Fluctuating environmental policies in the U.S. tend to obscure the fact that the transition toward refrigerants with a low global warming potential (GWP) continues. HVACR manufacturers, researchers, and facility owners worldwide are making significant progress thanks to consistent public policies but also from recent development of proven technologies.
Technologically, it’s worth looking at recent moves away from refrigerants with high GWPs — like HFC-134a and HFC-404A — and toward low-GWP formulations, like natural hydrocarbons (HCs) and hydrofluoroolefins (HFOs) with GWPs below 5. The HFOs have a low GWP because they break down in the atmosphere over a few days. Furthermore, HFOs, together with hydrofluorocarbons (HFCs), form low-GWP hybrids that have GWP ratings below 150.
Innovation is the key that is unlocking the potential of the new refrigerants to create a low-GWP future. Important developments include utilizing the thermodynamics of CO2 refrigerant — specifically, its expansion energy and heating properties — to make CO2 even more feasible for commercial refrigeration, the ongoing decarbonizing of the electric power supply, and boosting flexibility in electric consumption with demand response and thermal storage technologies. These developments are driving forward the adoption of low-GWP refrigerants in food and commercial refrigeration today.
MOVING FROM CONCERNS OVER OZONE DEPLETING TO GLOBAL WARMING REFRIGERANTS
Following the success of the 1987 Montreal Protocol enabling the transitions from high to low ozone depletion potential (ODP) refrigerants, the 2016 Kigali Amendment focused on transitioning from high- to low-GWP gases. Under the amendment, 197 countries committed to cut the production and consumption of HFC refrigerants, most of which have GWPs ranging from 675 to 3,985. In cutting HFC consumption by more than 80% by 2047, the Kigali Amendment aimed to prevent a modeled 0.5°C increase in global temperature by the end of the century.
The U.S. did not ratify the Kigali Amendment, which went into effect Jan. 1, 2019. Nevertheless, the U.S. Environmental Protection Agency (EPA) — through its 2016 Significant New Alternative Program (SNAP) rules — banned the use of high-GWP HFCs in many types of commercial refrigeration systems, including supermarket and commercial food equipment. Subsequent lawsuits resulted in the EPA withdrawing the HFC ban in 2018. Nevertheless, several states are developing HFC phasedown rules. California has adopted EPA SNAP Rules 20 and 21 and will be implementing GWP limit-based rules in the future. Other states are seeking to implement those EPA SNAP rules as well. Seven states have proposed or enacted 13 laws, regulations, or plans since 2018.
Fluctuating policies pose a problem for HVACR equipment manufacturers. Regulatory consistency would help smooth the transition from high- to low-GWP refrigerants, which has been technologically challenging.
In the earlier transition from high- to low-ODP refrigerants, manufacturers could generally use a “drop-in” approach — that is, simply replacing one refrigerant for another after modifying seals and other minor components. That is not always possible with the switch to low-GWP refrigerants. Natural refrigerants, such as ammonia and CO2, operate with different parameters compared to HFCs and require specially designed system components. Other natural refrigerants, such as propane, use components similar to those employed with HFCs, but special safety precautions need to be taken.
Depending on corporate goals and local regulations, manufacturers and end users worldwide are adopting low-GWP-refrigerant systems employing various technological innovations.
In the European Union, the progress of HFC phasedown has continued (Figure 1). Nevertheless, the phasedown was heavily challenged due to early stockpiling, misleading the market’s perception of HFC availability, and unused HFC refrigerant quotas from 2015. Consequently, a large amount of new high-GWP equipment was still on the market. In 2017, the market experienced a steep price increase and HFC scarcity, both of which drove the first step of the phasedown (Figure 2). Finally, from 2018-2020, HFC consumption continued to drop, low-GWP refrigerant prices started to decline and stabilize, and the conversion to low-GWP solutions gained momentum.
As a practical example of how innovation accelerates the transition, it’s worth examining the case of a military supermarket in a hot-climate region. In 2018, the United Nations Industrial Development Organization (UNIDO) supported the successful implementation of a CO2 refrigeration system in the store.
The region experiences 90°F (32°C) and higher ambient temperatures in the summer. Compared to using HFCs at those temperatures, employing CO2 refrigerant within its normally high operating pressures was not energy efficient. Nevertheless, several advanced technologies were employed to go beyond CO2’s traditional ambient temperature limitations. The system used the Danfoss Multi Ejector Solution™, consisting of a high-pressure valve, integrated pressure transmitter, and an intelligent system controller in conjunction with the compressor rack. The system operates reliably in the transcritical zone of the compression cycle, where pressures can exceed 1,067 psia. In the transcritical zone, heat rejection can efficiently occur even at high ambient temperatures — even at 97°F (36°C). The bottom line: The CO2 system supplying display cabinets has an extremely low GWP of 1 and provides up to 30% energy savings compared to the incumbent solutions based on R-22 and R-404A refrigerants. A technology hub has been established to explore adopting the transcritical CO2 solution for air conditioning in the store.
