HFC134a binary mixtures working as a drop-in of HFC134a in a domestic refrigerator

Accepted Manuscript Title: Comparative performance analysis of HFO1234ze/ HFC134a binary mixtures working as a drop-in of HFC134a in a domestic refrigerator Author: C. Aprea, A. Greco, A. Maiorino PII: DOI: Reference:

S0140-7007(17)30280-3 http://dx.doi.org/doi: 10.1016/j.ijrefrig.2017.07.001 JIJR 3701

To appear in:

International Journal of Refrigeration

Received date: Revised date: Accepted date:

13-3-2017 29-6-2017 2-7-2017

Please cite this article as: C. Aprea, A. Greco, A. Maiorino, Comparative performance analysis of HFO1234ze/ HFC134a binary mixtures working as a drop-in of HFC134a in a domestic refrigerator, International Journal of Refrigeration (2017), http://dx.doi.org/doi: 10.1016/j.ijrefrig.2017.07.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Comparative performance analysis of HFO1234ze/ HFC134a binary mixtures working as a drop-in of HFC134a in a domestic refrigerator

C. Aprea1, A. Greco2*, A. Maiorino1 1

Department of Industrial Engineering, University of Salerno, Via Giovanni Paolo II 132, 84084, Fisciano (SA), Italy

2

Department of Industrial Engineering, University of Naples Federico II, P.le Tecchio 80, 80125, Napoli, Italy

* Corresponding author: Tel. +39 0817282289; e-mail: [email protected] Research Highlights 

Substitution of HFC134a in a in a household refrigerator.



A new generation of low GWP refrigerant fluids: the Hydrofluoroolefins (HFOs)



HFO1234ze/HFC134a mixure (90/10 % weight)

as drop-in substitute of

HFC134a. 

The mixture ensures an energy saving of 14.1% on HFC134a and of 8.92 % on pure HFO1234ze.

Abstract The aim of the investigation has been to register and to evaluate the energetic performances of HFO1234ze binary mixtures with HFC134a, working as a drop-in refrigerant in a domestic refrigerator. A number of different tests have been conducted in order to establish, firstly, the optimal charge through pull-down tests and, once found, to evaluate energy consumptions during 24h tests. The experimental investigation follows the prescriptions of the UNI-EN-ISO 15502. The results collected demonstrate that a binary mixture HFC134a/HFO1234ze (10/90% weight) is characterized by a lower environmental impact in terms of global warming despite employing HFC134a. Indeed, both the indirect and the direct contribution to global warming are reduced. The direct contribution depends on the GWP of the refrigerant fluid that for the mixture is lower than 150 according to UE regulation 517/2014. The indirect

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contribution depends on the energy consumptions and the energy saving with HFC134a/HFO1234ze mixture is around 14%.

Keywords: HFC134a, HFO1234ze, binary mixtures, Drop-in refrigerants, Domestic Refrigerator, Energy Saving.

Nomenclature C E GWP h LFL N.A. ODP Pe p t T

specific heat electrical energy consumptions global warming potential enthalpy lower flammability limit Non Available Ozone Depletion Potential electrical power absorbed pressure of the refrigerant time temperature

[J kg-1 K-1] [Wh] [kJ kg-1] [% vol]

[W] [bar] [s] [°C]

Greek Symbols duty cycle

[%]

Subscripts 1y air c cond dis ev f H24 i o ON OFF p pd r ref suc sor v

along 1 year of air cabinet condensation, condenser discharge of the compressor evaporator at freezer along 1-day at inlet at outlet phase of working of the compressor phase of stop of the compressor constant pressure during the pull-down test at refrigerator of refrigerant suction of the compressor sorround constant volume

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1.

