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Applied Thermal Engineering 41 (2012) 30e35
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Applied Thermal Engineering
journal homepage: www.elsevier .com/locate/apthermeng
Comparison of a R744 cascade refrigeration system with R404A and R22conventional systems for supermarkets
Alessandro da Silva a, Enio Pedone Bandarra Filho b,*, Arthur Heleno Pontes Antunes b
aBitzer Compressores Ltda, Av. Joao Paulo Ablas 777, Sao Paulo 06711-250, Brazilb Faculty of Mechanical Engineering, Federal University of Uberlandia, Av. Joao Naves de Avila, 2121, Uberlandia-MG, Brazil
a r t i c l e i n f o
Article history:Received 29 April 2011Accepted 8 December 2011Available online 30 December 2011
Keywords:Cascade systemCO2
Carbon dioxideR744SupermarketR404AR22
* Corresponding author. Tel.: þ55 34 32394022; faE-mail addresses: [email protected]
mecanica.ufu.br (E.P. Bandarra Filho), a(A.H.P. Antunes).
1359-4311/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.applthermaleng.2011.12.019
a b s t r a c t
The present article focuses on the energy efficiency and climate performance of three different systemsused in supermarket applications. The refrigeration systems consist of a cascade cycle (CO2/HFC-404A) eprovide nominal refrigerating capacity e with carbon dioxide for subcritical operation and HFC-404A inthe high stage temperature stage (pump circuit for normal refrigeration and direct expansion for deep-freezing), and also HFC-404A and HCFC-22 with direct expansion systems. The cascade system presenteda lower refrigerant charge, 47 kg of both fluids, which represents less than a half of the refrigerant chargeof the other systems. An important factor is the total GWP in case of leakage, where the impact in theatmosphere of the cascade system operating with CO2 was much less than the two direct expansionsystems.
� 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Carbon dioxide is a climate-friendly refrigerant because it hasa low direct global warming potential with the reference value of 1.Due to its specific thermodynamic properties, including highoperating pressure, low critical temperature and low viscosity, CO2offers a great potential as a new energy-efficient product. Accord-ing to Parise and Marques [9], industry is now challenged toproduce modern systems with zero leak and minimum refrigerantcharge, leading to more compact and efficient heat exchangers.However, Bansal [1] suggests that there is very little informationavailable in the open literature on the fundamental boiling andcondensation heat transfer characteristics of CO2 at low tempera-tures below �30 �C and �15 �C, respectively. The appropriateoptimal design of new heat exchangers may be impeded due to thelack of this information. Furthermore, it will encourage the devel-opment of modern systems that will put the refrigeration industryon a more sustainable footing.
Two-stage cascade refrigeration systems are suitable for thesupermarket refrigeration industry, where the evaporating temper-ature of frozen-food cabinets ranges from �30 �C to �50 �C [5].
x: þ55 34 32394206.(A. da Silva), bandarra@
All rights reserved.
Refrigerant emissions from the commercial sector are relativelyhigh [10] performed a study in 220 supermarkets in Norway andobserved an annual leakage rate of 14% (not including stand-aloneequipment). In these conditions, a considerable emission ofgreenhouse gases to the atmosphere is observed and it reinforcesthe need to reduce the leakage rate and also search for alternativesfluids.
Considering centralized systems, there are, basically, threepossibilities to use the carbon dioxide. It can be used as a secondaryrefrigerant or it can be employed as a primary refrigerant in the lowtemperature stage of a cascade system. In all-CO2 centralizedsystems with the low temperature stage in cascade and, finally, thisrefrigerant can be used with separated circuits for LT and MTservice, both rejecting heat directly to the environment.
Casson [2] evaluated the COP for medium temperature (MT) andlow temperature (LT) for CO2 systems, with evaporation tempera-tures between �10 �C and �35 �C, respectively. This authorobserved that the COP decreases with the increase of the externalair temperature, obtaining a COP of 5.2 for MT and 2.5 for LT, whenthe ambient temperature was 0 �C, and 1.5 and 0.8, respectively, forhigher ambient temperature, 30 �C.
Girotto et al. [6] evaluated the efficiency of a centralized all-CO2
system with 120 kW of capacity and compared it with a directexpansion R404A system. The authors concluded that, for mediumtemperature applications, the efficiency was still somewhat lowerif compared to the R404A system. For medium temperature
A. da Silva et al. / Applied Thermal Engineering 41 (2012) 30e35 31
applications, indirect cooling and low temperature CO2 cascadesystem showed to be the best option available to reduce HFCrefrigerant charges.
