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An experimental investigation of the global environmental impact of the R22 retrofit with R422D
Energy 36 (2011) 1161e1170
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An experimental investigation of the global environmental impact of the R22 retrofit with R422D Ciro Aprea, Angelo Maiorino* Department of Mechanical Engineering, University of Salerno, Via Ponte Don Melillo 1, 84084 Fisciano (SA), Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 February 2010 Received in revised form 18 November 2010 Accepted 21 November 2010 Available online 22 December 2010
In recent years a new refrigerant, R422D, has been introduced as substitute of R22 for refrigeration systems. This new fluid is an easy-to-use, non-ozone-depleting HFC refrigerant and, differently from its predecessor (R407C), it is compatible with mineral oil. However, R422D has a very high GWP, and it tends to worsen the efficiency of retrofitted R22 systems. Consequently, even if R422D respects the limits of Montreal Protocol, its global environmental impact could be high. In this paper, we report an experimental analysis in terms of TEWI aimed to identify the global environmental impact of R22 systems retrofitted with R422D. For this purpose, we considered a direct expansion refrigerator for commercial applications and we investigated energy consumption with the temperature of the cold reservoir set to 5, 0, 5, 10 C. The experimental investigation confirmed that the system, when retrofitted with R422D, leads to an increase of TEWI. Therefore an optimization analysis aimed to eco-friendly scenarios was performed. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Experimentation R22 R422D Retrofitting Substitute TEWI
1. Introduction The Montreal Protocol banned ozone-depleting substances (ODSs) as refrigerants in current vapor-compression refrigeration systems. Fluor chemicals were the center of attention, with HCFCs for interim use and hydro fluorocarbons (HFCs) for longer term [1]. The Montreal Protocol sets limits (cap) for the HCFC consumption, defined as production plus imports less exports and specified destruction: in 1996 (freeze at calculated cap), 2004 (65% of cap), 2010 (25%), 2015 (10%), and 2020 (0.5%) with full consumption phase-out by 2030 in non-Article 5 countries [2]. Individual countries adopted different response approaches. Most western and central-European countries accelerated HCFC phase-out, while the majority of other developed countries required phase-out of R-22 (the most widely used refrigerant today) by 2010, and then banned all HCFC use in new equipment by 2020. The schedule for Article 5 countries begins with a freeze of the amount of HCFC in 2013 (based on 2009e2010 production and consumption levels) with declining limits starting in 2015 (90%), 2020 (65%), 2025 (32.5%), and 2030 (2.5%) followed by phase-out in 2040 [2]. Exports from Article 5 countries into non-Article 5 countries are effectively restricted to meet the more stringent non-Article 5 schedules. To
* Corresponding author: Tel.: þ39 089 96 4002; fax: þ39 089 96 4037. E-mail address: [email protected] (A. Maiorino). 0360-5442/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2010.11.032
avoid separate domestic and export products and to exploit newer technologies derived from joint ventures and licensing agreements, some products in Article 5 countries incorporate replacements earlier than required. The response to ozone depletion stands in sharp contrast to the deteriorating situation with climate change [3,4]. The Kyoto Protocol [5], pursuant to the United Nations Framework Convention on Climate Change (UNFCCC), sets binding targets for greenhouse gas (GHG) emissions based on calculated equivalents of carbon dioxide, methane, nitrous oxide, HFCs, perfluorocarbons (PFCs), and sulfur hexafluoride [5]. It does not address ODSs covered by the Montreal Protocol, although some are also very potent GHGs. National laws and regulations to implement the Kyoto Protocol differ, but they typically prohibit avoidable releases of HFC and PFC refrigerants and in some countries also control or tax their use. More recent measures (either adopted or proposed) at regional, national, state, and municipal levels are more stringent. These restrictions are forcing the shift to a fourth generation of refrigerants compliant with both ODP and GWP regulations [6]. In the field of the mobile refrigeration systems, the European Parliament already set F-Gases phase-out regulation [7] that bans the use of refrigerants having GWPs in excess of 150. Such regulation will be in effect from 2011 [7,8]. The EU Parliament rejected recommended measures banning HFCs as aerosol propellants by 2006, as foam blowing agents by 2009, and as refrigerants in stationery air conditioners and refrigeration by 2010. However, a revision of this decision is expected in 2011 [6].
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_ W
Nomenclature
Symbols COP E GWP h l m _ m ND ODP P r T TEWI
power (W)
Greek symbols D difference 3 efficiency
coefficient of performance (e) energy consumption (kWh) global warming impact (kgCO2 kgrefrigerant) enthalpy (kJ kg1) leakage rate per year (% yr1) refrigerant charge (kg) mass flow rate (kg s1) number of days (e) ozone depletion potential (e) Pressure (Pa) generation emission (kgCO2 kWh1) temperature (K) total equivalent warming impact (kgCO2)
Subscripts 100 horizon time equal to 100 years cold air inner to cold store D daily el electrical EV evaporator hot external air ambient i i-th in input m monthly out output
A conventional vapor-compression refrigeration system employs compressors, fans, and possibly pumps to shift heat either out of a cooled space or into a heated space. The system is responsible for direct Greenhouse emissions, such as leakage of the refrigerants into the environment, and indirect emissions generated by power grid consumption. If the refrigerant leaks out of the system during operation, is lost during maintenance, or is not recovered when the system is decommissioned, it contributes to global warming. The concept of Total Equivalent Warming Impact (TEWI) was developed to combine the global warming effects due to both lifetime refrigerant emissions (direct effect), and carbon dioxide emissions due to energy use over the lifetime of the system (indirect effect) [9]. As aforementioned, R22 (Table 1) is the most widely used refrigerant today for commercial, domestic and industrial applications, and its phase-out will impact a large number of plants in the world. Therefore retrofitting these systems would alleviate the R22 phaseout problem. This choice could be cheaper than installation of new plants, especially for supermarkets, data centers, factories and hospitals. Refrigerant replacement candidates have been evaluated for environmental and safety requirements, and compatibility with lubricant oil, filters, and sealing. In order to establish the best substitute in a specified system, it is necessary to estimate its energetic performance after refrigerant replacement. In the recent years, many teams researched in the development and characterization of refrigerants with higher energetic efficiency, and have specifically investigated the energetic performance of substitutes for R22 [11,12]. During this transition period, many industrial and commercial applications Table 1 Refrigerants data. R22
R422D
R407C
Composition (% wt)
CHClF2
ODP GWP100 (in accordance with [10] [23]) Bubble point temperature, 100 kPa ( C) Critical temperature ( C) Saturated vapor pressure at 40 C (kPa) Glide temperature at 40 C vapor saturation pressure ( C) Glide temperature at 0 C vapor saturation pressure ( C)
0.05 1700
31.5% R134a 65.1% R125 3.4% R600a 0 2230
23% R32 25% R125 52% R134A 0 1600
40.8
43.5
43.9
96.1 1533.6
79.6 1555.0
86.0 1749.0
0
2.46
4.90
0
3.56
6.12
used R407C (Table 1) to retrofit R22. Even if R407C has thermophysical properties similar to those of R22 and it is non-flammable and non-toxic, it is incompatible with mineral or alkyl-benzene oil. Consequently, a R22 system retrofitted with R407C requires the adoption of polyester oil, a difficult and expensive conversion. Furthermore experimental tests carried out with R407C showed a reduction in the energetic performances when compared to R22 [13]. Recent additions to the aforementioned alternative refrigerants for R22 are R422A, R422B, R422C and R422D. The U.S. environment protection agency reported that such alternative refrigerants could be used for household and light commercial air conditioning applications. In particular, R422D (Table 1) is an easy-to-install, non-ozonedepleting HFC refrigerant originally designed to replace R-22 in existing direct expansion water chiller systems. It can also be used in residential and commercial air conditioning and medium-low temperature (10 to 5 C) refrigeration systems. Minor equipment modifications (replacement of the filter drier and elastomeric seals/ gaskets that are exposed to refrigerant, refill of oil if required) or components tuning may be required in some applications. It is also compatible with mineral oil and there is no need to replace it with synthetic oil [14]. Field experience has shown that R422D provides performance that meets customer requirements in most retrofitted systems. It provides similar cooling capacity to R22 and it is capable to operate at significantly lower compressor discharge temperature [14]. In this scenario, it seems sensitive to investigate what is the actual impact of R422D on the environment, when it is employed in retrofitting R22 devices. It is well known that the GWP of R422D is higher than the GWP of R22 [10,15], but not much is known about the energy efficiency of R22 systems retrofitted by R422D. Arora and Sachdev [16] performed a theoretical energetic and exergetic analysis of R422 cycles and they found out that the energy performance of these refrigerants could be lower than that of R22. However, the result of a bibliographic research showed that no experimental investigation of the energetic performances of an actual refrigerator operating with R422 series refrigerants is available in literature. In this paper, we report an experimental TEWI analysis with the objective of identifying the environmental impact of a R22 system retrofitted with R422D. For this purpose, a comparison of the energy consumptions of R22 and R422D for a direct expansion refrigerator for commercial use is proposed. The experimental investigation has been carried out for a range of conditions (5 to 10 C): medium temperature refrigeration for meat, fish, and dairy cases and high temperature refrigeration for air conditioning and cooling of preparation rooms.