Introduction

The energy consumption due to industrial and domestic refrigeration is a highly topical issue since refrigeration and air conditioning cover almost about 20% of the whole worldwide energy consumptions. At the beginning of Vapour Compression Plants (VCP) diffusion, the benchmark refrigerant utilised were CFCs and HCFCs, forbidden lately by the Montreal Protocol (Montreal Protocol, 1987) since they reveal themselves to be ozone-depleting substances (Aprea et al., 1998; Greco et al., 1997; Llopis et al., 2015a; 2015b). Over time they have followed periodical meetings among the Parties to the Montreal Protocol. Since 2000 the usage of HCFCs in new refrigerating systems was forbidden, letting HFCs the only fluorinated refrigerants allowed because of their zero ODP characteristic. Since 2009, each meeting related to Montreal Protocol, initially dedicated to the phase-out of the substances depleting the stratospheric ozone layer, namely CFCs and HCFCs, had been led to conflicting exchanges on high GWP (Global Warming Potential) HFCs which replace CFCs and HCFCs most of the time. The 28th Meeting of the Parties (MOP28) (28th Meeting, 2016) to the Montreal Protocol, which was held in Kigali, Rwanda, from October 10 to 14, 2016, led to an international agreement on the phase-down of the production and consumption of HFCs. It represents a milestone agreement. As a matter of fact, the A2 countries (the “developed” countries) must reduce their production and consumption of HFCs from 2019, where a -10% is expected, until 2036, where the reduction will have to be of around 85%. The A5 zone (“developing” countries) are called upon to reduce HFCs consumption from 2024 in freezers to 2047 with a 80% drop-in. Domestic systems give one of the main contributors in refrigeration energy consumption. Most of them use HFC134a (GWP = 1430) as a refrigerant until the Kyoto Protocol (Kyoto Protocol, 1997) and, consequently the UE regulation 517/2014 (EU regulation, 2014) prescribed the phasing-out of all the refrigerants whose GWP is greater than 150. The above described general frameworks led the scientific community to study and apply (Aprea et al., 2012; 2013; Palm, 2008) resolutions with environmentally friendly gases, with small GWP and zero ODP. One of the most focused classes of new generation refrigerants is Hydrofluoroolefins (HFO) (Brown, 2009), descending of olefins rather than alkanes (paraffins) known as unsaturated HFCs, with environmentally friendly behaviour and quite low costs. Two well-known and promising HFOs are HFO1234yf and HFO1234ze (Akasaka 2011; Akasaka et al., 2014; Lai 2014a; 2014b; Mota-Babiloni et al., 2016; Tanaka et al., 2010). Such refrigerants present zero ODP and very small GWPs (Fukuda et al., 2016; Mc Linden et al., 2016; Sethi et al., 2016) which ensures a very brief duration once dispersed in the atmosphere; they are also good in miscibility (Akram et al., 2014; Fortkamp et al., 2015;

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Sedrez et al. 2015; Sun et al., 2014) with Polyolester and Mineral oil. The nowadays state of the art reveals that HFOs have been tested as drop-in replacement of domestic refrigerators already working with HFC134a. Therefore many papers have been published in order to report the related results (In et al., 2014; Jankovic et al. 2015; Molés et al. 2014; MotaBabiloni et al., 2014; Navarro-Esbrì et al., 2013; Ozgur, 2013; Ozgur et al., 2014; Yataganbaba et. al., 2015). In our earlier works (Aprea et al., 2016a; 2016b) we have tested HFO1234yf through an experimental apparatus, as a drop-in replacement of HFC134a in a domestic refrigerator. The results for HFO1234yf revealed that it could fit well the substitution, even if it carries some disadvantages like the high electric power absorbed by the compressor (+18% than HFC134a) together with its flammability (ASHRAE Safety Classification A2L) and its huge costs (around 200 €/kg). HFO1234ze exhibits zero ODP and an extremely low global warming potential which ensures a shorter life cycle in the atmosphere. HFO1234ze can be considered a near drop-in replacement of HFC134a and it can be used in existing equipment design with minimal changes. HFO1234ze is a mildly flammable refrigerant that belongs to A2L safety classification. Nevertheless, it is non flammable at room temperature (ANSI/ASHRAE, 2001; Kondo et al., 2014; Yang et al., 2015). The cost of this HFO is significantly lower than that of HFO1234yf (comparable with the cost of HFC134a, around 28€/kg). In this paper also a HFO1234ze mixture with HFC134a has been tested, in an experimental apparatus. The mixture HFC134a/HFO1234ze (10/90%w) is at the optimal composition in order to ensure a GWP smaller than 150 (as prescribed by the UE 517/2014) and the best affordability. A number of different tests have been conducted in order to establish, firstly, the optimal charge through pull-down tests and, once found, to evaluate energy consumption during 24h tests. The experimental investigation follows the prescriptions of the UNI-EN-ISO 15502 (2005).