Sawalha [8] used a numerical simulation model to investigatethe performance of two main CO2 transcritical system solutions:centralized with accumulation tank at the medium temperaturelevel and parallel, that consists in two separate direct expansion(DX) circuits; one serves the medium temperature level cabinetsand the other serves the freezers for low temperature level. For theambient temperature range from 10 �C to 40 �C (different climateconditions: cold, moderate and hot) the two-stage centralizedsystem solution presented the highest COP. In addition, the authorconcluded that the CO2 systems, except parallel, presented betterperformance for cold climates, whereas NH3eCO2 cascade system isbetter for hot climates. In this climate case, the CO2 modifiedcentralized system presented only 1% higher annual energyconsumption in comparison with the conventional R404A and themodifications on the centralized system solution proved to bemoreimportant for high ambient temperature operating conditions. Bothsystems proved to be better alternatives in relation to the R404A(DX) system for supermarket refrigeration.
Ge and Tassou [4] used the supermarket model called ‘SuperSim’
to compare the performance of a conventional R404A refrigerationsystem and a CO2 booster system. Both systems were found to leadto very similar energy consumption. Floating head pressure controlwas implemented for both systems when they were in subcriticalcycles; this strategy reduced significantly heat recovery opportu-nities from the R404A system. The booster CO2 system, on the otherhand, due to the higher cycle pressures and temperatures lendsitself for heat recovery even during operation at subcritical condi-tions. It was found that heat recovery can satisfy 40% of the spaceheating demand of the supermarket.
With the focus primarily on supermarket applications, thispaper will analyze energy efficiency comparisons carried outbetween the CO2 cascade system and the direct expansionconventional system using R404A and R22, and discusses theiradvantages and disadvantages, along with a comparison of a costanalysis with carbon dioxide. Relevant issues for the application ofCO2 will also be highlighted. These energy efficiency comparisonswere conducted in the CO2 Technology Center that has been
Fig. 1. Refrigeration racks used
operating in the Laboratory of the Bitzer Brazil since 2008. In thiscenter three refrigerating systems with similar cooling capacitieswere installed.
2. Experimental facilities
The experimental facilities consist of a cascade system withcarbon dioxide for subcritical operation in the high temperaturestage and HFC-404A (CO2 is pumped in the liquid phase to theevaporator with liquid recirculation and direct expansion for deep-freezing). Two others direct expansion systems were used forcomparison, one with the refrigerant HFC-404A and other with theHCFC-22. Figs. 1 and 2 show the three refrigeration racks. They cooldown storage rooms from 2 �C and a deep-freeze room, to minus25 �C.
There are also two deep-freeze islands working at minus 25 �Cthat are only connected to the carbon dioxide circuit. The coolingcapacity for normal refrigeration is about 20 kW, and about 10 kWin the deep-freeze range. The evaporators of the three refrigeratingsystems are designed as air-coolers and fitted under the ceiling ofeach cold room. The condensers operate with either air-cooling orwater-cooling. All machines and cold rooms are equipped withinfrared sensors and a carbon dioxide extraction system, since incase of leakage a dangerous situation can occur and also tomaintainthe CO2 concentration at lower level. Only one systemwas in use atany one time to allow for energy comparisons. They have beenrunning, week on week off, so an accurate comparison can bedrawn among them.
Table 1 presents the major technical data for each refrigerationrack of both the Medium Temperature (MT) and Low Temperature(LT) systems.
The cooling capacity of the MT and LT multicompressor refrig-eration systems is higher than the required thermal load from coldrooms and islands, as shown in the Table 2.
2.1. Compressors
The compressors of each rack also have the operating option ofboth a frequency inverter and a head pressure capacity control unit,except for compressor model 4TCS-8.2 which is used in connection
in the present research.
Fig. 2. (a) Thermostatic and electronic expansion valves used in air-coolers with R404A and R22; (b) CO2 manual expansion valve used in evaporators with liquid recirculation.
A. da Silva et al. / Applied Thermal Engineering 41 (2012) 30e3532
with the R22 in low temperature with controlled injection cooling(CIC), and also for the CO2 compressor model 2KC-3.2K which hasonly one head (two cylinder). As a result it is not possible for bothcompressors to operate with a head capacity control unit. Theapplication range varied from 30 Hz to 70 Hz for the compressorswith frequency inverters.