C. Aprea, A. Maiorino / Energy 36 (2011) 1161e1170
2. The TEWI analysis The concept of total equivalent warming impacts (TEWI) was developed to combine the effects of the direct emissions of refrigerants with the indirect effects of energy consumption due to the combustion of fossil fuels for power generation. TEWI provides a measure of the environmental impact of greenhouse gases from operation, service and end-of-life disposal of the equipment. TEWI is the sum of the direct contribution of greenhouse gases used to make or operate the systems and the indirect contribution of carbon dioxide emissions resulting from the energy required to run the systems over their normal lifetimes [17]. In order to calculate the TEWI for refrigeration systems, Coulbourne and Suen [18] proposed the following equation:
TEWI ¼ direct contribution þ indirect contribution ¼ ðm l Sl GWP100 Þ þ ðE Sl rÞ
(1)
Refrigerant charge (m) is the total amount of refrigerant introduced in the refrigeration system. It depends both on the dimensions of the plant and on the kind of refrigerant. Usually, manufacturers and operators define the correct charge as the amount of refrigerant necessary to guarantee that the fluid get the evaporator adequately wetted. Non-hermetic units, designed for servicing, are subject to leaking into the environment (l). Under the restrictions of the protocol of Kyoto, the new obligations introduced by F-Gases regulation help reducing the leakage rate of refrigerant. The European Parliament has made mandatory the recovery of refrigerant during plant servicing and at end of plant life for all stationary equipment. It was also imposed that adequately trained staff carries out installation, servicing and leakage checking. The leakage rate per year does not include the disposal percentage but only the accidental percentage due to operating conditions. Usually the service life (Sl) of a refrigeration system is based on the operation time. In this experimental investigation the service life is based on a reference period. The energy consumed by the systems (E), either in the form of electricity or combustion of fossil fuel, implies a release in the environment of an amount of carbon dioxide, based on the generation emission coefficient (r). Some indicative average carbon dioxide release levels for varies countries around the world are available in literature [19e22]. GWP expresses the extent to which a greenhouse gas directly contributes to global warming. The values depend on the quantity of gas emitted, the elapsed time before it is purged from the atmosphere, and the infrared energy absorption properties of the gas. GWP100 is based on a time horizon of 100 years and is referenced to the unitary value of CO2. The uncertainty of the TEWI has been calculated applying the error propagation theory to Eq. (1) and considering the uncertainty of the energy meter and of the balance (Table 2). Sand et al. [17] suggested that a minimum of 20% uncertainty exists for the GWP values assigned to refrigerants by the Intergovernmental Panel on Climate Change (IPCC). These
Table 2 Transducers specifications. Transducers
Range
Uncertainty
Coriolis effect flow meter RTD 100 4 wires Piezoelectric absolute pressure gauge
0/2 kg min1 100/500 C 1e10 bar; 1e30 bar 0e3 kW 0e1 MWh 0e100 kg
0.2% 0.15 C 0.2% 0.5% F.S 0.2% 1% 0.2%
Wattmeter Energy meter Balance
1163
uncertainties, when combined with other estimates and assumptions of the analysis lead to a TEWI uncertainty of 10%. Because of the error in the estimation, if the TEWI differences are lower than 10%, the technology that shows lower energy use should be favored; if the TEWI differences are higher than 10%, the technology that shows lower TEWI should be favored. 3. Investigation In order to obtain a TEWI analysis for refrigeration systems it is necessary to have values for every variable expressed in Eq. (1). For this purpose, we carried out an experimental investigation for both R22 and R422D to calculate the refrigerant charge and the energy consumption values, while we used literature data as source for the remaining unknowns. In addition, we investigated the energetic performance of the plant, with the purpose of finding ways of reducing the environmental indirect impact with the adoption of R422D. Then a sensitivity analysis for the TEWI difference between the refrigerants was performed. 3.1. Experimental facility The experimental vapor-compression refrigeration plant is shown in Fig. 1. It consists of a semi-hermetic reciprocating compressor, an air condenser followed by a liquid receiver, a R22 mechanic thermostatic expansion valve feeding an air-cooled evaporator inside the cold storage. The compressor, as specified by the manufacturer, can operate with the fluid R22 and it is lubricated with mineral oil. With an evaporation temperature range between 20 and 10 C, a 35 C condensing temperature, and utilizing R22 at the nominal frequency of 50 Hz, the compressor refrigerating capacity is in the range of 1.4e4.4 kW. A blower drives the airflow through a thermally insulated channel where some electrical resistances are installed with the objective of controlling the temperature of the airflow across the condenser. In order to control the temperature of the airflow, the electrical resistances are energized by a PID controller. The cooling load in the cold reservoir is simulated by additional electrical heaters wired to a voltage regulator. To keep the air temperature reasonably constant in the cold reservoir, an on/off refrigeration control system has been implemented. This is done by turning on/off the compressor and the fan of the heat exchangers. Table 2 reports the transducers specifications used (Coriolis effect mass flow meter, RTD 100 4 wires thermo-resistances, piezoelectric absolute pressure gauge, wattmeter). The thermo-resistances are located outside the pipe, with a layer of heat transfer compound (aluminum oxide plus silicon) placed between the sensor and the pipe in order to provide good thermal contact. The whole pipe is covered with 25 mm thick flexible insulation. The system of temperature measurement was calibrated against a sensor positioned inside a similarly insulated pipe. For the test conditions, the difference between the two measurements has been always less than 0.3 C. The wattmeter measures the electrical power absorbed by the compressor, the blowers and all additional components required for operation of the device. The energy consumption of the refrigeration system is measured by an energy meter. The test apparatus is equipped with 32 bit A/D converter acquisition cards linked to a personal computer that allows a high sampling rate (10 kHz). 3.2. Experimental procedure We started the experimental investigation by analyzing the operation of the plant with R22. Subsequently, we retrofitted the refrigeration system with R422D according with [14]. During the retrofitting operations, we changed the factory setting of the R22
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Fig. 1. Sketch of the experimental plant.
thermostatic expansion valve in order to keep the operating superheat value for R422D in the same range used for R22, which was performed by turning the setting adjustment screw of the valve. For both refrigerants, we used the same experimental procedure. Firstly, we proceeded with identifying the refrigerant charge necessary to guarantee that the fluid adequately wets the evaporator. For this purpose, we set the temperature of the air blown through the condenser to 24 C and the air in the cold reservoir to 5 C, while the cooling load was kept at 1000 W. We evacuated the circuit, and then we proceeded with introducing 0.40 kg of gas in the refrigerant circuit while the system was shut off to prevent the electrical motor of the compressor from overheating. Subsequently, we turned on the plant and the electrical heaters inside the cold storage. During the operation of the system, we monitored the refrigerant in the superheated region, defined as the difference between the temperature at end of the evaporating process (considering the pressure drop into the evaporator) and temperature at the compressor inlet. Additional 0.10 kg of refrigerant was introduced until, under steady state conditions, the operating superheat was greater than 10 C. Once the system was charged to the desired value (Table 3), we proceeded with the evaluation of the energy consumption due to one year of operation (storage investigation). In particular, we investigated four different cold reservoir temperatures (Tc): 5, 0, 5, and 10 C. We considered as external air temperature reference the values reported in Table 4, which represent typical conditions in Milan (Italy). Since
this table provides the daily change of external air temperature for each month, we planned 12 experiments each 24 h long. Data in Table 4 were used for the PID controller, which modulates the voltage supply to the electrical resistances varying the temperature of the air intake. In order to evaluate the energetic performance additional experiments analyzing the behavior of the plant under steady state conditions (performance investigation). For this purpose, we planned 4 experiments with the same cold temperature Tc of 5, 0, 5, and 10 C. During the experiments, we shunted the refrigeration control and we set the temperature of the air blown through the condenser to a reference value of 21 C, which the mean value from Table 4. Usually, the start-up time was about one hour, and steady state conditions were assumed to be reached when the deviations of all controlled variables were less than 0.5 C for temperatures and Table 3 Parameters for the Eq. (1). Parameter