2. HFO1234ze-HFC134a binary mixture HFO1234ze belongs to the fourth generation of refrigerants, the Hydrofluoroolefins (HFO), unsaturated HFCs, descending of olefins. Considering the UE 517/2014 normative, which prescribes to employ refrigerants GWP smaller than 150, starting from January 1st 2015, since GWP of HFO1234ze and with HFC134a are 6 and 1430, respectively, the HFO1234zeHFC134a mixture has been obtained with particular shrewdness toward the mixing ratio. In particular, it has been determined the maximum mixing ratio of the binary mixture employable as domestic refrigerant whose GWP fulfils the normative. Therefore the maximum percentage of HFC134a, avoided is given by:

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(1) As a result, the maximum

resulting is 10.11%. Therefore the binary mixture

considered is composed by 90% of HFO1234ze and 10% of HFC134a. In Table 1, it is reported a short comparison between the characteristics of HFC134a, HFO1234ze and their binary mixture. The thermodynamic properties of the fluids studied in the present paper are evaluated with the computer Program Refprop 9.1 (Lemmon et al., 2010).

The above-mentioned mixture has very similar properties to HFC134a and therefore can be used as a drop-in in an existing plant. Figure 1 presents the temperature glide of the mixture as a function of HFC134a percentage varying the pressure at typical evaporating pressures (in the range 0.50-3.0bar). The Figure clearly shows that the glide never exceed 1°C at the evaporator.

Figure 2 reports the temperature glide of the mixture as a function of HFC134a percentage varying the pressure at typical condensing pressures (in the range 8.0 – 16 bar). It is evident that in both the condenser and the evaporator the temperature glide never exceed 1°C. The objective of the present paper is to explore the possibility of using a mixture of HFO1234ze and HFC134a as a drop-in substitute of HFC134a in a domestic commercial refrigerator. To this aim, a commercial device built for working with HFC134a has been instrumented.

3. Experimental setup The schematic of the experimental setup of the single evaporator HCF134a domestic refrigerator (with a total volume of 473 l) is reported in Figure 3. The experimental apparatus considered for testing the above mentioned binary mixture is composed by: an hermetic reciprocating compressor, a forced air cooled condenser, a capillary tube and an evaporator operating in forced convection. The evaporator is placed in the freezer and an air distribution system connects the refrigerator to the freezer. A damper valve, moved using a thermostatic mechanical drive, controls the amount of air delivered to the refrigerator compartment. The capillary tube is wrapped for a good portion of its length (>90%) around the suction tube of the compressor. In this way, the refrigerant at the evaporator outlet cools the refrigerant that is laminated. This leads to an increase of the

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enthalpy variation at the evaporator together with an addition overheating of the refrigerant at the compressor inlet.