2.2. Condensers
Each rack has the operating option of both air-cooled and water-cooled condensers (mainly the high stage of the subcritical CO2rack). Air-cooled and water-cooled condensers can be used tocompare the energy efficiency of the system. The air-cooledcondenser fans also have the option of operating with frequencyinverters as well as On/Off control pressure switches to control thecondensing temperature. The water-cooled condenser types are ofthe shell-and-tube type and they operate with a cooling tower.
2.3. Evaporators
The air-coolers that use R404A and R22, which are fitted in thecold rooms, are direct expansion (DX) type and use either ther-mostatic expansion valves (TEV) or electronic expansion valves(EEV). The CO2 air-coolers are used for both MT cold rooms and LTdeep-freeze room. The air-cooler used in the LT deep-freeze room isDX and uses only an electronic expansion valve. The other two CO2air-coolers, for medium temperature, run with liquid recirculationand only use manual expansion valves to control the refrigerantflow.
Table 1Technical data of multicompressor refrigeration systems.
SubcriticalCO2 rack (CO2/R404A)
R404A rack R22 rack
MT designcondition
TCond ¼ �5 �C (CO2) TEvap ¼ �10 �C TEvap ¼ �10 �CTEvap ¼ �10 �C(high stage)TCond ¼ 40 �C(high stage)
TCond ¼ 40 �C TCond ¼ 40 �C
LT designcondition
TEvap ¼ �30 �C(CO2 e DX)
TEvap ¼ �30 �C TEvap ¼ �30 �C
TCond ¼ �5 �C (CO2) TCond ¼ 40 �C TCond ¼ 40 �CCompressor
models01 � 2KC-3.2K (CO2) 01 � 4CC-9.2Y
(MT)01 � 4CC-9.2(MT)
01 � 4CC-9.2.Y (R404A) 01 � 4TCS-8.2Y(LT)
01 � 4TCS-8.2(LT)
MT coolingcapacity
21.0 kW 21.0 kW 19.8 kW
LT coolingcapacity
9.8 kW 10.7 kW 9.9 kW
All relevant information comes together in a central monitoringunit that can also be controlled via LAN and the Internet. Mediumtemperature (MT) evaporator defrosting is achieved by off cycle(air) while low temperature (LT) evaporator defrosting is achievedwith an electric heater, mainly for the LT CO2 evaporators (Islandsand LT deep-freeze room).
3. System architecture
3.1. R404A and R22 refrigeration racks
Both refrigeration racks work with two semi hermetic pistoncompressors (Octagonmodel 4CC-9.2 for MTand 4TCS-8.2 for LT) inparallel applications. Each rack has a common discharge line, butthe suction header is split for MT and LT suction lines, while thedischarge is collected in a common header and directed intoa single oil separator. The oil return pipe enters into an oil receiver,which pushes the oil since it is equipped with a combination of anoil separator-reservoir. No float valve was installed into oil sepa-rator-reservoir. Refrigerant flow from the discharge line to thecondenser and then goes to a vertical liquid receiver, wherea header liquid line distributes the liquid to the evaporators. Theoperating conditions are �30 �C for low temperature (LT), �10 �Cfor medium temperature (MT) and 40 �C for condensationtemperature.
3.2. CO2/R404a subcritical rack
Fig. 3 shows a schematic diagram of the cascade CO2/R404Asystem. According to this figure, the MT CO2 evaporators run withliquid recirculation at �5 �C, while the LT CO2 evaporators runwithdirect expansion at�30 �C of evaporating temperature, through thevapor compressor cycle using a semi hermetic reciprocatingcompressor.
As shown in this figure, in the R404A/CO2 cascade system, theCO2 and the R404A are in two separate circuits. These two circuitscome into thermal contact in the interstage heat exchanger (alsocalled cascade condenser) where they exchange heat with eachother without mixing the two refrigerants. The interstage heatexchanger serves as a condenser for the CO2 system and as anevaporator for the R404A system. CO2 is used as pumped liquid fornormal refrigeration and direct expansion for deep-freezing.
The design of the CO2 rack has some unusual features, which arerequired to maintain the compressor temperatures at the recom-mended level. It was found that the performance of the CO2compressor decreases in very low operating temperatures, which ifleft unchecked, would result in a high concentration of refrigerant
Table 2Overview of refrigeration points.
