ID: 515



## HYBRID SUPERMARKET SYSTEM USING LOW GWP REFRIGERANT S

RINNE F. (*) 

### , MINOR B. (**) 

### , SALEM K. (***)

(*) DuPont de Nemours Deutschland (GmbH), Hugenottenal lee 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, G ermany

kahtan.salem@tebeg.de



### ABSTRACT

Global pressure has intensified to reduce the use o f R-404A due to high global warming potential and relatively high leak rates in supermarket systems. In Europe, several design modifications such as ca scade systems and new refrigerant choices are being inves tigated. One of the new leading options is to util ize a hybrid cascade system using CO 2 in low temperature refrigeration circuit and R-134a in medium temperature. R-134a has higher efficiency than R-4 04A 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 an d is also non-flammable. This paper will show resu lts of experimental calorimeter and supermarket system per formance. A TEWI analysis will also be presented to demonstrate the significant reduction in environmen tal impact if XP10 is used in a hybrid cascade syst em with CO 2

.



### 1. INTRODUCTION

When replacements for chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants were needed in the early 1990s due to the ozone issue, h ydrofluorocarbon (HFC) refrigerants rapidly emerged as leading alternatives. They had no ozone depletion potential because chlorine was eliminated from thei r chemical structure. They exhibited low toxicity an d were non-flammable and thermally stable. And the y offered a significantly lower global warming potent ial (GWP) reduction versus CFC refrigerants. Howe ver, 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 condit ioning and large supermarket systems where leaks ar e more difficult to control. The automotive industr y 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 e ven 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 whic h have very large refrigerant charge sizes.

In Europe, which has been a leader in addressing cl imate change, supermarket technologies have been reevaluated in an attempt to eliminate the use of the preferred HFC based refrigerant R-404A which ha s 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). CO 2 is the low temperature refrigerant which can operate below its critical point and R-134a is the medium temperature refrigerant which has higher eff iciency

than R-404A. An R-134a/CO 2 cascade system provides a 75% direct refrigerant G WP reduction versus use of R-404A in both medium and low temp. There was o pportunity 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-flam mable 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 t o be rated class A1 by ASHRAE. It has potential to be used, f or example, in the medium temp circuit of a hybrid R134a/CO 2 cascade system to replace R-134a. An XP10/CO 2 hybrid cascade system can reduce the direct GWP by 85-90% compared to an all-R404A system witho ut concern for flammability. XP10 is thermally stable and compatible with metals, plastics and ela stomers used in refrigeration systems. It is also completely miscible with polyolester (POE) lubrican ts.



### 2. THERMODYNAMIC AND CALORIMETER PERFORMANCE

To evaluate the cooling performance, thermodynamic cycle modeling was performed for XP10 versus R134a under the following medium temperature refrige ration 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 compressio n 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 capaci ty and equivalent energy efficiency to R-134a. The discha rge 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 thre e different evaporating temperature conditions. Res ults are shown in Figure 1 and are quite consistent with thermodynamic performance data (6-10% increase in c apacity, 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 TemperatureRelative to R-134a Capacity

COP

Figure 1. Capacity and COP of XP10 relative to R-1 34a in compressor calorimeter

### 3. TESTING IN A SUPERMARKET

3.1 Test Setup In order to measure system performance of XP10, a t ypical German discount supermarket was selected. Th e market has a size of approximately 1000 m 2

.

Figure 2. Supermarket system schematic

Figure 2 shows the system schematic of the discountmarket. The seven medium temperature open multideck cabinets and the three medium temperature cold rooms are connected to a multi-compressor rack wit h three semi-hermetic compressors. The refrigerant i n the rack is R-134a. All evaporators have thermost atic control valves. The low temperature cold room has a single R-404A cascade compressor rejecting the hea t into one medium temperature cold room. The condense r is placed on the roof of the building and has var iable 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 herme tic compressor and condenser rejecting the heat int o the market and use refrigerant R-290.

The system has modular electrical control which all ows complete remote operation to analyze the system performance. The intelligent telecommunications sof tware permits the central monitoring of the connect ed system around the clock. The software is used to mo nitor, analyze and parameterize the control circuit s. The compressor rack is controlled with floating suction and discharge pressures as a function of the cooli ng demand and the ambient conditions. The compressor r ack suction pressure is determined by the cabinet o r cold room with the lowest performance. For each coo ling cabinet and cold room, a theoretical evaporati ng temperature is calculated based on a simulation mod el using the air-on and air-off temperature and oth er parameters. To analyze the system performance, for each cabinet the theoretical evaporating temperatu re is compared with the actual evaporating temperature. This shows immediately which cabinet or cold room i s not working well, assuming that all cabinets should operate at similar conditions.

Each cabinet or cold room is equipped with three te mperature sensors for air-on, air-off and the evapo rator surface temperature. In order to measure the evapor ator superheat, additional sensors at the evaporato r exit were installed (see Figure 2). Due to a small diffe rence in mass flow rate of R-134a and XP10 it was necessary to open the TXV to allow a higher mass fl ow 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 w ere 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 s hown.