Value
Note
Sl r
1 yr 0.59
l
10%
mR22 mR422D
2.50 kg 2.30 kg
See text In accordance with [21,24] In accordance with [22,18] Experimental result Experimental result
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Table 4 Change of the external air temperature (in C) for Milan (Italy). Hours
January
February
March
April
May
June
July
August
September
October
November
December
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
11.4 10.8 10.2 9.8 9.4 9.3 9.5 10.1 11.2 12.8 14.6 16.6 18.5 20.1 20.9 21.3 20.9 20.1 18.8 17.2 15.6 14.3 13.1 12.2
12.7 12.1 11.5 11.1 10.7 10.6 10.8 11.4 12.5 14.1 15.9 17.9 19.8 21.3 22.2 22.6 22.2 21.4 20.1 18.5 16.9 15.6 14.4 13.5
15.7 15.9 14.5 14 13.7 13.5 13.8 14.4 15.5 17 18.8 20.9 22.8 24.2 25.2 25.5 25.2 24.3 23 21.5 19.9 18.6 17.4 16.4
17.5 17.8 16.3 15.9 15.5 15.4 15.6 16.2 17.3 18.9 20.7 22.7 24.6 26.1 27 27.4 27 26.2 24.9 23.3 21.7 20.4 19.2 18.3
19.9 20.2 18.7 18.3 17.9 17.8 18 18.6 19.7 21.3 23.1 25.1 27 28.5 29.4 29.8 29.4 28.6 27.3 25.7 24.1 22.8 21.6 20.7
21.6 21.9 20.4 19.9 19.6 19.4 19.7 20.3 21.4 22.9 24.7 26.8 28.7 30.1 31.1 31.4 31.1 30.2 28.9 27.4 25.8 24.6 23.3 22.3
22.2 21.6 21 20.5 20.1 20 20.2 20.8 21.9 23.5 25.3 27.3 29.2 30.7 31.6 32 31.6 30.8 29.5 27.9 26.4 25 23.8 22.9
22.35 21.75 21.15 20.65 20.25 20.15 20.35 20.95 22.05 23.65 25.45 27.45 29.35 30.85 31.75 32.15 31.75 30.95 29.65 28.05 26.55 25.15 23.95 23.05
21 20.4 19.8 19.4 19 18.9 19.1 19.7 20.8 22.4 24.2 26.2 28.1 29.6 30.5 30.9 30.5 29.7 28.4 26.4 25.2 23.9 22.7 21.8
18.6 18 17.4 17 16.6 16.5 16.7 17.3 18.4 20 21.8 23.8 25.7 27.2 28.1 28.5 28.1 27.3 26 24.4 22.8 21.5 20.3 19.4
15.1 14.5 13.9 13.5 13.1 13 13.2 13.8 14.9 16.5 18.3 20.3 22.2 23.7 24.6 25 24.6 23.8 22.5 20.9 19.3 18 16.8 15.9
12.2 11.6 11 10.5 10.1 10 10.3 10.9 11.9 13.5 15.3 17.3 19.3 20.7 21.7 22 21.7 20.8 19.5 17.9 16.4 15.1 13.9 12.9
15 kPa for pressures. This was evaluated in the following manner. Data logging was performed with 0.5 Hz acquisition frequency for 60 s. Then the 120 samples recorded were averaged for each channel. After 180 s, three mean values were obtained and compared for steady state using the above criteria (DT 0.5 C and Dp 15 kPa). 3.3. Data elaboration We developed a software application called FrigoCheck v.1.0 able to show in real time the coefficient of performance, the entropy and the enthalpy values of all points of the thermodynamic cycle. In addition, it shows the whole cycle on peh diagram and it evaluates the steady state condition. Since we measured the daily energy consumption for each month (Ed,i), we calculated the monthly energy consumption (Em,i) by means of the following equation
Em;i ¼ Ed;i NDi
(2)
where the subscript i refers to the generic month and ND is equal to the number of days for the ith month. We obtained yearlong energy consumption (E) by summing the monthly energy consumptions (Em,i):
E ¼
X
Em;i
(3)
i
The uncertainty of the yearlong energy consumption is equal to 1% (Table 2). To evaluate the TEWI, we considered the service life, the emission generation, the GWP, and the leakage rate reported both in Tables 1 and 3. The reference period for the service life was equal to one year. Under steady state conditions, the overall efficiency performance of the plant is expressed by the COP, calculated as the ratio between the refrigeration capacity and the electrical power supplied to the plant (compressor, blowers and accessories):
_ hout;EV hin;EV m COP ¼ _ W
(4)
el
A COP accuracy analysis has been performed according to [25], resulting in 2.5%. In order to identify the efficiency of the plant, we considered the following ratio:
3¼
COP 1=½ðTex =Tcold Þ 1
(5)
Table 5 Daily energy consumption measured. Daily energy consumption (Ed,i) 5 C
January February March April May June July August September October November December
0 C
þ5 C
10 C
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
4848 5017 5430 5701 6075 6348 6436 6461 6246 5864 5346 4944
5080 5280 5772 6098 6551 6884 6991 7022 6759 6295 5671 5193
3051 3166 3448 3635 3893 4082 4143 4161 4011 3747 3390 3116
3392 3529 3868 4093 4405 4636 4710 4731 4549 4229 3798 3470
1800 1873 2053 2173 2339 2461 2500 2512 2415 2245 2016 1842
2097 2188 2416 2567 2779 2937 2987 3002 2878 2660 2369 2149
1039 1086 1202 1279 1387 1468 1494 1501 1437 1326 1178 1066
1334 1395 1547 1648 1791 1897 1931 1941 1857 1710 1516 1369
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Table 6 Monthly energy consumption calculated by means of the Eq. (2). Monthly energy consumption (Em,i) 5 C
January February March April May June July August September October November December
0 C
þ5 C
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
150,295 140,481 168,338 171,040 188,323 190,455 199,505 200,298 187,370 181,794 160,377 153,268
157,473 147,833 178,940 182,945 203,066 206,521 216,713 217,685 202,755 195,150 170,141 160,987
94,568 88,637 106,893 109,037 120,670 122,471 128,433 128,984 120,329 116,157 101,711 96,591
105,144 98,814 119,904 122,777 136,553 139,068 145,995 146,668 136,463 131,084 113,953 107,557
55,809 52,451 63,650 65,177 72,494 73,833 77,511 77,868 72,449 69,589 60,490 57,091
64,994 61,272 74,888 77,024 86,164 88,105 92,610 93,070 86,327 82,448 71,070 66,604
32,220 30,406 37,250 38,368 43,002 44,029 46,299 46,534 43,119 41,105 35,335 33,037
41,354 39,060 47,951 49,452 55,517 56,907 59,862 60,173 55,708 53,019 45,467 42,425
which represents the ratio between the actual COP and that of an equivalent Carnot’s cycle.
3.4. Scenario and sensitivity analysis for the TEWI difference Once completed the experimental investigation and the data elaboration, we focused our attention on the following question: after the retrofitting operations, how can one reduce the R422D TEWI? In Eq. (1), we individuated two parameters that can be optimized for the purpose: Leakage rate per year, which acts on the direct effect; Energy saving, which acts on the indirect effect. For our first analysis, we kept the yearlong energy consumptions unchanged while we varied the leakage rate per year (5e10%). For each leakage rate used, we calculated the new R422D TEWI and compared it with the R22 TEWI by means of the following equation:
DTEWI ¼
TEWIR422D TEWIR22 TEWIR22
(6)
We repeated this procedure for each test condition, obtaining the change of the TEWI difference as a function of the leakage. As
2500
a second analysis, we kept the leakage rate as reported in Table 3 and we varied the yearlong energy consumptions by considering an energy saving included in the range 0e100%. Following an equivalent procedure used to evaluate the sensitivity to the direct effect, we obtained the change of the TEWI difference at each test conditions as a function of the energy saving. Since a very low leakage rate or a high energy saving could result technically unfeasible or very expensive, we finally investigated the simultaneous change of both parameters. 4. Results and discussion The first step of the experimental investigation led to identifying the correct charge for both refrigerants. As reported in Table 3, the mass of R22 resulted 0.20 kg larger than that of R422D, which means an 8% reduction of refrigerant mass. With the storage investigation we estimated the daily energy consumptions (Ed,i) for each test conditions (Table 4). From Eq. (2) we converted the results shown in Table 5 in monthly energy consumptions (Em,i) (Table 6) and then in yearlong energy consumptions (Fig. 2). It can be seen that the yearly energy consumption pertaining to R422D is larger than that of R22 (7.10e28.9%) for each test. These results are in agreement with theoretical predictions by other authors [16]. Furthermore, for both refrigerants the energy consumption intuitively diminishes with the increase of Tc. In Fig. 3, we have drawn
2500 2240
Yearlong energy consumption (kWh)
10 C
R422D
2092
R422D
R22
2000
2000
R22
1925 1659
1504
1500
1491
1500
1334
1212 945
1000
1000
798
1161 896
961 703
607 471
500
0
500
0 -5°C
0°C
5°C
10°C
Air temperature inner to cold store Fig. 2. Yearlong energy consumption vs. air temperature inner to cold store (1%).
-5°C
0°C
5°C
Air temperature inner to cold store
Fig. 3. TEWI vs. air temperature inner to cold store (10%).
10°C
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1167
Fig. 4. Difference percentage of indirect, direct and TEWI vs. air temperature inner to cold store.
the TEWI relative to one year of operation as function of the air temperature in the refrigerated volume. Since the first term of Eq. (1) is constant for both refrigerants and for each test condition, it is clear that the change of TEWI directly strictly depends on the energy consumption. As remarked in Fig. 4, the adoption of R422D increases the environmental impact. Even if retrofitting R22 led to a 8% reduction of refrigerant mass, the direct effect due to the R422D resulted 42% higher than that of R22 (Fig. 4) because the GWP of R422D is 50% higher (Table 1). As shown in Fig. 4, the indirect effect of R422D is also higher than that of R22. In particular, the difference between the indirect effect of R422D and that of R22 grows with the increase of the storage temperature. Consequently, the increment of the TEWI, due to the adoption of R422D, changes from a minimum of 7.1% to a maximum of 28.9%.
Fig. 5. COP and efficiency of the plant vs. air temperature inner to cold store (2.5%).
Fig. 6. Condensing and evaporating pressure vs. air temperature inner to cold store.