Adding to the momentum are philanthropic-funded initiatives, such as the Kigali Cooling Efficiency Program (KCEP) promoting low-GWP solutions in developing countries. Other non-governmental organizations (NGOs) and academic institutions are also stepping up to help raise the level of innovation to define the HFC-free cooling technologies of the future.
SPEED BUMPS IN ACCELERATING TOWARD LOW-GWP REFRIGERANTS
Several HFO refrigerant formulations have been readily adopted for a number of applications. R1234yf is used by automotive manufacturers for car air conditioners. R1234ze(E) is used in innovative centrifugal compressors employing magnetic bearings, such as Danfoss Turbocor® compressors.
Some low-GWP refrigerants are flammable, some are toxic, and some are both. ASHRAE 34 and International Standards Organization (ISO) 817 standards have been developed to classify flammability and toxicity (Figure 2).
Lower-GWP properties tend to correlate with higher flammability/toxicity characteristics. For example, HFC refrigerant R-410A (with a 2,088 GWP) is nontoxic, nonflammable, and classified A1. The HFO refrigerant R1234yf (with a 4 GWP) is nontoxic, mildly flammable, and classified A2L. HC refrigerants (R-600a isobutane and R-290 propane) are highly flammable (A3). Ammonia (R-717) has high toxicity and flammability (B2). CO2 (R-744) is an exception with no flammability or toxicity (A1).
The correlation between GWPs, refrigerant density (weight per volume), and safety classifications of various refrigerants is of great concern to HVACR system manufacturers and specifiers (Figure 3).
Blends of HFOs and HFCs are being developed to optimize performance and safety. Whether using HFOs, natural refrigerants, or blends, HVACR manufacturers must innovate technologies that maximize efficiency and minimize risk for the selected refrigerant.
Development of new technologies make it easier for manufacturers to balance safety and environmental responsibilities. Some leading retailers have been using R-290 (propane) in equipment for over a decade. Taking advantage of R-290’s thermodynamic properties, such as volumetric capacity and coefficient of performance (COP), systems are operating successfully with a charge limited to 150 grams (5 ounces) for safety. Further research and product development led the International Electrotechnical Commission (IEC) to propose a 500-gram (1.1-pound) limit for R-290 in single commercial refrigeration appliances.
As time passes, it’s logical to think that Europe and the U.S. will continue to explore the balance between safety, efficiency, and the environment but not at the expense of endangering users and technicians.
New design and safety measures are needed to avoid flammability in occupied spaces and during servicing. For more than a century in the U.S., HVACR manufacturers and service technicians have been working with A1 refrigerants.
The service industry, in particular, will need to become more familiar with flammable refrigerants.
“Installation and service are the areas where proper guidelines, training, certification, and standards are the most important,” said Bill Goetzler, partner, Guidehouse (formerly Navigant Consulting). “The lines carrying flammable refrigerants may be opened during various servicing operations, and service personnel also may be working with a high-temperature ignition source. Those are really places to be very careful and to be sure we’ve got standards and guidelines in place to minimize the risk.”
Safety is a vital factor relative in a refrigerant sustainability triangle that includes environmental and economic factors (Figure 4).
Other factors come into play depending on the properties of the refrigerant. With some HFO refrigerants, for example, flammability can present a safety issue, as previously discussed. Cost can also be a factor, as HFO formulations are more expensive to produce and supplies are constrained. Finally, environmental concerns can still be an issue in several countries, because HFOs break down in the lower atmosphere, forming fluorinated breakdown substances. Trifluoroacetic acid (TFA) is an HFO breakdown substance but also occurs naturally in seawater. TFA has recently been found accumulated in ice cores from the Arctic. Hydrogen fluoride (HF) is another HFO breakdown substance that is very toxic; however, it is harmless when dissolved in water in small quantities. The small amounts of TFA and HF are not expected to pose global or regional problems.
