The requirements for environmentally friendly refrigerants promote application of CO2 and water as working fluids. However there are two problems related to that, namely high temperature limit for CO2 in condenser due to the low critical temperature, and low temperature limit for water being the result of high triple point temperature. This can be avoided by application of the hybrid adsorption-compression system, where water is the working fluid in the adsorption high temperature cycle used to cool down the CO2 compression cycle condenser. The adsorption process is powered with a low temperature renewable heat source as solar collectors or other waste heat source. The refrigeration system integrating adsorption and compression system has been designed and constructed in the Laboratory of Thermodynamics and Thermal Machine Measurements of Cracow University of Technology. The heat source for adsorption system consists of 16 tube tulbular collectors. The CO2 compression low temperature cycle is based on two parallel compressors with frequency inverter. Energy efficiency and TEWI of this hybrid system is quite promising in comparison with the compression only systems. Nomenclature GW P -global warming potential CO2 equivalent E -energy use of the cycle per year, kWh f -refrigerant recovery L -emission to the atmosphere, kg/yr m -amount of refrigerant in installation, kg n -cycle life, yr N -supplied electric power of the cycle, kW tr -yearly number of work hours, h z -CO2 emission for the electric energy; in Poland z = 0, 94 kgCO2/kWh

Wymagania dotyczące użycia przyjaznych dla środowiska czynników chłodni-czych promują zastosowanie CO 2 i wody jako czynników roboczych. Oba rozwiązania posiadają wady, będące wynikiem ograniczeń dla maksymalnej temperatury CO 2 i dolnej granicy temperatury dla wody. Można tego uniknąć przez zastosowanie hybrydowego adsorpcyjno-sprężarkowego systemu chłodniczego, w któ-rym woda jest cieczą roboczą w cyklu adsorpcyjnym, który zaś stosuje się w celu ochłodzenia skraplacza CO 2 w cyklu sprężarkowym. Proces adsorpcji jest zasilany energią niskotemperaturową z odnawialnego źródła ciepła, taką jak kolektory słoneczne lub poprzez inne źródła ciepła odpadowego. Rozwiązanie takie to nasz własny pomysł i nie odnotowano go w żadnym innym źródle literatury. Natomiast różne warunki otoczenia przez cały rok wymagają specjalnie zaprojektowanych procedur sterowania i rozwiązań automatyki. Algorytm sterujący musi kontrolować działanie dodatnich i ujemnych źródeł ciepła, zawory, pompy, wentylatory i pracę układu sprężarkowego. W algorytmie tym temperatura otoczenia i warunki słoneczne lub z innego źródła ciepła na przykład odpadowego muszą być wprowadzone jako jego parametry, biorąc pod uwagę działanie obiegów w celu osią-gnięcia maksymalnej wydajności całego systemu. Zapotrzebowanie na zimno powinno być wzięte pod uwagę zarówno pod względem mocy chłodniczej jak itemperatury.Słowa kluczowe: hybrydowy adsorpcyjno-sprężarkowy system chłodniczy, sterowanie 1 Autor do korespondencji: Piotr Cyklis, Politechnika Krakowska, al. Jana Pawła II 37, Kraków, tel. 12 628 35 83,

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.

Abstract. The compression anticlockwise cycle is mostly used for refrigeration. However due to the environmental regulations, the use of classic refrigerants: F-gases is limited by international agreements. Therefore the combined compression-adsorption hybrid cycle with natural liquids: water/carbon dioxide working as the energy carriers is a promising solution. This allows to utilize the solar or waste energy for the refrigeration purpose. In this paper application of the solar collectors as the energy source for the adsorption cycle, coupled with the low temperature (LT) refrigerating carbon dioxide compression cycle is shown. The control of the system is an essential issue to reduce the electric power consumption. The control of the solar heat supply and water sprayed cooling tower, for the adsorption cycle re-cooling, is presented in this paper. The designed control system and algorithm is related to the LT compression cycle, which operates according to the need of cold for the refrigeration chamber. The results of the laboratory investigations of the full system, showing the reduction of the energy consumption and maximum utilization of the solar heat for different control methods are presented.

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