ID: 515 

HYBRID SUPERMARKET SYSTEM USING LOW GWP REFRIGERANTS 

RINNE F.(*), MINOR B.(**), SALEM K.(***)

(*) DuPont de Nemours Deutschland (GmbH), Hugenottenallee 173-175, Neu-Isenburg, 63263, Germany 

frank.rinne@dupont.com

 (**) DuPont Fluoroproducts, CRP 711-Bdg, Wilmington, DE, 19880, USA 

barbara.h.minor@usa.dupont.com

(***) tebeg , Liebigstrasse 21a, Würzburg, 97080, Germany 

kahtan.salem@tebeg.de

ABSTRACT 

Global pressure has intensified to reduce the use of R-404A due to high global warming potential and 

relatively high leak rates in supermarket systems. In Europe, several design modifications such as cascade 

systems and new refrigerant choices are being investigated. One of the new leading options is to utilize a 

hybrid cascade system using CO2 in low temperature refrigeration circuit and R-134a in medium 

temperature. R-134a has higher efficiency than R-404A and about one third the direct global warming 

potential (GWP). To make even greater gains in GWP reduction, a new lower GWP refrigerant has been 

developed that is retrofittable in the medium temp R-134a circuit with minimal system changes. This 

refrigerant has less than half the GWP of R-134a and is also non-flammable. This paper will show results of 

experimental calorimeter and supermarket system performance. A TEWI analysis will also be presented to 

demonstrate the significant reduction in environmental impact if XP10 is used in a hybrid cascade system 

with CO2. 

1. INTRODUCTION 

When replacements for chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants were 

needed in the early 1990s due to the ozone issue, hydrofluorocarbon (HFC) refrigerants rapidly emerged as 

leading alternatives. They had no ozone depletion potential because chlorine was eliminated from their 

chemical structure. They exhibited low toxicity and 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. The automotive industry selected a new low GWP hydro-fluoro-olefin HFO1234yf (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 refrigerant charge size was small, it could be safely used in vehicles. This however, HFO-1234yf would 

likely not be suitable for supermarket systems which have very large refrigerant charge sizes. 

 

In Europe, which has been a leader in addressing climate change, supermarket technologies have been 

reevaluated in an attempt to eliminate the use of the preferred HFC based refrigerant R-404A which has a 

high GWP at 3922 (IPCC, 2007). An important design that has emerged is a system which cascades from 

low to medium temperature (Rinne and Minor, 2010). CO2 is the low temperature refrigerant which can 

operate below its critical point and R-134a is the medium temperature refrigerant which has higher efficiency 

than R-404A. An R-134a/CO2 cascade system provides a 75% direct refrigerant GWP reduction versus use 

of R-404A in both medium and low temp. There was opportunity with the introduction of HFO-1234yf for 

further reduction in GWP if a non-flammable option could be developed for use in supermarket systems. 

This has led to the development of XP10, a non-flammable low GWP blend based on HFO-1234yf. 
XP10 is a developmental non-flammable (ASTM, 2004) azeotropic refrigerant with no ODP and a GWP 

near 600. It is a very close performance match to R-134a. It exhibits low toxicity and is expected to be rated 

class A1 by ASHRAE. It has potential to be used, for example, in the medium temp circuit of a hybrid R134a/CO2 cascade system to replace R-134a. An XP10/CO2 hybrid cascade system can reduce the direct 

GWP by 85-90% compared to an all-R404A system without concern for flammability. XP10 is thermally 

stable and compatible with metals, plastics and elastomers used in refrigeration systems. It is also 

completely miscible with polyolester (POE) lubricants. 

2. THERMODYNAMIC AND CALORIMETER PERFORMANCE 

To evaluate the cooling performance, thermodynamic cycle modeling was performed for XP10 versus R134a under the following medium temperature refrigeration conditions: Evaporator temperature = -10°C, 

Condenser temperature = 40°C, Subcool amount = 6K, Suction temperature = 18°C and compressor 

isentropic efficiency = 70%. Results are shown in Table 1. 

Table 1: Thermodynamic Cycle Performance 

 Suction 

Pressure 

(kPa) 

Discharge 

Pressure 

(kPa) 

Comp 

Ratio 

Compressor 

Disch 

Temp (°C) 

Capacity 

(kJ/m3) 

Capacity 

Rel to 

R134a 

COP COP 

Rel to 

R134a 

134a 201 1017 5.1 90 1497 100% 3.06 100% 

XP10 223 1070 4.8 82 1575 105% 3.04 99% 

XP10 suction and discharge pressures and compression ratio are very similar to R-134a indicating it is a 

suitable direct replacement for an existing R-134a system. It exhibits slightly higher cooling capacity and 

equivalent energy efficiency to R-134a. The discharge temperature is also lower than R-134a which can be 

beneficial for compressor life. 

