Author: Andre Patenaude, Director, Food Retail Marketing and Growth Strategy, Cold Chain. Emerson Commercial & Residential Solutions
For decades, ammonia (aka NH3 or R717) has been the backbone of many cold storage applications in the large industrial refrigeration market. More recently, the increasing popularity of CO2 (R744) in commercial applications has led refrigeration manufacturers to look for ways to incorporate this natural refrigerant in industrial systems. With the technology to combine the benefits of both refrigerants and facilitate this transition coming to fruition, a shift in the industry may be coming.
NH3 has excellent performance efficiency and ultra-low environmental impact, making it a near-perfect refrigerant. However, its toxicity causes hesitancy in use. Tightening regulations by the Occupational Safety and Health Administration (OSHA) has sought to improve the safety of NH3 systems, requiring operators to provide documentation for systems charged with at least 10,000 pounds of ammonia.
Enter NH3/CO2 cascade technology, a system architecture that has been successfully deployed in many commercial applications with HFCs on the high side, to leverage ammonia’s efficiency and limit the potential for toxic exposure to workers and product spoilage.
Transitioning to the large industrial market does cause several concerns that need to be addressed, such as
- Finding a way to deliver high-tonnage refrigeration capacity while keeping ammonia charges low
- Ease documentation requirements
- Lowering the potential for exposure
- Complexities related to installation, commissioning, operation and servicing requirements
- Potential heat exchanger leaks of CO2 and NH3 that can mix and create ammonium carbamate, resulting in system failure
- Maintaining uptime during the transition from a legacy system to a new cascade system
Self-contained systems
Meeting high-tonnage, cold storage requirements while addressing the known operational challenges of ammonia and CO
2 meant that manufacturers have had to expand upon the existing cascade architecture. Developing a self-contained system that integrates an entire NH
3/CO
2 cascade system into a modular refrigeration unit seemed to be the best solution. Designed to be located on the rooftop or next to a building of a cold storage facility, this modular refrigeration unit combines CO
2 and NH
3 compression technologies and electronic controls in a cascade system that contains two independent CO
2 and NH
3circuits with separate condensers and evaporators (including a shared cascade heat exchanger). The self-contained, modular unit essentially serves as the system’s mechanical room, enabling installation and efficiencies typically not found in traditional systems. Existing facilities can even install this system while their legacy system is still running, positioning the unit at the desired rooftop location and connecting the ductwork in as little as a few days.Then, as soon as the facility manager is ready, he/she can simply shut down the old system and let the new system assume refrigeration duties.The simplicity of this drop-in, plug-and-play design also lowers maintenance requirements while improving serviceability throughout the lifecycle.
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