- Email: [email protected]
Comprehensive investigation of transport refrigeration life cycle climate performance
Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Contents lists available at ScienceDirect
Sustainable Energy Technologies and Assessments journal homepage: www.elsevier.com/locate/seta
Original article
Comprehensive investigation of transport refrigeration life cycle climate performance Gang Li ⇑ Ingersoll Rand Residential Solutions, 6200 Troup Highway, Tyler, TX 75707, United States Ingersoll Rand Engineering and Technology Center-Asia Pacific, Shanghai 200051, PR China
a r t i c l e
i n f o
Article history: Received 27 October 2016 Revised 6 February 2017 Accepted 18 April 2017
Keywords: Life cycle climate performance Food transport refrigeration R452A Global warming Alternative technologies Food product refrigerating temperature
a b s t r a c t This paper presents the comprehensive investigations for the total lifetime CO2-equivalent emissions for food transport refrigeration system under various influencing factors. The new R404A alternative refrigerant—R452A, is investigated to provide an improved environmental performance. With a lower global warming potential (GWP = 1945), which is around half GWP of the currently existing R404A, R452A can make a 5–15% emission reduction for the food transport refrigeration system. In the R452A system, reducing the ambient temperature from 90 °F (32 °C) to 60 °F (15.5 °C) can produce up to 60% emission reduction for the fresh product case while 39% reduction for the frozen. Decreasing the annual leak rate from 25% to 10% can give a 13% emission reduction for the R452A fresh product case while 4% reduction for the frozen. Increasing the food product refrigerating temperature (evaporating temperature) set-point from 10 °F (23 °C) to 50 °F (10 °C) can lead to more than 80% emission reduction. In addition, a 15% annual insulation degrade rate can provide a 13% emission reduction for the fresh and 14% for the frozen. Moreover, the Cycle Sentry running mode can result in a 14–21% emission saving than the Continuous. Furthermore, the sunny/cloudy conditions, system efficiency improvement rate, and alternative transport refrigeration technologies other than the conventional hydrofluorocarbon (HFC) based vapour compression refrigeration systems, are also investigated to explore the possibility to minimize environmental impacts. Ó 2017 Elsevier Ltd. All rights reserved.
Introduction Climate change and global warming, have been emerged and described as serious issues on the international agenda during the past decades. The ever-increasing greenhouse gas (GHG) emissions can turned out a series of negative consequences, such as deteriorating the patterns and amounts of precipitation, weakening the ice and snow cover, raising the sea level, swelling the acidity of the oceans, shifting the ecosystem characteristics and increasing threats to human health. Based on the Fourth Assessment Report of Intergovernmental Panel on Climate Change (IPCC) in 2007 [1], an increase of 0.74 K for the average global surface temperature were obtained during the past 100 years (1906– 2005), which is higher than the that of 0.6 K in the Third Assessment Report published in 2001. This comparison indicates that the ice reduction and sea level rise are performed at an accelerating ⇑ Address: Ingersoll Rand Residential Solutions, 6200 Troup Highway, Tyler, TX 75707, United States. E-mail address: [email protected] http://dx.doi.org/10.1016/j.seta.2017.04.002 2213-1388/Ó 2017 Elsevier Ltd. All rights reserved.
rate. Another study has been summarized that, for the last 50 years, the global temperature rose at an average rate of 0.13 °C per decade—around twice as fast as the value of 0.06 °C per decade increase observed over the previous half-century [2]. This study is also projected that in the next 20 years, the global average temperature will rise by 0.2 °C per decade [2]. Facing such challenges, researchers, governmental agencies, and policy makers are raising attention to the human activities to minimize the GHG emissions. The food transport refrigeration sector, is generally recognized to consume energy heavily to maintain the coldchain and thus result in large GHG emissions. A study showed that over a million refrigerated road vehicles are used to distribute refrigerated foods throughout the world [3]. The freight transport consumes nearly a quarter of all the petroleum worldwide and produces more than 10% of carbon emissions from fossil fuels [4]. In another study, the statistics showed that the food transport could produce 19 million tons of CO2 in 2002, among which 10 million tons were emitted in the UK (almost all from road transport), representing 1.8% of the total annual UK CO2 emissions [5]. Food transport accounts for one quarter of all Heavy-Goods Vehicle
34
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Nomenclature Abbreviations AHRTI Air-conditioning, Heating, and Refrigeration Technology Institute CARB California Air Resources Board CFC chlorofluorocarbon COP coefficient of performance DDE diesel direct electric DLL dynamic link library EOL loss end of life EPA Environmental Protection Agency EU European Union FCMT fuel consumption modeling tool
miles in the UK, with the average number of miles that food travelling doubling in the last 30 years [6]. Under the increasing pressure to address global warming issues, it is necessary for the industry to spend more efforts to understand the environmental impact of transport refrigeration system under various influencing factors, with the hope that the industry can be actively implementing improvements thus tending to reduce fuel usage and costs in the long run. The transport refrigeration system, is usually operated under a much harsher environment, and thus it has the higher reliability requirements than the conventional stationary refrigeration systems and lower energy efficiencies. In addition, the wide range of transported goods, home delivery and quality expectations, are placing high pressures on the industry for GHG emission reductions. Based on the literature review from the published peerreviewed journal articles, currently there are limited studies on the in-depth and systematical evaluation of environmental impacts for the food transport refrigeration systems. More studies are focused on the environmental impact of the stationary refrigeration systems, such as residential and commercial air conditioners and heat pumps. For the convenience of readers, some tools are briefly introduced to evaluate the product environmental performance (for more detail please check Section 2). First, the tool— Total Equivalent Warming Impact (TEWI) is used to evaluate both the direct GHG emissions from a product, as well as the indirect emissions from the energy consumption aspect. This tool is used particularly for air conditioners and ignores the emissions during chemical manufacturing, the energy embodied in product materials, and end-of-life losses. Another tool is the web-based interactive life cycle climate performance (LCCP) modeling program for stationary refrigeration systems [7]. This tool also has the Excel Version, named ORNL LCCP Excel Tool, which can be used for air conditioners, heat pumps, chiller, etc. LCCP is a methodology that is used to assess the total global warming potential (GWP, which will be introduced in more detail in Section 2.1) impacts (both direct and indirect emissions). It is expressed as CO2 equivalent mass (kg-CO2 eq.), over the lifetime of a particular refrigerant, piece of equipment or system with different climate inputs. It can be expressed as a summation of all sources of the direct and indirect source emissions. From the comparison it indicates that the LCCP can evaluate the product emissions in a more reasonable way than the TEWI. It should be noted there is another tool prior to ORNL LCCP Excel Tool: the Air-conditioning, Heating, and Refrigeration Technology Institute (AHRTI) LCCP model, which is only used for residential heat pumps [8]. It has similar methodology to the web-based tools. The International Institute of Refrigeration (IIR) has set up a working group to discuss and assess the merits of