The scheme is fitted with an adaptive defrost control system that lies in electric resistors arranged in the proximity of the evaporator. The insulation of the entire pipes of the plant is ensured using a 25 mm thick flexible tube. The location of all the sensors of the experimental plant is shown in Fig.3. Temperature measurements have been carried out by seven PT100 thermo-resistances (accuracy ± 0.15 K) placed in the circuit. The four wires thermo-resistances have been located outside the pipe, with a layer of heat transfer compound (aluminium oxide plus silicon) to offer a better thermal contact. Pressure measurements have been carried out using two piezoelectric absolute pressure gauge (accuracy ± 0.2%) placed at the inlet and the outlet of the compressor. An energy meter measured both the electric energy and the electric power absorbed by the refrigerator during the tests (accuracy ±1%). A thermo-hygrometer monitored the temperature and relative humidity of the air in the room test (accuracy ± 0.15°C, ±1%). To evaluate the refrigerant charge of the plant, an electronic balance was used with an accuracy of ±0.1g. According to Moffat (Moffat 1988) the uncertainty on the mixture mass fraction is + 1%. Each sensor was connected to a 32-bit A/D acquisition system attached to a personal computer that allows a sample rate up to 10 kHz. Each sample was checked against the corresponding mean value and it was rejected if it did not lay within the fixed range. If more than 5% of the samples were rejected, the whole test is discarded. Each test was iterated three times, in order to check reproducibility. Frigocheck 2.0, a virtual instrument developed in Labview area, has been utilized for realtime monitoring of pressure and temperature evolutions in the whole domestic experimental apparatus. With the measured, steady state values of pressure and temperature along the circuit, it is possible to evaluate the refrigerant enthalpy using the computer program RefProp 9.1. For different operating conditions, it was estimated for the enthalpy an accuracy within the range: + 1.10-1.95%.

4. Experimental procedure In this paper the experimental facility, a domestic refrigerator that belongs to the A+ class for energy efficiency, has been equipped to make a comparison between HFC134a and the dropin substitutes: pure HFO1234ze and the mixture HFC134a/HFO1234ze (10/90 % weight). Drop-in experiments have been carried out without any modifications of the set-up.

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All the experimental tests have been conducted according to the UNI-EN-ISO15502. The standard requires 24-hour tests while the refrigerator is in an environment which presents 25°C as average temperature and a relative humidity confined in the 45÷75% range. The freezer set-point has been set to -18 °C. The refrigerator thermostat has been adjusted so as to maintain the temperature at + 5 °C. To operate in accordance with the above standard, it is also necessary that during the 24-hour tests, the refrigerator experiences at least one defrost cycle. As per manufacturer’s recommendation, 100 g of HFC134a has been charged in the experimental plant for conducting baseline tests. Then, the refrigerator was charged with HFO1234ze and the optimal charge has been identified (135 g). With the optimal charge different kind of experimental tests has been performed. Finally, the HFO1234ze was recovered and the experimental plant was charged with different amounts (between 110 and 137 g) of refrigerant mass of the mixture HFC134a/HFO1234ze (10/90 % weight). Two kinds of experimental tests have been carried out: the pull-down and 1-day energy consumption tests. During the pull-down tests the optimal charge has been identified. In 1-day energy consumption tests the average duty cycle  has been evaluated according to the following equation: (2) where tON and tOFF are the time when the compressor has been working (ON) and when the compressor has been kept off (OFF).

5. Results and discussions Pull down time is the time required to reduce the air temperature inside the refrigerator from the ambient condition (25 °C) to the desired freezer and cabinet air temperature of -18 and 5 °C, respectively (according to UNI-EN-ISO15502). The first part of the experimental analysis has been devoted to identifying the optimal charge of HFO1234ze with the pull-down tests. To identify the optimal charge of HFO1234ze, the amount of refrigerant mass has been varied from 95 to 145 g by adding refrigerant into the system in 10 g increments. Whereas, the charge of HCF134a has been fixed at 100g. In Figure 4 the temperature profile of the air inside the freezer (Tair, f) is reported as a function of time in the pull-down tests. It was observed that with HFC134a, the freezer has employed 5592 s to reach the desired Tair,f of -18 °C. As a consequence of the drop-in with HFO1234ze the plant has slightly increased the total pull-down time. In particular, with low HFO refrigerant charge (i.e. 95,105,115,125 g) an increase in pull-time was observed due to insufficient refrigerant quantity. At 135 and

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145 g the times are respectively 5900 and 5997 s, leading to a delay compared to HFC134a, of about 400 s (+ 5.5%).

