United States Cold Storage invests in CO2/NH3 cascade systems

United States Cold Storage (USCS) is investing in state-of-the-art CO₂/NH₃ cascade refrigeration systems, which are proving to be safer to operate and easier to maintain than typical two- or single stage ammonia refrigeration systems. Over a quarter of USCS storage space is cooled using CO₂/NH₃ refrigeration, including the newly expanded USCS Fresno warehouse.

By mid August it is expected that USCS Fresno, California, which is expanding for third time, will add another 4.5 million ft³(0.13 million m³). According to Dave Arnett, USCS Western Regional Engineer, the Fresno warehouse boasts one of the industry’s most effective and energy-efficient refrigeration systems, a CO₂/NH₃ Cascade unit, a system capable of ultra-low (-20ºF or -29°C) temperatures that has been integrated into several USCS warehouses.

Improving warehouse energy efficiency at UGSC

Since UGSC first began benchmarking its CO₂ emissions in 2006, the company has set an overall sustainability goal of achieving a 1.5% year over year reduction in energy usage. With refrigeration and warehouse lighting comprising 90% of the electrical demand of USCS warehouses, the company is making a series of investments in energy efficiency improvements, including:

CO₂/NH₃ cascade refrigeration systems
Variable Frequency Drives on evaporators and condensers:
High efficiency motor s and electronic starters
High efficiency evaporator and condenser design
Energy optimized refrigeration control systems
Bi-level fluorescent and Pulse Start HID Lighting
Highly-reflective white roof membranes
High speed bi-parting freezer doors
High frequency battery chargers

CO₂/NH₃ cascade systems meet need for low charge ammonia system

Whilst ammonia is an excellent refrigerant, concerns regarding the large ammonia charges at USCS warehouses, and the impact that ammonia has on day-to-day operations with respect to PSM and RMP operations, spurred USCS to look into CO₂/NH₃ cascade refrigeration solutions. What is more, the cascade systems avoid the need to have ammonia circulating in any of the storage areas.

To date six USCS warehouses are now refrigerated using cascade CO₂/NH₃ systems. All six cascade systems maintain temperatures within –3°F to –8°F (-19°C to -22°C) in the storage freezers, 32°F to 35°F (0°C to 2°C) in the refrigerated storage rooms and 38°F to 40°F (3°C to 4°C) on the docks.

Fresno cascade system 5.8% more efficient than conventional NH₃ system

The part load performance of the reciprocating compressors used on the low side or the CO₂ first stage combined with the pressure drop-temperature increase relationship between carbon dioxide vs. ammonia, results in excellent efficiencies for the CO₂/NH₃ systems. At the recently expanded Fresno warehouse, six months of extensive testing and measurement revealed that the cascade CO₂/NH₃ system has a 5.8% overall efficiency improvement over the Conventional NH₃ system.

The Fresno warehouse has been expanded for a third time, only six years after first opening. This time additional blast capacity is being added to enable the blast freezing of customers’ product at -55°F (-48°C).

With another 20,000 pallet positions, upon completion USCS Fresno will span 14 million ft³(0.4 million m³), with 65,000 pallet positions and 60 truck dock doors.

About United States Cold Storage

USCS has been providing refrigerated storage since 1889, and today has 35 facilities covering nearly 200 million ft³(5.6 m³) of storage space across the US.