GHG GWP HCFC HFC IIR IPCC LCA LCCP TEWI TRU ULETRU
greenhouse gas global warming potential hydrogen chlorofluorocarbon hydrofluorocarbon International Institute of Refrigeration Intergovernmental Panel on Climate Change life cycle assessment life cycle climate performance total equivalent warming impact transport refrigeration units Ultra-Low-Emission Transport Refrigeration Unit In-Use Performance Standards
various methods for LCCP evaluation and produce implementation protocols [9]. It has the Excel-based IIR Working Group residential heat pump LCCP tool. Several studies have been performed with aforementioned tools. A LCCP study is performed for supermarket systems and the transcritical CO2 booster system has the lowest emissions in cold climates [10]. This study also showed that shifting towards low GWP refrigerants decreases the effect of the annual leak rate [10]. In other studies, the packaged air conditioners and heat pumps are evaluated from the product’s life time. It shows that the energy consumption accounts for the largest emission contributor, followed by annual refrigerant leakage effect [11,12]. The drop in LCCP of low GWP refrigerants R-32, L-41a and D2Y60 are conducted compared with baseline R410A for heat pumps for residential application, and the low GWP refrigerants can produce a 4–27% GHG emission reduction [13]. In addition to the tools above, there is one more tool: GREEN-MAC-LCCP, which is only automotive air conditioning application [14]. However, to the best knowledge of the author, there is a lack of the complete and comprehensive transport refrigeration LCCP investigation in detail comparing various influencing parameters to achieve the lowest environmental impact. In the present study, the new LCCP simulation tool for transport and bus refrigeration/air conditioning products, was developed for analyzing the environmental impacts for only private use for Ingersoll Rand. The tool was first briefly introduced at 2014 ASHRAE Annual Conference [15]. Since there are some unique challenges for the food transport refrigeration, the new transport LCCP tool, involves the open-shaft compressor model, and this model could have a higher leakage rate than the hermetic systems. The fuel consumption modeling tool (FCMT) can facilitate calculation of indirect emissions due to the unit energy or fuel consumption in the LCCP tool, and it is capable of analyzing a wide range of transport product lines. This paper will provide detailed LCCP assessments from various influencing parameters with the latest refrigeration transporttrailer technologies. The trailer products from Thermo-King are selected for the LCCP investigation. In this study, it will calculate the equivalent mass of CO2 released into the atmosphere for the trailer products under various climates, system efficiency improvements, refrigerant leakage rates, food classification, etc. In addition, the new refrigerant R452A, as current R404A alternative, is investigated for environmental performance. Thermo-King was the first to announce the adoption of this new refrigerant as a lower GWP option for its transport refrigeration customer and soon which is becoming the industry standard. The LCCP investigation is conducted comprehensively, from both direct and indirect emission aspects. The perspectives drawn from this study are beneficial for the researchers, policy makers, and manufactures to minimize
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
the total environmental impact through maximizing the energy efficiency and maintaining the maximum sustainability and safety for consumers. Environmental impact of refrigeration system method review As mentioned briefly in Section 1, the environmental impact for the refrigeration systems can be assessed by various methodologies and indexes. In this section, the commonly used evaluation indexes are introduced in more detail. Different assessment approaches are listed to identify the efficient solutions towards a green environmental impact. Global warming potential The GWP, which is an index that characterizes the participation of a refrigerant molecule in the greenhouse increase, is calculated through the comparison with the contribution to the greenhouse effect of the reference molecule, a molecule of CO2, presenting a GWP = 1. Usually the comparison for the refrigerants can be made according to heating effect caused by a molecule of refrigerant during the most common used 100 years (GWP100). The GWP is depended on the: (1) infrared radiation absorptivity of the gas, (2) the gas lifetime in the atmosphere, and (3) the selected time frame [16]. The GWP, then, just reflects the impact of the gas properties on the global warming. With the aid of the Kyoto Protocol, the GHGs in the atmosphere including chlorofluorocarbons (CFCs), hydrogen chlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), should be controlled at an appropriate level to prevent the harmful effect of climate change on humans [17]. In addition, the CFCs and HCFCs can also split and release the ozone destructive chlorine atoms, which can add the harmful ultraviolet radiation for the earth. Thus, they are gradually reduced and eventually phased out in the Montreal Protocol. Currently, most refrigerants in the refrigeration systems are the HFCs family. However, they are still presenting a high-GWP values up to 4000.
Life cycle climate performance From Section 2.2, it can be observed that the TEWI has not consider the indirect emissions resulting from manufacturing, delivery and recycling of refrigerants aspects. Then LCCP has developed. It extends the concept of TEWI, with the consideration of the environmental impact associated with the energy consumed to manufacture both the refrigerant and the raw materials used for the manufacturing of the refrigerant, and the direct warming impact of any fugitive greenhouse gases emitted during the refrigerant manufacture [19]. Currently the LCCP can be regarded as a more complete and complex index to evaluate the global warming performance of a technology, and there are several tools for study: ORNL LCCP Excel Tool for various stationary refrigeration systems [7], the AHRTI LCCP model for residential heat pumps [8], and GREEN-MAC-LCCP for only automotive air conditioning application [14]. The LCCP is calculated from the Eq. (2) [7]. It can be found that the complexity for the LCCP can enhance the grades of freedom of the applicant and can be more flexible and applicable to various input parameter settings.
Emtotal ¼ Emdirect; ref leak þ Emdirect; ref acci þ Emdirect; ref service þ Emdirect; ref EOF þ Emdirect; ref prod transport þ Emdirect; ref; other þ Emindirect; consumption þ Emindirect; manufacture þ Emindirect; EOF þ Emindirect; transport
TEWI ¼ GWPðL n þ mð1 CÞÞ þ ðn E bÞ
ð1Þ
where: GWP – Global Warming Potential; L – Annual amount of the refrigerant emissions (leakage) [kg/year]; n – Lifetime of the refrigeration system [year]; m – Refrigerant charge [kg]; C – Recovery factor/refrigerant recycling [between 0 and 1]; E – Annual energy consumption of the refrigeration system [kWh/year]; b – The amount of the CO2 equivalent mass emissions for 1 kWh energy generation, kg/kWh.