In Figure 5 is reported the electrical energy consumption (Epd) during the pull-down test for HFC134a and HFO1234ze (with the different refrigerant charges). The Figure clearly shows that increasing the charge of HFO1234ze the reduction of the pull-down time has been accompanied by a considerable reduction of the electrical energy consumption compared to HFC134a. In particular, a refrigerant charge of 135g leads to the maximum reduction of Epd (5%). Therefore, we have identified 135 g as the optimal pure HFO1234ze charge in pulldown tests. To identify the optimal charge of the mixture HFO/HFC, the amount of refrigerant mass has been varied between 100 and 137 g. Whereas, the charge of HFC134a and HFO1234ze has been fixed at 100 and 135 g, respectively. In Figure 6 is reported the freezer air temperature versus time. The figure clearly shows that with 137 g of the HFO/HFC mixture the pull-down time is about 5370 s, whereas with HFC134a and HFO1234ze is 5592 and 5900 s, respectively. Therefore, there is a reduction of the pull-down time of -4% with respect to HFC134a and -9.6% with respect to pure HFO. It should be noted that HFO and HFC134a thermodynamic properties are different. In particular, the saturation pressure of HFO at fixed temperature is always lower than that of HFC134a. Therefore, the compression ratio corresponding to a greater mass of HFO (and of its mixture) is lower than that of HFC134a. With high probability, a lower compression ratio suggests that the compressor operating with the mixture was subjected to a higher volumetric efficiency. The better volumetric efficiency leads to a mass flow rate greater than that obtained with HFC134a. Therefore, a greater refrigerant power is obtained. This leads to a lower time required to reduce the air temperature inside the refrigerator from the ambient condition (25 °C) to the desired freezer temperature of -18°C. With a mixture charge of 100 g there is a significant increase of the pull-down time (+25 % with respect to HFC134a). This is due to an insufficient refrigerant quantity. In Figure 7 is reported the electric power consumption during the ON phase of the compressor in pull down-tests for HFO1234ze, HFC134a, and the mixture with the charge of 137 g. The Figure clearly shows that, due to the higher charge, an higher starting current is required when the plant works with the mixture. This leads to an higher power consumption during the starting. Although the power consumption of the plant working with the mixture is slightly higher that that of HFC134a, the reduction of the pull down time leads to a lower energy consumption. In Figure 8 is reported the electrical energy consumption during the pull down tests.

