ALTERNATIVE REFRIGERANTS typically much higher.


Maintenance and operating conditions Although CO2


refrigeration systems are designed


to operate at pressures much higher than the HFC DX systems, it is always good to consider a maintenance program for the continued use and wear of the equipment. These high pressures and relative performance through the heat rejection and expansion process, pose inherent challenges to its efficiency as a refrigerant at these high operating and pressure conditions. As an additional consideration, CO2


systems


equipment in place, the systems used for leak detection, legislation, maintenance, support and the environmental messaging, CO2


can pose a


concentrations play an important function as part of the Occupational Safety and Health Administration (OSHA) exposure limits if there were to be a leak event. Typical figures stipulated for CO2


huge potential health hazard to humans when seen in high concentrations. O2


exposure by OSHA are:


 5,000 ppm – Occupational Exposure Limit (OEL)


 40,000 ppm – Immediately Dangerous to Life or Health (IDLH)


is part of the air we breathe (around 0.04% or 400 parts per million), it can be challenging to measure leaking CO2


Since CO2 refrigerant in


low concentrations, due to its natural background level. When measuring for background CO2


in


Parts Per Million (PPM) for example in a retail supermarket, the levels vary depending on how many customers are in the area of the sample. It also depends if dry ice is being used in the area, as that too, could add to the overall concentration. Similarly, if a bakery section was sited in a food retail where yeast proofing took place or if the food manufacturing or processing function involved fermentation or carbonating, carbon dioxide levels may well fluctuate considerably. Typically, the PPM levels in this type of application would range from 600 – 1400 PPM CO2


.


refrigerant leak occurs, it tends to fill the space more rapidly and become more catastrophic quicker. This means the amount of refrigerant lost is much higher and can cause more disruption to trade, higher inventory or stock losses and be


systems operate at much higher pressures than systems used with other types of refrigerants, such as HFC DX systems, when a CO2


Since CO2


dangerous to life and health. Leakage rate for CO2 when compared with their HFC refrigerants, is


are more expensive than their HFC/HCFC DX equivalents due to the use of the electronics controls at all the fixtures and the extra elements required to operate and control CO2


may carry more upfront costs than a traditional type of system, therefore, financial justification from a retailer’s perspective is an important consideration for the initial capital expenditure.


Refrigerant leak detection technology


The technology and equipment used in CO2 refrigerant detection is either an aspirated system, which pulls air from sample points in various zones located at distances of up to 1200 feet or four football fields, or a local / point sensing head, which uses diffusion to detect the gas.


Whichever technology is adopted; non- dispersive infrared (NDIR) sensing is the choice for sensing CO2


. The choice between aspirated


and point sensing is an end-user preference, as both are suitable technologies to use, and aspirated will always be the better solution over the long term/life cycle of the system. CO2


and safety reasons, to protect operations and personnel, especially in confined spaces i.e. walk-in coolers/freezers and confined rack rooms from exposure to high CO2 ppm. Regardless of the CO2 alarming for CO2


, typically 5,000 sensing technology is the same and tends to follow:


 Additional alarms/sirens for confined areas to alert people in those spaces:  Inside the walk-in/cooler freezer  Outside the CO2


rack rooms


 Additional signage in the confined areas to alert people in those spaces:  Inside the walk-in/cooler freezer  Outside the CO2


rack rooms systems. They


the ‘natural’ refrigerant choice for the food retail and cold chain sector?


Is CO2 The environmental benefits of using CO2 as


a refrigerant far outweighs the risk of using synthetic refrigerants, the potential harm through refrigerant emissions, and the risks involved.


With zero ODP and very low global warming potential, CO2


can be a great asset for food retail,


food production and processing and cold chain applications. The principles of a comprehensive refrigerant management strategy remains the same.


They are simply tweaked on the local leak detection deployment based on the refrigerant’s toxicity and flammability properties. With an effective refrigerant management


users must have leak detection for health


strategy coupled with leak detection systems, CO2 can provide any forward-thinking refrigeration manager or food retailer with reduced operating costs, improved system uptime, protection for their employees and responsibility for their environmental footprint.


www.acr-news.com


December 2019 33


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