ð2Þ
Emdirect, ref leak – Emission due to refrigerant leakage; Emdirect, ref acci – Irregular emission due to such things as accidents; Emdirect, ref service – Emission due to leakage of refrigerant from servicing; Emdirect, ref EOF -Emission due to end-of-life of system where refrigerant is lost; Emdirect, ref prod transport- Emission due to leakage from refrigerant production and transportation; Emdirect, ref other -Reaction byproducts from the atmospheric breakdown of refrigerant emissions; Emindirect, consumption– Emission due to energy consumption during system’s lifetime; Emindirect, manufacture–Emission due to energy used to manufacture refrigerant and components; Emindirect, EOF–Emission due to energy used for end of life of components and refrigerants; Emindirect, transport–Emission due to energy used to transport equipment
Total equivalent warming impact Section 2.1 mainly discusses the GWP from the refrigerant aspects. In fact, during the system operation in its lifetime, the emissions is not only caused by refrigerant leakage into the atmosphere, but also affected by the system energy consumption. Thus, the new concept/tool-TEWI has developed, which includes of direct emissions (refrigerant leakages) and indirect emissions (emissions resulting from electricity production that is consumed by the refrigeration system, as shown in Eq. (1) [18]. It can be found that the direct emissions depend on the refrigerant GWP, the amount of refrigerant leakage, the equipment running time, etc. While the indirect emissions depend on the energy consumption during operation and the emissions per unit energy generation:
35
Life Cycle Assessment The Life Cycle Assessment (LCA), which is the cradle-to-grave analysis for environmental impact valuation of a given product or service caused by its existence, can extend the LCCP approach to the other relevant aspects, such as the eutrophisation potential, acidification potential, ozone depletion potential, etc. The main advantage for the LCA present in relation to LCCP is in its standardization: LCA is ruled under ISO 14000 Standards. The emissions are resulting from the whole lifecycle of refrigerant and the devices that supports it (i.e. the entire components of a refrigeration system [20]):
Design and development of technologies; Row material acquisition and transformation; Production of system devices components and refrigerant; Process of assembly; Operation (includes servicing);
36
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Recovery, recycling or destruction of refrigerant and system devices. If only the GHG emissions are taken account, the LCA and LCCP should lead to same results with existing known energy consumption inputs. However, in the case of refrigeration, it is not so flexible for the LCA inputs under the various operating conditions, such as high/low ambient conditions and location information for heat pumps, etc. Thus, for a specific refrigeration system emissions during its lifetime, the LCCP is more powerful and reliable to evaluate and minimize the environmental performance impact. Transport LCCP modeling methodology In this section, the fuel consumption modeling tool (FCMT), which is the Thermo King Fuel Simulator, together with the transport LCCP tool are introduced for the transport LCCP modeling methodology. The FCMT can facilitate calculation of indirect emissions due to unit energy or fuel consumption in the LCCP tool, which is capable of analyzing a wide range of transport product lines. Since the transport LCCP comprehensive investigation under various influencing factors has not been investigated in detail and it is different from the LCCP for the stationary refrigeration systems, for the convenience of readers, the modeling methodology is shown here. Thermo King Fuel Simulator Prior to the LCCP simulation tool, the FCMT, is used to calculate the most important indirect emission caused by the energy or fuel consumption. Fig. 1 shows three Simulink models: box model, control model and plant model. The box model can calculate the cooling load required by the system to maintain the box at a pre-set temperature. It can be decided and influenced by the box dimensions, insulation material, ambient temperature, and box temperature, and such factors can be used to calculate the heat loss through the box walls with knowing the thermal conductivity of the insulating material. Ref. [15] also mentioned that, alternatively, the box loss may be known directly if it is tested experimentally following TTMA RP38-07 [21]. Either method (specifying materials or entering know loss values) for the box loss calculation can be used in the FCMT. A solar load is computed and factored into the box model to account for the actual skin temperature of the box exterior in relation to the ambient temperature, vehicle speed, and location [15]. Door openings during the refrigeration system
operation is also accounted as part of the heat loss for in the box model. The plant model can predict the system energy efficiency and capacity under environmental boundary conditions. The control model, with the aid of the specific refrigeration control valves in response to coded temperature control algorithms, is used to control the engine speed, fan speed, and refrigeration capacity. The plant model is affected by the control model. The control model and plant model are hence proprietary models based on the Thermo King’s specific design and control architecture. The three models work together to predict energy/fuel consumption for any given operating route and conditions. Then the Simulink model can be converted to the standalone dynamic link library (DLL) file via the MATLABÒ platform. Then the fuel consumption can be calculated and the DLL file (FCMT_win32.dll and FCMT_Engine.dll) can run with Excel with worksheet input and VBA programs, thus the energy or fuel consumption can be calculated. Transport LCCP calculation This section introduces the transport LCCP calculation, as shown in Fig. 2 and Eq. (3).
X TransportLCCP ¼ ðR þ RP ÞfYðL þ LSA Þ þ Eg þ Y ðC F F þ C K KÞ X X X CM M þ C M MR þY FT CF þ
ð3Þ
RP – Atmospheric reaction products from the atmospheric breakdown of HFCs; R – Refrigerant Global Warming Potential (GWP); Y – Lifetime, in years L – Annual regular emissions due to refrigerant leaks from the system during operation; LSA– Annual regular emissions due to leakage in assembly plants, irregular emissions due to accidents and service emissions from servicing operations; E – Refrigerant loss at the End-of-Life (EOL) of the unit; K – Annual energy consumption from the refrigeration or AC unit operation; MR, M– Mass of refrigerants and components for manufacturing and EOL energy purpose; M– Energy from additional fuel consumption to transport the refrigeration or AC unit mass on board the vehicle during its lifetime. FT– Annual energy from additional fuel consumption to transport the refrigeration or AC unit mass on board the vehicle during its lifetime;
Fig. 1. Flow chart of the Thermo King Fuel Simulator.
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
37
Fig. 2. Transport LCCP composition.
CF – Equivalent CO2 kg/kg Fuel; CK – Equivalent CO2 kg/kWh; CM – Equivalent CO2 kg/kg material of refrigerants or components for manufacturing and EOL energy purpose; The Microsoft Excel-based LCCP tool architecture flowchart is shown in Fig. 3. The DLL file created from the MATLABÒ based FCMT and a series of VBA macros were implemented with the LCCP Excel program for the energy calculation. All direct or indirect emissions are computed with the VBA program. To start for the LCCP calculation process, the pre-set inputs should be provided in the ‘‘main” worksheet for refrigerant, fuel type, name of the refrigeration system information sheet. Then the vehicle models and types (trailer, truck, bus A/C, etc.), box dimensions, insulation conditions, ambient conditions, control modes, product pre-set points, etc., should set for the fuel consumption input worksheet from FCMT. Once all input data are provided and click the ‘‘Run” button, the program can read in climate data from a typical meteorological year (TMY3) database, conducts annual energy or fuel consumption calculations from the defined vehicle running schedule, and computes all indirect and direct emissions. The ‘‘Results” sheet displays the detailed calculation results including direct and indirect emissions, etc. The transport tool can beneficial for easy implementation of updated versions of the accompanying FCMT. Transport refrigeration LCCP results and discussion In this section, various influencing factors are investigated to assess the LCCP to minimize the total environmental impacts.
The vehicle, which is a single compartment diesel-driven tractor trailer with swing type doors, has exterior dimensions of 53.1 feet (16.2 m) length, 8.5 feet (2.6 m) width, and 9.5 feet (2.9 m) height with a box loss of 180 Btu/h/R (0.53 W/K), a life expectancy of 15 years with a 15 percent nominal leak rate. The charge amount for refrigerants is set to be 13.0 lbs (5.9 kg) even though a small change may be produced with an alternative refrigerant. The daily distribution used for the study represents the fresh products at setpoint 30 °F (1 °C) or frozen products at set-point 10 °F (23 °C). Application conditions are short haul daily distribution runs of 5 days/week for 50 weeks. The haul load was 40,000 lbs (14,930 kg) for both cases. Operation of fresh/frozen conditions is a 1-h pull-down followed by 14 h of operation. Operation includes six door openings of 20 min each. The road condition is the rural with sunny condition with Cycle Sentry running mode. The values of mass of various system components with different materials from Ingersoll Rand product windchill database are incorporated into the transport LCCP tool for calculation. The components are frame, bulkhead, engine, generator, compressor, refrigeration heat exchangers, tubing and VCS components, air flow components, control box & harness, skins-covers & nameplate and fluids. The material emission factor is shown in Table 1. Effect of low GWP alternative R452A for LCCP investigation The pressures to control climate change and to minimize the environmental impacts are driving the development of new regulatory policies to restrict and lower the direct GWP impact of Fgases. The R404A (GWP = 3943) is commonly used in current air cooled application types, and specifically in transport refrigeration.
Fig. 3. Transport LCCP flowchart.