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The Figure clearly shows that with 137 g charge of HFC134a/HFO1234ze the reduction of the pull-down time has been accompanied by a reduction of the electrical energy consumption compared to HFC134a and pure HFO (-7 and -1.5 %, respectively). Therefore, a mass of HFC134a/ HFO1234ze mixture equal to 100 g has resulted insufficient for the refrigerator here considered. Consequently, a mass of 137g can be considered the optimal mixture charge and will be used in the 1-day consumption tests. The 1-day consumption tests have been carried out for each refrigerant fluid to characterise the actual operating conditions of the domestic refrigerator. In these tests, according to UNIEN-ISO15502, the refrigerator experiences at least one defrost cycle. In Figures 9,10 and 11 are shown the temperatures in key points of the plant (according to the schematic of Figure 3) in 24h tests of all the refrigerant fluids. Comparing the temperature graphs for the different refrigerant fluids, one can observe that the general trends are very similar. Therefore, a domestic refrigerator working with pure HFO or with the HFC/HFO mixture achieves the same temperature levels of HFC134a in the freezer and the refrigerator cabinet. The temperatures of the mixture all over the plant are always slightly lower than that of both HFC134a and pure HFO. The evaporating temperature of HFC134a exceeds that of the mixture and HFO1234ze within 2.7 and 1.7 K, respectively. Whereas in the condenser, these differences are within 0.3 and 1.3 K, respectively. In the condenser, the refrigerant subcooling of the mixture (3.5 K) is greater than that of HFC134a (0.5 K) but is lower than that of pure HFO (8.1 K). Another important parameter which influences the stability of lubricants and the compressor component is the temperature at the compressor outlet. The above-reported figures reveal that the temperature of the mixture is always lower than that of both HFC134a (-3.5 K) and HFO1234ze (-0.7 K). Therefore a longer compression life can be expected using the mixture as refrigerant fluid. In Figures 12, 13 and 14 are reported the pressures at the compressor inlet and outlet for HFC134a, HFO1234ze and HFC/HFO mixture. It is evident that the mixture pressure values are close to those of HFC134a and are higher than that of pure HFO. Indeed, this depends on the thermodynamic properties of HFO1234ze that at a fixed temperature is characterised by a lower value of the saturation pressure. Figures 15, 16 and 17 report the electric power absorbed during the 1-day tests for the different refrigerant fluids. The peak of electric power in the Figures represents the defrosting phase required by the normative UNI-EN-ISO15502. The mean ON power are 48 W for HFC134a, 47.6 W for HFC/HFO mixture and 45.8 for pure HFO. Therefore, there is a very limited electric power saving using pure HFO or HFC/HFO mixture. Figure 18 reports the yearly ( electric energy consumption for all the refrigerants and the energy saving respect to HFC134a. is recorded over a 24-hours test and is the projection of annual consumptions, calculated as follows:

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(3) It is evident that using HFC/HFO there is a yearly energy saving of 14.1% on HFC134a and of 8.92 % on pure HFO. Therefore the energetic performance of the mixture is better than that of pure HFO. Table 2 summarises the experimental results obtained during the 1-day tests. This Table reports for each refrigerant fluid: the charge, the daily and yearly energy consumption, the average electric power consumption during the ON phase of the compressor, the average ON and OFF time (the time when the compressor has been working and has been kept off), the average duty cycle.

One can observe that the ON time of the mixture is significantly lower than that of both HFC and HFO. Therefore, despite the electric power of the mixture is only slightly lower than that of HFC134a, there is a significant energy saving on the daily and the yearly energy consumption. The presented analysis reveals that both pure HFO1234ze and HFC134a/HFO1234ze mixture can be used as a drop-in of HFC134a in a domestic refrigerator. Their adoption would be at zero cost for the manufacturers since it doesn’t involve any modification to the cooling circuit of the plant designed to operate with HFC134a. Furthermore, a refrigerator working with the mixture provides lower environmental impact despite employing HFC134a. Indeed, both the indirect and the direct contribution to global warming are reduced. The direct contribution depends on the GWP of the refrigerant fluid. The indirect contribution depends on the energy consumptions, and the energy saving with HFC134a /HFO1234ze is around 14%. 6.Conclusions In this paper an experimental analysis has been carried out between HFC134a, pure HFO1234ze, and a binary mixture HFC134a/HFO1234ze (90/10% in weight). The experiments have been conducted in a commercial refrigerator designed for working with HFC134a. The experimental tests have been conducted under sub-topical conditions in accordance with the UNI-EN-ISO15502 standard. Two kinds of tests have been shown: pull down and 1-day energy consumption. From the experimental evidence the following conclusions can be drawn:

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

Both pure HFO1234ze the binary mixture can be considered as a drop in of HFC134a in an existing plant, regarding the temperatures that can be reached in the freezer and the refrigerator compartment.



The plant is designed for working with 100 g of HFC134a. The optimal charge of pure HFO and the mixture are 35 and 37% greater than that of HFC134a, respectively.



The pull down-time of the cycle is reduced using the binary mixture. The reduction is of 4% on HFC134a and 9.6% on pure HFO.



The plant working with pure HFO or with the HFC/HFO mixture achieves the same temperature levels of HFC134a in the freezer and the refrigerator cabinet.



In 1-day tests, the ON time of the compressor for the mixture is significantly lower than that of both HFC (-33) and HFO (-25%).