The increase of the energy consumption has also been confirmed by the performance investigation (steady operating conditions). Fig. 5 illustrates both the change of COP and efficiency (3) as a function of Tc. Clearly the adoption of R422D results in a lower efficiency of the plant. In particular, the difference between the COP for R22 and that for R422D is, on average, 20% and it increases with the increase of the air temperature of the cold reservoir. The deterioration of the energy performance, due to the use of R422D as substitute of R22, is also clear in Fig. 6. During the performance investigation, we observed a substantially different behavior of the condenser. As reported in Fig. 6 the condensing pressure of R422D was higher than that of R22, while the evaporating pressure for both refrigerants was similar. This gain in terms of pressure at condenser shows that, when R422D is used as refrigerant, the heat exchange surface of the condenser is insufficient to reject the thermal power. Furthermore, a higher condensing pressure leads to an increase in electrical power absorbed by the compressor further reducing the
Fig. 7. Difference of TEWI vs. leakage rate per year and operating scenarios.
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COP. Since it seems that this observation might hold the key to improve the efficiently performance of the retrofitted system, particular attention should be given to the condenser. In fact, based on theoretical considerations [16], it is possible to expect a 15% increase of COP for a 1.5 bar reduction of the condensing pressure. Furthermore, by increasing the heat transfer, the fluid leaving the condenser would be further sub-cooled, allowing a gain of the specific heat of evaporation. Consequently, a lower mass flow rate could be used, and then the power absorbed by the compressor could be reduced. In order to enhance the heat exchange at condenser two methods could be considered: if the blower has a variable operating speed, select the highest speed available, otherwise, change the blower with another having higher volumetric capacity; replace the condenser with one having a larger surface.
Fig. 8. Difference of TEWI vs. energy saving per year and operating scenarios.
It is important to underline that the first solution is cheaper and technically easier, but it could lead to a larger absorption of electrical power by blowers, negatively affecting the COP. When R422D is used as refrigerant, a further improvement of the energy performance could be obtained by installing an electronic expansion valve instead of the thermostatic one. As showed by Lazzarin and Noro [26], for any refrigerant the electronic expansion valve allows a lower condensation pressure in systems equipped
Fig. 9. Operating scenario charts (a) at 5 C, (b) at 0 C, (c) 5 C and (d) 10 C.
C. Aprea, A. Maiorino / Energy 36 (2011) 1161e1170
with air-cooled condensers, thanks to the ability of monitoring the variations of the outside air temperature. Consequently, it was indicated [26] an 8% reduction of energy consumption for Mediterranean locations and 15% for North-European locations. Once completed the experimental investigation, we considered a sensitivity analysis for the TEWI difference, now aimed to highlight a way of reducing the environmental impact of the R22 retrofit with R422D. For this purpose, we have reported in Fig. 7 the change of the TEWI difference percentage as a function of the leakage rate per year, while Fig. 8 illustrates it is function of the energy saving per year. For both figures, we have identified three scenarios: Scenario A: it represents the parameter domain, for which for every test conditions the environmental impact for R422D becomes higher than that for R22. Scenario B: it represents the parameter domain of transition, for which at least for one test condition the environmental impact for R422D becomes lower than that for R22. Scenario C (or eco-friendly scenario): it represents the parameter domain, for which for every test conditions the environmental impact for R422D becomes lower than that for R22. The intersection of the two dashed axes represents the breakeven point between the TEWI of R22 and that of R422D. Fig. 7 shows that for leakage rate per year lower than 5.7% the TEWI of R422D becomes lower than that of R22. The scenario B is very narrow and this allows achieving of the breakeven point almost simultaneously for all operating conditions. Considering 5% as technical limit for no-hermetical plant, it can see that the scenario C (Fig. 7) occurs for leakage rate per year in the narrowest range of 5.0e5.4%, and it leads to a maximum DTEWI (absolute value) included between 6.0 and 2.0%. The scenario C is technically feasible but it leads to an increase of the management costs: more frequent leakage check could help in reducing the leakage rate, as indicated in [7,8], but it would increase the maintenance cost. In terms of change of energy saving (Fig. 8), it can be seen that scenario B is very large: w20 to 70%. This result is not reassuring, because a 70% energy saving should correspond to a plant efficiency equal to 30%, while for actual plant efficiency does not exceed 25%. Inversely, 20% energy saving could be achieved with a heat exchange improvement and an electronic expansion valves. As aforementioned, a very low leakage rate or a high energy saving could result technically not feasible or very expensive,, then it is necessary to consider an simultaneous parameter change which was performed in the final scenario. In Fig. 9 we have reported four different charts, each referring to different test condition in terms of cold reservoir temperature. For each chart, we have drawn a solid black line, which identifies the limit between the scenario characterized by a negative TEWI difference (eco-friendly scenario) and that by a positive TEWI difference. This time the eco-friendly scenario is identified by a 2D domain (leakage rate & energy saving): one has to select one couple of values for leakage rate and energy saving per year in order to obtain a reduction of TEWI. Overlaying the effects allows obtaining strong TEWI reduction by means of inexpensive operations: minor reductions of leakage rate and energy saving are required. 5. Conclusions An experimental investigation has been carried out to study the environmental impact of the R22 retrofit with R422D and to draw possible eco-friendly scenarios. The experimental investigation consisted of two parts: Real world conditions simulations, aimed at developing the TEWI analysis.
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Performance investigation, aimed at analyzing the behavior of the plant under steady state conditions. For both investigations, we have considered four operating conditions in terms of the air temperature inner to cold store: 5, 0, 5, 10 C. To simulate actual operating conditions, we choose Milan temperatures. Subsequently, a scenario and sensitivity analysis for the TEWI difference has been introduced to study ways of reducing the environmental impact of the R22 retrofit with R422D. For this purpose leakage rate and improved efficiency have been considered as parameters and three parametric analyses have been developed: two have been carried out by changing only one parameter per time, while the other one by changing simultaneously both parameters. Based on our investigation, we can draw the following conclusions: 1. The storage investigation have demonstrated that for each test the R22 retrofit with R422D leads to an increase of the energy consumption up to 28.9%. 2. Since the GWP of R422D is much higher than that of R22 and even if the charge of R422D is 8% lower than that of R22, the direct effect of the R422D is 42% higher than that of R22. 3. As a consequence of the retrofit with R422D, the plant investigated has shown an increase of TEWI up to 36.8%. 4. The performance investigation highlighted that the operation with R422D is less efficient than that with R22. In particular, the difference between the COP for R22 and that for R422D is, on average, 20%, and it grows with the raising of the air temperature of cold reservoir. 5. R22 retrofit with R422D leads to an increase of the condensing pressure, which indicates that the heat exchange surface of the condenser is insufficient to reject the thermal power, worsening the efficiency. 6. To improve the energy performance and then to reduce the indirect effect, we proposed two ways: increasing the heat exchange surface and adoption of electronic expansion valves. Based on theoretical considerations it is possible to obtain a 20% reduction of energy consumption. 7. The scenario and sensitivity analysis for the TEWI difference have demonstrated that for each test there are some operating eco-friendly conditions. In particular, if the parameters change simultaneously, some eco-friendly scenarios result technically feasible and it can be obtained by both reducing the leakage rate and increasing efficiency.
References [1] Montreal protocol on substances that deplete the ozone layer. New York, NY, USA: United Nations (UN); 1987 (1987 with subsequent amendments). [2] UNEP. Decisions adopted by the nineteenth meeting of the parties to the Montreal protocol on substances that deplete the ozone layer. Nairobi, Kenya: United Nations Environment Programme (UNEP) Ozone Secretariat; 2007. [3] Brohan P, Kennedy JJ, Harris I, Tett SFB, Jones PD. Uncertainty estimates in regional and global observed temperature changes: a new dataset from 1850. J Geophys Res 2006;111:D12106. [4] Rayner NA, Brohan P, Parker DE, Folland CK, Kennedy JJ, Vanicek M, et al. Improved analyses of changes and uncertainties in marine temperature measured in situ since the mid-nineteenth century: the HadSST2 dataset. J Climate 2006;19:446e69. [5] Kyoto protocol to the United Nations framework convention on climate change. New York, NY, USA: United Nations (UN); 1997. [6] Calm JM. The next generation of refrigerants e historical review, considerations, and outlook. Int J Ref 2008;31:1123e33. [7] Horrocks P. EU F-gases regulation and MAC directive, ECCP-1 review. Brussels, Belgium: European Commission Environment Directorate; 2006. [8] Regulation (EC) No 842/2006 of the European Parliament and of the Council of 17 May 2006 on certain fluorinated greenhouse gases. Official J E.U. 2006;49:L161.