38
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49 Table 1 Material emission factor. Material
Emission factor CO2-eq. (kg/kg)
Aluminum Copper Plastics Steel Cast Iron Brass Engine Oil Rubber Lead
1.6 3.3 3.0 2.3 1.6 2.5 3.3 3.1 2.1
Thermo-King, is the first and only provider that offers its customers an entire portfolio of truck and trailer refrigeration units that use the new, lower GWP refrigerant R452A (GWP = 1945) for a better environmental performance. This gives companies a choice to reduce their emissions and maintain the same high performance of their refrigerated fleet. R452A is an ASHRAE 34 newly classified A1 refrigerant (lower toxicity/non-flammable) that is developed to be nearly design-compatible to replace R404A specifically in transport refrigeration. It is a blend of R32/R125/R1234yf at a composition of 11%/59%/30% by weight. As shown in Fig. 4 and Fig. 5, R452A was designed compositionally to best match R404A’s pressure enthalpy and temperature entropy characteristics, indicating the transport refrigeration units compatible with next generation R452A refrigerant. Based on the two industry accepted transport refrigeration equipment standards-AHRI Standard 1110 2013 [22] and ATP Standard [23]), the laboratory testing reveals that R452A can achieve acceptable and equivalent system performance when it is substituted in R404A transport refrigeration equipment. The expansion valve was set to get maximal cooling capacity and this setting was maintained under other temperature conditions. Under close refrigerant charge amount, R452A has the down 5.5% net cooling capacity relative to R404A at ambient temperature 100 °F (38 °C) (AHRI rating condition) at low return air temperature (20 °F, 29 °C) and at compressor high speed. R452A has comparable cooling capacity practically to R404A at higher return air temperatures (35°F, 1.7 °C). Same trend can be achieved at ambient temperature 86 °F (30 °C) (ATP rating condition), but the capacity difference is smaller in this case. In addition, for ATP rating condition, the R-452A performance of coefficient of performance (COP) and fuel efficiency ratio relative to R-404A is within 1%. It has been
Fig. 4. Pressure-Enthalpy comparison for R404A and R452A.
Fig. 5. Temperature-Entropy comparison for R404A and R452A.
proved that the R452A can achieve the equivalent and acceptable capacity and efficiency to R404A Fig. 5. There are 3 scenarios for the LCCP comparison. R404A Baseline is from the early Thermo King product SB series and the refrigerant is R404A. R404A Precedent is from the Thermo King series of Precedent transport refrigeration units (TRU) and it is at the forefront of green energy, delivering double-digit fuel savings, best-in-class performance and lower life cycle costs. R452A Low-GWP represents the new, lower GWP R452A as standard in the vehicle powered range of units. Field tests indicate that it has equivalent capacity and efficiency to R404A Precedent. The R452A product of trailers and other vehicle-powered refrigeration units is available in Europe in Jan.1, 2016. To have a deep understanding about the product LCCP, the CO2eq. emission contributors are revealed, as shown in Fig. 6, Fig. 7 and Table 2. The direct emission is the refrigerant leakage emission, including manufacturing leakage emission, service leakage emission, annual regular leakage, EOL leakage emission, accident leakage emission and decomposition leakage emission. The direct emission includes emissions caused by the energy for equipment manufacturing, installation, maintenance, and the emissions from the all fuel consumptions by the system operation. Three product categories are compared for the fresh product condition (30 °F set-point) and frozen product condition (10 °F set-point). Basically, in the case of the fresh product, as shown in Fig. 6, the fuel consumption, services as the main indirect emission and consumes approximately 70–80% of the total emissions. While the regular refrigerant leakage, services as the main direct emission and consumes 15–25% of the total emissions. Direct emissions from refrigerant service leakage and loss end of life (EOL) produce 2–3% and 1–2% total emissions, respectively. The total indirect emission is appropriately 69–82% for the fresh case. Fig. 6 indicates that R404A Precedent lifetime emission can give a 19% emission reduction compared with R404A Baseline for the fresh product and the two scenarios have the same direct emissions. This is because the Precedent platform utilizes an all-new and advanced Diesel Direct Electric (DDE) architecture to drive optimum efficiencies. It’s a smarter approach and it can already meet much stricter Tier 4 final emissions certification by the Environmental Protection Agency (EPA) and California Air Resources Board (CARB). Further, it can comply with CARB’s Ultra-Low-Emission Transport Refrigeration Unit In-Use Performance Standards (ULETRU). In addition, the superior temperature control is also used. The laboratory tests
39
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49 Table 2 LCCP evaluation for 3 scenarios (kg CO2-Eq.) Fresh/frozen condition
Fresh product (30 °F)
Frozen product (10 °F)
Scenario
R404A Baseline
R404A Precedent
R452A Low-GWP
R404A Baseline
R404A Precedent
R452A Low-GWP
Total lifetime emission Total direct emission Emission Manufacturing Emission Service Emission Leakage Emission EOL Total indirect emission Emission equipment Mfg Emission equipment installation Emission fuel consumption Emission maintenance Emission equipment EOL
257,908 63,765 444.7 6670.1 52026.5 4624.6 194,142 1693.2 105.5 192,119 99.5 124.9
208,635 63,765 444.7 6670.1 52026.5 4624.6 144,869 1693.2 105.5 142,846 99.5 124.9
176,410 31,541 219.9 3299.3 25734.6 2287.5 144,869 1693.2 105.5 192,119 99.5 124.9
736577.1 63765.9 444.7 6670.1 52026.5 4624.6 672,811 1693.2 105.5 670,788 99.5 124.9
642267.5 63765.9 444.7 6670.1 52026.5 4624.6 578,501 1693.2 105.5 576,478 99.5 124.9
610,043 31541.5 220.0 3299.3 25734.7 2287.5 578,501 1693.2 105.5 576,478 99.5 124.9
Fig. 6. Effect of refrigerants on LCCP for fresh products.
40
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 7. Effect of refrigerants on LCCP for frozen products.
Fig. 8. Effect of ambient temperature on LCCP.
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 9. System operating performance metrics under various ambient temperatures.
41
42
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 10. Effect of US cities on LCCP.
Fig. 11. Effect of US cities on LCCP.
Fig. 12. Effect of annual refrigerant leakage rate on LCCP.
including both the fresh Cycle Sentry test and frozen Cycle Sentry hill test both indicate double-digit fuel savings can be achieved. The R452A Low-GWP type leads to a 15% emission reduction compared to the R404A Precedent. The Kyoto Protocol recognizes HFCs
as one of the potent GHG that most developed countries have agreed to restrict. European Union (EU) and Japan are already developing HFC regulations as part of their Kyoto compliance scheme. The EU 2014 F-Gas Regulation caps and phases-down
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
43
Fig. 13. Effect of food product refrigerating temperature set-point on LCCP.
HFCs refrigerants in most applications including stationary and mobile refrigeration based on their GWP. EU has also implemented product bans based on refrigerant and several European countries have, or are planning GWP-based taxes on HFCs. In response to such changes and environmental needs, the industry are pushed to exploit lower GWP refrigerants. R452A and R404A have the equivalent capacity and efficiency, but the former has half the GWP of the latter. Thus, the former has more environmental benefits. As for the case of frozen product in Fig. 7, R404A Precedent can achieve a 13% CO2-eq. reduction compared with the R404A Baseline and R452A has a 5% CO2-eq. reduction compared with the R404A Precedent type. While the comparison between the fresh product case and frozen indicates the fuel consumption of the later is larger. This is because a lower food evaporating temperature (from 30 °F set-point for the fresh products to the 10 °F setpoint for the frozen) can result in a lower energy efficiency. This section indicates enough attentions should be paid for low GWP refrigerant utilization as well as energy efficiency enhancements.
