Centralized or distributed systems

Myths and realities of this kind of systems implemented in commercial refrigeration in supermarkets and supermarkets.

by Giovanni Barletta *

The refrigeration of supermarkets, and large surfaces, also called "cold food", has always been the subject of conceptualization on the ideal way to design the architecture that involves the furniture, and the (or the) production plants of "cold". And all this happens, from different technologies, for many refrigerant options and a number of new and recent regulations.

From the traditional systems of direct expansion, through natural refrigerant technologies, such as CO2, Ammonia, among others, and the recently called "wáter Loop" arrangements that use condensers of the type cooled by water, resembling more self-contained.

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Traditionally, two architectures have been discussed: both with successful trajectories in many end users and markets and also differs from country to country, even competing according to trends between the West and Europe.

Conceptualization of most common architectures
Typically the two most common and widespread options move between centralized systems and distributed systems and this connotation has impacts not only from the location of the cold plant itself with respect to refrigerated furniture, but also as regards copper pipe networks, systems of control, wiring, labor and a myriad of other factors that we will try to summarize in schemes and criteria that, while not universal, are valid in favor of one or the other.

We could say in some way that the centralized system is understood as the "traditional" system and we will try to show the most recent trend and migration towards an architecture that proposes control from the furniture, and "loop" networks or also what this article states as "distributed system".

In the Centralized Systems, we will find a cooling station packed with elements: multiple copper pipes entering and exiting-hence they also call it "multicircuit" to this type of architecture, with solenoid in each branch, suction pressure regulating valves that comes pre-installed by the manufacturer, likewise all the control managed from an intelligent central and from there commands everything, only depending on analog input signals from sensors coming from the point of sale and from the refrigerated furniture and cameras, also all the wiring of force and control reaches the rack.

Numerous cards of entrances and exits to be able to command all these maneuvers which are in the board receiving and returning signals of the control.

The network of copper pipes at the point of sale becomes very extensive, since each exhibitor's line requires its own supply. This extensive network of copper pipes is associated with an important load of refrigerant, in its installation a qualified workforce, support costs, insulation and accessories. From the point of view of efficiency, there is also a penalty for pressure drops, due to the long routes and accessories that this demands.
In Distributed Systems or control from the furniture, we find a network of "loop" pipes also called in some markets as "fishbone", where very few branches come from the rack and are subdivided to each piece of furniture or group. At the same time, a controller is nearby, autonomous and capable of acting on its own, only sending signals, interconnected to each other, to the central unit located in the rack. Figure 1 shows the different control scheme between both architectures for the same store arrangement.

Figure 1. Differences in control systems for two types of architecture.

From the point of view of control, the implementation and addition of control elements that allow better regulation are facilitated, such as electronic expansion valves, and better de-icing system, condensation control, as summarized in Figure 2.

Simultaneously this type of scheme requires a smaller amount of pipes and with it a lower amount of refrigerant charge

Figure 2. Components associated with distributed systems that improve control and regulation.

Before this the question arises: What has generated this change in the tendencies? Why migrate from a traditional system to new control architectures and pipeline layouts?

Figure 3 shows how the variables of energy, labor, the impact on the carbon footprint and the unpredictable cost of copper in international markets have behaved in the last 20 years. To all the above, it is added that the costs of electronic furniture controls due to the development of the production systems of electronics have decreased considerably and make it more competitive.

Perhaps the factor that has most impacted the migration from one architecture to another has been the cost of energy. Figure 4 shows how distributed systems, which began in Europe many years ago and in the United States only from the 90 's, coincides with the fact that the Old Continent has more than 90% in distributed systems vs. the 20% that USA currently has (Figure 4).

The best and clearest evidence of the way these two variables are associated can be seen in Figure 5, where at higher energy costs, more% of stores with distributed systems in Europe, contrary to what is happening in the United States.

Figure 3. Variables that impact migration to distributed systems.

Figure 4. Participation of technologies in the world market.

Figure 5. Comparison between US and Europe and its growth in distributed systems vs the cost of energy.

Although some of these statements are relative and depend on the market and in the country in which it is analyzed based on the costs of energy, labor and other indirect costs, it could be generalized saying that the benefits of distributed architectures or control from the furniture They are summarized in the following:

  • Low installation cost, impacted by minor: pipe laying, less welding and insulation, less electrical panels in the field, less sensor wiring, and less refrigerant gas charge.
  • Lower energy consumption, by finer adjustment in electronic expansion valves and in turn benefits in low condensing applications.
  • Lower maintenance cost because it does not require adjusting the thermostatic expansion valve, and the store's starting time is shorter. Additionally it allows control of lights.
  • Higher quality / food safety, by finer temperature control.
  • Environmental benefits due to lower refrigerant charge and lower carbon footprint.

This concept of shortening pipe runs and avoiding efficiency penalties due to the pressure drop in the pipes also generated more compact and lighter cold power stations which are very close to the refrigerated furniture, either on the roofs or on the roof. head of the refrigerated linear. Its appearance is similar to an air conditioning condensing unit, as shown in Figure 6. This is possible thanks to technologies such as the Scroll compressor that being very light with respect to its capacity allows these models of the well-known MiniRack'o Scroll Pack.

Figure 6. Cooling unit for distributed architectures.

Under this concept, pipe laying is reduced, as shown in Figure 7, under the idea that the units are located near the furniture. All this must be analyzed in the balance of the cost overruns, on reinforcing the covers vs. the benefit of not occupying sales area in the machine room

Figure 7. Difference in the routes of pipes between a centralized system and a distributed one.

References
- Energy & Store Development Conference (FMI) Minneapolis Sept 2010
DOE (US Department of Energy)
- http://betterbuildingssolutioncenter.energy.gov/alliance/technology-solution/refrigeration

* Giovanni Barletta is the Technical Manager of the Andean Area, Caribbean and Central America of Emerson, and current president of the Colombian Association of Air Conditioning and Refrigeration (ACAIRE). You can be contacted at the e-mail: presidenteacaire@acaire.org

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