Description
Project partners expect to propose R744 refrigeration systems equipped with ejectors having the value of system energy efficiency higher than the ordinary R744 booster system and the HFC systems. Enhancement of energy efficiency of R744 ejector system, reached for commercial installations rather than laboratory test facilities, should moderate the cautiousness the European manufacturers of refrigeration equipment presented towards the ejector technology until now. The target group is the whole refrigeration engineering community. Project is needed to confirm advantages of the R744 ejector system over other systems. This will be proved by the results of field tests performed for real systems installed and tested in supermarkets at various load profiles and ambient conditions. Scientific partnership will concern common work in two main areas: experimental tests and numerical research. Partnership will achieve continuous exchange of experience and younger researchers. Both partners will prepare joint publications available worldwide.
Summary of project results
Supermarkets are commercial buildings with major energy consumption and relatively large contribution to direct emissions of greenhouse gases through refrigerant emissions. The majority of the European systems are applying HFC-404A as working fluid. Average annual leakage rates in Europe are in the range of 15-20% of the total charge. Worldwide the figure is about 30% with HCFC-22 being the main refrigerant. Therefore more than 2000 supermarkets with systems applying R-744 as the only refrigerant have already been developed. However, these systems still have large potential in development with respect to energy efficiency, heat recovery and cost efficiency. In this project efficiencies and capacities for an R-744 supermarket system layout with ejectors are investigated. During the first stage of the project, the CFD model was adapted to the parametric optimization of the ejector. The in-house code EjectorPL was developed, which enables the fully automated pre–processing, solver setup, running of computations and finally the post–processing. This new tool was used to perform the substantial number of computer simulations which showed that the influence of the dimensions of the mixing section on the total ejector performance is significant. Simultaneously, the operating regimes for the refrigeration systems were defined simulating high, typical and low inlet parameters (temperature and pressure). These base geometries were numerically analysed and the performance indicators (such as the mass entrainment ratio and the ejector efficiency) for all proposed geometries were calculated. The mixing section of the base ejectors was also optimized to increase the performance of the device. The obtained results allowed to make the characteristics of the ejectors performance for the purposes of the whole refrigeration system analysis. Finally, the detailed ejectors designs were sent to the contractor who was responsible for the manufacturing and installing the ejectors in the super market refrigeration units. Finally two supermarkets located in hot-climate-conditions (HT), i.e. Spiazzo in Italy as well as cold-climate-conditions (LT), i.e. in Trondheim in Norway, were selected, refurbished and equipped in the Multi-ejector modules. To compare the COP of the booster system and the Multi-ejector systems, the installed refrigeration units were configured to work in 50/50 mode, i.e. the 50% of the operating period covered by the Multi-ejector pack when the other 50% should be covered by the flashing valve operation.
Summary of bilateral results
All results obtained in this project are shared. No doubts they improve knowledge on both sides and help to understand details of R744 flow through ejector. Very important issue were bilateral meetings and visits. Some PhD and MSc students spent longer time in Norwegian partner’s labs. What is also essential this direct cooperation allowed to validate all results of advanced computational simulations of R744 flows through ejector by the very demanding experimental measurements. As a result visibility of that international working group is strengthen considerably.