A night cooling system for a greenhouse using solar energy

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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.