The difference between direct cooling systems and indirect cooling systems, also known as secondary refrigeration, lays in the physical separation between the primary circuit, where the cold is generated, and the secondary system, where cooling takes place. The cold generated in the primary circuit is transported by the heat transfer fluid to the place where food or other products must be cooled. Obviously the coolant must remain fluid at all temperatures prevailing in the system and preferably the viscosity should be as low as possible.
Depending on the required cooling temperatures, and the properties of the place or product to be cooled, as well Zitrec M, Zitrec L, Zitrec S, Zitrec F or Freezium can be used.
In indirect refrigerant systems heat transfer fluids are needed, which have 2 basic functions : not only must it transfer the cold, the heat transfer fluid, also called secondary fluid, must also protect the system against corrosion.
During the transport of the cold it is obvious that the fluid must remain
liquid at all temperatures
prevailing in the system and preferably the
viscosity should be as low as possible. We refer to the calculation section
of our program
Prozit to help you
understand the different viscosity behaviour of the different fluids.
Additionally the fluid must protect the entire installation against corrosion. Compared to many other applications, the corrosioin protection at low temperatues requires a different set of inhibitors and protection mechanism. Our Zitrec products are designed to offer maximum protection under all conditions.
There are many benefits to indirect refrigerant systems : a minimum amount of refrigerant, a reduced risk for leakage of the primary refrigerant, a reduced system size and less severe demands towards piping and pumps. Smaller primary cooling circuits further benefit in fewer legally mandatory maintenance and checking operations. A secondary system is also simpler to modify, which makes it extremely interesting for production processes requiring flexibility. And in an indirect system, the secondary fluid can easily be carried away from the system and cooled at a convenient distance, and as such, the potential problem of transporting refrigerant over a long distance is avoided.
The combination of these benefits is why typically in public buildings, such
as supermarkets, indirect systems are promoted.
In supermarkets, the cold needs to be transported to a variety of fresh and frozen displays in an effective, safe and economical way. 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, can provide heating for the supermarket when required. In this way the use of unwanted refrigerant such as ammonia in a public place is avoided, although it can still be used in the primary system, kept in a safe sealed room, away from the public.
If previously the system has been using inorganic salt brines a very strict flushing is necessary. Especially if chlorine rich solutions, such as Calcium chloride, were used before, the flushing must be carried out with particular care because any residues in the system tend to undermine the corrosion protection properties of the coolant.
Temperatures for this application can vary from –30°C to 40°C.
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