This paper outlines a hybrid cold storage system and briefly presents experimental results. The system consists of an ice thermal storage system (ITS) and water thermal storage system (WTS) using nocturnal radiative cooling. The cold storehouse is divided into two rooms by a partition; one is refrigerated by ITS with an ice bank, and the other is cooled by WTS having a water tank and flat-plate type of sky radiators mounted on the rooftop of the storehouse. Sky radiators are employed at nighttime in order to obtain cool water at about 15°C or below, depending on the weather conditions. An air-washer type of water-air heat exchanger was installed inside each room for cooling by cooled water, which can easily project low-temperature and high-humidity air by blowing room air directly through a water shower. Experiments with this system conducted at Tsukuba, Japan proved that with favorable weather conditions at the end of April, by using the cooled water produced by sky radiators the temperature of the medium-cold room was kept below the setting temperature of 14°C till the following afternoon. The measurements in mid October showed that about 1.3 to 3.8 MJ of cold thermal energy was stored as 340 kg of cool water per square meter of sky radiator through one night. That amount of energy was 0.9 to 1.9 times as much as the electric energy consumed for water circulation. The thermal vegetable models placed in the medium-cold room could be cooled from 22°C to 14°C in about 18 hours through evening to the following morning.
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