Cold storage facilities are facing new challenges with their industrial refrigeration systems as regulatory requirements are calling for the reduction or elimination of dangerous components. Ozone-depleting R-22 refrigerants are being phased out requiring facilities to find a more environmentally friendly alternative. And while Ammonia continues to be the most popular replacement, many facilities are looking for ways to increase safety by reducing their system’s ammonia use.
Phasing out R-22
One of the industry’s most popular refrigerants, R-22 has been under fire for some time due to its ozone-depleting qualities. The Montreal Protocol on Substances that Deplete the Ozone Layer link calls for the elimination of R-22 altogether by 2030. Manufacturers ceased production of any new R-22 refrigeration systems in 2010 and the refrigerant itself will no longer be produced or imported as of 2020. This has left many cold storage facilities with questions. How long will I be able to purchase R-22? Will my existing R-22 system be obsolete? What are the alternatives to R-22?
The cost to maintain existing R-22 systems will begin to increase as fewer machines are in use and as the refrigerant becomes scarcer. Recycled R-22 will be available for some time beyond 2020, but as the available supply decreases, the cost will inevitably rise. The average life span of an R-22 system is 15 years, so many machines will be due for replacement prior to the 2020 deadline.
Some system manufacturers are touting the benefits of retrofitting an existing R-22 system. Yet this is not necessarily a feasible option for many cold storage facilities. Changing out the refrigerant requires shutting down the system, changing out seals and other components and flushing it numerous times, which can require significant downtime. This may be a short-term option for smaller systems, but for bigger systems it becomes too costly and time consuming.
Facilities with aging R-22 systems should begin planning now for a new system that uses acceptable environmentally friendly refrigerants. Newer units do offer increased reliability and efficiency, resulting in less energy consumption and lower energy costs.
The EPA produces a list of alternatives based on suitable ozone depletion potential, global warming potential, toxicity, flammability and exposure potential. R404A, R407C, R410a, andR507 are some of the more popular alternatives, typically a blend of two or three refrigerants. Some do have a relatively high global warming potential, which potentially puts them at risk for phase out at some future date.
Reducing ammonia charge
Ammonia is a natural refrigerant with zero ozone depletion and zero global warming potential. Yet while it continues to be a preferred refrigerant due to its efficiency and low cost, it is a dangerous substance and many facilities continue to look for ways to reduce the amount used.
Implementing a cascade system, employing two refrigerants with a heat exchanger in the middle, is one method of reducing ammonia. This allows the engineer to take advantage of the best characteristics of each refrigerant. At lower temperatures, generally between –31°F and –60°F, a NH3/CO2 cascade system becomes more efficient than a two-stage ammonia system. A cascade system allows the charge of each refrigerant to be reduced. Engineers can also design this process so that ammonia is confined to the machine room to increase safety throughout the rest of the facility.
Incorporating a secondary refrigerant can also increase safety by reducing the ammonia charge. Typically, ammonia is piped from the machine room out to the facility to all points of use. Piping a secondary refrigerant to these points allows ammonia, the primary refrigerant, to remain confined to the machine room, which further reduces the risk of any leak. Ammonia can be closely monitored and any breakdowns can be repaired in the primary system while secondary cooling capability is still maintained. Compared to a conventional system, it greatly reduces the risk of an ammonia leak.
A glycol/brine solution is also used as a secondary refrigerant for temperatures above 0°F. When temperatures fall below that level, special heat transfer fluids are required.While most secondary refrigerants only transfer sensible heat, CO2 can be used as a volatile brine. This allows much higher heat transfer, dramatically reducing pipe size and pumping horsepower.Because a heat exchanger is required to go from the ammonia to the secondary refrigerant, there is decreased efficiency.In addition, the pumping horsepower associated with a secondary refrigerant will be higher than directly distributing ammonia.
Luke Facemyer serves as Director of Refrigeration Engineering for Stellar. His responsibilities include managing the refrigeration division’s engineering department to provide a high level of refrigeration and mechanical expertise. Facemyer’s experience includes projects with Carolina Pride Foods, Food Lion, General Mills, Kraft Foods and many others.