XP10 performance was also compared to R-134a using a reciprocating compressor in a calorimeter at three 

different evaporating temperature conditions. Results are shown in Figure 1 and are quite consistent with 

thermodynamic performance data (6-10% increase in capacity, 0-2% increase in COP). 

90%

92%

94%

96%

98%

100%

102%

104%

106%

108%

110%

112%

-23C/41C -21C/41C -12C/41C

Evaporator/Condenser Temperature

Relative to R-134a

Capacity

COP

Figure 1. Capacity and COP of XP10 relative to R-134a in compressor calorimeter 
3. TESTING IN A SUPERMARKET 

3.1 Test Setup 

In order to measure system performance of XP10, a typical German discount supermarket was selected. The 

market has a size of approximately 1000 m2

. 

Figure 2. Supermarket system schematic 

Figure 2 shows the system schematic of the discount market. The seven medium temperature open multideck cabinets and the three medium temperature cold rooms are connected to a multi-compressor rack with 

three semi-hermetic compressors. The refrigerant in the rack is R-134a. All evaporators have thermostatic 

control valves. The low temperature cold room has a single R-404A cascade compressor rejecting the heat 

into one medium temperature cold room. The condenser is placed on the roof of the building and has variable 

speed blower fans. Not shown in Figure 2 are the 16 low temperature frozen food islands. These islands with 

sliding glass doors on top have an integrated hermetic compressor and condenser rejecting the heat into the 

market and use refrigerant R-290. 

The system has modular electrical control which allows complete remote operation to analyze the system

performance. The intelligent telecommunications software permits the central monitoring of the connected 

system around the clock. The software is used to monitor, analyze and parameterize the control circuits. The 

compressor rack is controlled with floating suction and discharge pressures as a function of the cooling 

demand and the ambient conditions. The compressor rack suction pressure is determined by the cabinet or 

cold room with the lowest performance. For each cooling cabinet and cold room, a theoretical evaporating 

temperature is calculated based on a simulation model using the air-on and air-off temperature and other 

parameters. To analyze the system performance, for each cabinet the theoretical evaporating temperature is 

compared with the actual evaporating temperature. This shows immediately which cabinet or cold room is 

not working well, assuming that all cabinets should operate at similar conditions. 

Each cabinet or cold room is equipped with three temperature sensors for air-on, air-off and the evaporator 

surface temperature. In order to measure the evaporator superheat, additional sensors at the evaporator exit 

were installed (see Figure 2). Due to a small difference in mass flow rate of R-134a and XP10 it was 

necessary to open the TXV to allow a higher mass flow through the valve by about a 1/4 turn or 90°. 
3.2 System Performance Data 

In order to compare both systems, the system data were stored 14 days before and after the conversion with a 

higher frequency than usual operation. In Figure 3 the superheat with R-134a and XP10 is shown. 

Figure 3. Superheat of R-134a vs XP10 

Even though the TXVs were opened by a 1⁄4 turn, the superheat with XP10 is still 2 K higher and a further 

adjustment is planned. In Figure 4, the energy consumption is shown before and after the conversion. 

Figure 4. Energy consumption before and after the conversion 

R-134a

 XP10

Energy consumption kWh with R-134a 

minimum ambient temperature 

maximum ambient temperature 
After the conversion to XP10, the average ambient temperature increased from 10.6°C to 12.6°C during the 

time the system was operated with XP10. This has an impact on the energy consumption. A comparison 

with R-134a over 8 days showed an increase by 3.6%. Furthermore, the slightly higher energy consumption 

is also due to the higher evaporator superheat. On 30th of April and 20th of May, the average ambient 

temperatures were equal at 17.1°C (circled areas in Figure 4) and therefore were used for the performance 

comparison. 

For both days the temperature distribution and the actual energy consumption for R-134a and XP10 is shown 

in Figure 5. During the time when the store was opened from 8am to 8pm the energy consumption of R-134a 

was higher even at lower ambient temperatures during this time. The integrated electric power over 24 hours 

shows 3.3% reduction energy consumption for XP10. These results will be confirmed as additional data is 

collected from this and other field trials. 

Figure 5. Temperature profile and energy consumption for R-134a on April 30 and XP10 on May 20 

Figure 6 shows the evaporation temperature (to), the compressor suction temperature (ts), the condensing 

temperature (tc) and the discharge temperature (tsup). The condenser control with variable blower fans

maintains constant temperatures for both refrigerants. The results with XP10 showed 6K lower discharge

temperatures which confirms the theoretical calculations. The superheat with XP10 is still higher but also the 

temperature at the evaporator exit has a slightly higher fluctuation. The reason is that evaporator is designed 

for R-404A. The supplier of the cabinets has since optimized the heat exchanger circuitry to reduce pressure 

drop to achieve evaporating temperatures of -6°C. This was recently confirmed by additional laboratory tests 

not shown here, which would result in further improvements. 

