High energy consumption challenges the multi-span greenhouse industry in China. To address this, a greenhouse heating system utilizing energy transfer between greenhouses based on the dual source heat pump (ETGHP) was designed in our previous research. However, its performance in practical application remains largely unexplored. This study conducted a field test to comprehensively assess this system. Results showed stable heating effects, and the heat collection of the system in Chinese solar greenhouse (CSG) air source heating mode accounted for 2.1% to 28.2% of the total, validating the feasibility of energy transfer between greenhouses. The use of CSG air source increased heating capacity by 27% and coefficient of performance (COP) by 23% for air source heat pumps. Then the dual source configuration achieved a 10.8% increase in heat collection and a 7.9% improvement in COP compared with the single air source. During the test, the COP of the system achieved 2.8 during heat collection and 2.5 for heating the multi-span greenhouse. Outdoor weather, greenhouse structures and management were found to influence system operation. This study also conducted performance comparation and explored the economic and environmental benefits for the system, proving it to be an efficient solution for multi-span greenhouse heating.

Large-scale greenhouse can be expected to serve as the future direction in the horticulture industry. However,the multi-span greenhouses can consume a large amount of energy for heating in winter in northern China, resulting in low profitability and sustainability. In this study, a multi-span greenhouse was designed with large roofs and external insulation, in order to reduce the heat loss of the greenhouse roof. The external insulation system was innovatively applied to the multi-span greenhouse. The greenhouse design was expected to improve thermal insulation performance and reduce heating energy consumption. A field test was carried out in Shouguang, Shandong Province, China. Taking the Venlo-type multi-span greenhouse in the same area as a reference, a systematic investigation was made on the light and thermal environment, thermal insulation performance of the multi-span greenhouse with external insulation. The experimental data were analyzed from continuous 40 winter days. The results show that: 1) The average solar radiation was 152 W/m~2 above the crop canopy inside the tested greenhouse during the day（10: 00-16: 00）, and the total light transmittance was 40%, which was 7 percentage points higher than that of Venlo type multi-span greenhouse. The best daylighting was found in the middle of the greenhouse span, due to the influence of the gutter. The solar radiation intensity at the east and west of the greenhouse span and under the gutter was reduced by 17%, 29%, and 46%,respectively, compared with the middle. 2) There was the folded in turn for the external thermal blankets covering the east and west greenhouse roofs after the sun rose. Specifically, the indoor air temperature rose at 1.9 ℃/h from 09:30 to 12:00, which was 0.3 ℃/h slower than that of the Venlo-type one. However, the sudden drop in the air temperature of the multi-span greenhouse with the external insulation was reduced by 0.3℃ within 10 min after folding insulation devices. The tested greenhouse was heated by the internal air circulation, with the air coming out from the ground and then returning to the equipment room through the inner side windows. During the heating period（20:00-07:00）, the average temperature difference of indoor air in the horizontal direction did not exceed 1.2 ℃, without exceeding 1.0 ℃in the vertical direction. The uniform distribution was observed in the horizontal temperature of the multi-span greenhouse with the external insulation. The vertical temperature difference was smaller than that of the Venlo-type one.3) The average air temperature at nighttime inside the multi-span greenhouse with external insulation ranged from 13.1to 16.1 ℃, and the average temperature difference between indoor and outdoor air was 12.8-21.0℃. The average heat flux of the glass roof that was covered with the external thermal blanket was 50.0-97.7 W/m~2, while the single-layer glass roof was 217.6-367.9 W/m~2. The greenhouse covering with the external thermal blanket was reduced by 75% in the heat loss of the glass greenhouse roof. At the same time, the average heat flux was 141.1-232.2 W/m~2 in the Venlo-type one with double-layer indoor thermal screens in use. The roof heat loss of the multi-span greenhouse with the external insulation was reduced by 36%, indicating a better insulation performance. The mean heat energy input of the multi-span greenhouse with external insulation was measured to be 74.5 W/m~2 during the heating period, maintaining an average temperature difference between indoor and outdoor air of 17.4 ℃. Thus, the energy consumption of heating the multi-span greenhouse with the external insulation was low. Finally, the fitted influence of indoor and outdoor air temperature differences on the heat fluxes of greenhouse roofs was presented, and the tested greenhouse showed better goodness of fitting. This finding can provide a new type of greenhouse structure for the low-carbon and energy-saving production of multi-span greenhouses. A data basis can also be offered for the optimal design and engineering application of the multi-span greenhouse with external insulation.

Multi-span greenhouses consume enormous amounts of energy for heating in northern China, resulting in poor profitability and unsustainability. A greenhouse heating system, utilizing energy transfer between greenhouses based on a dual source heat pump, was designed to remedy this issue. The system collects surplus air heat inside Chinese solar greenhouses (CSGs) for heating multi-span greenhouses. Through enabling a greenhouse energy transfer in time and space, improved utilization efficiency of surplus air heat in CSGs is achievable, resulting in an overall reduction of heating costs. This study defines the heating approach and describes the overall system design. The dual source heat pump acts as the core component, with two separate evaporators placed in the CSG and ambient air. Calculations for system sizing are then presented, including a heating load model of multi-span greenhouses, a surplus air heat model of CSGs, the selection of required equipment (dual source heat pump, heat storage tank, and surface air cooler of the combined air conditioning unit), and the area matching. Finally, a case study illustrates the implementation processes of the heating system. The available CSG surplus air heat ranged 100.8-112.6 W m(-2) for system sizing, and the minimum area of CSGs was suggested to be twice the multi-span greenhouse area. The pilot test showed that the running status and heating effect of the system was stable. The coefficient of performance (COP) of the heat pump reached 4.3-4.8 when using CSG surplus air heat as the heat source, performing 23-26 % higher than when using ambient air over the same periods. Throughout the entire course of heat collection, dual source heat pumps, switching sources based on their setting, achieved a total COP of 3.4-4.2, increased by 6-11 % compared with air source heat pumps. This study provides a novel heating approach and an energy-saving system for multi-span greenhouses.

为降低北方地区连栋温室冬季生产能耗、提高温室保温性能,设计了大斜面外保温连栋玻璃温室,即寿光型智能玻璃温室.该温室采用大天沟设计,安装了外保温被及传动机构,因此形成了较宽的遮阴带,影响了栽培区的太阳辐射及温室透光率.为分析天沟尺寸对室内光环境的影响,构建了连栋温室天沟对温室栽培区内不同位置辐射强度影响的动态模型,并基于该模型对室内光环境进行了均匀性与敏感性分析.结果 表明:天沟结构对栽培区内日累积辐射平均值的影响程度从大到小依次为天沟间距、天沟宽度、天沟垂直厚度和天沟高度;寿光型智能玻璃温室的天沟设计为相邻两天沟间距12.00m、天沟水平宽度1.60m、垂直厚度0.86m、天沟下沿离地面高度6.30m,可以保证栽培区内最佳的光照均匀性.不同情景下的模型模拟结果表明,为确保栽培区内光照均匀性,在栽培区内辐射强度变异系数最小的情况下,山东省寿光地区温室天沟高度、天沟垂直厚度之和与天沟间距、天沟宽度之和的比值在0.49 ～0.54之间.本研究可为寿光型智能玻璃温室在不同地区的设计应用提供理论依据.