Experience in the implementation of a transcritical carbon dioxide refrigeration unit in the Auchan chain store in Pushkino

As you know, according to the Kigali Amendment to the Montreal Protocol, the use of refrigerants based on hydrofluorocarbons, including R404A, R507A and R134a, will be reduced. By 2036, the total volume of their use should be reduced by 85%, so carbon dioxide schemes are becoming more relevant and in demand in the commercial refrigeration market.

On December 12, 2019, a new Auchan hypermarket was opened in Pushkino, Moscow region. One of the distinctive features of the store is a refrigeration unit, which for the first time in the Auchan network in Russia operates on carbon dioxide according to a transcritical refrigeration cycle for all temperature consumers.

The refrigeration unit, designed and installed at the facility by LAND, has the following cooling capacity:

* medium temperature circuit – 534 kW;

* low-temperature circuit - 62 kW;

* climate system – 195 kW.

The total cooling capacity is divided equally into two refrigeration circuits. The design solution allows, if necessary, to switch all consumers to one system. So, in winter, when the required cooling capacity may fall by 50-70%, this may allow in some cases to work completely on one system, which ensures uninterrupted operation of the store during scheduled or repair work.

Fig. 3. The engine room on the roof of the building of the shopping complex

For the LAND company, the Auchan Pushkino facility is not the first project of this type. To date, the specialists of LAND have designed, installed and put into operation 19 carbon dioxide facilities. Compressor units based on Dorin compressors and pumping stations for the coolant were assembled at the Russian Elementum plant (Fig. 1 and 2). The control system is based on electronic and mechanical components manufactured by Danfoss. Thus, a multifunctional modular controller for AK-PC 782A transcritical systems has been used to control all groups of compressors, high-pressure valves and bypass valves, as well as gas coolers. Controllers for commercial equipment АК-СС 550A, equipped with adaptive algorithms, paired with pulse valves of the AKV series ensure the supply of an optimal amount of refrigerant to the evaporators. Programmable logic controllers of the MСX series are used for auxiliary systems.

The monitoring system is based on the AKSM 850 master controller, which is responsible for the operation of such automatic optimizing functions as floating boiling pressure and adaptive coordinated defrost, as well as for the processing of alarms and the collection of parameter history.

In addition to standard work related to refrigeration equipment, the Auchan facility has carried out work on the design and installation of the engine room on the roof of the building with full provision of fire and building regulations (Fig. 3). This solution allows you to place refrigeration equipment without allocating a separate room inside the building.

Холодильное оборудование
CO2 refrigeration equipment for Auchan Pushkino

Auchan Retail Russia already has experience in using cascade systems based on carbon dioxide. Currently, cascade schemes using two refrigerants are widely used, for example, R134a, R404/R744(CO2) or, mainly for industrial systems, R717 (ammonia) / R744 (CO2), where carbon dioxide is only partially used.

For ease of understanding, depending on the presence or absence of a pumping supply of refrigerant, we will name the schemes of refrigeration units: subcritical pumping and subcritical non-pumping. In the transcritical scheme, carbon dioxide works as the only refrigerant. Let's analyze the main characteristics of these three schemes and evaluate their energy efficiency.

1. Subcritical pumping circuit (Fig. 4). This circuit has three interconnected circuits that must be coordinated with each other, and the imbalance of one of them affects the rest. The presence of three compressor groups and one pumping station significantly complicates the scheme, reduces fault tolerance, and increases the risk of equipment failure, as well as increases capital and operating costs. The implementation of such a scheme requires high qualifications not only from the installation organization but also from service engineers at the maintenance stage.

The presence of R404A refrigerant in the circuit with a high global warming coefficient does not allow this scheme to be classified as environmentally friendly, and the use of R717 (ammonia) is severely limited by legislative norms.

2. Subcritical pumpless circuit (fig. 5).

The main difference from the pumping scheme is the possibility of using R744 (CO2) as a refrigerant only for low-temperature consumers. The circuit solution from the point of view of installation and operation is simpler than the previous one but still has two circuits with different refrigerants that require coordination among themselves. It is also worth noting that the further use of HFC refrigerant will lead to an increase in operating costs due to the projected increase in its cost caused by the tightening of environmental regulations in Russia.

3. Transcritical booster scheme implemented in the Auchan Pushkino hypermarket (Fig. 6).

This is a classic cooling system in which carbon dioxide (CO2) serves as a refrigerant for both high-temperature and medium-temperature and low-temperature consumers.

To compare the energy efficiency of various schemes, the Pack Calculation program was used, developed by Danfoss together with Danish and international companies with partial financing by the Danish Energy Agency Dansk Energy within the framework of the ELFORSK program.

As a result of the calculation, the annual energy consumption of refrigeration systems is determined. The same load profiles and climatic conditions were used in all systems.

The traditional freon scheme on the refrigerant R404A was taken as the starting point of comparison, where the lower limit of the floating condensation pressure of 25C was adopted.

As calculations have shown (see table), subcritical circuits do not provide adequate efficiency and are at the level of existing systems on R404A refrigerant, provided that the functions of floating condensation and boiling pressure, as well as adaptive overheating control in evaporators are used.

Comparison of the energy efficiency of schemes:

For facilities of similar formats located in this region, the most promising solution from the point of view of energy efficiency and environmental safety is a transcritical cooling system, which even in the basic configuration allows achieving annual energy savings of 15%. It should be noted that the efficiency of using a transcritical refrigeration system increases with increasing cooling capacity and it can be recommended for use in warehouses and distribution centers. Solutions to increase the efficiency of transcritical systems allow achieving a more significant effect. For example, the addition of ejector technology (in this calculation, a liquid ejector), as can be seen from the table, allows you to achieve energy savings of 27%.

Evgeny Pronyakin, Chief Engineer of AUCHAN Retail Russia refrigeration Systems, notes the following: "Auchan Company pays great attention to taking care of the environment, therefore, schemes based on natural refrigerants are widely used in Europe and have now found application in Russia. In the transition to natural refrigerants, we also see an opportunity to gain economic advantages in terms of operating costs. The calculated data demonstrate good indicators of energy savings, the Auchan Pushkino facility provides an excellent opportunity to confirm these figures in practice and make a decision on the further use of transcritical technologies in Auchan chain stores in Russia."