be used in smaller, compact systems with low refrigerant charges, like residential A/C units and heat pumps,” the report states. “Furthermore, a rising trend can be seen in its use with commercial refrigeration systems and chillers.”
Consideration when sizing components can be given to the relatively low mass flow (approximately 55 to 60 percent compared to R-22) it requires thus allowing for less of a refrigerant charge relative to R-22 in similarly sized systems.
Following EPA approval, 2013 saw the first domestic storewide use of R-22 with a majority of the display cases and walk-ins utilizing self-contained propane units. While this type of whole store adoption of R-22 use has since then be limited, the continued use and development of stand-alone display case applications has proceeded.
One manufacturer for instance, has released a self-contained island-style display case that achieves a 20-50 percent reduction in energy use compared to cases using HFC refrigerants; another benefit of propane’s greater efficiency.
While charge restrictions have limited propane use in the U.S. food retail industry to the stand-alone single condensing unit display cases, it’s been a different story in Europe. A Norwegian convenience store (c-store) chain for instance, has begun using similar types of cases (commonly referred to as cabinets in Europe) but instead of operating them as stand-alone units, ties them together in a micro-distributed system.
One U.S. manufacturer is testing the waters with a similar approach that uses a closed water loop to remove rejected heat from the cases. This allows the use of R-290 to be extended from island cases to multi-deck and door cases. The units are charged with just 150 grams, or 5.3 liquid ounces per circuit reducing the total amount of refrigerant needed for a full-store application by 95 percent or more.
Sample of an R290 self-contained island case.
Like any other refrigerant, R-290 is not without its concerns. Drawbacks that have mostly stood in the way of its use have to do with its flammability requiring that any use in systems be in accordance with flameproof regulations. In light of this concern, propane systems in the U.S. cannot have a charge greater than one hundred and fifty grams.
At least as recently as 2015, besides flammability and globally mandared low charge limits of 150g that restrict its use, other concerns were voiced regarding difficulties in getting it approved in light of fire and building codes. Likewise, special handling requirements and certifications were seen as potential hurdles. Even now, five years later a lack of trained and certified field technicians remains another stumbling block for many users.
But the basic issue of flammability means the demands for the safety technology required for its use include special devices to protect against excess pressures and special arrangements for the electrical system. It also means that innovative approaches to extending its use beyond stand-alone display cases as in the Norwegian and domestic chilled-loop examples, must be further developed.
On the plus side, propane’s use in plants requires practically no special features in the medium- to low-temperature ranges. It is therefore conceivable that at least on the industrial side, propane’s use domestically could considerably expand as more potential users become aware of its benefits.
Much wider usage in the retail food category seems at this point dependent on further advances in loop system technologies. In the meantime, however, increasing numbers of users are becoming sold on the merits of stand-alone applications for individual display cases. These units are typically equipped with casters that allow their use around the store since otherwise the only requirement there is, is to have an outlet in which to plug them into. As of 2017, discussions were underway among U.S. regulators to increase the charge limit for R-290 applications from the current 150g to 300g. Doing so, would likely propel propane’s use considerably forward.