temperature increased by 2.9 °C, relative humidity decreased by 8.7%, and vapor pressure differential stabilized between 0.44 and 0.51 kPa. The payback period was 1.26 years. This novel humid-heat management system achieves a balance between thermal performance, dehumidification effectiveness, and economic viability through passive design, offering a viable solution for low-carbon winter cultivation in cold-region greenhouses.