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The continuous derivation of the ambient temperature and cooling demand in CO 2 refrigeration and air-conditioning systems equipped with multi-ejector modules for supermarkets requires the analysis of the fixed ejector utilisation in a very wide range of the operational envelope. Therefore, performance mapping of the four R744 ejectors installed in the multi-ejector pack was performed. The investigations of a single ejector's work were performed based on the proposed hybrid reduced-order model to predict the performance of each ejector under arbitrary operating conditions. The proposed model was validated and generated by use of the experimental data together with the computational fluid dynamic model results. The ejector efficiency mapping indicated the area of the best ejector performance in the range from approximately 50 bar to 100 bar. The mass entrainment ratio of all four ejectors was presented for different ambient temperatures and the pressure lift. An area of the mass entrainment ratio greater than 0.3 was obtained by each ejector at ambient temperature above approximately 15 • C for pressure lift below 10 bar. The approximation functions of the ejector pressure lift in terms of the ambient temperature for air-conditioning operating conditions to reach the best efficiency of each ejector are proposed.

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Due to the development of high efficiency R744 air conditioning systems, the main aim of this paper is the investigation of a control concept for swash plate compressors. This paper presents three different control concepts for a swash plate compressor using a built-in control valve. Therefore a model for a one-phase R744 expansion valve was developed and adapted to detailed measurement data. To achieve high reliability in the simulation, the entire R744 refrigerant cycle was validated using analyses of measurement data from an IfT test bench. The simulation of the refrigeration cycle components was realised using TIL (TLK-IfT-Library). The main focus was set as the description of the compressor with its internal and external mass flow rates. The internal mass flow, which is directed through the crankcase, directly affects the crankcase pressure. It is also called the control mass flow. As a result of the crankcase pressure an adjustable mechanism regulates the displacement as shown in figure 1. The greater the displacement, the greater is the inclination angle. This is caused by different load incidence points on the swash plate e.g. by springs, pistons and pressure states. A comparison of different control concepts shows the characteristic and control behaviour of each of them relating to control time and control mass flow rate. Whenever a control mass flow occurs, it implicates throttle losses. The dissipated energy can be minimised using another control concept.

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