FOUR TECHNOLOGICAL DEVELOPMENTS THAT CAN BUILD A STEADY TRANSITION PLATFORM
The search for refrigerants that perfectly balance environmental, economic, and safety concerns is continuing. Unfortunately, this quest throws customers and end users off balance. Planning is stressful when the future is subject to change. Fortunately, in recent years, technology has developed to the point that it is possible to build a long-lasting platform for low-GWP commercial refrigeration. Proven technologies are now available in four areas:
1.Developments in CO2 refrigeration — Until recently, it’s been impossible to apply the energy efficiency, safety, and environmental benefits of transcritical CO2₂ systems in all climates. Following years of engineering and field testing, the Danfoss Multi Ejector Solution™ was developed. As previously explained, Danfoss Multi Ejector and the AK-PC 782A Pack Controller technology enables a CO2 refrigeration system to operate in a transcritical zone, even in warm climates. The result is up to 10% annualized savings compared to prior transcritical parallel compression systems and up to 30% energy savings during the hottest hours of the year compared to booster systems. Moreover, compressor discharge temperatures in transcritical operation can exceed 250°F (120°C). This heat, which is usually rejected by a gas cooler, can be reclaimed by heat exchangers mounted before the gas cooler. This combination of technologies brings all the safety, economic, and environmental benefits of CO2 to many large and mid-size U.S. commercial refrigeration applications, regardless of location.
2.Developments in Demand Response — The high usage of electricity by supermarkets can make it very advantageous to participate in demand-response programs. As the name implies, in a demand-response program, the utility sends a signal to a central control unit that utilizes the flexibility of the application to reduce power to motors, compressors, and other electrical equipment. The signal triggers a reduction in electric consumption for brief periods ranging from less than 1 minute to long periods within a 24-hour interval, depending on the application.
Not every utility offers demand-response programs. The utilities offering these programs pass on the prospective savings to participants. Economic benefits are based on the customer’s commitment to respond. A carefully designed demand-response program using appropriate refrigeration control and management systems can achieve substantial energy savings while protecting food integrity.
For example, the Danfoss ADAP-KOOL® System Manager AK-SM 800 Series not only features a full web interface for remote monitoring and data management, it also incorporates built-in demand-response capabilities that can take advantage of utility incentive programs. Additionally, it supports heat-reclaim technology and a variety of refrigerants, including CO2.
Store owners and energy managers should consult with utilities to evaluate their flexibility to shift the demand and the time of electric consumption.
3. Developments in thermal storage and related thermal-shifting technologies — Thermal storage makes it possible to shift electricity consumption from expensive peak rates during the day to lower rate periods during the night. Thermal storage tanks hold a liquid medium chilled at night for cooling display cases, reducing equipment run time.
In a supermarket application, the display cases can themselves function as a form of thermal storage. Lowering display-case temperatures during off-peak hours enables compressors to run less during peak hours. Thermal storage capacity can be used to produce a revenue stream when it’s connected to other stores through a district heating and cooling (DHC) system. Heat recovery technology can also be used to capture heat otherwise rejected by the refrigeration system’s condensers. For stores using CO2 with a heat-reclaim system, the size of a separate heat source, such as a boiler, can be greatly reduced or even eliminated.
4. Developments in the decarbonized grid — Called “the largest machine ever built,” the more than century-old electric grid is the largest producer of greenhouse gasses. Fortunately, technology exists today to re-engineer that machine to cut CO2 emissions dramatically. Increased use of renewable power (wind and solar), continued use of stable nuclear power, and use of responsive hydropower are low-carbon resources that are gradually creating a decarbonized electricity supply. Models of a moderately decarbonized electricity system for the year 2050 estimate CO2 emissions intensity could be 60%-80% lower than today’s U.S. grid.
In the U.S., more than 21 million kWh of electricity in 2017 was used in process cooling and refrigeration for food. By using low-GWP refrigerants, demand-response and thermal storage technologies compatible with an increasingly decarbonized grid, air conditioning can help shrink its share of greenhouse gas emissions (Figure 5).
Recent technological developments are supporting the transition to low-GWP refrigerants. While policies may fluctuate, research and innovation are bringing proven products and platforms to market that can be implemented today in more food and commercial refrigeration applications than ever before. HFOs, in conjunction with oil-free system developments, are very viable options in air conditioning and, eventually, heat pump applications. Advances in transcritical CO2 systems are also providing an attractive value proposition for many supermarkets. Other developments — demand response, thermal storage, and heat reclaim — complement the trend toward a decarbonized electric grid and significantly reduce commercial refrigeration’s carbon footprint. Utilities and regulators play a vital role in creating an HFC-free future. Incentives and policies can reassure supermarket owners operating on tight margins that their investment will pay off by boosting profits in the short term, as well as the environment in the long run.