Barbara Minor is an Engineering Fellow at DuPont Fluoroproducts, Wilmington, DE; Ward Wells is a Senior Engineer at DuPont 

Fluoroproducts, Wilmington, DE. 

Low GWP R-404A Alternatives for 

Commercial Refrigeration 

Barbara Minor Ward Wells 

Member ASHRAE Member ASHRAE 

ABSTRACT 

R-404A has been the global industry standard HFC refrigerant for commercial refrigeration in both small and large 

systems. Due to the high global warming potential of R-404A however (AR4 100 year GWP = 3922), interest is growing to 

identify low GWP alternatives which match R-404A performance. The new low GWP refrigerant HFO-1234yf (100 year 

GWP = 4) has been found to be a suitable component in mixtures which can be formulated to match R-404A performance 

while reducing GWP. Two approaches have been investigated. The first is to develop the lowest GWP R-404A alternative 

possible (GWP ~1400) while maintaining nonflammability. This is desirable for large supermarket systems and for retrofit of 

existing R-404A systems in the field which were designed for nonflammable refrigerants. The second approach is to drive to 

the lowest GWP (e.g. ~250), but with mild flammability which meets ASHRAE A2L classification. This could be suitable for 

systems where a small degree of flammability may be allowed with smaller refrigerant charge sizes based on industry codes 

and standards. These two approaches will be evaluated by thermodynamic cycle analysis and through experimental testing 

in an R-404A self contained freezer. Several parameters will be measured compared to an R-404A baseline, including energy 

consumption, pressures and temperatures and mass flow rate. 

INTRODUCTION 

When replacements for chlorofluorocarbon (CFC) and hydrochlorofluorcarbon (HCFC) refrigerants were needed in the 

early 1990s due to the ozone issue, hydrofluorocarbon (HFC) refrigerants rapidly emerged as the leading alternatives. They 

had no ozone depletion potential because chlorine was eliminated from their chemical structure. They had low toxicity, were 

non-flammable and thermally stable. And they offered a significantly lower global warming potential (GWP) reduction 

versus CFC refrigerants. However, they still exhibited relatively high GWPs compared to non-fluorinated options. When 

climate change emerged as a leading environmental issue, HFCs came under challenge, particularly their use in more 

emissive applications such as automotive air conditioning and large supermarket systems where leaks are more difficult to 

control. Commercial refrigeration is also of concern because the leading HFC refrigerant in use is R-404A with a 100 year 

GWP of 3922 (IPCC 2007), among the highest of the HFC refrigerants. The automotive industry selected a new low GWP 

hydrofluoroolefin HFO-1234yf (CF3CF2=CH2

) (SAE 2009) with a 100 year GWP of 4 (Minor and Spatz 2008) as the 

preferred alternative for automotive air conditioning. They determined that even though HFO-1234yf was mildly flammable, 

because the charge size was small, it could be safely used in vehicles. There was therefore an opportunity to employ HFC1234yf as a component in developing low GWP mixtures to match R-404A performance. 

Two candidate refrigerants have been developed with performance similar to R-404A. The first, DR-7 has a GWP of 

about 250 which is 94% lower than R-404A. It is mildly flammable (ASTM E681-04 2004) and therefore may have some 

limitations for use in larger charge systems. DR-33 is formulated to be nonflammable (ASTM E681-04 2004 and ASHRAE 
Std 34-2010 2010), with a GWP of about 1400 which is about 65% lower than R-404A. Its GWP is also lower than other 

alternatives for R-404A such as R-407A (36% lower) and R-407F (23% lower). Performance of both refrigerants has been 

evaluated in a reach-in freezer originally designed for R-404A. 

THERMODYNAMIC PROPERTIES AND PERFORMANCE 

A comparison of thermophysical properties of DR-7 and DR-33 compared to R-404A are shown in Table 1 below. 