MT cold room MT walk-in cooler LT Deep-freeze room aLT islands
Dimensions 3.5 m � 4 m � 3.5 m 3.5 m � 4 m � 3.5 m 3.5 m � 4 m � 3.5 m 5 m total lengthThermal load 7.5 kW 7.5 kW 7.5 kW 2.5 kWInternal temperature 0 �C þ2 �C �25 �C �25 �C
a The two LT Islands only run with the CO2 refrigeration rack.
A. da Silva et al. / Applied Thermal Engineering 41 (2012) 30e35 33
in the lubricating oil within the compressor sump, causingpremature compressor failure. Superheating degrees between 20 Kup to 30 K at the CO2 compressor suctionwere required tomaintainacceptable sump temperatures in the CO2 rack.
To prevent this, an additional heat exchanger was addedbetween the CO2 suction line and the R404A high temperaturestage liquid line, which maintained the CO2 suction gas tempera-ture at the compressor between �10 �C and 0 �C. It is interesting toobserve that the low temperature of the vapor at the inlet of thecompressor is sometimes a problem, since the high density of CO2in the vapor phase, the CO2 has a much larger capacity to absorbheat of the compressor castings than other gases. This can result inthe compressor being chilled to a point where the compressordischarge line, and the compressor crankcase are covered in frostand ice and this will almost certainly means that the oil is beingdiluted by the refrigerant. Any refrigerant dilution will have anadverse effect on the life expectance of the compressors runninggear. It is best to keep the compressor sump temperature at least atbody temperature and the discharge should always be with hightemperatures.
The control of the CO2 superheating degree had an importanthole to be provided by some means such as liquid-suction heatexchangers, using the R404A in the liquid phase thus providing thesubcooling of the high stage liquid. Some types of control must beinstalled to limit the compressor return vapor temperature, eithera bypass system or multiple heat exchangers staged to provideaccurate control of the vapor inlet temperature. Either dischargevapor temperature or suction return temperature can be used tocontrol the heat exchanger operation. Low return vapor super-heating will give rise to oil and lubrication problems, while highsuperheat levels will cause motor overheating and subsequentfailures, as well as high discharge temperatures.
Fig. 3. Schematic diagram of the
4. Results
The cascade system design can also take advantage of a highdegree of liquid subcooling in the high stage circuit with R404A,which results in substantial reductions in pipe line diameters and,as consequence, a reduced refrigeration charge based on the tubediameter, compared to conventional refrigerants such as R404Aand R22. Table 3 shows this comparison, including some data fromTable 4, using the softwares [7] and [3].
The Table 5 presents the comparison among the tubes in termsof mass divided by length (kg/m), only relating the suction andliquid lines used in each evaporator.
As a general guide, pipeline sizes, mainly the suction pipe worklines, can be reduced to approx 1/5 of the line sizes currently usedwith R404A and R22 for the same system capacity.
Table 6 shows the total refrigerant charge used each rack. Due tothe purchase price of CO2 being considerably less expensive thanthat of refrigerants currently in commercial use, such as R404A andR22, the total cost of the refrigerant charge can be significantlyreduced.
4.1. Energy analysis
These three refrigeration systems were monitored and a super-visory system was used to acquire and integrate the variables suchas temperature, pressure, refrigerant mass flow and also, it was ableto capture the total power consumption of the entire system. Powerwas recorded at 15min intervals for the systems in operation, andincluded all aspects, such as the compressor motors and sumpheaters, fan motors defrost heaters, evaporator fans, and so on. Theenergy efficiency comparisons were an average over one year
cascade CO2/R404A system.
Table 5Total pipework used in two cold rooms for MTas well as in the deep-freeze room forLT.
Pipe work real length (m) e only suction line (SL) and liquid line (LL) eachevaporator
Diameter (mm) 9.52 12.7 15.88 28.58 34.93R22 Cold room 01 15 LL 15 SLR22 Cold room 02 11 LL 11 SLR22 Deep-freeze room 15 LL 15 SLR404A Cold room 01 15 LL 15 SLR404A Cold room 02 11 LL 11 SLR404A Deep-freeze room 15 LL 15 SLCO2 Cold room 01 15 LL 15 SLCO2 Cold room 02 11 LL 11 SLCO2 Deep-freeze room 15 LL 15 SL
ASTM B-280 e kg/m 0.186 0.294 0.424 0.971 1.314 TOTAL (kg)R22 41 LL 41 SL 51.86R404A 41 LL 26 SL 15 SL 62.34CO2 41 LL 41 SL 25.01
Table 3Suction and liquid line size comparison used in the two cold rooms forMT using CO2,R404A and R22.
