A variety of systems are currently used in supermarkets and retail food stores. These include central refrigeration systems connected to food display cases, self-contained display cases, and walk-in refrigerators and freezers.
New designs, known as distributed systems, are also being used that place refrigeration compressors and associated components near the display cases that are being refrigerated. And in indirect systems, a primary refrigeration system cools a secondary fluid, which then circulates through a secondary loop to the display cases.
In each case, the choice of refrigerant depends on the specific requirements of the application.
Environmental considerationsSince the mid-1980s, commercial refrigeration systems have undergone a transition from using ozone-depleting refrigerant compounds, including CFCs, to low- or non-ozone-depleting compounds, such as HCFCs and HFCs. Ammonia, hydrocarbons, and carbon dioxide are being used to a lesser extent.
Several of these compounds, while non-ozone depleting, do have global warming potential (GWP).
Two aspects to global warming must be considered when selecting a refrigerant. One is the GWP of the refrigerant compound itself if emitted; the “direct effect.” The other concerns the amount of energy consumed to operate the equipment, the “indirect effect.” The two together represent the most significant portions of Life Cycle Climate Performance (LCCP).
Significant additional considerations include the cost of the system and the safety of users, service technicians, and the public.
LCCP analysis for four configurationsFluorocarbon replacements for CFC-502 and CFC-12 include HCFC-22, HCFC-22-based blends, and HFCs such as 134a, 404A, and 507. Other replacements can also be used, although significant system modifications may be required to manage properly the fire/explosion and pressure hazard potential, greatly increasing the cost.
An analysis of four configurations was performed using LCCP for a typical, 60,000-sq-ft, U.S. supermarket constructed in 1999 (see Table 1, page 24).
The distributed systems with HFCs are clearly the right choice based on LCCP. The 404A or 507 distributed system had an LCCP less than half the direct-expansion system, and was at least 15% better than either secondary-loop system.
The secondary-loop system with ammonia has an LCCP similar to that of the secondary-loop HFC system. However, a 1999 report by A.D. Little estimates that using ammonia would add costs of $660 million per year in the U.S. alone due to additional safety equipment, hardware, and increased energy consumption.
HFCs: A balanced solutionWhen all factors are considered, HFCs offer the best solution for meeting the requirements of the commercial refrigeration industry.
Commercially available throughout the world, HFCs are energy efficient, low in toxicity, cost effective, can be used safely, and are reusable.
When used in energy-efficient applications, their excellent LCCP reduces fossil fuel consumption and with it emissions of carbon dioxide, the most prevalent greenhouse gas.
The environmental and cost superiority of HFCs in commercial refrigeration systems must be complemented with responsible HFC use.
The commercial refrigeration industry is committed to providing products that provide the best LCCP that technology, availability, and financial assessment allow. This differs across the various products and applications, and will continuously be evaluated as technology develops.
In addition to significant operating efficiency improvements, the industry has already taken significant steps to reduce emissions of refrigerants by designing leak-tight equipment, minimizing system charge, and promoting refrigerant recycling.
The industry actively promotes the following general principles that should be followed for all refrigerants:
- Use in tight systems that are leak tested and then frequently monitored after installation to eliminate direct refrigerant emissions.
- Recover, recycle, and reclaim of all refrigerants.
- Train all personnel involved in the refrigerant handling.
- Comply with standards that govern proper refrigeration installation and maintenance of machinery spaces (e.g., ASHRAE 15, ISO 5149).
- Size equipment to match the specific need, thereby minimizing the refrigerant amount required.
- Design, install, and operate the equipment to optimize energy efficiency.