What Is going on in the world of Supermarket Refrigeration?
Building Mechanical Electrical HVAC Systems
It comes as no surprise to anyone that supermarkets are under pressure to embrace green. As applied to the refrigeration portion of a supermarket this translates into: reduce carbon footprint, lower Global Warming Potential (GWP), reduce refrigerant charge, reduce electrical consumption and increase efficiency.
Let’s discuss the GWP portion.
Figure 1 compares refrigerant usage in a sample of over 8000 existing U.S. supermarkets and how that usage trends between 2007 and 2013. As one would expect, it shows a dramatic move away from R-22. This is a reflection of a two pronged effort to reduce R-22 use in supermarkets; new stores transitioning to refrigerants other than R-22, and existing R-22 supermarkets converting to a lower GWP alternative.
It is no surprise to see the percentage of stores using R-22 decrease. It is equally of no surprise to see the use of R-404A increase. What might appear surprising on the surface is R-407A’s appearance as a contender. The fact is that R-407A offers a good capacity comparison to R-22 (approximately 103 per cent in medium temperature applications, and approximately 95 per cent in low temperature applications). In low temperature applications R-407A will have a significantly lower discharge temperature (approximately 60F) than R-22, reducing the need for capacity robbing demand cooling.
Additionally, the mass flow requirements for R-407A are very close to R-22, meaning that there are no TEV or distributor nozzle replacements required when converting an existing R-22 system to R-407A. Finally, as a refrigerant that is out of patent, it has a wide base of distribution at very competitive prices.
What might be a little more telling is the information in Figure 2, which is based on information provided by OEMs in 2012. Here you see that approximately 40 per cent of all new supermarket equipment is built for use with R-407A. This is a reflection of several major supermarket chains changing their refrigerant specification to R-407A. This certainly constitutes a trend towards using a refrigerant with a lower GWP.
Remarkably, this shift towards R-407A (a lower GWP refrigerant) was done without government regulation. Even so, in the U.S., a presidential executive order was signed in 2013 directing the EPA to use Significant New Alternatives Policy (SNAP) to reduce emissions of HFCs. In response to that executive order, the EPA recently issued a final ruling that changes the status of certain refrigerants and their use in certain applications.
Particularly targeted were R-404A and R-507, due to their relatively high respective GWPs of 3900 and 3922. Beginning January 1, 2017, both of these refrigerants will be banned from use in new store installations consisting of systems with more than one compressor (including multiplex compressor racks, distributed systems, secondary refrigerant systems, and so on).
The same ban will apply to single condensing units, beginning January 1, 2018. In addition, any supermarket refrigeration system undergoing a refrigerant conversion will be banned from using R-404A/R-507 beginning July 20, 2018.
This ruling does not affect existing R-404A/R-507 systems, nor does it require a phase out of the importation of new production of R-404A/R-507.
While the move away from R-404A and R-507 now has the power and authority of the government behind it, the supermarket industry and the associated marketplace are continuing in their effort to anticipate future regulations. As such, there are two new refrigerants in the offing; R-448A (a Honeywell product) and R-449A (a DuPont product). These are zeotropic blends that are somewhat similar to the current crop of R-22 alternatives, in that they are blended from the same building blocks used in many currently available R-22 alternatives (R-32, R-125 and R-134A). Where they differ is that these blends also contain a percentage of one or both of the ultra low GWP HFO (Hydrofluoroolefin) refrigerants HFO-1234yf and HFO-1234ze.
These two refrigerants look promising. In addition to a significantly lower GWP, they offer slightly higher capacity and efficiency than R-404A. As with any new refrigerant under patent, you can expect them to initially be more expensive. They have not been SNAP approved as of yet.
In addition to replacing R-404A and R-507 with lower GWP alternatives, there are other designs that are trending, which result in the reduction of refrigerant charge. These include distributed and secondary systems.
Distributed systems are smaller multi-compressor racks (typically scroll compressors), strategically located closer to the fixture/box loads they are providing capacity for. Not only does this eliminate the extra expense of a dedicated machine room, but the shorter piping runs result in smaller refrigerant charges.
