Research on performance of active heat storage-release system for canopy warming

To further improve the thermal energy use efficiency of an active heat storage-release system (AHS) and provide a reference for crop warming, an active heat storage-release system for canopy warming (AHSCW) was designed and tested for its performance. The AHSCW, based on the sixth generation AHS, uses solar energy absorbed by solar panels on the north wall of the Chinese Solar Greenhouse (CSG) as the heat source. The solar energy is stored in the heat storage tank through water recirculating pipes during the day and released at night to heat canopy air. To analyze the heating effect of the AHSCW, relevant environment parameters (solar radiation, canopy air temperature and water temperature), crop parameters (tomato plant height, stem diameter and yield in different periods) and pump power consumption were collected in two CSGs, with AHSCW installed in one of the CSGs. The average heat storage capacity of AHSCW was 553.3-646.7 kJ m^‑2 (per unit land area), the average heat storage power was 25.7-30.0 W m^‑2. At night, the average heat energy released was 430.0-473.3 kJ m^‑2, and the average heat release power was 15.0-16.3 W m^‑2. The heat use efficiency was 67-86%. In addition, canopy air temperature could be increased by 1.4-3.0°C. Tomato yield after 141 days since planting in the CSG with AHSCW was 1.77 times than the reference CSG.