The boiling points are very similar and the critical points of DR7 and DR-33 are higher than R-404A. Vapor pressures and 

liquid densities are also similar. The vapor densities of DR-7 and R-33 are slightly lower than R-404A which will reduce 

mass flow rate. 

Table 1: Thermophysical Properties 

R-404A DR-7 DR-33 

Boiling Point °C (°F) -47 (-53) -48 (-54) -46 (-50)

Critical Point °C (°F) 72 (162) 81 (178) 82 (180) 

Vapor Pressure at 25°C (77°F) in 

kPa (Psia) 

1254 (181) 1372 (199) 1271 (184) 

Liquid Density at 25°C (77°F) in 

kg/m3 (lb/ft3) 

1044 (65.2) 1133 (70.7) 1139 (71.1) 

Vapor Density at 25°C (77°F) in 

kg/m3 (lb/ft3) 

65.3 (4.07) 46.8 (2.92) 48.9 (3.05) 

To evaluate the thermodynamic cooling performance, cycle modeling was performed for DR-7 and DR-33 versus R404A. The conditions were chosen to be fairly comparable to the system conditions in the reach-in freezer tested at 32°C 

(90°F) ambient temperature: Evaporator temperature = -26°C (-15°F), Condenser temperature = 43°C (110°F), Subcool 

amount = 14K (25°F), Suction temperature = -4°C (25°F) and compressor isentropic efficiency = 75%. Results are shown in 

Table 2. 

Table 2: Thermodynamic Cycle Performance 

 Suction 

Pressure 

kPa 

(Psia) 

Discharge 

Pressure 

kPa (Psia) 

Comp 

Ratio 

Compressor 

Disch Temp 

C (F) 

Average 

of Evap 

and Cond 

Temp 

Glide C 

(F) 

Capacity 

kJ/m3 

(Btu/ft3) 

Capacity 

Rel to 

R-404A 

COP COP 

Rel to 

R-404A 

R-404A 242 (35) 1969 (286) 8.1 86 (187) 0.4 (0.7) 1442 

(38.8) 

100% 2.03 100% 

DR-7 230 (33) 1987 (288) 8.6 107 (225) 5.7 (10.3) 1488 

(40.0) 

103% 2.05 101% 

DR-33 207 (30) 1869 (271) 9.0 103 (217) 4.3 (7.7) 1372 

(36.9) 

95% 2.07 102% 

DR-7 and DR-33 both exhibit pressures and compression ratios comparable to R-404A. They both have higher 

temperature glides than R-404A, but temperature glides are comparable to some other commercial refrigerants in use today. 

For example, R-407C, which has been used successfully for many years, under these conditions has a temperature glide of 

4.8°C (8.6°F). Compressor discharge temperatures are also somewhat higher than R-404A; however, the cooling capacity and 

energy efficiency is a very close match to R-404A. 
SYSTEM TESTING

In order to measure system performance of DR-7 and DR-33 in a system, a reach-in freezer was selected, fully 

instrumented and placed in a constant temperature room. The freezer is a 52 ft3

 (1.5 m3) double-door unit designed for R404A with a refrigerant charge size of 1.15 kg (2.54 lb). It has a reciprocating compressor which uses a polyol ester (POE) 

32 centistokes lubricant. The test setup was selected to conform as closely as possible to AHAM Standard HRF-1-2008 

Energy and Internal Volume of Refrigerating Appliances (AHAM 2008). It was not possible to use ANSI/ASHRAE 

Standard 72 because the system was not set up to open and close freezer doors during the test. The reach-in freezer is 

controlled with two thermostatic expansion valves (TXVs). A picture of the unit is shown in Figure 1. 