In secondary systems, chillers are common for comfort cooling or industrial applications. They are large self-contained packages, where the refrigeration capacity is dedicated to cooling or chilling a secondary fluid down to a temperature required by the system design. This secondary fluid is then pumped to the spaces that need cooling capacity. As applied in a supermarket, the chiller will reduce the temperature of a secondary fluid (propylene glycol or CO2), which is then pumped to heat exchangers in display cases or walk-in boxes.
While there is a second stage of heat transfer in a chiller application, adding inefficiency to the system, the reduction in refrigerant charge is significant. In addition, the thousands of feet of pipe, array of control valves, solenoid valves, thermostatic valves have all been removed from the refrigerant circuit, resulting in a dramatic reduction in leak potential.
Despite the significant reductions in GWP that can be realized with R-407A, or the upcoming R-448A/R-449A, the aptly named natural refrigerants are still looming on the horizon. These include CO2 (R-744), ammonia (R-717) and propane (R-290). While each of these has its own specific application challenges, their major benefit is that they are non-ozone depleting and have essentially no effect on global warming. Indeed, the GWP of CO2 is one. Other refrigerant’s GWP is a reflection of its impact on global warming in comparison to CO2.
2006 saw the first application of CO2 in a U.S. supermarket. It was utilized in a chiller application, with the CO2 performing the function of the pumped secondary fluid to the various low temperature fixtures. With CO2’s greater latent heat capacity, design flow rates are significantly compared to other secondary fluid alternatives. The resulting smaller pipe size requirement yields lower material costs.
Since that first application nearly a decade ago, many of the major supermarket chains have tested the viability of CO2. In 2008, the first Canadian supermarket to use carbon dioxide (CO2) as a heat transfer fluid for frozen food display cases was opened by Loblaws in Scarborough, ON. Quebec has the majority of Canada’s CO2 supermarkets (53 out of 74 in 2013) with Alberta and Ontario having the remaining installations (11 and four respectively in 2013). While it still comprises a minority of installations, CO2 does provide another option for those seeking GWP reductions.
In the very small minority, there have been applications of ammonia based secondary systems. In these applications ammonia is the primary refrigerant providing cooling capacity to reduce the temperature of the secondary fluid being circulated to the refrigerated space.
Even propane is seeing some use in prototype supermarket applications. As a natural refrigerant, its impact on the environment is considered negligible. Of course, propane has one minor drawback and that is its flammability. However, if the total system charge does not exceed 150 grams it can be used in commercial applications.
As an alternative
to investing in an expensive CO2 system, one supermarket chain recently opened a store utilizing propane refrigeration systems. While the application presented some challenges, specifically the 150-gram charge limit, a workable design was achieved by utilizing individual self-contained condensing units for each glass door display case, and some walk-in boxes. The reduced load resulting from doors on cases allowed small charge systems to be a workable solution.
In addition to using an environmentally friendly refrigerant, the relative simplicity of these systems eliminated a significant portion of the installation charge. The self-contained nature eliminated the need for large amounts of pipe to connect remote compressor racks to the evaporators and the necessary labour to do so. In addition, the hope is that the simplistic design will greatly reduce the maintenance expense. Should a catastrophic failure occur with the self-contained unit, it can simply be replaced rather than repaired, not unlike a household appliance.
Certainly the modern supermarket, with the amount of refrigerated product available to the consumer and the volume of refrigeration system capacity necessary to maintain the integrity of that product, has been a focus for sustainability from environmental agencies. Do not expect this to change. In fact, you can count on ever increasing regulations requiring the larger commercial ventures utilizing refrigeration equipment to be held to higher and higher standards.
Whether you agree with the debate about global warming or not, there will be ongoing government regulation to ensure that businesses minimize their affect on potential damage to our environment.
Dave Demma holds a degree in refrigeration engineering and worked as a journeyman refrigeration technician before moving into the manufacturing sector where he regularly trains contractor and engineering groups. He can be reached at firstname.lastname@example.org.
Figure 2 Comparative refrigerant usage in new supermarkets
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May 11, 2022