Refrigerant CO2 R404A R22
Suction line (wet return linefor CO2, dry return linefor R404A and R22)
Cooling capacity (kW) 10 10 10DT (K) 0.67 0.47 0.55Velocity (m/s) 6.64 10.36 9.02Diameter (mm) 12.7 28.58 28.58
Liquid line (�5 �C for CO2) Velocity (m/s) 1.36 0.84 0.57Diameter (mm) 9.52 15.88 12.7
Cold room # 1 and # 2 for MT (TEvap ¼ �10 �C; TCond ¼ 40 �C); Leqv ¼ 20 (m).
A. da Silva et al. / Applied Thermal Engineering 41 (2012) 30e3534
where the condensing temperature was maintained of the order of38 �C.
It is most likely that with a CO2 system, a good proportion of theenergy savings can be attributed to the subcooling of the high stageliquid, by the low stage suction gas.
According to the Table 7, CO2 presented a higher efficient,around 22.3% in comparison with the R404A system, and 13.7%with the R22 system (both systems operates with frequencyinverter and electronic expansion valves). However, when both theR404A and R22 systems used thermostatic expansion valves, CO2became even more efficient, in which it represented 24.7% inrelation to the R404A system and 15.5% to the R22 system. Elec-tronic expansion valves save more energy costs since it is morereliable and precise in its way to control the refrigerant mass flowthrough the evaporator, as it receives all the information regardingthe temperature and pressure in the evaporator outlet in order tocontrol the opening and closing of the valve, according to thesuperheating.
4.2. Environmental analysis
The direct global warming potential (GWP) of the three systems,due to direct emissions in the event of a total loss of the entirerefrigerant charge, was also evaluated and represented greatimportance. CO2 is used as the base unit for measuring GWP, in thiscase is equal to 1. One kg of R404A has a GWP of 3260; one kg of R22has a GWP of 1500. Therefore, the CO2/R404A cascade system hasa total value of GWP of 48932, the R404A system has 407500 andthe R22 system has 172500, according to each refrigerant charge inthe system. As can be noted, the difference between the CO2/R404Acascade system and R404A system is of the order of 358468 and forR22 is 123568.
4.3. Cost analysis
While the medium temperature system through the liquidrecirculation system does not generally provide significant reduc-tions in energy costs, substantial savings can be achieved througha reduced refrigerant charge and a real reduction in the actual costof the refrigerant.
The cost of the three racks, the six air-cooled evaporators andthe condensers, were all tracked and a complete comparison could
Table 4Suction and liquid line size comparison used in the two deep-freeze room for LTusing CO2, R404A and R22.
Refrigerant CO2 R404A R22
Suction line (dry returnline for CO2, R404Aand R22)
Cooling capacity (kW) 10 10 10DT (K) 0.35 0.53 0.39Velocity (m/s) 8.35 11.42 10.28Diameter (mm) 15.88 34.93 28.58
Liquid line (�5 �C for CO2) Velocity (m/s) 0.85 0.97 0.68Diameter (mm) 9.52 15.88 12.7
Deep-freeze room LT (TEvap ¼ �30 �C; TCond ¼ 40 �C); Leqv ¼ 20 (m).
be drawn, since it is important to highlight that the CO2 rack andCO2 evaporators were built and had to be air freighted from abroad.The rack system costs were calculated separately. This has beendone because the contractor supplies the interconnecting pipework, as well as the pipe insulation, between the various items.
The two racks that make up the cascade system using CO2 onlow temperature and R404A on high temperature stage were foundto be 18.5% (based on 2008 values) more expensive than singlestage racks using R22 and R404A based on the same coolingcapacity. This higher cost was largely due to the additional safetyequipment that the CO2 system required under the Brazilianoccupational health and safety codes, and the fact that a reasonableamount of the components were specially built and had to be airfreighted from Australia. As CO2 gains in popularity and more CO2equipment becomes available this additional cost will be reduced.
