A night cooling system for a greenhouse using solar energy

在日本农业中，大量的电能被消耗在夜间的温室冷却中。本研究探讨了太阳能的利用，并开发了一套利用太阳能的温室夜间降温系统。那是一种间歇吸收式制冷系统。太阳能作为白天溶液浓度差的能量储存起来，用于夜间降温。通过实验验证了系统的工作原理。该系统由回热器/散热器、真空罐和蒸发器/冷凝器3个测量部件组成。回热器/散热器在白天收集太阳能热量，并在夜间辐射吸收的热量。该组件使用了改进的平板太阳能集热器。真空罐的内部被分成3个部分。它们是一个分离器，一个吸收器和一个储存器。吸收塔内填充大量聚丙烯空心小球，以增加汽液接触面积。蒸发器/冷凝器由铜管制成，其上附有翅片以增加传热面积。水和溴化锂液体被用作制冷剂-吸收剂对。从实验结果来看，证实了所开发的系统的原理没有问题。吸收剂在白天被太阳热聚集。在夜间，冷凝水蒸发并冷却冷凝器外部的水。实验结果表明：1.在足够高的温度下收集太阳能热量用于再生溴化锂吸收器; 2.吸收性能良好; 3.吸收热量引起的温升在可接受的范围内; 4.溴化锂没有从溶液中析出; 5.由于传热面积不足，冷凝器的性能受到限制。面积应该更大。

In Japanese agriculture, a lot of electric energy is consumed for greenhouse cooling in nighttime. In this study, the utilization of solar energy was discussed, and a night cooling system for a greenhouse using solar energy was developed. That is an intermittent absorption refrigerating system. Solar energy is stored as the energy of concentration differentials of the solutions at daytime, which is used for cooling at nighttime. The experiments ware carried out to confirm the operating principle of the system. From the experimental results the heat balance was calculated.The system consists of 3 measure components, those are a regenerator/radiator, a vacuum tank and a evaporator/condenser. The regenerator/radiator collects solar heat at daytime, and radiates the absorption heat at nighttime. A modified flat plate solar collector was used for the component. The inside of the vacuum tank was separated in 3 parts. Those are a separator, an absorber and a reservoir. The absorber was filled with a lot of small polypropylene hollow-body balls to increase the contact area of vapor and liquid. The evaporator/condenser was made of copper tubes on which fins were attached to increase the area of heat transfer. Water and lithium bromide liquid were used as the refrigerant-absorbent pair. From the results of experiments, it was confirmed that the principle of the developed system had no problem. The absorbent was concentrated by solar heat at daytime. At nighttime the condensed water was vaporized and cooled the water outside of the condenser. The experimental results are summarized as follows,1.Solar heat was collected at a sufficiently high temperature for regenerating the absorbent.2.Performance of absorption was sufficient.3.Temperature rise with the absorption heat was an acceptable level.4.Lithium bromide was not precipitated out of the solution.5.Because the heat transfer area was not enough, performance of the condenser was limited. The area should be larger.