Figure 1 Picture of R-404A Reach-in freezer used in experimental testing 

The empty freezer (per AHAM HRF-1-2008) was placed in a constant temperature room and fully instrumented with 

temperatures (T), pressures (P), mass flow rate (M) and energy measurement (W) as shown in Figure 2. Though humidity 

was not required to be controlled in the chamber (per the standard Section 5.3.2) , tests at each condition for each refrigerant 

were repeated three times to insure results were reproduced and any humidity variation was not impacting results. 
Figure 2 Schematic showing instrumentation of reach-in freezer 

Tests were conducted at three ambient conditions 32°C (90°F) required by the standard and also 24°C (75°F ) and 21°C 

F (70°). An R-404A baseline was tested at the three ambient conditions first. At each condition, the evaporator exit 

superheat was controlled by adjusting the TXV to 3-4K (6-7F). The evaporator superheat was calculated from the suction 

pressure and the temperature reading at the exit of the evaporator. The freezer internal average compartment temperature 

(average of four thermocouple readings (placed throughout the freezer compartment) was controlled to -17°C (1.4F). The 

compressor was allowed to cycle to maintain the cabinet set point temperature. Temperatures and pressures are reported as 

averages only while the compressor was running. After testing, R404A was replaced with DR-7, then DR-33. In each test, 

the system was flushed to remove lubricant and a new charge of the same type of POE lubricant was added to the system. No 

other changes were made to the system except to adjust the evaporator superheat with the TXV to match R-404A superheat 

conditions. For both candidate refrigerants, the TXVs were closed one turn. Steady state results are shown in Table 3 for SI 

units and in Table 4 for I-P units. 
Table 3. Reach-in Freezer Steady State Test Results – SI Units 

Energy 

Consumption 

(kWhr/day) 

Energy 

Cons Rel 

to R404A 

Evap 

Exit 

Sup 

Heat 

(K) 

Mass 

Flow 

Rate 

(kg/hr) 

Suction 

T(°C) 

Suction 

Pressure 

(kPa) 

Discharge 

Pressure 

(kPa) 

Compr 

Ratio 

Comp 

Disch 

Temp 

(°C) 

Ambient T = 32°C 

R404A 33.46 100% 4 44 -5.2 211 2027 10 90 

DR-7 30.81 92% 3 34 0.7 191 2133 11 105 

DR-33 32.16 96% 4 30 4.6 172 1931 11 104 

 

Ambient T = 24°C 

R404A 25.11 100% 3 46 -9.7 198 1647 8 75 

DR-7 23.91 95% 4 35 1.9 184 1728 9 91 

DR-33 25.00 100% 3 31 0.6 172 1551 9 88 

 

Ambient T = 21°C 

R404A 23.39 100% 3 48 -13.1 199 1558 8 70 

DR-7 22.62 97% 3 36 -0.7 179 1600 9 85 

DR-33 23.41 100% 3.00 33 0.7 172 1448 8 83 

Table 4. Reach-in Freezer Steady State Test Results – I-P Units 

Energy 

Consumption 

(kWhr/day) 

Energy 

Cons Rel 

to R404A 

Evap 

Exit 

Sup 

Heat 

(F) 

Mass 

Flow 

Rate 

(lb/hr) 

Suction 

T(°F) 

Suction 

Pressure 

(Psia) 

Discharge 

Pressure 

(Psia) 

Compr 

Ratio 

Comp 

Disch 

Temp 

(°F) 

Ambient 

T = 90°F 

 

R404A 33.46 100% 7 96 22.6 31 294 10 194 

DR-7 30.81 92% 6 75 33.3 28 309 11 221 

DR-33 32.16 96% 7 65 40.3 25 280 11 219 

 

Ambient 

T = 75°F 

 

R404A 25.11 100% 6 102 14.5 29 239 8 167 

DR-7 23.91 95% 7 76 35.4 27 249 9 195 

DR-33 25.00 100% 6 68 33.0 25 225 9 190 

 

Ambient 

T = 70°F 

 