Effect of climates for LCCP investigation Fig. 8 shows that in the R452A system, reducing the ambient temperature from 90 °F (32 °C) to 60 °F (15.5 °C) can produce up to 60% emission reduction for the fresh product case while 39% reduction for the frozen. The direct emissions remain constant. A higher ambient temperature indicates a larger product heat load, which needs more fuel sources. To reveal the heat load more clearly, Fig. 9 displays the system operating performance metrics under various ambient temperatures with 1 h pre-cooling and 14 route hours for one day. In the case of fresh product, reducing the ambient temperature from 90 °F to 60 °F can decrease the food heating load and thus shorten the engine running time (from 3.91 h to 1.25 h per day). Fig. 9(a)– (d) show that reducing R452A system ambient temperature can shorten the engine high speed and low speed duration percentage by 17.7% (from 26% to 8.3% of the total engine on percentage). In addition, during the pull-down test period with 1 h pre-cooling, a higher ambient temperature indicates a longer high-speed engine duration time. Fig. 9(d) and (e) show a comparison between the fresh product and frozen product with the ambient temperature 60 °F. It can be observed that a huge amount of engine on duration percentage (up to 51%) can be achieved for the frozen product while it is only 8.3% for fresh. Thus a massive energy consumption can be produced in the frozen case.
Six cities, Minneapolis, Boston, Richmond, Los Angeles, San Antonio, Phoenix, from cold areas to hot areas, are conducted to investigate the LCCP, as shown in Fig. 10. The maximum and minimum weather data source is collected from 1981 to 2010 by the NOAA Notational Climatic Data Center of the United States. In Fig. 10 the variation from the cold area of Minneapolis to the scorching hot area of Phoenix give a 66% emission reduction for the fresh product case while 53% for frozen. In addition, Fig. 11 shows the effect of sunny/cloudy conditions, which have different solar heat fluxes, for the lifetime emissions. The sunny/cloudy condition has much less effect than the ambient conditions on the LCCP. A switch from sunny condition to the night condition produces a 7% emission reduction for the fresh product case while less than 4% for frozen. Effect of annual refrigerant leakage rate for LCCP investigation Most transport refrigeration/air conditioning equipments utilize the open-shaft compressors, which could have a higher regular leakage rate than the hermetic systems. In this section, the annual leak rate range from 25% to 10% has been chosen to investigate the LCCP, as shown in Fig. 12. It can be noticed that only the emission from the regular leakage varies while others remain constant. Decreasing the R452A annual leak rate from 25% to 10% can give a 13% emission reduction for the fresh product case while 4% reduction for the frozen. R404A products produce more emissions since R404 has approximately double GWP values than R452A. Effect of food product refrigerating temperature set-point for LCCP investigation Fig. 13 shows the effect of food product refrigerating temperature (i.e. the evaporating temperature) set-point on the LCCP. Increasing the R452A system set-point from 10 °F (23 °C) to 50 °F (10 °C) can lead to more than 80% emission reduction. A lower evaporating temperature indicates a lower energy efficiency, leading to a higher fuel consumption. To explore more detail for the effect of the food product set-point, Fig. 14 shows detail about the system operating performance metrics with 1 h pre-cooling and 14 route hours for one day. Increasing the R452A system setpoint from 10 °F to 50 °F gives a 9.1 engine running time reduction per day (from 10.7 h to 1.6 h per day). Fig. 14(a)–(d) indicates increasing the set-point results in 60.5% engine duration percentage reduction (from 71.5% to 11% of the total engine on percentage). A significant emission reduction can be achieved as the
44
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 14. System operating performance metrics under various food product refrigerating temperature set-points.
food product set-point temperature increases. It can be noticed that the food product set-point has even higher effect on the LCCP than the climate condition.
less heat loss to the ambient, thus leading a lower fuel source energy consumption. The food box insulation condition has less effect on the LCCP than the climate condition and food product temperature set-point.
Effect of box insulation condition for LCCP investigation Effect of system operation control condition for LCCP investigation Fig. 15 shows the effect of food box insulation condition on the LCCP. A 15% R452A annual insulation degrade rate can provide a 13% emission reduction for the fresh and 14% for the frozen. Only the emission from the fuel consumption varies while other items remain constant. A lower annual insulation degrade rate indicates
There are two running modes supported in this version–Cycle Sentry and Continuous. When Cycle-Sentry mode is selected the unit will start and stop automatically to maintain the set-point, keep the engine warm, and keep the battery charged. When
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
45
Fig. 15. Effect of annual insulation degrade rate on LCCP.
Fig. 16. Effect of system control-running mode on LCCP.
Continuous mode is selected, the unit will start automatically and run continuously to maintain the set-point and provide the constant airflow. Three product set-point temperatures: 0 °F (17.8 °C), 5 °F (15 °C) and 10 °F (12 °C) are selected to investigate for two running modes. Fig. 16 shows that the Cycle Sentry has a 14 21% emission saving than the Continuous. To reveal the mechanism in more detail, Fig. 17 shows the system operating performance metrics with 1 h pre-cooling, 14 route hours for one day, and 10 °F food product set-point. The switch from Continuous mode to Cycle-Sentry gives a 6.8 h engine running time reduction per day. Fig. 17(a) and (b) indicates the switch shows 45.5% engine duration percentage reduction (from 86% to 40.5%). Usually the Continuous mode has the more accurate temperature control and run continuously to maintain set-point, which can be seen from the comparison for the return air temperature curve between the two modes, but at the cost of a higher energy consumption. Thus, a reasonable selection for the two options should be performed to maintain the quality of the food products while minimize the environmental impact at the same time. Effect of system efficiency improvement for LCCP investigation Fig. 18 shows the effect of system efficiency improvements on the LCCP. Energy efficiency, can be enhanced via the utilization of more reliable and efficient compressors, optimized coil design,
reduced heat loss with ambient, etc. Increasing the R452A system efficiency improvement rate from baseline 0% to 15% produces the 11% emission reduction for the fresh products and 12% for the frozen. The emission due to the fuel consumption varies while other items remain constant. Effect of alternative transport refrigeration technologies for LCCP investigation As for the food transport refrigeration systems, although the vapour compression cycle is well established for system operation, the rising cost of fuel/electricity and pressure to reduce the environmental impacts have renewed the interest in other alternative transport refrigeration technologies. The thermally driven technologies and other innovative technologies could offer the environmental advantages over the conventional vapour compression cycle in the near future. R404A, the predominant high-GWP refrigerant, and other HFC refrigerants, are extensively unemployed with the alternative technologies. This section discusses various alternative technologies for LCCP comparison with existing vapour compression cycle technology. (1) Adsorption technology Adsorption technology is shown in Fig. 19(a). The ‘thermal compressor’ (desorption/adsorption bed) is used to replace
46
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 17. System operating performance metrics under two running modes.