The main factors at stake here are the large reduction in the sizeof the pipe work and insulation respectively. In addition, the CO2evaporators were physically smaller and less expensive due to theincreased specific cooling capacity of the refrigerant. It was foundthat the both R404A and R22 evaporators need approximately 20%more surface area to achieve the same thermal performance as theCO2 evaporators (based on the same temperature differencebetween evaporating and room temperature).
Refrigerant charge in each of the three systems also has aninfluence on the total cost. According to the Table 6 the cascadesystem has 32 kg of CO2 as well as an additional 15 kg of R404A,(32 þ 15 ¼ 47 kg). The other two racks using R404A and R22, theyhave 125 kg and 115 kg, respectively.
In Brazil, the refrigerant HFC-404A has an average cost in 2011 of$35 (thirty five dollars) per kg, the HCFC-22 costs $13 (thirteendollars) per kg, while CO2 has a cost of $ $2.0 (two dollars) per kg.The CO2/R404A cascade system has an advantage over the R404Asystem of the $3786 and for the R22 system of $906. It is importantto observe that the price of R22 in Brazil will increase sinceaccording to the Montreal Protocol the production and consump-tion will be frozen in 2013.
Fig. 4 shows the comparison of each tested system. This analysisshows the total charge of refrigerant as well as the cost of pipes and
Table 6Total of refrigerant charge used in each rack.
Refrigerationrack
CO2/R404A(subcritical rack)
R404A rack R22 rack
Total refrigerantcharge
CO2 e32 kgR404A e 15 kg
R404A e 125 kg R22 e 115 kg
Table 7Total power consumption of the usage data.
Power consumption per year CO2 system [kWh](compressor with frequency inverter; LT evaporator with EEV)
103.234
Power consumption per year R404A system [kWh](compressor with frequency inverter; evaporators with EEV’s)
126.295
Power consumption per year R22 system [kWh](compressor with frequency inverter; evaporators with EEV’s)
117.435
Difference in percentage [%] e CO2 vs. R404A; CO2 vs. R22 22.33 (R404A);13.75 (R22)
Power consumption per year CO2 system [kWh](compressor with frequency inverter; LT evaporator with EEV)
103.234
Power consumption per year R404A system [kWh](compressor with frequency inverter; evaporators with TEV’s)
128.701
Power consumption per year R22 system [kWh](compressor with frequency inverter; evaporators with TEV’s)
119.212
Difference in percentage [%] e CO2 vs. R404A; CO2 vs. R22 24.67 (R404A);15.47 (R22)
Fig. 4. Comparison between the three racks designs.
A. da Silva et al. / Applied Thermal Engineering 41 (2012) 30e35 35
refrigerant. It is important to observe that the direct impact of theGWP (Global Warming Potential) obtained for the R404A rack isalmost 10 times higher in comparison with the R744/R404A rack.
5. Conclusion
This comparison showed high performance and environmen-tally friendly process can be applied to reduce the effects of directand indirect of the global warming, achieving long term costreduction of the equipment.
Clearly, there are numerous advantages, which will ensure thatcarbon dioxide cascade systems have a place in refrigeration
systems. Many advantages of CO2 system in relation to R404A andR22 can be listed, such as: (i) Reduction of the electric energyconsumption (in this case it can varies between 13 and 24%); (ii)Low compression ratio and increase of the useful life of the CO2compressor; (iii) High CO2 density and high pressure in the lowpressure stage; (iv) Reduction of CO2 piping diameter sizes; (v)Reduction of CO2 refrigerant charge; (vi) Lowprice of CO2 purchase;(vii) Higher enthalpy, degree of liquid subcooling and coolingcapacity; (viii) Low GWP and less carbon taxes (CO2); (ix) Smallvolumetric displacement and smaller sized CO2 compressors; (x)Smaller refrigeration rack, compact installation and lowercompressor numbers; (xi) Smaller and efficient evaporator coils;(xii) Reduced installation and lower maintenance costs.
Due to the rapidly changing cost of refrigerants and the expec-ted reduction in the cost of CO2 compatible components and takingin account the high volatility of the energy cost around the world, itwill be possible to verify the increase of the new installations usingCO2 as refrigerant.
Acknowledgements
The authors gratefully acknowledge all support, technicalassistance and research materials, which attributed to this inves-tigation by BITZER Brazil, BITZER Australia, Carel Brazil, Carel Italyand FAPEMIG.
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