Electric Power 4/30/10 in kW 

Electric Power 4/30/10 in kW (XP10) 

average ambient temperature XP10

Electric Power 4/30/10 in kW (R134a) 

average ambient temperature R134a
Figure 6. System data for R-134a on April 30 and XP10 on May 20 

4. TEWI ANALYSIS 

Total Equivalent Warming Impact (TEWI) is a widely recognized tool to understand total refrigeration 

system environmental impact including both the direct global warming potential (GWP) of the refrigerant 

due to leakage and the indirect effect from energy consumption during equipment operation. A 

computational TEWI analysis was conducted for several refrigerant technologies using a typical European 

supermarket store design. The following assumptions were made: 

- Supermarket equipment life – 15 years 

- Supermarket operating power – 75 kW for medium temp and 20 kW for low temp 

- Fractional run time – 55% for medium temp and 85% for low temp 

- Refrigerant charge size – 200 kg in medium temp, 100 kg in low temp 

- Average refrigerant leak rate – 15% per year 

- Refrigerant recovered at end of life – 80% of charge 

- CO2 emitted from electricity generation (Brouwers, 2007) – 0.616 kg CO2/kw-hr 

Designs evaluated include (1) an uncoupled standard DX system using R-404A in both medium and low 

temp circuits, (2) a cascade system with CO2 in both medium and low temp circuits which was evaluated in 

both a northern and southern European climate due to differences in CO2 performance sub- and trans-critical, 

(3) an R-134a-CO2 cascade system and (4) an XP10-CO2 cascade system. Values of CO2-CO2 cascade 

systems were specified to match published data on energy consumption relative to an R-404A DX system 

(Seinel and Finckh, 2007). Results in Figure 7 show the XP10-CO2 cascade system has the lowest TEWI and 

therefore, lowest overall environmental impact. This analysis demonstrates the potential XP10 has for use in 

hybrid systems with CO2. 
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

XP10 - CO2 CCD

134a - CO2 CCD

CO2 - CO2 CCD N EU

CO2 - CO2 CCD S EU

404A - 404A DX

million Kg CO2 Equivalent over 15 year life

INDIRECT-MT

INDIRECT-LT

RFR LEAK-MT

RFR LEAK -LT

MT - LT

Figure 7. TEWI analysis of different refrigeration system options 

5. CONCLUSIONS 

XP10 is a developmental non-flammable, azeotropic refrigerant designed to replace R-134a in supermarket 

systems which have large refrigerants charge sizes and therefore restrictions for using flammable 

refrigerants. XP10 provides an excellent match with R-134a thermophysical properties, but with less than 

half the global warming potential and no ozone depletion potential. Replacing a medium temperature and 

low temperature direct expansion R-404A system with a cascade system employing XP10 at medium temp 

and CO2 at low temp would result in a direct GWP reduction of 85 to 90% and reduced energy consumption. 

XP10 also demonstrates the lowest total environmental impact when compared to R404A DX and all-CO2

cascade systems, regardless of climate. 

A supermarket rack refrigeration system was converted from R-134a to refrigerant XP10. During the 

conversion, only the TXV setting was changed slightly. The performance at equivalent ambient conditions 

showed 3.3% lower energy consumption for XP10 versus R-134a. All other operating parameters were very 

similar except for lower discharge temperature for XP10 which can improve compressor life. Further 

improvements in performance are possible if heat exchangers are optimized for XP10 versus R404A and 

with further adjustments to achieve comparable superheat. 
6. REFERENCES 

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. 

Brouwers, C., 2007, Trends in Supermarket Technology within the European Union, International 

Conference on Co2ol Food, Berlin, May 23. 

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>. 

Minor, B. H. and M. Spatz. 2008, Low GWP Refrigerant Update. Proceedings of the 12th International 

Refrigeration and Air Conditioning Conference at Purdue. West Lafayette, IN, Jul 14-17. 

Rinne, F. and B. H. Minor. 2010, Low GWP Refrigerants for Refrigeration and Air Conditioning, Chillventa 

Nuremberg, October 12-15. 

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&RELEA

SE_ID=1109, November 10. 

Seinel, T. and O. Finckh, 2007, CO2-DX systems for Medium and Low Temperature Refrigeration in 

Supermarket Applications, 22nd International Congress of Refrigeration, Beijing. 

Disclaimer: 

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