Fig. 18. Effect of system efficiency improvement on LCCP.
the conventional vapour compression cycle mechanical compressor and the sorbent/low-GWP refrigerant serves as the working fair. This is beneficial for the system to achieve the lower environmental impact. In addition, it can utilize the low grade waste heat for better thermal integration of transport refrigeration processes. A study was performed to design, model, built and test a trailer refrigeration and bus air-conditioning air cooled adsorption system with activated carbon sorbent beds as the sorbents and ammonia (R717) as a refrigerant [24]. The theoretically characterization for the system was for the purpose of being capable of maintaining temperatures in the range 18 to 4.5 °C for transport refrigeration. It mentioned that the heat available
from diesel engines in the power range 225–525 hp was determined to be 40–60 kW from the engine cooling circuit and 40–140 kW from the exhaust gases. It also mentioned that the practical COP used for system design was in the range 0.6–1 and specific cooling power rates were considered to be around 614 W per kilogram of carbon for ammonia (R717) refrigerant and 198 W per kilogram of carbon for R134a refrigerant. (2) Air cycle technology Air cycle technology is shown in Fig. 19(b). The environmentally friendly gaseous refrigerant (air) is the working fluid. The air in the cycle can produce cold with a sequence of processes comprising compression, followed by constant
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
pressure cooling, and then expansion to the original pressure to achieve a final temperature lower than at the start of compression. A study [25] was conducted to accommodate the air cycle system within the physical envelope of an existing conventional R404A vapour compression refrigeration trailer unit to achieve an equivalent refrigeration capacity
47
(specified as 12 kW at 0 °C trailer temperature and 7.2 kW at 20 °C trailer temperature, both at 30 °C ambient). The commercially available or existing parts, including the diesel engine prime mover and air circulation fans of the vapour compression system were utilized for the air cycle system. The standard exhaust turbocharger components were selected for the two compressor stages and the modified turbine for the air cycle. It could achieve a full-load capacity of 7.8 kW at 20 °C (8% higher than the existing unit), but at 0 °C the cooling capacity was 9.5 kW (21% lower than the existing unit). Based on the test results of the demonstrator unit, an optimised air cycle unit with thermodynamic model employing state of the art technology predicted overall COP to be 0.53 at 20 °C and 7.8 kW refrigeration capacity, which was only 7% lower than the corresponding COP for the vapour compression unit [26]. (3) Ejector technology Ejector refrigeration is shown in Fig. 19(c). It is a thermally driven technology and has the benefits of the simplicity of structure, no moving parts, more environmental free working fluids, low grade heat source above 80 °C. However, it has lower COPs, 0.2–0.3, compared with vapour compression cycle or other thermally driven technologies. Currently there are no commercially available off the shelf for the ejector food transport refrigeration system. The water can be used as a refrigerant in the design and application of bespoke steam ejector systems for cooling applications above 0 °C. In general, the rising energy costs can encourage more effective utilization of waste heat for better thermal integration of refrigerant transport processes. Thus, it is expected that the ejector technology is beneficial for the transport environmental impact and deserves the further investigation for efficient steady flow ejectors in the near future. Here the alternative transport refrigeration technologies are integrated for the investigation of LCCP. The ejector technology is not employed since it has very low energy efficiencies. In addition, for the convenience of readers, the fuel source of gasoline is also compared for the LCCP, as shown in Fig. 20. It is noticed that with R452A, gasoline gives an 11–13% emission reduction compared with diesel. As for the adsorption cycle, it can utilize the free available waste heat or renewable energy as the load driving source, and such driving source can emit few emissions. In addition, the main fuel consumption can be caused due to the weight of the adsorption system. Thus, considerable emission reduction can be achieved for the adsorption cycle. As for the air cycle, it has the benefit that the working fluid air is environmental friendly media. The emission reduction can be obtained for the fresh product case while not for the frozen since the direct emission takes a less percentage for the latter. While it should be noted that the air cycle technology should be investigated further to achieve a higher system efficiency performance. In addition, the thermal energy storage with phase change materials (PCMs) can also be integrated in the food transport system to minimize the environmental impact if the PCMs are charged with the renewable energy. Conclusion
Fig. 19. Alternative transport refrigeration technologies.
The LCCP is used to evaluate the total lifetime emissions for the food transport refrigeration system under various influencing factors. The low GWP R452A (GWP = 1945), is investigated to provide an improved environmental performance. The switch from R404A Baseline to R404A Precedent gives 13–19% emission reduction. This is mainly because the Precedent platform can drive optimum efficiencies and achieve double-digit fuel savings across real-world applications. As for R404A
48
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 20. Effect of alternative transport refrigeration technologies on LCCP.
Precedent, when the R404A is replaced with R452A, a 5–15% emission reduction can be achieved since R452A has around half GWP of existing R404A. In the R452A system, reducing the ambient temperature from 90 °F (32 °C) to 60 °F (15.5 °C) can produce up to 60% emission reduction for the fresh product case while 39% reduction for the frozen. The direct emissions remain constant. A higher ambient temperature indicates a larger product heat load, which needs more fuel sources. A switch from sunny condition to the night condition produces a 7% emission reduction for the fresh product case while less than 4% for frozen. Decreasing the R452A annual leak rate from 25% to 10% can give a 13% emission reduction for the fresh product case while 4% reduction for the frozen. Increasing the R452A system food product refrigerating temperature (i.e. the evaporating temperature) setpoint from 10 °F (23 °C) to 50 °F (10 °C) can lead to more than 80% emission reduction. A lower evaporating temperature indicates a lower energy efficiency, leading to a higher fuel consumption. A 15% R452A annual insulation degrade rate can provide a 13% emission reduction for the fresh and 14% for the frozen. Only the emission from the fuel consumption varies while other items remain constant. A lower annual insulation degrade rate indicates less heat loss to the ambient, thus leading a lower fuel source energy consumption. The food box insulation condition has less effect on the LCCP than the climate condition and food product temperature set-point. Two running modes Cycle Sentry and Continuous are compared. The comparison shows that the Cycle Sentry can lead to a 14–21% emission saving than the Continuous. This is because the Continuous, which has the more accurate temperature control and run continuously to maintain set-point, has the higher duration percentage for both the engine on high speed and low speed. A reasonable selection for the two options should be performed to maintain the quality of the food products while minimize the environmental impact at the same time. Increasing the R452A system efficiency improvement rate from baseline 0% to 15% produces the 11% emission reduction for the fresh products and 12% for the frozen. The emission due to the fuel consumption varies while other items remain constant. The alternative transport refrigeration technologies may also have the environmental benefits than the conventional HFC based vapour compression refrigeration systems. This aspect deserves further investigation. As for the adsorption technology, it can utilize the free available waste heat or renewable energy as the cooling load driving source, and the main fuel consumption can be caused due to the weight of the adsorption system. Thus, considerable emission reduction can be achieved. As for the air cycle, it has
the benefit that the working fluid air is environmental friendly media. While both the adsorption technologies and the air cycle technologies should be investigated further to achieve a higher system efficiency performance. Acknowledgement No funding support. The author would like to express the deepest appreciation to Z.Li and P.Li for their endless love, support, and encouragement during the uncertainty of career path. References [1] Intergovernmental Panel on Climate Change (IPCC), 2007. IPCC Fourth Assessment Report, the Physical Science Basis. http://www.ipcc.ch/ ipccreports/ar4-wg1.htm (accessed May 2013.). [2] LuAnn Dahlman. Climate Change: Global Temperature. https:// www.climate.gov/news-features/understanding-climate/climate-changeglobal-temperature (accessed June 2016.). [3] Billiard F. Refrigerating equipment, energy efficiency and refrigerants. Bulletin of the IIR [2005-1]; 2005. [4] Estrada-Flores S. Chain of thought [Vol. 1, No. 2, April 2008]. http://www.foodchain.com.au/FCI_enews2.pdf; 2008. [5] AEA Technology. The validity of food miles as an indicator of sustainable development – Final report for DEFRA. Didcot: AEA Technology, UK; 2005. [6] Department for Environment, Food and Rural Affairs (defra). The validity of food miles as an indicator of sustainable development. London: Defra, UK; 2005. [7] Life Cycle Climate Performance, V1.0, 2014. Available at: http://lccp. umd.edu/ ornllccp/. [8] Zhang M. and Muehlbauer J. Life Cycle Climate Performance Model for Residential Heat Pump Systems, 14th International Refrigeration and Air Conditioning Conference, Purdue University, West Lafayette, Indiana, USA; 2012. [9] IIR LCCP WP: http://www.iifiir.org/medias/medias.aspx?INSTANCE= EXPLOITATION&PORTAL_ID=portal_model_instance__WP_LCCP_Evaluation. xml. [10] Beshr M, Aute V, Sharma V, Abdelaziz O, Fricke B, Radermacher R. A comparative study on the environmental impact of supermarket refrigeration systems using low GWP refrigerants. Int J Refrig 2015;56:154–64. [11] Li G. Investigations of life cycle climate performance and material life cycle assessment of packaged air conditioners for residential application. Sustainable Energy Technol Assess 2015;11:114–25. [12] Li G. Comprehensive investigations of life cycle climate performance of packaged air source heat pumps for residential application. Renew Sustain Energy Rev 2015;43:702–10. [13] Li G, Alabdulkarem A, Hwang Y, Radermacher R. Drop in life cycle climate performance of low GWP R-410A alternatives for heat pumps. 11th IIR-Gustav Lorentzen Conference on Natural Refrigerants – GL2014; 2014. [14] Papasavva S, Hill W, Andersen S. GREEN-MAC-LCCP: A Tool for Assessing the Life Cycle Climate Performance of MAC Systems. J Environ Sci Technol 2010;44:7666–72. [15] Nasuta D, Srichai R, Zhang M, Martin C, Muehlbauer J. Life Cycle Climate Performance Model for Transport Refrigeration/Air Conditioning Systems, ASHRAE Annual Conference, Seattle, WA; 2014.