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[9] Sand JR, Fisher SK, Baxter VD, TEWI analysis: its utility, its shortcomings, and its results. Proceedings of the Taipei international conference on atmospheric protection; 1999. [10] Third assessment report, Intergovernmental Panel on Climate Change; 2001. http://www.ipcc.ch/. [11] Jabaraj DB, Narendran A, Mohan Lal D, Renganarayanan S. Evolving an optimal composition of HFC407C/HC290/HC600a mixture as an alternative to HCFC22 in window air conditioners. Int J Therm Sci 2007;46:276e83. [12] Sarkar J. Cycle parameter optimization of vortex tube expansion transcritical CO2 system. Int J Therm Sci 2009;48:1823e8. [13] Aprea C, Mastrullo R, Renno C, Vanoli GP. An evaluation of R22 substitutes performances regulating continuously the compressor refrigeration capacity. Appl Therm Eng 2004;24:127e39. [14] DuPont, Retrofit guidelines for DuPontTM IsceonÒ M029 (R422D) refrigerant, techincal information art.46; 2007. http://www.refrigerants.dupont.com. [15] Calm JM, Horahan GC. Refrigerant data summary. Eng Syst 2001;18(11):74e88. [16] Arora A, Sachdev HL. Thermodynamics analysis of R422 series refrigerants as alternative refrigerants to HCFC22 in a vapor compression refrigeration system. Int J Energy Res 2009;33(8):753e65. [17] Sand JR, Fisher SK, Baxter VD. Energy and global warming impacts of HFC refrigerants and emerging technologies, Report sponsored by alternative fluorocarbons environmental acceptability study (AFEAS). U.S. Department of Energy, www.afeas.org; 1997.
[18] Coulbourne D, Suen KO. Expanding the domain of TEWI calculations. In: Proceedings of the 20th congress of refrigeration, vol. III. Sydney, Australia: IIF/IIR; 1999. no. 250. [19] Malla S. CO2 emissions from electricity generation in seven Asia-Pacific and North American countries: a decomposition analysis. Energy Policy 2009; 37:1e9. [20] Quadrelli R, Peterson S. The energy-climate challenge: recent trends in CO2 emissions from fuel combustion. Energy Policy 2007;35:5938e52. [21] Weber C, Koyama M, Kraines S. CO2 emissions reductions potential and costs of a decentralized energy system for providing electricity, cooling and heating in an office-building in Tokyo. Energy 2006;31:3041e61. [22] Psomopoulos CS, Skoula I, Karras C, Chatzimpiros A, Chionidis M. Electricity savings and CO2 emissions reduction in buildings sector: how important the network losses are in the calculation? Energy 2010;35:485e90. [23] Guidelines method of calculating TEWI, (2). British Refrigeration Association; 2006. R Table 3. [24] Johnson E. Global warming from HFC. Environ Impact Ass Rev 1998;18 (6):485e92. L Table 3. [25] Moffat RJ. Using uncertainty analysis in the planning of an experiment. Trans ASME J Fluids Eng 1985;107:173e8. [26] Lazzarin R, Noro M. Experimental comparison of electronic and thermostatic expansion valves performances in an air conditioning plant. Int J Ref 2008;31:113e8.
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An experimental investigation of the global environmental impact of the R22 retrofit with R422D Ciro Aprea, Angelo Maiorino* Department of Mechanical Engineering, University of Salerno, Via Ponte Don Melillo 1, 84084 Fisciano (SA), Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 February 2010 Received in revised form 18 November 2010 Accepted 21 November 2010 Available online 22 December 2010
In recent years a new refrigerant, R422D, has been introduced as substitute of R22 for refrigeration systems. This new fluid is an easy-to-use, non-ozone-depleting HFC refrigerant and, differently from its predecessor (R407C), it is compatible with mineral oil. However, R422D has a very high GWP, and it tends to worsen the efficiency of retrofitted R22 systems. Consequently, even if R422D respects the limits of Montreal Protocol, its global environmental impact could be high. In this paper, we report an experimental analysis in terms of TEWI aimed to identify the global environmental impact of R22 systems retrofitted with R422D. For this purpose, we considered a direct expansion refrigerator for commercial applications and we investigated energy consumption with the temperature of the cold reservoir set to 5, 0, 5, 10 C. The experimental investigation confirmed that the system, when retrofitted with R422D, leads to an increase of TEWI. Therefore an optimization analysis aimed to eco-friendly scenarios was performed. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Experimentation R22 R422D Retrofitting Substitute TEWI
1. Introduction The Montreal Protocol banned ozone-depleting substances (ODSs) as refrigerants in current vapor-compression refrigeration systems. Fluor chemicals were the center of attention, with HCFCs for interim use and hydro fluorocarbons (HFCs) for longer term [1]. The Montreal Protocol sets limits (cap) for the HCFC consumption, defined as production plus imports less exports and specified destruction: in 1996 (freeze at calculated cap), 2004 (65% of cap), 2010 (25%), 2015 (10%), and 2020 (0.5%) with full consumption phase-out by 2030 in non-Article 5 countries [2]. Individual countries adopted different response approaches. Most western and central-European countries accelerated HCFC phase-out, while the majority of other developed countries required phase-out of R-22 (the most widely used refrigerant today) by 2010, and then banned all HCFC use in new equipment by 2020. The schedule for Article 5 countries begins with a freeze of the amount of HCFC in 2013 (based on 2009e2010 production and consumption levels) with declining limits starting in 2015 (90%), 2020 (65%), 2025 (32.5%), and 2030 (2.5%) followed by phase-out in 2040 [2]. Exports from Article 5 countries into non-Article 5 countries are effectively restricted to meet the more stringent non-Article 5 schedules. To
* Corresponding author: Tel.: þ39 089 96 4002; fax: þ39 089 96 4037. E-mail address: [email protected] (A. Maiorino). 0360-5442/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2010.11.032
avoid separate domestic and export products and to exploit newer technologies derived from joint ventures and licensing agreements, some products in Article 5 countries incorporate replacements earlier than required. The response to ozone depletion stands in sharp contrast to the deteriorating situation with climate change [3,4]. The Kyoto Protocol [5], pursuant to the United Nations Framework Convention on Climate Change (UNFCCC), sets binding targets for greenhouse gas (GHG) emissions based on calculated equivalents of carbon dioxide, methane, nitrous oxide, HFCs, perfluorocarbons (PFCs), and sulfur hexafluoride [5]. It does not address ODSs covered by the Montreal Protocol, although some are also very potent GHGs. National laws and regulations to implement the Kyoto Protocol differ, but they typically prohibit avoidable releases of HFC and PFC refrigerants and in some countries also control or tax their use. More recent measures (either adopted or proposed) at regional, national, state, and municipal levels are more stringent. These restrictions are forcing the shift to a fourth generation of refrigerants compliant with both ODP and GWP regulations [6]. In the field of the mobile refrigeration systems, the European Parliament already set F-Gases phase-out regulation [7] that bans the use of refrigerants having GWPs in excess of 150. Such regulation will be in effect from 2011 [7,8]. The EU Parliament rejected recommended measures banning HFCs as aerosol propellants by 2006, as foam blowing agents by 2009, and as refrigerants in stationery air conditioners and refrigeration by 2010. However, a revision of this decision is expected in 2011 [6].
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_ W
Nomenclature
Symbols COP E GWP h l m _ m ND ODP P r T TEWI
power (W)
Greek symbols D difference 3 efficiency
coefficient of performance (e) energy consumption (kWh) global warming impact (kgCO2 kgrefrigerant) enthalpy (kJ kg1) leakage rate per year (% yr1) refrigerant charge (kg) mass flow rate (kg s1) number of days (e) ozone depletion potential (e) Pressure (Pa) generation emission (kgCO2 kWh1) temperature (K) total equivalent warming impact (kgCO2)
Subscripts 100 horizon time equal to 100 years cold air inner to cold store D daily el electrical EV evaporator hot external air ambient i i-th in input m monthly out output
A conventional vapor-compression refrigeration system employs compressors, fans, and possibly pumps to shift heat either out of a cooled space or into a heated space. The system is responsible for direct Greenhouse emissions, such as leakage of the refrigerants into the environment, and indirect emissions generated by power grid consumption. If the refrigerant leaks out of the system during operation, is lost during maintenance, or is not recovered when the system is decommissioned, it contributes to global warming. The concept of Total Equivalent Warming Impact (TEWI) was developed to combine the global warming effects due to both lifetime refrigerant emissions (direct effect), and carbon dioxide emissions due to energy use over the lifetime of the system (indirect effect) [9]. As aforementioned, R22 (Table 1) is the most widely used refrigerant today for commercial, domestic and industrial applications, and its phase-out will impact a large number of plants in the world. Therefore retrofitting these systems would alleviate the R22 phaseout problem. This choice could be cheaper than installation of new plants, especially for supermarkets, data centers, factories and hospitals. Refrigerant replacement candidates have been evaluated for environmental and safety requirements, and compatibility with lubricant oil, filters, and sealing. In order to establish the best substitute in a specified system, it is necessary to estimate its energetic performance after refrigerant replacement. In the recent years, many teams researched in the development and characterization of refrigerants with higher energetic efficiency, and have specifically investigated the energetic performance of substitutes for R22 [11,12]. During this transition period, many industrial and commercial applications Table 1 Refrigerants data. R22
R422D
R407C
Composition (% wt)
CHClF2
ODP GWP100 (in accordance with [10] [23]) Bubble point temperature, 100 kPa ( C) Critical temperature ( C) Saturated vapor pressure at 40 C (kPa) Glide temperature at 40 C vapor saturation pressure ( C) Glide temperature at 0 C vapor saturation pressure ( C)
0.05 1700
31.5% R134a 65.1% R125 3.4% R600a 0 2230
23% R32 25% R125 52% R134A 0 1600
40.8
43.5
43.9
96.1 1533.6
79.6 1555.0
86.0 1749.0
0
2.46
4.90
0
3.56
6.12
used R407C (Table 1) to retrofit R22. Even if R407C has thermophysical properties similar to those of R22 and it is non-flammable and non-toxic, it is incompatible with mineral or alkyl-benzene oil. Consequently, a R22 system retrofitted with R407C requires the adoption of polyester oil, a difficult and expensive conversion. Furthermore experimental tests carried out with R407C showed a reduction in the energetic performances when compared to R22 [13]. Recent additions to the aforementioned alternative refrigerants for R22 are R422A, R422B, R422C and R422D. The U.S. environment protection agency reported that such alternative refrigerants could be used for household and light commercial air conditioning applications. In particular, R422D (Table 1) is an easy-to-install, non-ozonedepleting HFC refrigerant originally designed to replace R-22 in existing direct expansion water chiller systems. It can also be used in residential and commercial air conditioning and medium-low temperature (10 to 5 C) refrigeration systems. Minor equipment modifications (replacement of the filter drier and elastomeric seals/ gaskets that are exposed to refrigerant, refill of oil if required) or components tuning may be required in some applications. It is also compatible with mineral oil and there is no need to replace it with synthetic oil [14]. Field experience has shown that R422D provides performance that meets customer requirements in most retrofitted systems. It provides similar cooling capacity to R22 and it is capable to operate at significantly lower compressor discharge temperature [14]. In this scenario, it seems sensitive to investigate what is the actual impact of R422D on the environment, when it is employed in retrofitting R22 devices. It is well known that the GWP of R422D is higher than the GWP of R22 [10,15], but not much is known about the energy efficiency of R22 systems retrofitted by R422D. Arora and Sachdev [16] performed a theoretical energetic and exergetic analysis of R422 cycles and they found out that the energy performance of these refrigerants could be lower than that of R22. However, the result of a bibliographic research showed that no experimental investigation of the energetic performances of an actual refrigerator operating with R422 series refrigerants is available in literature. In this paper, we report an experimental TEWI analysis with the objective of identifying the environmental impact of a R22 system retrofitted with R422D. For this purpose, a comparison of the energy consumptions of R22 and R422D for a direct expansion refrigerator for commercial use is proposed. The experimental investigation has been carried out for a range of conditions (5 to 10 C): medium temperature refrigeration for meat, fish, and dairy cases and high temperature refrigeration for air conditioning and cooling of preparation rooms.
