Carbon Dioxide Refrigeration Training Gets Due Attention

CO₂ refrigerant characteristics

Compared to traditional hydrofluorocarbon (HFC) refrigerants, CO₂ has many unique performance characteristics, some of which must be managed in different ways than traditional refrigerants:

• Higher saturation pressure than HFCs (a CO₂ refrigerant tank sitting at a 70 F ambient will have an internal pressure of 838 psig)
• Higher discharge pressures (up to 1,500 psig on a hot summer day)
• Standstill pressures, which refers to the pressure in each section of the system when it is powered off
• Pressure relief valves are required in every section of the system operating at different pressures as a mitigation strategy during service and power outages
• Lower critical point (1,056 psig, 87.8 F) determines its modes of operation:
• Subcritical operation exists below critical point (gas cooler is controlled by sub-cooling setpoint)
• Transcritical operation exists above critical point (gas cooler is controlled by optimizing COP)
• High triple point (61 psig) introduces the potential for dry ice formation (technicians must charge with vapor until equalized system pressures are well over 61 psig — preferably over 100 psig — before starting to charge with liquid)
• Higher relative density versus air (1.52) requires leak detection sensors located approximate 18-in. off the ground.

Reliance on electronic controls

Unlike traditional centralized direct expansion (DX) systems using HFCs, CO₂ systems require the use of electronic controls to:

• Automate aspects of system installation, setup and commissioning
• Integrate with cases and electronic expansion valves (EEVs)
• Manage dynamic system pressures during normal operation.

Many technicians are not accustomed to relying on system controls to this degree. Understanding how these controls may impact servicing requirements and system performance is essential. Technicians will require hands-on experience and classroom training to familiarize themselves with CO₂’s unique characteristics.

Industry collaborates on CO₂ training materials

Emerson is currently participating in efforts to help third-party industry organizations develop CO₂-specific training programs for the entire commercial refrigeration supply chain of wholesalers/distributors, OEMs, end users and service technicians.

The North American Sustainable Refrigeration Council (NASRC) is a 501(c)3 nonprofit focused on addressing barriers to natural refrigerant adoption. In collaboration with the ESCO Group and other industry stakeholders, the NASRC is leading the development of the first-ever CO₂ curriculum for community college and trade school HVACR programs in the U.S.

As an industry steward of CO₂ adoption and a provider of fully integrated CO₂ refrigeration solutions — including compressors, facility management system controller, valves, case controls and associated components — Emerson is pleased to participate in this effort. According to Morgan Smith, program and communications director at the NASRC, the new CO₂ curriculum will be rolled out in early 2022 and cover a wide range of topics, including:

• Basic terms and definitions of CO₂ characteristics and systems
• CO₂ safety fundamentals, such as: handling, tools and gauges, relief requirements, leak rates and room sensors
• Core curriculum, including: required experience; understanding CO₂ as a refrigerant; operating characteristics; types of CO₂ systems; working with non-traditional system components, compressor types, control systems and equipment applications
• Installation procedures: handling CO₂ as a refrigerant; installation fundamentals and piping insulation
• System commissioning procedures
• Service and maintenance procedures, such as: system charging and discharging; repairing and replacing components; CO₂ oil management; CO₂ system recovery; defrost methods and custom systems
• Troubleshooting.

Smith said that the goal of the collaboration is to integrate this CO₂ curriculum into the commercial refrigeration tracks at technical colleges.

“Because CO₂ is so new to the U.S. commercial refrigeration market, technicians and end users have varying degrees of hesitation. We hope these training programs will help remove some of the mystery and concerns about using this efficient and environmentally friendly natural refrigerant,” she said.

CO₂ training programs and initiatives

Emerson continues to expand on its CO₂-specfic training initiatives. In 2019, we launched our third-generation CO₂ mobile training unit to serve Canada and the continental U.S.; it has trained more than 1,000 industry professionals in North America. However, with the onset of the COVID-19 pandemic, this unit has remained a stationary fixture within Emerson’s training facility in Brantford, Ontario.

In 2022, a second CO₂ mobile training unit will be housed at Emerson Educational Services’ primary location in Sidney, Ohio. Once there, it will become the centerpiece of a two-day training program designed to give contractors, OEMs, wholesalers and end users a hands-on experience of what it’s like to work on a CO₂ transcritical booster refrigeration system.

Emerson CO₂ trainers provide an open 360-degree view of a CO₂ transcritical booster system. Emerson’s CO₂ trainers are designed to give attendees firsthand CO₂ experience and familiarize themselves with key system elements, including:

• Low- (LT) and medium-temperature (MT) compressors
• Variable-frequency drives (VFDs) for compressors
• Oil management systems
• Facility management system and CO₂ refrigeration controls
• System high-pressure control and valves
• Case controls and electronic expansion valves

The open design of the CO₂ mobile trainer enables visibility to all components and dial gauges that indicate the pressures and temperatures at various points of the system.

To demonstrate the volatility of R-744, the unit includes a phase change cell that shows how the refrigerant changes states as pressures increase — from liquid to vapor to supercritical fluid to gas. Then, as pressure drops within the cell, trainees can see the reverse of this transition as CO₂ returns to a liquid state and then forms into dry ice. Emerson is scheduling CO₂ training classes to begin in Q1 of 2022.

Emerson Educational Services currently offers two virtual and in-person training courses related to CO₂:

• Two-day “CO₂ Refrigeration” course specifically designed to train technicians
• One-day course entitled, “Fit for the Future: Working with Natural Refrigerants, A2Ls, and A1 HFO Blends”

As COVID-related health guidelines permit, we hope to send our CO₂ mobile training units back on the road to be featured at industry events and support training sessions.

To learn more about the CO₂ training programs at Emerson, visit the course schedule here, or contact Emerson Educational Services at [email protected].

Don Gillis joined Emerson in July of 2017. Don has 27 years of HVACR industry experience, including roles as an installer, service technician, service manager, technical support, and full-time HVACR instructor.