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49 [16] World Meteorological Organization (WMO). Scientific assessment of stratospheric ozone. Report no 44. In: Presented at the WMO Global Ozone Research and Monitoring Project; 1999. [17] United Nations Framework Convention on Climate Change (UNFCCC), 1998. Kyoto protocol to the United Nations framework convention on climate change. http://unfccc.int/essential_background/kyoto_protocol/items/1678. php (accessed June 2012.). [18] Orfeo S.R. A history of the TEWI process. In: Presented at the Proceedings of International Conference on Ozone Protection Technologies, Washington DC, USA; 1996. [19] Little A. Global Comparative Analysis of HFC and Alternative Technologies for Refrigeration, Air Conditioning, Foam, Solvent, Aerosol Propellant, and Fire Protection. Arthur D. Little, Inc, Cambridge, Massachusetts; 2002. [20] Rebitzer G, Ekvall T, Frischknecht R, Hunkeler D, Norris G, Rydberg T, et al. Life cycle assessment: Part 1: Framework, goal and scope definition, inventory analysis, and applications. Environ Int 2004;30(5):701–20.
49
[21] TTMA RP 38-07, 2007, Method of Testing and Rating Heat Transmission of Controlled Temperature Vehicle/Domestic Containers. [22] ANSI/AHRI Standard 1110 2013 Standard for Performance Rating of Mechanical Transport Refrigeration Units, Air-Conditioning, Heating, & Refrigeration Institute, Arlington VA, 22201. [23] Agreement on the International Carriage of Perishable Foodstuffs and on the Special Equipment to be used for Such Carriage (ATP). UNECE Transport Division publication ECE/TRANS/219. [24] Christy C, Toossi R. Adsorption Air-Conditioning for Containerships and Vehicles. Available from: http://www.metrans.org/research/final/99-19_ Final.pdf/#search=%22C%20Christy%2C%20R%20Toossi.%20Adsorption%20AirConditioning%20for%20Containerships%20and%20Vehicles%22; 2004. [25] Spence SWT, Doran WJ, Artt DW. Design, construction and testing of an aircycle refrigeration system for road transport. Int J Refrig 2004;27:503–10. [26] Spence SWT, Doran WJ, Artt DW, McCullough G. Performance analysis of a feasible air-cycle refrigeration system for road transport. Int J Refrig 2005;27:381–8.
Contents lists available at ScienceDirect
Sustainable Energy Technologies and Assessments journal homepage: www.elsevier.com/locate/seta
Original article
Comprehensive investigation of transport refrigeration life cycle climate performance Gang Li ⇑ Ingersoll Rand Residential Solutions, 6200 Troup Highway, Tyler, TX 75707, United States Ingersoll Rand Engineering and Technology Center-Asia Pacific, Shanghai 200051, PR China
a r t i c l e
i n f o
Article history: Received 27 October 2016 Revised 6 February 2017 Accepted 18 April 2017
Keywords: Life cycle climate performance Food transport refrigeration R452A Global warming Alternative technologies Food product refrigerating temperature
a b s t r a c t This paper presents the comprehensive investigations for the total lifetime CO2-equivalent emissions for food transport refrigeration system under various influencing factors. The new R404A alternative refrigerant—R452A, is investigated to provide an improved environmental performance. With a lower global warming potential (GWP = 1945), which is around half GWP of the currently existing R404A, R452A can make a 5–15% emission reduction for the food transport refrigeration system. In the R452A system, reducing the ambient temperature from 90 °F (32 °C) to 60 °F (15.5 °C) can produce up to 60% emission reduction for the fresh product case while 39% reduction for the frozen. Decreasing the annual leak rate from 25% to 10% can give a 13% emission reduction for the R452A fresh product case while 4% reduction for the frozen. Increasing the food product refrigerating temperature (evaporating temperature) set-point from 10 °F (23 °C) to 50 °F (10 °C) can lead to more than 80% emission reduction. In addition, a 15% annual insulation degrade rate can provide a 13% emission reduction for the fresh and 14% for the frozen. Moreover, the Cycle Sentry running mode can result in a 14–21% emission saving than the Continuous. Furthermore, the sunny/cloudy conditions, system efficiency improvement rate, and alternative transport refrigeration technologies other than the conventional hydrofluorocarbon (HFC) based vapour compression refrigeration systems, are also investigated to explore the possibility to minimize environmental impacts. Ó 2017 Elsevier Ltd. All rights reserved.
Introduction Climate change and global warming, have been emerged and described as serious issues on the international agenda during the past decades. The ever-increasing greenhouse gas (GHG) emissions can turned out a series of negative consequences, such as deteriorating the patterns and amounts of precipitation, weakening the ice and snow cover, raising the sea level, swelling the acidity of the oceans, shifting the ecosystem characteristics and increasing threats to human health. Based on the Fourth Assessment Report of Intergovernmental Panel on Climate Change (IPCC) in 2007 [1], an increase of 0.74 K for the average global surface temperature were obtained during the past 100 years (1906– 2005), which is higher than the that of 0.6 K in the Third Assessment Report published in 2001. This comparison indicates that the ice reduction and sea level rise are performed at an accelerating ⇑ Address: Ingersoll Rand Residential Solutions, 6200 Troup Highway, Tyler, TX 75707, United States. E-mail address: [email protected] http://dx.doi.org/10.1016/j.seta.2017.04.002 2213-1388/Ó 2017 Elsevier Ltd. All rights reserved.