The average duty cycle obtained with the mixture in 24 hours is 6 and 3.2 % lower than that of HFC134a and pure HFO1234ze, respectively.



After 24 hours of working a 14 and 5.6 % energy savings can be obtained with the mixture and with pure HFO1234ze, respectively.

On

the

basis

of

the

above-mentioned

considerations,

we

can

say

that

HFC134a/HFO1234ze mixture is the best drop-in refrigerant fluid for HFC134a in our experimental plant.

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Moffat, R.J., 1988. Describing the uncertainties in experimental results. Exp. Therm. Fluid Sci. 1, 3–17. doi:10.1016/0894-1777(88)90043-X. Molés, F., Navarro-Esbrì, J., Peris, B., Mota-Babiloni, A., Barragàn-Cervera, Àngel, 2014. Theoretical energy performance evaluation of different single stage vapour compression refrigeration configurations using R1234yf and R1234ze(E) as working fluids. Int. J. Refrig. 44, 141–150. doi:10.1016/j.ijrefrig.2014.04.025 Montreal Protocol on substances that deplete the ozone layer. United Nation Environment Program (UN), New York (NY), USA, 1987. Mota-Babiloni, A., Navarro-Esbrì, J., Barragàn, Àngel, Molés, F., Peris, B., 2014. Drop-in energy performance evaluation of R1234yf and R1234ze(E) in a vapor compression system as HFC134A replacements. Appl. Therm. Eng. 71, 259–265. Mota-Babiloni, A., Navarro-Esbrí, J., Molés, F., Barragán-Cervera, A., Peris, B., Verdù, G., 2016. A review of refrigerant R1234ze(E) recent investigations. Appl. Therm. Eng. 95, 211–222. doi:http://dx.doi.org/10.1016/j.applthermaleng.2015.09.055 Navarro-Esbrí, J., Mendoza-Miranda, J.M., Mota-Babiloni, A., Barragán-Cervera, A., Belman-Flores, J.M., 2013. Experimental analysis of R1234yf as a drop-in replacement for HFC134A in a vapor compression system. Int. J. Refrig. 36, 870–880. Özgür, A.E.. 2013. Theoretical investigation of vapor compression cooling cycle using HFO1234yf and HFO-1234ze.| Journal of the Faculty of Engineering and Architecture of Gazi University, 28 (3), pp. 465-472. Özgür, A.E., Kabul, A., Kizilkan, O. 2014. Exergy analysis of refrigeration systems using an alternative refrigerant (HFO-1234yF) to R-134a. International Journal of Low-Carbon Technologies 9 (1), cts054, pp. 56-62 Palm B Hydrocarbons as refrigerants in small heat pump and refrigeration systems – A review. Int J of Refr 2008;31 4 p.552-563. Righetti, G., Zilio, C., Longo, G. a., 2015. Comparative performance analysis of the low GWP refrigerants HFO1234yf, HFO1234ze(E) and HC600a inside a roll-bond evaporator. Int. J. Refrig. 54, 1–9. doi:10.1016/j.ijrefrig.2015.02.010 Sedrez, P.,C., Barbosa, J.R. Jr., 2015, Relative permittivity of mixtures of HFC134A and R1234yf and polyol ester lubricating oil. Iny. J. Refrig. 49, 141-150. doi: 10.1016/j.ijrefrig.2014.09.019 Sethi, A., Becerra, E.V., Motta, S.Y., 2016. Low GWP HFC134a replacements for small refrigeration (plug-in) applications. Int. J. Refrig. In Press. doi:http://dx.doi.org/10.1016/j.ijrefrig.2016.02.005 Sun, Y., Wang, X., Gong, N., Liu, Z., 2014. Solubility of trans-1,3,3,3-tetrafluoroprop-1-ene (R1234ze(E)) in pentaerythritol tetrapentanoate (PEC5) in the temperature range from 283.15 to 353.15 K. Int. J. Refrig. 48, 114–120. doi:10.1016/j.ijrefrig.2014.09.013 Tanaka, K., Takahashi, G., Higashi, Y., 2010. Measurements of the vapor pressures and p-T properties for trans -1,3,3,3-tetrafluoropropene (HFO-1234ze(E)). J. Chem. Eng. Data 55, 2169–2172. doi:10.1021/je900756g The European Parliament and the Council, 2014. No 517/2014 of the European Parliament and of the Council of 16 April 2014 on fluorinated greenhouse gases and repealing Regulation (EC) No 842/2006 Text with EEA relevance. Off. J. Eur. Union L. Yang, Z., Wu, X., Tian, T., 2015. Flammability of Trans-1, 3, 3, 3-tetrafluoroprop-1-ene and its binary blends. Energy 91, 386–392. doi:10.1016/j.energy.2015.08.037 Yataganbaba, A., Kilicarslan, A., Kurtba, I., 2015. Exergy analysis of R1234yf and R1234ze as HFC134A replacements in a two evaporator vapour compression refrigeration system. Int. J. Refrig. 60, 26–37. doi:10.1016/j.ijrefrig.2015.08.010

