Refrigeration is the heart and soul of food business because food business is run on fresh and nutritious food. Refrigeration is the key to keep the food business running by always having enough food supply. There is a very wide range of refrigeration appliances available in the market. Each and every different type of refrigeration appliances like commercial chest freezer or even domestic fridges is designed for some specific function. Refrigeration is used in stores, restaurants, cafes, bars, convenience stores and supermarkets.
The most commonly used combinations of refrigerant technologies for supermarket refrigeration systems are as following:
Centralized direct expansion:
The central direct expansion system uses HFC for loads of medium temperature and low temperature, which means it is used in frozen, chilled display refrigerators. Both LT and MT use a ‘multi-compressor pack’ which is central, and it consists of either three or eight scroll compressors also known as semi-hermetic reciprocating. A very high pressure liquid refrigerant is pumped in to refrigerators with the help of a liquid receiver. After that the refrigerant vapors return to the compressor with the help of suction line.
The pressure of the condenser in this type of system is controlled by changing the flow of the air. This allows you to keep condensing pressure as low as required and keeps it in pace with satisfactory expansion valve, in case the outer temperature becomes really low.
The leakage of refrigerant from refrigeration technologies used in supermarkets varies in different places basing on how they are installed. Even in the best installed system there will be refrigerant leakage to some extent. In Europe the average refrigerant leakage is calculated to be 15 %.
The major reasons behind the leakage can be:
- The ball or Schrader valves are shut.
- Problem with mechanical joints.
- Some problem with pressure relief valves or fusible plugs.
- Check the condensers and evaporators.
Distributed direct expansion:
In this system the compressor is either placed adjacent to inside the condenser. It does not has a central plant room but has a number of small compressors which are mounted inside each condensing unit. The condenser units are most of the time roof mounted which helps in avoiding very long refrigerant lines. Refrigerant leakage can be avoided if there are no long refrigeration line for commercial refrigeration. The use of this system depends mainly on the location where the refrigeration system is being installed.
Cascade system:
This is one of the refrigeration technologies which is used for medium temperature load and low temperature load systems. It has a separate circuit which discharges its heat into the suction area of the medium temperature system.
A low condensation temperature is used for low temperature circuit, which makes R744 very suitable for this system and can be applied without any chance of excessive pressure. The challenges of the system are not very different from the conventional refrigerants. The discharge pressure is around 30 to 35 bar and it is within the limits of usual design for components and refrigeration pipe work.
Secondary system:
The secondary system has the feature of distributing the medium temperature cooling at the supermarket. The arrangements of low temperature is same to the cascade system described. The circulation of the secondary fluid helps in transference of medium temperature of heat-evaporator from the chill cabinets. The heat exchanger can be located near to the compressors while the air-cooled compressor is being assembled. This helps in a significant reduction of MT refrigerant leakage.
This system requires a pump so that the coolant can circulate easily around the supermarket. There is also an extra heat exchanger temperature drop. A temperature difference is required by the heat exchanger because it derives the heat transfer.
Booster transitional system:
The refrigerant used in the refrigeration with this system uses R744 in both MT and LT system. The compressors of LT act as boosters so that the vapor pressure can be increased to the MT evaporator levels. The refrigerant is distributed in both MT and LT cabinets like normal glass fronted fridge with the help of a liquid line at the intermediate temperature.
