Secondary Refrigerant Systems for Supermarket Application with Brine or Carbon Dioxide

The interest in application of secondary refiigerant systems in supermarket refrigeration is increasing. Reduced refrigerant losses i and the chance for lower installation and operation costs is promoting this development. There are also !options to use natural refrigerants, more efficient refrigerants and gas or waste heat driven absorption proc;esses. First installations of secondary refrigerant systems in the United States were based on propylene glycol solutions as secondanr refrigerant and thus were limited to the medium temperature sector. More recently, highly efficient brfue fluids based on organic salt solutions have been introduced which can be used for low temperature *pplication as welL Plastic tubing for secondary refrigerant distribution is an option for increased flexibility and efficiency while it is reducing the installation costs. There are also supemYrrket systems using carbon dioxide as secondary refrigerant, thus showing that there are :further options. The use of carbon dioxide as low temperature refrigerant in a cascade system is a most promising option duel to the high energetic efficiency. Installation costs may become higher for the carbon dioxide systems delspite smaller pipe diameter due to the high pressure of carbon dioxide. The presentation will illustrate $-d compare these options. INTRODUCTION Commercial Refrigeration The commercial refrigeration and air conditioning sector accounts for the largest ammmt of refrigerant released into the atmosphere with the exception of automotive air conditioning /11. Commercial refiigeration includes a wid~ variety of systems, but the majority of released refrigerant can be attn'buted to supermarket AC and refrigeration systems. The amount of refrigerant charged in these systems is large, and they typically contain a large number of connections, valves, tubes and other posst'ble locations for leaks. They are installed on-Site, and only a few of the components can be premanufactured, assembled and leak tested at the point of qaanufacture. To avoid these leaks without changing the system design will be expensiVe. This situation led to th'e development of secondary refrigerant systems for commercial refrigeration and air conditioning, and illany companies today supply such systems. Figure 1 gives a schematic of a direct expansion system while Figure 2 gives a sketch of a system with secondary refrigerant. An additional interest to use those secoridary refrigerant systems is the option of gas-cooling and wast heat driven technologies based on sorption processes. I i Secondary Refrigerant Systems I The basic secondary refrigerant system uses a brine or other one-phase liquid fluid. The secondary