Multi-span greenhouses have been widely used in recent years. Conventional negative pressure fan-pad cooling has suffered from the low uniformity of indoor air temperature and the integrity of the cultivation area. Existing positive pressure ventilation with the air-handling corridor is also limited to low integration and difficult to control. In this study, a packaged positive pressure ventilation and cooling system was designed for highly efficient and quality crop production in the multi-span greenhouses during warm seasons. This system consisted of an equipment room, a combined air conditioning unit with three-sided air intake, ventilation ducts, and a control module. It can be further extended with heat sources and a water recirculating system, enabling integrated greenhouse climate conditioning based on positive pressure ventilation. The procedure of the air flows during cooling was as follows: The outdoor air entered the equipment room via outer vents, evaporative cooling in the air conditioning unit, and the air was conveyed into the greenhouse via underground ducts, while warm air was exhausted under roof vents. Field tests were conducted in Shouguang, Shandong Province, China. The results showed that the cooling system with the external shading screen maintained the daily mean air temperature between 28.4 and 32.5 ℃, which was 0.8 to 3.8 ℃ lower than the outdoor temperature during the peak temperature hours (10:00-16:00) in summer. The vapor pressure deficit of the indoor air averaged 0.87-1.33 kPa during operation. The daily mean relative humidity ranged from 62% to 80%, 17-29 percentage points higher than outdoors. The air was uniformly distributed over the cultivation area at the terminal air outlets. The airflow was also delivered at the velocities of 7.7-13.3 m/s, with the uniformity (standard deviation) of 1.9 m/s. In horizontal, the uniformity of air temperature reached 0.4 ℃ inside the greenhouse under the supply air condition. Vertically, the air temperature increased with height, with a temperature gradient of 0.76 ℃/m, and a 3.1 ℃ difference between the tomato canopy and the greenhouse roof. The high-pressure fogging system was installed inside the greenhouse. A three-dimensional cooling performance was achieved to reduce the vertical temperature gradient to 0.5 ℃/m. The designed specific ventilation rate of the greenhouse was 0.028 m/s for cooling purposes. The actual ventilation rate and system power consumption were 0.014 m/s and 15.2  W/m², respectively, during the test. The good performance was achieved in the average cooling capacity of 144.2 W/m² in the greenhouse, an energy efficiency ratio of 9.5, and an average indoor–outdoor air temperature difference of 2.1 ℃ (08:30–17:30). The overall cooling efficiency reached 95.9%. The daily average water consumption rate ranged from 0.033 to 0.065 g/(m²·s) for evaporative cooling. Compared with the negative pressure fan-pad cooling system, the proposed packaged positive pressure ventilation and cooling system requires a lower specific ventilation rate to achieve the same greenhouse cooling amplitude, while exhibiting superior cooling uniformity and efficiency. In comparison with the air-handling corridor based positive pressure ventilation system, the proposed system offers a longer air supply distance, though with relatively higher energy consumption. This finding can provide an efficient mechanical ventilation solution for cooling multi-span greenhouses and support the design of semi-closed greenhouses.

The integration of the active heat storage system utilizing multiple heat storage and release media for prefabricated solar greenhouses with flexible material wall (PGFMW) can solve the problem of "good thermal insulation and weak heat storage" in PGFMW. However, it is still unclear on the heat storage and exothermic properties of the multiple media in the combined heat storage system. This study aims to perform on a PGFMW that equipped with a combined "air source ground heat exchange-back wall water circulation (AGHE-WWC)" heat storage system. A systematic investigation was also made on the individual and combined heat storage and release properties. A series of experimental tests were conducted to calculate the energy transfer. The results indicated that the minimum temperature of indoor air at night time was maintained above 10℃, and the maximum difference in temperature between indoors and outdoors was 26.5 °C in winter. The primary heat storage medium was identified as the 0-50 cm soil layer of the cultivation area in the PGFMW. Furthermore, the heat storage capacity of the soil layer reached 706.30 MJ on sunny days, accounting for 63.5% of the total heat storage. The difference in temperature between the inlet and outlet of the underground heat exchange was up to 10.8 °C, which increased by 54.4% in the heat storage capacity of the soil layer. The water circulation was used to store the heat energy of 424.04 MJ on the day, which accounted for up to 45.1% of the total heat storage. Specifically, after cloudy days, the temperature of 8 m³ of water in the storage tank increased from 11 to 35℃ by water circulation over two sunny days. In order to evaluate the rate of heat storage and release for the system in combination and individually, an evaluation index called the heat storage and release efficiency ratio (HRE) was inducted to assess system performance. It was found that the maximum absolute value of the HRE for water circulation system was 1.62, which was 1.8 times than the soil HRE on the same day. It proved that the water circulation system releases heat more rapidly compared to the soil on cloudy days. In terms of the total heat, the soil was remained the primary source of indoor heat release on the consecutive cloudy days. In addition, the "AGHE-WWC" heat storage system was realized to fullfill the heat demand for a total of three consecutive cloudy days. Meanwhile, the average heating coefficient of performance (COP) and the uderground heat exchange COP were 9.16 and 6.82, respectively. The combined COP of the "AGHE-WWC" heat storage system was 8.85, while the energy saving rate was as high as 60.26%, compared with the heat pump. The finding can provide a strong reference for heat storage and release in combined heat storage systems.