C. Aprea, A. Maiorino / Energy 36 (2011) 1161e1170
2. The TEWI analysis The concept of total equivalent warming impacts (TEWI) was developed to combine the effects of the direct emissions of refrigerants with the indirect effects of energy consumption due to the combustion of fossil fuels for power generation. TEWI provides a measure of the environmental impact of greenhouse gases from operation, service and end-of-life disposal of the equipment. TEWI is the sum of the direct contribution of greenhouse gases used to make or operate the systems and the indirect contribution of carbon dioxide emissions resulting from the energy required to run the systems over their normal lifetimes [17]. In order to calculate the TEWI for refrigeration systems, Coulbourne and Suen [18] proposed the following equation:
TEWI ¼ direct contribution þ indirect contribution ¼ ðm l Sl GWP100 Þ þ ðE Sl rÞ
(1)
Refrigerant charge (m) is the total amount of refrigerant introduced in the refrigeration system. It depends both on the dimensions of the plant and on the kind of refrigerant. Usually, manufacturers and operators define the correct charge as the amount of refrigerant necessary to guarantee that the fluid get the evaporator adequately wetted. Non-hermetic units, designed for servicing, are subject to leaking into the environment (l). Under the restrictions of the protocol of Kyoto, the new obligations introduced by F-Gases regulation help reducing the leakage rate of refrigerant. The European Parliament has made mandatory the recovery of refrigerant during plant servicing and at end of plant life for all stationary equipment. It was also imposed that adequately trained staff carries out installation, servicing and leakage checking. The leakage rate per year does not include the disposal percentage but only the accidental percentage due to operating conditions. Usually the service life (Sl) of a refrigeration system is based on the operation time. In this experimental investigation the service life is based on a reference period. The energy consumed by the systems (E), either in the form of electricity or combustion of fossil fuel, implies a release in the environment of an amount of carbon dioxide, based on the generation emission coefficient (r). Some indicative average carbon dioxide release levels for varies countries around the world are available in literature [19e22]. GWP expresses the extent to which a greenhouse gas directly contributes to global warming. The values depend on the quantity of gas emitted, the elapsed time before it is purged from the atmosphere, and the infrared energy absorption properties of the gas. GWP100 is based on a time horizon of 100 years and is referenced to the unitary value of CO2. The uncertainty of the TEWI has been calculated applying the error propagation theory to Eq. (1) and considering the uncertainty of the energy meter and of the balance (Table 2). Sand et al. [17] suggested that a minimum of 20% uncertainty exists for the GWP values assigned to refrigerants by the Intergovernmental Panel on Climate Change (IPCC). These
Table 2 Transducers specifications. Transducers
Range
Uncertainty
Coriolis effect flow meter RTD 100 4 wires Piezoelectric absolute pressure gauge
0/2 kg min1 100/500 C 1e10 bar; 1e30 bar 0e3 kW 0e1 MWh 0e100 kg
0.2% 0.15 C 0.2% 0.5% F.S 0.2% 1% 0.2%
Wattmeter Energy meter Balance
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uncertainties, when combined with other estimates and assumptions of the analysis lead to a TEWI uncertainty of 10%. Because of the error in the estimation, if the TEWI differences are lower than 10%, the technology that shows lower energy use should be favored; if the TEWI differences are higher than 10%, the technology that shows lower TEWI should be favored. 3. Investigation In order to obtain a TEWI analysis for refrigeration systems it is necessary to have values for every variable expressed in Eq. (1). For this purpose, we carried out an experimental investigation for both R22 and R422D to calculate the refrigerant charge and the energy consumption values, while we used literature data as source for the remaining unknowns. In addition, we investigated the energetic performance of the plant, with the purpose of finding ways of reducing the environmental indirect impact with the adoption of R422D. Then a sensitivity analysis for the TEWI difference between the refrigerants was performed. 3.1. Experimental facility The experimental vapor-compression refrigeration plant is shown in Fig. 1. It consists of a semi-hermetic reciprocating compressor, an air condenser followed by a liquid receiver, a R22 mechanic thermostatic expansion valve feeding an air-cooled evaporator inside the cold storage. The compressor, as specified by the manufacturer, can operate with the fluid R22 and it is lubricated with mineral oil. With an evaporation temperature range between 20 and 10 C, a 35 C condensing temperature, and utilizing R22 at the nominal frequency of 50 Hz, the compressor refrigerating capacity is in the range of 1.4e4.4 kW. A blower drives the airflow through a thermally insulated channel where some electrical resistances are installed with the objective of controlling the temperature of the airflow across the condenser. In order to control the temperature of the airflow, the electrical resistances are energized by a PID controller. The cooling load in the cold reservoir is simulated by additional electrical heaters wired to a voltage regulator. To keep the air temperature reasonably constant in the cold reservoir, an on/off refrigeration control system has been implemented. This is done by turning on/off the compressor and the fan of the heat exchangers. Table 2 reports the transducers specifications used (Coriolis effect mass flow meter, RTD 100 4 wires thermo-resistances, piezoelectric absolute pressure gauge, wattmeter). The thermo-resistances are located outside the pipe, with a layer of heat transfer compound (aluminum oxide plus silicon) placed between the sensor and the pipe in order to provide good thermal contact. The whole pipe is covered with 25 mm thick flexible insulation. The system of temperature measurement was calibrated against a sensor positioned inside a similarly insulated pipe. For the test conditions, the difference between the two measurements has been always less than 0.3 C. The wattmeter measures the electrical power absorbed by the compressor, the blowers and all additional components required for operation of the device. The energy consumption of the refrigeration system is measured by an energy meter. The test apparatus is equipped with 32 bit A/D converter acquisition cards linked to a personal computer that allows a high sampling rate (10 kHz). 3.2. Experimental procedure We started the experimental investigation by analyzing the operation of the plant with R22. Subsequently, we retrofitted the refrigeration system with R422D according with [14]. During the retrofitting operations, we changed the factory setting of the R22
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Fig. 1. Sketch of the experimental plant.
