A night cooling system for a greenhouse using solar energy

在日本农业中，大量电能在夜间用于温室降温。本研究对太阳能的利用进行了探讨，并开发了一套太阳能温室夜间降温系统。这是一种间歇式吸收式制冷系统。太阳能在白天储存为溶液的浓度差能量，在夜间用于制冷。进行了实验，确定了系统的工作原理。系统由回热器/散热器、真空箱和蒸发器/冷凝器3个测量部件组成。回热器/散热器白天收集太阳热，夜间辐射吸收热。该组件采用了改进型平板太阳能集热器。真空罐的内部被分成三部分。它们是分离器、吸收器和储液器。吸收塔内填充了大量的聚丙烯小空心球，以增加气液接触面积。蒸发器/冷凝器由铜管制成，在铜管上安装翅片以增加换热面积。采用水和溴化锂溶液作为制冷剂-吸收剂对。从实验结果可以看出，所研制的系统原理上是没有问题的。这种吸收剂在白天被太阳热能集中。在夜间，冷凝水被汽化并冷却冷凝器外的水。实验结果总结如下：1.在足够高的温度下收集太阳能用于再生吸收剂.2.吸收性能良好.3.随着吸收热的升高，温度升高是可以接受的.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.面积应该更大一些。

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.