Year-round operation the solar powered hybrid adsorption-compression refrigeration cycle

Abstract

In our earlier papers a hybrid adsorption-compression refrigeration cycle was presented. The hybrid, two stages cycle is based only on the natural refrigerants: water and carbon dioxide. The main advantage of the hybrid cycle is that the carbon dioxide compression cycle is subcritical because during the year-round operation it is possible to maintain the condensing temperature below 20°C. During the hot season, this is achieved by adsorption cooling, during cold seasons the wet cooling tower is sufficient. Already several years of experience, allowed to gather a considerable amount of measurement data. The refrigeration system is working in our laboratory constantly since 2013. In 2015 the adsorption system was upgraded by the manufacturer. In 2017 frequency inverter for wet tower fan controlling was introduced. The refrigeration chamber was used for tests with different content and operation of the refrigeration chamber (loading and unloading). The assumed CO2 evaporating temperature was-35°C. The averaged for HT (High Temperature) part of the cascade (adsorption cycle only) COPHT=0.51 for the whole year 2018. This may be considered a very good performance. Averaged total COP for the cascade system: COP=0.9 compared to COP=0.84 for compression only refrigeration cascade, with much higher TEWI index. For comparison for two-stage compression (R407CHT+R744LT) cycle was used. This means that if the cooling tower fan operation is controlled using an inverter, adjusted to the actual heat removal demand, the hybrid cycle is not only ecological but also energetically efficient.