thermostatic expansion valve in order to keep the operating superheat value for R422D in the same range used for R22, which was performed by turning the setting adjustment screw of the valve. For both refrigerants, we used the same experimental procedure. Firstly, we proceeded with identifying the refrigerant charge necessary to guarantee that the fluid adequately wets the evaporator. For this purpose, we set the temperature of the air blown through the condenser to 24 C and the air in the cold reservoir to 5 C, while the cooling load was kept at 1000 W. We evacuated the circuit, and then we proceeded with introducing 0.40 kg of gas in the refrigerant circuit while the system was shut off to prevent the electrical motor of the compressor from overheating. Subsequently, we turned on the plant and the electrical heaters inside the cold storage. During the operation of the system, we monitored the refrigerant in the superheated region, defined as the difference between the temperature at end of the evaporating process (considering the pressure drop into the evaporator) and temperature at the compressor inlet. Additional 0.10 kg of refrigerant was introduced until, under steady state conditions, the operating superheat was greater than 10 C. Once the system was charged to the desired value (Table 3), we proceeded with the evaluation of the energy consumption due to one year of operation (storage investigation). In particular, we investigated four different cold reservoir temperatures (Tc): 5, 0, 5, and 10 C. We considered as external air temperature reference the values reported in Table 4, which represent typical conditions in Milan (Italy). Since
this table provides the daily change of external air temperature for each month, we planned 12 experiments each 24 h long. Data in Table 4 were used for the PID controller, which modulates the voltage supply to the electrical resistances varying the temperature of the air intake. In order to evaluate the energetic performance additional experiments analyzing the behavior of the plant under steady state conditions (performance investigation). For this purpose, we planned 4 experiments with the same cold temperature Tc of 5, 0, 5, and 10 C. During the experiments, we shunted the refrigeration control and we set the temperature of the air blown through the condenser to a reference value of 21 C, which the mean value from Table 4. Usually, the start-up time was about one hour, and steady state conditions were assumed to be reached when the deviations of all controlled variables were less than 0.5 C for temperatures and Table 3 Parameters for the Eq. (1). Parameter
Value
Note
Sl r
1 yr 0.59
l
10%
mR22 mR422D
2.50 kg 2.30 kg
See text In accordance with [21,24] In accordance with [22,18] Experimental result Experimental result
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Table 4 Change of the external air temperature (in C) for Milan (Italy). Hours
January
February
March
April
May
June
July
August
September
October
November
December
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
11.4 10.8 10.2 9.8 9.4 9.3 9.5 10.1 11.2 12.8 14.6 16.6 18.5 20.1 20.9 21.3 20.9 20.1 18.8 17.2 15.6 14.3 13.1 12.2
12.7 12.1 11.5 11.1 10.7 10.6 10.8 11.4 12.5 14.1 15.9 17.9 19.8 21.3 22.2 22.6 22.2 21.4 20.1 18.5 16.9 15.6 14.4 13.5
15.7 15.9 14.5 14 13.7 13.5 13.8 14.4 15.5 17 18.8 20.9 22.8 24.2 25.2 25.5 25.2 24.3 23 21.5 19.9 18.6 17.4 16.4
17.5 17.8 16.3 15.9 15.5 15.4 15.6 16.2 17.3 18.9 20.7 22.7 24.6 26.1 27 27.4 27 26.2 24.9 23.3 21.7 20.4 19.2 18.3
19.9 20.2 18.7 18.3 17.9 17.8 18 18.6 19.7 21.3 23.1 25.1 27 28.5 29.4 29.8 29.4 28.6 27.3 25.7 24.1 22.8 21.6 20.7
21.6 21.9 20.4 19.9 19.6 19.4 19.7 20.3 21.4 22.9 24.7 26.8 28.7 30.1 31.1 31.4 31.1 30.2 28.9 27.4 25.8 24.6 23.3 22.3
22.2 21.6 21 20.5 20.1 20 20.2 20.8 21.9 23.5 25.3 27.3 29.2 30.7 31.6 32 31.6 30.8 29.5 27.9 26.4 25 23.8 22.9
22.35 21.75 21.15 20.65 20.25 20.15 20.35 20.95 22.05 23.65 25.45 27.45 29.35 30.85 31.75 32.15 31.75 30.95 29.65 28.05 26.55 25.15 23.95 23.05
21 20.4 19.8 19.4 19 18.9 19.1 19.7 20.8 22.4 24.2 26.2 28.1 29.6 30.5 30.9 30.5 29.7 28.4 26.4 25.2 23.9 22.7 21.8
18.6 18 17.4 17 16.6 16.5 16.7 17.3 18.4 20 21.8 23.8 25.7 27.2 28.1 28.5 28.1 27.3 26 24.4 22.8 21.5 20.3 19.4
15.1 14.5 13.9 13.5 13.1 13 13.2 13.8 14.9 16.5 18.3 20.3 22.2 23.7 24.6 25 24.6 23.8 22.5 20.9 19.3 18 16.8 15.9
12.2 11.6 11 10.5 10.1 10 10.3 10.9 11.9 13.5 15.3 17.3 19.3 20.7 21.7 22 21.7 20.8 19.5 17.9 16.4 15.1 13.9 12.9
15 kPa for pressures. This was evaluated in the following manner. Data logging was performed with 0.5 Hz acquisition frequency for 60 s. Then the 120 samples recorded were averaged for each channel. After 180 s, three mean values were obtained and compared for steady state using the above criteria (DT 0.5 C and Dp 15 kPa). 3.3. Data elaboration We developed a software application called FrigoCheck v.1.0 able to show in real time the coefficient of performance, the entropy and the enthalpy values of all points of the thermodynamic cycle. In addition, it shows the whole cycle on peh diagram and it evaluates the steady state condition. Since we measured the daily energy consumption for each month (Ed,i), we calculated the monthly energy consumption (Em,i) by means of the following equation
Em;i ¼ Ed;i NDi
(2)
where the subscript i refers to the generic month and ND is equal to the number of days for the ith month. We obtained yearlong energy consumption (E) by summing the monthly energy consumptions (Em,i):
E ¼
X
Em;i
(3)
i
The uncertainty of the yearlong energy consumption is equal to 1% (Table 2). To evaluate the TEWI, we considered the service life, the emission generation, the GWP, and the leakage rate reported both in Tables 1 and 3. The reference period for the service life was equal to one year. Under steady state conditions, the overall efficiency performance of the plant is expressed by the COP, calculated as the ratio between the refrigeration capacity and the electrical power supplied to the plant (compressor, blowers and accessories):
_ hout;EV hin;EV m COP ¼ _ W
(4)
el
A COP accuracy analysis has been performed according to [25], resulting in 2.5%. In order to identify the efficiency of the plant, we considered the following ratio:
3¼
COP 1=½ðTex =Tcold Þ 1
(5)
Table 5 Daily energy consumption measured. Daily energy consumption (Ed,i) 5 C
January February March April May June July August September October November December
0 C
þ5 C
10 C
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
4848 5017 5430 5701 6075 6348 6436 6461 6246 5864 5346 4944
5080 5280 5772 6098 6551 6884 6991 7022 6759 6295 5671 5193
3051 3166 3448 3635 3893 4082 4143 4161 4011 3747 3390 3116
3392 3529 3868 4093 4405 4636 4710 4731 4549 4229 3798 3470
1800 1873 2053 2173 2339 2461 2500 2512 2415 2245 2016 1842
2097 2188 2416 2567 2779 2937 2987 3002 2878 2660 2369 2149
1039 1086 1202 1279 1387 1468 1494 1501 1437 1326 1178 1066
1334 1395 1547 1648 1791 1897 1931 1941 1857 1710 1516 1369
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Table 6 Monthly energy consumption calculated by means of the Eq. (2). Monthly energy consumption (Em,i) 5 C
January February March April May June July August September October November December
0 C
þ5 C
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
R22 (Wh)
R422D (Wh)
150,295 140,481 168,338 171,040 188,323 190,455 199,505 200,298 187,370 181,794 160,377 153,268
157,473 147,833 178,940 182,945 203,066 206,521 216,713 217,685 202,755 195,150 170,141 160,987
94,568 88,637 106,893 109,037 120,670 122,471 128,433 128,984 120,329 116,157 101,711 96,591
105,144 98,814 119,904 122,777 136,553 139,068 145,995 146,668 136,463 131,084 113,953 107,557
55,809 52,451 63,650 65,177 72,494 73,833 77,511 77,868 72,449 69,589 60,490 57,091
64,994 61,272 74,888 77,024 86,164 88,105 92,610 93,070 86,327 82,448 71,070 66,604
32,220 30,406 37,250 38,368 43,002 44,029 46,299 46,534 43,119 41,105 35,335 33,037
41,354 39,060 47,951 49,452 55,517 56,907 59,862 60,173 55,708 53,019 45,467 42,425
which represents the ratio between the actual COP and that of an equivalent Carnot’s cycle.
3.4. Scenario and sensitivity analysis for the TEWI difference Once completed the experimental investigation and the data elaboration, we focused our attention on the following question: after the retrofitting operations, how can one reduce the R422D TEWI? In Eq. (1), we individuated two parameters that can be optimized for the purpose: Leakage rate per year, which acts on the direct effect; Energy saving, which acts on the indirect effect. For our first analysis, we kept the yearlong energy consumptions unchanged while we varied the leakage rate per year (5e10%). For each leakage rate used, we calculated the new R422D TEWI and compared it with the R22 TEWI by means of the following equation:
DTEWI ¼
TEWIR422D TEWIR22 TEWIR22
(6)
We repeated this procedure for each test condition, obtaining the change of the TEWI difference as a function of the leakage. As
2500
a second analysis, we kept the leakage rate as reported in Table 3 and we varied the yearlong energy consumptions by considering an energy saving included in the range 0e100%. Following an equivalent procedure used to evaluate the sensitivity to the direct effect, we obtained the change of the TEWI difference at each test conditions as a function of the energy saving. Since a very low leakage rate or a high energy saving could result technically unfeasible or very expensive, we finally investigated the simultaneous change of both parameters. 4. Results and discussion The first step of the experimental investigation led to identifying the correct charge for both refrigerants. As reported in Table 3, the mass of R22 resulted 0.20 kg larger than that of R422D, which means an 8% reduction of refrigerant mass. With the storage investigation we estimated the daily energy consumptions (Ed,i) for each test conditions (Table 4). From Eq. (2) we converted the results shown in Table 5 in monthly energy consumptions (Em,i) (Table 6) and then in yearlong energy consumptions (Fig. 2). It can be seen that the yearly energy consumption pertaining to R422D is larger than that of R22 (7.10e28.9%) for each test. These results are in agreement with theoretical predictions by other authors [16]. Furthermore, for both refrigerants the energy consumption intuitively diminishes with the increase of Tc. In Fig. 3, we have drawn
2500 2240
Yearlong energy consumption (kWh)
10 C
R422D
2092
R422D
R22
2000
2000
R22
1925 1659
1504
1500
1491
1500
1334
1212 945
1000
1000
798
1161 896
961 703
607 471
500
0
500
0 -5°C
0°C
5°C
10°C
Air temperature inner to cold store Fig. 2. Yearlong energy consumption vs. air temperature inner to cold store (1%).
