E360 Outlook: Cold and Calculated
Canadian grocery chain creates cold storage facility with zero global warming impact
Rapid growth can be a mixed blessing for an organization that takes its environmental responsibilities seriously, but growing pains aren’t stopping Metro Inc. from keeping a 240,000-square-foot warehouse chilly without depleting the ozone layer.
As Metro’s steadily increasing retail operations made it necessary to expand its primary facility for storing cold food and dairy products, the company considered the upgrade to an efficient and safe refrigeration system just as important as meeting its capacity needs. To meet the diverse challenges of the expansion, Metro reached out to CIMCO, an international leader in industrial refrigeration, food and beverage cold storage; and Dessau, one of Canada’s largest engineering and construction firms.
It was clear from the outset that hydrofluorocarbon refrigerants, known for their high global warming potential, would be out of the question. Instead, the project team developed a design incorporating a dual-temperature, low-charge ammonia package refrigeration system.
Low-charge ammonia systems like the one applied for Metro are growing in popularity for large-capacity cooling applications in the 75–750 kW range. This is partly because of their efficiency, but also because the low ammonia refrigerant charge improves safety and reduces certification costs. Safety is further enhanced by completely isolating the ammonia from the warehouse.
Saving energy—and operational costs
Single-screw slide valves ensure optimum part-load performance in the system, matching any fluctuations in refrigeration load. This combination eliminated the need for expensive inverter drives, improving part-load performance, saving energy and cutting C$100,000 from Metro’s capital cost.
The secondary circuit met another of Metro’s crucial requirements: to minimize the total amount of ammonia used on-site to just 0.12 kg/kW. Microprocessors with process temperature controls fine-tune the function of the entire unit by regulating starting, stopping and capacity control.
Combined with the dual-slide design on the screw compressors, this setup allows the system to function in a range of 20 to 100 percent of flow while continuously operating at the ideal compression ratio throughout the part-load range. This permits the compressor to match the system flow requirements to make cooling as low-cost and efficient as possible, operating at an estimated 15 percent higher efficiency than comparable technologies.