Performance study of an active solar water curtain heating system for Chinese solar greenhouse heating in high latitudes regions

Thermal preservation and heat storage performance cannot be fully realized in the traditional design of the Chinese solar greenhouse (CSG) north wall. To increase greenhouse thermal efficiency and maximize solar en-ergy utilization, researchers have divided greenhouse into the independent solar heating system as well as the independent north wall heat preservation system. The wall-mounted solar heating system used water as a me-dium with the characteristics of chemical stability, liquidity preference and high specific heat capacity for heat transport and storage have been developed. To explore and create a better suitable greenhouse thermal envi-ronment, we proposed an active solar water curtain heating system with a non-woven fabric liner between the two-layer polyethylene film coated with black water-based paint. The greenhouse heating load was estimated based on energy balance theories during the nighttime and the water mass for heat transfer was calculated. Field tests were carried out to verify theories and investigate the thermal performance of the system. The average heat collection ratio was about 80.1 % and 63 % of the stored heat was released at night with the 3.6 degrees C improvement in interior air temperature and 6.6 % reduction in interior air relative humidity. The heating COP of the system was 12.5 on average and the energy saving rate was 92 %. Besides, the greenhouse with the solar heating system can save energy consumption cost about 348 USD yr(-1) as the cost of solar heating system can be repaid in 1.4 years. The system combined the energy balance method to design with more efficient thermal performance, energy conservation, utilization of solar energy and affordable payback period thereby creating a suitable thermal environment in the Chinese solar greenhouse, which is recommended for practical application.