温室水循环太阳能利用系统高效节能控制策略

针对目前温室水循环太阳能利用系统无法在合理时间集热的问题，开发模面装置，基于其表面综合温度提出高效节能控制策略。理论分析表明，日间表面综合温度反映集热器表面可集太阳余热，利用该温度与蓄热水池内水温之间的差值可较准确地判断集热时机；夜间表面综合温度接近于室内气温，利用该温度进行放热控制的方式实质上就是利用室内气温的方式。通过现场试验，测试提出的控制策略下实现的中空板水循环太阳能利用系统的集放热效果，并与现有的基于设定时间点或室内气温的控制方式的能力进行对比。试验结果表明中空板系统在提出的集热控制策略下获得的晴天的集热量（404.1 MJ）与多云天和阴天的集热量（分别为225.9和62.7 MJ）差异显著。而设定时间点控制集热，导致少集热（1.4 h）、无效运行（1.7 h）等问题。基于室内气温方式浪费集热时机：集热初期，太阳辐射较强，系统本可集热（31.8 MJ），且集热量远大于能耗，集热COP（Coefficient of Performance）达20.2，但因气温低，并不运行；集热末期，还出现短期无效运行（多云天为0.7 h；阴天为2.4 h）。该研究提出的集热控制策略能以更低能耗实现更高集热量；放热控制方式也具有一定优势。

High-efficiency and energy-saving control strategy for the water-circulating solar energy system in the greenhouse

Abstract: A water-circulating solar energy system has been widely used in the field of greenhouse heating. But, real-time heat harvesting is still lacking in the arrangement of time points or indoor air temperature. It is a high demand to consider the thermal condition of the collector surface in the current operation control system. This study aims to explore the high-efficiency and energy-saving operating system. An intelligent control device was first developed for solar heat collection and release. A simulation was then performed on the appearance and condition of the water-circulating solar collector (also as the heating radiator) without the impact of water flow. A new control strategy was finally proposed using the simulating device. Specifically, the difference between the surface sol-air temperature and the tank water temperature was utilized to control the daytime heat collection, whereas, the surface sol-air temperature was to control the nighttime heat release. A theoretical analysis was also implemented to verify the control strategy. The surface sol-air temperature of the device surface in the daytime was used to reveal the collectible excess solar heat on the collector surface. As a result, the balance was achieved between the solar radiant heat absorbed by the surface and the heat exchanged between the surface and the internal environment, and between the surface and the greenhouse environment. Thereby, the control strategy accurately enables heat collection at the right time. The sol-air surface temperature at night was closely related to the indoor air temperature. Correspondingly, heat-releasing control was essential using indoor air temperature. The field tests were carried out to investigate the solar heat collection and release effect of the control strategy applied to the water-circulating solar energy system with an indoor collector (as a heating radiator during nighttime) constructed of hollow polycarbonate sheets. And a comparison was also made with the existing control strategy capability. During daytime, weather conditions had significant influence on the surface sol-air temperature. The maximum temperature reached 59.9°C on a sunny day, much higher than those on cloudy and overcast days (47.2 and 35.0°C, respectively). The heat collection on a sunny day (404.1 MJ) was also much higher than those on cloudy and overcast days (225.9 and 62.7 MJ, respectively). Obviously, the setting time points led to some issues for the heat collection control, such as less heat collection (1.4 h) or ineffective operation (1.7 h) on a sunny day, and long-term ineffective operation on cloudy and overcast days. The control system of indoor air temperature also missed some heat collection opportunities, due to the low air temperature. Particularly, the heat (31.8 MJ) needed to be collected for a significant energy saving (coefficient of performance: 20.2) in the early stage of heat collection with the strong solar radiation. Besides, the short-term ineffective operation often occurred (0.7 and 2.4 h on cloudy and overcast days, respectively). By contrast, the new control strategy of heat collection was achieved in the higher heat collection with the lower energy consumption. The heat release control also performed better to reduce the ineffective operation time, due to the rapid response of surface sol-air temperature to exchange in solar thermal energy. The control strategy was also applied in the water circulation systems, in order to tap the harnessing potential of solar energy and saving energy. Besides, the heat collection control strategy can be expected to apply in forced-circulation solar water heating systems. The control strategy can be further optimized for the more ideal heat collection and release. The finding can provide the technical reference to improve the structure and installation of the simulating device in the temperature change management of heat release.