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Fig.1 Temperature glide as a function of HFC134a mass fraction varying the evaporating pressure.

Fig.2 Temperature glide as a function of HFC134a mass fraction varying the condensing pressure.

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Fig. 3 A schematic of the experimental plant

Fig. 4 Temperature profiles of the air inside the freezer compartment as a function of the time.

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Fig. 5 Electric energy consumption during the pull-down tests

Fig. 6 Temperature profiles of the air inside the freezer compartment as a function of the time.

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Fig. 7 Power consumption as a function of time

Fig. 8 Electric energy consumption during the pull-down tests

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Figure 9 Temperatures of HFC134a during 1-day tests.

Figure 10 Temperatures of HFO1234ze during 1-day tests.

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Figure 11 Temperatures of HFC134a/ HFO1234ze mixture (10/90% weight) (137 g charge) during 1-day tests.

Figure 12 Pressures at the compressor inlet and outlet in 1-day tests for HFC134a.

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Figure 13 Pressures at the compressor inlet and outlet in 1-day tests for HFO1234ze.

Figure 14 Pressures at the compressor inlet and outlet in 1-day tests for HFC134a/ HFO1234ze (10/90 % weight) with a charge of 137 g.

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Fig. 15 Electric power absorbed by HCF134a during the 1-day test.

Fig. 16 Electric power absorbed by HFO1234ze during the 1-day test.

Fig. 17 Electric power absorbed by HFC134a /HFO1234ze mixture (137 g charge) during the 1-day test.

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Fig. 18 Yearly electric energy consumption and energy saving for the refrigerant fluids.

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Tab. 1 Comparison between HFC134a, HFO1234ze and the mixture. Parameter

HFC134a

HFO1234ze

Critical T [°C]

101.1

79

90%HFO1234ze10%HFC134a 81

Critical p [bar]

40.59

36.32

40.163

Normal boiling point [°C] Density[kg m-3]

-26.0

-20.0

3.67

3.19

-21.4 T = 0.93°C 3.2

-1

-1

870

895

900

-1

-1

Cp [J kg K ]

779

813

818

GWP [kgCO2 kg-1]

1430

6

150

ODP

0

0

0

Molecular Weight

102

114.04

112.836

Safety Class

A1

A2L

N.A.

Cv [J kg K ]

Table 2. Comparison between the different refrigerant fluids

Refrigerant

Charge EH24 (kWh day1) (g)

HFC134a 100 HFO1234ze 136 HFC134a/HFO1234ze 137 (10/90 % weight)

0.79 0.74 0.68

E1y (kWh year-1)

Pel (W)

tON tOFF  (min) (min)

289.40 273.06 248.70

48.0 45.8 47.6

35.63 32.04 24.04

19.83 19.77 20.30

0.64 0.62 0.60

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