“One of the things companies should review is the type of refrigeration technology they use,” says Monika Witt, chairperson of eurammon, the European initiative for natural refrigerants. “There are big differences in this area. Plants using natural refrigerants like ammonia or hydrocarbons consume up to 30 percent less energy than other refrigeration plants. That really adds up for the plant operators.”
Additionally, natural refrigerants such as ammonia and carbon dioxide, with hydrocarbons such as butane and propane, do not deplete the ozone layer or contribute to global warming (table 1), which makes them a sustainable approach alternative for refrigeration.
Refrigerated Warehouses the Size of Football FieldsThe Metro Group, one of the world’s largest trading groups, is one company that relies on natural refrigerants. The company operates food distribution centers in Bremen and Hamm, both in Germany. Goods that are delivered directly to the centers by the manufacturers are put into interim storage and are later shipped to Metro Cash & Carry, Real or Extra supermarkets. The centers are equipped with central ammonia refrigeration plants furnished by Axima Refrigeration.
The food distribution center in Bremen comprises 47,360 ft 2(4,400 m2) of refrigerated and deep-freeze storage. Forklifts and order pickers are remote controlled, and pallets are automatically loaded and removed. An air-cooled, two-stage ammonia refrigeration system ensures storage temperatures of between -11 and 54oF (-24 and 12oC). The refrigerant is compressed by two screw compressor units for each stage, which safeguards the reliable operation of the refrigeration system. The system is charged with approximately 11,000 lb (5,000 kg) of ammonia.
The ambient air is cooled by quiet, energy-efficient insulated air coolers. Air ducts integrated in the ceiling ensure a draft-free distribution of the chilled air in the warehouses by sending cold air “trickling down.” The waste heat from the oil coolers is used to heat the service water. Because the facility is integrated into Axima Refrigeration’s remote maintenance system, the plant manufacturer’s customer service team can view and optimize the operating data online. Axima Refrigeration was able to hand over the facility to Metro after a planning and construction period of just four months.
Freshness WinsIn southern Germany, a German food retailer operates one of Europe’s largest logistics centers for frozen foods and fresh produce. The heart of the building is a central ammonia cooling plant that was installed by York Deutschland.
The mammoth facility comprises 10 ammonia compressors, 140 air coolers and 25 insulated unit coolers that operate in two stages. The low-temperature stage provides direct cooling for frozen foods using two low-pressure compressors with a combined output of 1,100 kW at 15/-38oF (-9/-39oC). Chilled brine is circulated in the high-temperature stage to cool the fruit and vegetables, the fresh produce department and the meat-processing rooms. Six high-pressure compressors in the high-temperature stage generate a combined output of 5,400 kW at 12/113oF (-11/45oC). The brine is cooled in the corresponding plate units and conducted to the heat exchangers through two frequency-controlled pumps using nine air-cooled condensers with a total output of 6,700 kW.
In addition to the two-stage refrigeration facility, York installed another brine loop that supplies cold energy to several meat-processing rooms and the fresh produce area. This loop consists of two compressors with a combined refrigeration output of 1,360 kW at -2/113oF (-19/45oC). Three air-cooled heat exchangers with a total output of 1,940 kW ensure that the brine returns the heat again. The condensers, along with the insulated units, brine coolers and heat exchangers, were manufactured by Güntner.
The Future of Food LogisticsIn both of these applications, the energy consumption is about 30 percent less than conventional refrigeration systems. This benefit, as well as the sustainability of ammonia, is leading to a broader acceptance of refrigeration systems based on natural refrigerants.
“Whether you’re looking at food logistics centers or other process cooling applications, systems that use natural refrigerants such as ammonia or hydrocarbons have proven their productive efficiency again and again,” says Witt.