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17 January 2022
Food logistics – too much energy bills? General principles of designing refrigeration systems in logistics

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Industrial refrigeration systems are a typical example of form serving function. Typically, the entire facility is architecturally designed so that the flow of goods is optimal. That is, only in one direction while maintaining the refrigeration sequence.

As a refrigeration expert, I focus on temperatures and not on ISO, SANEPID, or other issues.

A typical object is shown in the diagram below.

A typical logistics center will have the following zones:

  • Receipt of goods

    Goods after transport are unloaded into this zone

  • Refrigerators for storing goods

    Due to practical factors, two or more cold stores are often designed. This is of particular importance when the stored goods require different storage temperatures or humidity.

  • Freezer for storing goods

    Due to the large difference in temperature between the cold store and the rooms to which the gates lead, it is good practice to use vestibules

  • Delivery of the goods

    Goods prepared for release are temporarily stored in this zone.

Refrigeration balance
There are two methods of determining the required cooling power for logistics centers. Academic and factor. In the academic method, I count all the heat profits for a given room (walls, open gates, goods, machines, lighting, etc.). However, it is often difficult to determine in advance what the flow of goods will be in the future, which is why the coefficient method is also used. It results from the experience of the designer A consists in multiplying the coefficient by the volume of the room. For correct calculations, both of these values ​​should be equal and contain a certain supply.

Construction of premises
The main material for the partitions of refrigerated rooms is a sandwich panel made of polyurethane or glass wool (simplification). Rooms with temperatures above 0C do not require insulation of the substrate. However, one should take into account the risk of dripping moisture on the floor in adjacent uncooled rooms. This problem should be solved at the design stage. It is good practice for cold storage to be built in the “box in box” technology. In the case of rooms with an area of ​​more than 1000 m2, it is good practice to use insulation panels with a minimum thickness of 100 mm.

In the case of a cold store, it is necessary to use the “box in box” technology and to insulate and protect the floor against frost. Typically, a sandwich panel with a thickness of 160 to 200 mm is used.

Refrigeration installation
In each cooled room, air coolers are installed, adapted in terms of their construction and parameters to the logistics equipment (shelves, robots, etc.) and in locations ensuring optimal air flow.

There are many technologies for “transporting cold” to air coolers. Most often, glycol or direct evaporation of the refrigerant is used.

Although it is possible to install external chillers, it is good practice to build a machine room. This room should contain all cooling units, power and control cabinets for units, tanks for recycled hot water, etc. Gas-coolers or condensers are installed in the immediate vicinity of the engine room or on its roof.

The engine room should have drains in the floor and large doors that will allow easy work.

Between cooling units and air coolers, pipelines are installed to transport glycol or refrigerant.

Above, I have described in a very basic way the main elements of the refrigeration system. The technology used, insulation thickness, pipeline diameters, and selection parameters of all components will affect the ease of use, failure-free operation and, above all, energy consumption of the constructed installation.

The technologies available today vary greatly in terms of running costs. I am talking about a nearly two-fold difference, which in the case of the largest facilities will translate into millions of zlotys in electricity bills each year. As of the date of writing this column, the payback of high energy efficiency technologies compared to the simplest is at the level of 2 years.