-5°C
0°C
5°C
Air temperature inner to cold store
Fig. 3. TEWI vs. air temperature inner to cold store (10%).
10°C
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Fig. 4. Difference percentage of indirect, direct and TEWI vs. air temperature inner to cold store.
the TEWI relative to one year of operation as function of the air temperature in the refrigerated volume. Since the first term of Eq. (1) is constant for both refrigerants and for each test condition, it is clear that the change of TEWI directly strictly depends on the energy consumption. As remarked in Fig. 4, the adoption of R422D increases the environmental impact. Even if retrofitting R22 led to a 8% reduction of refrigerant mass, the direct effect due to the R422D resulted 42% higher than that of R22 (Fig. 4) because the GWP of R422D is 50% higher (Table 1). As shown in Fig. 4, the indirect effect of R422D is also higher than that of R22. In particular, the difference between the indirect effect of R422D and that of R22 grows with the increase of the storage temperature. Consequently, the increment of the TEWI, due to the adoption of R422D, changes from a minimum of 7.1% to a maximum of 28.9%.
Fig. 5. COP and efficiency of the plant vs. air temperature inner to cold store (2.5%).
Fig. 6. Condensing and evaporating pressure vs. air temperature inner to cold store.
The increase of the energy consumption has also been confirmed by the performance investigation (steady operating conditions). Fig. 5 illustrates both the change of COP and efficiency (3) as a function of Tc. Clearly the adoption of R422D results in a lower efficiency of the plant. In particular, the difference between the COP for R22 and that for R422D is, on average, 20% and it increases with the increase of the air temperature of the cold reservoir. The deterioration of the energy performance, due to the use of R422D as substitute of R22, is also clear in Fig. 6. During the performance investigation, we observed a substantially different behavior of the condenser. As reported in Fig. 6 the condensing pressure of R422D was higher than that of R22, while the evaporating pressure for both refrigerants was similar. This gain in terms of pressure at condenser shows that, when R422D is used as refrigerant, the heat exchange surface of the condenser is insufficient to reject the thermal power. Furthermore, a higher condensing pressure leads to an increase in electrical power absorbed by the compressor further reducing the
Fig. 7. Difference of TEWI vs. leakage rate per year and operating scenarios.
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COP. Since it seems that this observation might hold the key to improve the efficiently performance of the retrofitted system, particular attention should be given to the condenser. In fact, based on theoretical considerations [16], it is possible to expect a 15% increase of COP for a 1.5 bar reduction of the condensing pressure. Furthermore, by increasing the heat transfer, the fluid leaving the condenser would be further sub-cooled, allowing a gain of the specific heat of evaporation. Consequently, a lower mass flow rate could be used, and then the power absorbed by the compressor could be reduced. In order to enhance the heat exchange at condenser two methods could be considered: if the blower has a variable operating speed, select the highest speed available, otherwise, change the blower with another having higher volumetric capacity; replace the condenser with one having a larger surface.
Fig. 8. Difference of TEWI vs. energy saving per year and operating scenarios.
It is important to underline that the first solution is cheaper and technically easier, but it could lead to a larger absorption of electrical power by blowers, negatively affecting the COP. When R422D is used as refrigerant, a further improvement of the energy performance could be obtained by installing an electronic expansion valve instead of the thermostatic one. As showed by Lazzarin and Noro [26], for any refrigerant the electronic expansion valve allows a lower condensation pressure in systems equipped
Fig. 9. Operating scenario charts (a) at 5 C, (b) at 0 C, (c) 5 C and (d) 10 C.
C. Aprea, A. Maiorino / Energy 36 (2011) 1161e1170
with air-cooled condensers, thanks to the ability of monitoring the variations of the outside air temperature. Consequently, it was indicated [26] an 8% reduction of energy consumption for Mediterranean locations and 15% for North-European locations. Once completed the experimental investigation, we considered a sensitivity analysis for the TEWI difference, now aimed to highlight a way of reducing the environmental impact of the R22 retrofit with R422D. For this purpose, we have reported in Fig. 7 the change of the TEWI difference percentage as a function of the leakage rate per year, while Fig. 8 illustrates it is function of the energy saving per year. For both figures, we have identified three scenarios: Scenario A: it represents the parameter domain, for which for every test conditions the environmental impact for R422D becomes higher than that for R22. Scenario B: it represents the parameter domain of transition, for which at least for one test condition the environmental impact for R422D becomes lower than that for R22. Scenario C (or eco-friendly scenario): it represents the parameter domain, for which for every test conditions the environmental impact for R422D becomes lower than that for R22. The intersection of the two dashed axes represents the breakeven point between the TEWI of R22 and that of R422D. Fig. 7 shows that for leakage rate per year lower than 5.7% the TEWI of R422D becomes lower than that of R22. The scenario B is very narrow and this allows achieving of the breakeven point almost simultaneously for all operating conditions. Considering 5% as technical limit for no-hermetical plant, it can see that the scenario C (Fig. 7) occurs for leakage rate per year in the narrowest range of 5.0e5.4%, and it leads to a maximum DTEWI (absolute value) included between 6.0 and 2.0%. The scenario C is technically feasible but it leads to an increase of the management costs: more frequent leakage check could help in reducing the leakage rate, as indicated in [7,8], but it would increase the maintenance cost. In terms of change of energy saving (Fig. 8), it can be seen that scenario B is very large: w20 to 70%. This result is not reassuring, because a 70% energy saving should correspond to a plant efficiency equal to 30%, while for actual plant efficiency does not exceed 25%. Inversely, 20% energy saving could be achieved with a heat exchange improvement and an electronic expansion valves. As aforementioned, a very low leakage rate or a high energy saving could result technically not feasible or very expensive,, then it is necessary to consider an simultaneous parameter change which was performed in the final scenario. In Fig. 9 we have reported four different charts, each referring to different test condition in terms of cold reservoir temperature. For each chart, we have drawn a solid black line, which identifies the limit between the scenario characterized by a negative TEWI difference (eco-friendly scenario) and that by a positive TEWI difference. This time the eco-friendly scenario is identified by a 2D domain (leakage rate & energy saving): one has to select one couple of values for leakage rate and energy saving per year in order to obtain a reduction of TEWI. Overlaying the effects allows obtaining strong TEWI reduction by means of inexpensive operations: minor reductions of leakage rate and energy saving are required. 5. Conclusions An experimental investigation has been carried out to study the environmental impact of the R22 retrofit with R422D and to draw possible eco-friendly scenarios. The experimental investigation consisted of two parts: Real world conditions simulations, aimed at developing the TEWI analysis.
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Performance investigation, aimed at analyzing the behavior of the plant under steady state conditions. For both investigations, we have considered four operating conditions in terms of the air temperature inner to cold store: 5, 0, 5, 10 C. To simulate actual operating conditions, we choose Milan temperatures. Subsequently, a scenario and sensitivity analysis for the TEWI difference has been introduced to study ways of reducing the environmental impact of the R22 retrofit with R422D. For this purpose leakage rate and improved efficiency have been considered as parameters and three parametric analyses have been developed: two have been carried out by changing only one parameter per time, while the other one by changing simultaneously both parameters. Based on our investigation, we can draw the following conclusions: 1. The storage investigation have demonstrated that for each test the R22 retrofit with R422D leads to an increase of the energy consumption up to 28.9%. 2. Since the GWP of R422D is much higher than that of R22 and even if the charge of R422D is 8% lower than that of R22, the direct effect of the R422D is 42% higher than that of R22. 3. As a consequence of the retrofit with R422D, the plant investigated has shown an increase of TEWI up to 36.8%. 4. The performance investigation highlighted that the operation with R422D is less efficient than that with R22. In particular, the difference between the COP for R22 and that for R422D is, on average, 20%, and it grows with the raising of the air temperature of cold reservoir. 5. R22 retrofit with R422D leads to an increase of the condensing pressure, which indicates that the heat exchange surface of the condenser is insufficient to reject the thermal power, worsening the efficiency. 6. To improve the energy performance and then to reduce the indirect effect, we proposed two ways: increasing the heat exchange surface and adoption of electronic expansion valves. Based on theoretical considerations it is possible to obtain a 20% reduction of energy consumption. 7. The scenario and sensitivity analysis for the TEWI difference have demonstrated that for each test there are some operating eco-friendly conditions. In particular, if the parameters change simultaneously, some eco-friendly scenarios result technically feasible and it can be obtained by both reducing the leakage rate and increasing efficiency.
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