There are two reasons for using an indirect refrigerant system. First, the amount of refrigerant can be kept at a minimum. Second, the risk of leakage of primary refrigerant is decreased. This means that refrigerants that are not wanted in systems in public buildings (e.g. ammonia) can still be used in the primary system, which can be kept in a safe sealed room.
Using a brazed plate heat exchanger as both evaporator and condenser in a refrigerant system will result in the most efficient and compact refrigeration system available. Utilizing secondary fluids (water or brines) as carriers for the cold and heat will bring the system size and refrigerant charge to an absolute minimum.
No bulky air coil condenser is needed adjacent to the refrigerant system, which reduces the problem of noise. Instead, the secondary fluid can easily be carried away from the system and cooled at a convenient distance in a dry cooler. Additionally, the potential problem of transporting refrigerant over a long distance is avoided.
A good example of indirect refrigeration systems is in a supermarket (see Figure 10.4). All the cooling effect required is produced in the machine room, far from the display cases, resulting in high flexibility and a lower risk of leakage. A heat recovery system, also situated in the machine room, provides heating for the supermarket when required. As discussed in chapter 10.1, the use of dual circuit heat exchangers, such as the SWEP True Dual models, is advantageous because the independent refrigerant circuits increase the safety and availability of cooling.
This can be important in supermarkets, for example, where the total value of refrigerated or frozen groceries could reach significant levels. In the case of an indirect refrigeration system, the evaporator (see Figure 10.4) can be changed to a True Dual brazed plate heat exchanger.