Figure 3. Superheat of R-134a vs XP10

Even though the TXVs were opened by a 1⁄4 turn, the s uperheat with XP10 is still 2 K higher and a furthe r adjustment is planned. In Figure 4, the energy con sumption is shown before and after the conversion.

Figure 4. Energy consumption before and after the c onversion 

# R

- 134 a XP10

Energy consumption kWh with R-134a minimum ambient temperature maximum ambient temperatureAfter the conversion to XP10, the average ambient t emperature increased from 10.6°C to 12.6°C during t he

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 consumptio n 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 performa nce comparison.

For both days the temperature distribution and the actual energy consumption for R-134a and XP10 is sh own in Figure 5. During the time when the store was ope ned from 8am to 8pm the energy consumption of R-134 a was higher even at lower ambient temperatures durin g 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 consumpti on for R-134a on April 30 and XP10 on May 20

Figure 6 shows the evaporation temperature (to), th e compressor suction temperature (ts), the condensi ng temperature (tc) and the discharge temperature (tsu p). The condenser control with variable blower fans maintains constant temperatures for both refrigeran ts. The results with XP10 showed 6K lower discharge temperatures which confirms the theoretical calcula tions. The superheat with XP10 is still higher but also the temperature at the evaporator exit has a slightly h igher 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 pr essure drop to achieve evaporating temperatures of -6°C. T his was recently confirmed by additional laboratory tests not shown here, which would result in further impro vements.

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 temperat ure R134aFigure 6. System data for R-134a on April 30 and X P10 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 dire ct global warming potential (GWP) of the refrigeran t due to leakage and the indirect effect from energy consumption during equipment operation. A computational TEWI analysis was conducted for sever al refrigerant technologies using a typical Europea n supermarket store design. The following assumption s 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% f or low temp

- Refrigerant charge size – 200 kg in medium temp, 10 0 kg in low temp

- Average refrigerant leak rate – 15% per year

- Refrigerant recovered at end of life – 80% of charg e

- CO 2 emitted from electricity generation (Brouwers, 200 7) – 0.616 kg CO 2 /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 CO 2 in both medium and low temp circuits which was eva luated in both a northern and southern European climate due t o differences in CO 2 performance sub- and trans-critical, (3) an R-134a-CO 2 cascade system and (4) an XP10-CO2 cascade system. Values of CO 2 -CO 2 cascade systems were specified to match published data on e nergy consumption relative to an R-404A DX system (Seinel and Finckh, 2007). Results in Figure 7 sho w the XP10-CO 2 cascade system has the lowest TEWI and therefore, lowest overall environmental impact. Th is analysis demonstrates the potential XP10 has for use in hybrid systems with CO 2

.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 refrigeratio n system options



### 5. CONCLUSIONS

XP10 is a developmental non-flammable, azeotropic r efrigerant designed to replace R-134a in supermarke t systems which have large refrigerants charge sizes and therefore restrictions for using flammable refrigerants. XP10 provides an excellent match wit h R-134a thermophysical properties, but with less t han half the global warming potential and no ozone depl etion potential. Replacing a medium temperature an d low temperature direct expansion R-404A system with a cascade system employing XP10 at medium temp

and CO 2 at low temp would result in a direct GWP reduction of 85 to 90% and reduced energy consumption.

XP10 also demonstrates the lowest total environment al impact when compared to R404A DX and all-CO 2 cascade systems, regardless of climate.

A supermarket rack refrigeration system was convert ed from R-134a to refrigerant XP10. During the conversion, only the TXV setting was changed slight ly. The performance at equivalent ambient conditio ns showed 3.3% lower energy consumption for XP10 versu s 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 ex changers are optimized for XP10 versus R404A and with further adjustments to achieve comparable supe rheat.

### 6. REFERENCES

ASTM E681-04. 2004, , "Standard Test Method for Co ncentration Limits of Flammability of Chemicals (Vapors and Gases)," American Society for Testing and Materials (ASTM), West Conshohocken, PA.

Brouwers, C., 2007, Trends in Supermarket Technolog y within the European Union, International Conference on Co2ol Food , Berlin, May 23.

IPCC. 2007, “Intergovernmental Panel on Climate Cha nge Fourth Assessment Report – Climate Change 2007: Synthesis Report,” [Jallow, B.P., L. Kajfez-B ogataj, R. Bojaru, D. Hawkins, S. Diaz, H. Lee, A. Allali, I. Elgizouli, D. Wratt, O. Hohmeyer, D. Gri ggs, and N. Leary (eds.)]. <http://www.ipcc.ch/ipccreports/ar4-syr.htm>.

Minor, B. H. and M. Spatz. 2008, Low GWP Refriger ant Update. Proceedings of the 12 th International Refrigeration and Air Conditioning Conference at Pu rdue. West Lafayette, IN, Jul 14-17.

Rinne, F. and B. H. Minor. 2010, Low GWP Refrigeran ts 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=P ressReleases&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, 22 nd International Congress of Refrigeration , Beijing.

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