R404A 23.39 100% 6 105 8.4 29 226 8 158 

DR-7 22.62 97% 6 78 30.8 26 232 9 184 

DR-33 23.41 100% 6 73 33.3 25 210 8 182 

Experimental results in the reach-in freezer show DR-7 and DR-33 exhibit similar performance compared to R404A, with both demonstrating improved energy efficiency at higher ambient conditions. DR-7 consumed 8% less energy 

at 32°C (90°F) ambient temperature and DR-33 4% less energy. At lower ambient conditions, DR-7 still demonstrated 3-5% 

improved efficiency, whereas DR-33 was equivalent to R-404A. For both refrigerants, the suction temperature was slightly 

higher than R-404A and for all three refrigerants, somewhat higher than expected. This may be due to the fact that the 

suction temperature thermocouple was located as close to the compressor as possible and conduction of heat from the 

compressor may have elevated the suction temperature readings. The mass flow rate was slightly lower and the discharge 
temperature was slightly higher. However, the discharge temperatures were still low enough to not require liquid injection 

which is usually needed at temperatures great than 135°C (275°F). Evaporator superheats and compression ratios for both 

refrigerants were also similar to R-404A. 

CONCLUSION

Two new low GWP refrigerants have been developed which can potentially replace R-404A in commercial 

refrigeration. The first, DR-7 has a GWP of about 250 which is 94% lower than R-404A. It is mildly flammable (2L) and 

therefore may have some limitations for use in larger refrigerant charge systems such as supermarket racks. However, it 

could be suitable for single condensing unit systems and stand-alone coolers and freezers. DR-33 is formulated to be 

nonflammable, with a GWP of about 1400 which is about 65% lower than R-404A. It is suitable for large rack systems and 

other refrigeration units where use of flammable refrigerants is not preferred or is restricted. Performance of both refrigerants 

has been evaluated in a reach-in freezer originally designed for R-404A. The only changes made to the system were a TXV 

adjustment to compare at equivalent evaporator superheat. Overall, energy consumption for both refrigerants is at least 

equivalent to R-404A while other performance parameters are similar. At higher ambient conditions, DR-33 and DR-7 

exhibit 4 and 8% lower energy consumption respectively. Use of these low GWP refrigerants can effectively reduce the 

environmental impact of refrigeration systems by allowing transition away from R-404A with minimal system changes. 

REFERENCES 

AHAM HRF-1-2008. 2008. Energy and Internal Volume of Refrigerating Appliances: Association of Home Appliance 

Manufacturers. 

ASHRAE Standard 34-2010. 2010. Designation and Safety Classification of Refrigerants: American Society of Heating, 

Refrigerating and Air-Conditioning Engineers (ASHRAE), Atlanta, GA, 2010. 

ASTM E681-04. 2004. Standard Test Method for Concentration Limits of Flammability of Chemicals (Vapors and Gases): 

American Society for Testing and Materials (ASTM), West Conshohocken, PA, 2004. 

IPCC. 2007. Intergovernmental Panel on Climate Change Fourth Assessment Report – Climate Change 2007: Synthesis 

Report. [Jallow, B.P., L. Kajfez-Bogataj, R. Bojaru, D. Hawkins, S. Diaz, H. Lee, A. Allali, I. Elgizouli, D. Wratt, O. 

Hohmeyer, D. Griggs, and N. Leary (eds.)]. <http://www.ipcc.ch/ipccreports/ar4-syr.htm>. 

Nielson, O.J., Javadi, M.S., Sulbaek Andersen, M.P., Hurley, M.D., Wallington, T. J., and R. Singh. 2007. Atmospheric 

Chemistry of CF3CF=CH2: Kinetics and mechanisms of gas-phase reactions with Cl atoms, OH radicals and O3. 

Chemical Physics Letters, 439 (2007):18-22. 

SAE. 2009. SAE International Releases Test Results of the Low GWP Refrigerant for Automotive Air Conditioning. 

http://www.sae.org/servlets/pressRoom?OBJECT_TYPE=PressReleases&PAGE=showRelease&RELEASE_ID=1109, 

November 10, 2009. 

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is intended for use by persons having technical skill, at their own risk. Since conditions of use are outside our control, we 

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