rate. Another study has been summarized that, for the last 50 years, the global temperature rose at an average rate of 0.13 °C per decade—around twice as fast as the value of 0.06 °C per decade increase observed over the previous half-century [2]. This study is also projected that in the next 20 years, the global average temperature will rise by 0.2 °C per decade [2]. Facing such challenges, researchers, governmental agencies, and policy makers are raising attention to the human activities to minimize the GHG emissions. The food transport refrigeration sector, is generally recognized to consume energy heavily to maintain the coldchain and thus result in large GHG emissions. A study showed that over a million refrigerated road vehicles are used to distribute refrigerated foods throughout the world [3]. The freight transport consumes nearly a quarter of all the petroleum worldwide and produces more than 10% of carbon emissions from fossil fuels [4]. In another study, the statistics showed that the food transport could produce 19 million tons of CO2 in 2002, among which 10 million tons were emitted in the UK (almost all from road transport), representing 1.8% of the total annual UK CO2 emissions [5]. Food transport accounts for one quarter of all Heavy-Goods Vehicle
34
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Nomenclature Abbreviations AHRTI Air-conditioning, Heating, and Refrigeration Technology Institute CARB California Air Resources Board CFC chlorofluorocarbon COP coefficient of performance DDE diesel direct electric DLL dynamic link library EOL loss end of life EPA Environmental Protection Agency EU European Union FCMT fuel consumption modeling tool
miles in the UK, with the average number of miles that food travelling doubling in the last 30 years [6]. Under the increasing pressure to address global warming issues, it is necessary for the industry to spend more efforts to understand the environmental impact of transport refrigeration system under various influencing factors, with the hope that the industry can be actively implementing improvements thus tending to reduce fuel usage and costs in the long run. The transport refrigeration system, is usually operated under a much harsher environment, and thus it has the higher reliability requirements than the conventional stationary refrigeration systems and lower energy efficiencies. In addition, the wide range of transported goods, home delivery and quality expectations, are placing high pressures on the industry for GHG emission reductions. Based on the literature review from the published peerreviewed journal articles, currently there are limited studies on the in-depth and systematical evaluation of environmental impacts for the food transport refrigeration systems. More studies are focused on the environmental impact of the stationary refrigeration systems, such as residential and commercial air conditioners and heat pumps. For the convenience of readers, some tools are briefly introduced to evaluate the product environmental performance (for more detail please check Section 2). First, the tool— Total Equivalent Warming Impact (TEWI) is used to evaluate both the direct GHG emissions from a product, as well as the indirect emissions from the energy consumption aspect. This tool is used particularly for air conditioners and ignores the emissions during chemical manufacturing, the energy embodied in product materials, and end-of-life losses. Another tool is the web-based interactive life cycle climate performance (LCCP) modeling program for stationary refrigeration systems [7]. This tool also has the Excel Version, named ORNL LCCP Excel Tool, which can be used for air conditioners, heat pumps, chiller, etc. LCCP is a methodology that is used to assess the total global warming potential (GWP, which will be introduced in more detail in Section 2.1) impacts (both direct and indirect emissions). It is expressed as CO2 equivalent mass (kg-CO2 eq.), over the lifetime of a particular refrigerant, piece of equipment or system with different climate inputs. It can be expressed as a summation of all sources of the direct and indirect source emissions. From the comparison it indicates that the LCCP can evaluate the product emissions in a more reasonable way than the TEWI. It should be noted there is another tool prior to ORNL LCCP Excel Tool: the Air-conditioning, Heating, and Refrigeration Technology Institute (AHRTI) LCCP model, which is only used for residential heat pumps [8]. It has similar methodology to the web-based tools. The International Institute of Refrigeration (IIR) has set up a working group to discuss and assess the merits of
GHG GWP HCFC HFC IIR IPCC LCA LCCP TEWI TRU ULETRU
greenhouse gas global warming potential hydrogen chlorofluorocarbon hydrofluorocarbon International Institute of Refrigeration Intergovernmental Panel on Climate Change life cycle assessment life cycle climate performance total equivalent warming impact transport refrigeration units Ultra-Low-Emission Transport Refrigeration Unit In-Use Performance Standards
various methods for LCCP evaluation and produce implementation protocols [9]. It has the Excel-based IIR Working Group residential heat pump LCCP tool. Several studies have been performed with aforementioned tools. A LCCP study is performed for supermarket systems and the transcritical CO2 booster system has the lowest emissions in cold climates [10]. This study also showed that shifting towards low GWP refrigerants decreases the effect of the annual leak rate [10]. In other studies, the packaged air conditioners and heat pumps are evaluated from the product’s life time. It shows that the energy consumption accounts for the largest emission contributor, followed by annual refrigerant leakage effect [11,12]. The drop in LCCP of low GWP refrigerants R-32, L-41a and D2Y60 are conducted compared with baseline R410A for heat pumps for residential application, and the low GWP refrigerants can produce a 4–27% GHG emission reduction [13]. In addition to the tools above, there is one more tool: GREEN-MAC-LCCP, which is only automotive air conditioning application [14]. However, to the best knowledge of the author, there is a lack of the complete and comprehensive transport refrigeration LCCP investigation in detail comparing various influencing parameters to achieve the lowest environmental impact. In the present study, the new LCCP simulation tool for transport and bus refrigeration/air conditioning products, was developed for analyzing the environmental impacts for only private use for Ingersoll Rand. The tool was first briefly introduced at 2014 ASHRAE Annual Conference [15]. Since there are some unique challenges for the food transport refrigeration, the new transport LCCP tool, involves the open-shaft compressor model, and this model could have a higher leakage rate than the hermetic systems. The fuel consumption modeling tool (FCMT) can facilitate calculation of indirect emissions due to the unit energy or fuel consumption in the LCCP tool, and it is capable of analyzing a wide range of transport product lines. This paper will provide detailed LCCP assessments from various influencing parameters with the latest refrigeration transporttrailer technologies. The trailer products from Thermo-King are selected for the LCCP investigation. In this study, it will calculate the equivalent mass of CO2 released into the atmosphere for the trailer products under various climates, system efficiency improvements, refrigerant leakage rates, food classification, etc. In addition, the new refrigerant R452A, as current R404A alternative, is investigated for environmental performance. Thermo-King was the first to announce the adoption of this new refrigerant as a lower GWP option for its transport refrigeration customer and soon which is becoming the industry standard. The LCCP investigation is conducted comprehensively, from both direct and indirect emission aspects. The perspectives drawn from this study are beneficial for the researchers, policy makers, and manufactures to minimize
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
the total environmental impact through maximizing the energy efficiency and maintaining the maximum sustainability and safety for consumers. Environmental impact of refrigeration system method review As mentioned briefly in Section 1, the environmental impact for the refrigeration systems can be assessed by various methodologies and indexes. In this section, the commonly used evaluation indexes are introduced in more detail. Different assessment approaches are listed to identify the efficient solutions towards a green environmental impact. Global warming potential The GWP, which is an index that characterizes the participation of a refrigerant molecule in the greenhouse increase, is calculated through the comparison with the contribution to the greenhouse effect of the reference molecule, a molecule of CO2, presenting a GWP = 1. Usually the comparison for the refrigerants can be made according to heating effect caused by a molecule of refrigerant during the most common used 100 years (GWP100). The GWP is depended on the: (1) infrared radiation absorptivity of the gas, (2) the gas lifetime in the atmosphere, and (3) the selected time frame [16]. The GWP, then, just reflects the impact of the gas properties on the global warming. With the aid of the Kyoto Protocol, the GHGs in the atmosphere including chlorofluorocarbons (CFCs), hydrogen chlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), should be controlled at an appropriate level to prevent the harmful effect of climate change on humans [17]. In addition, the CFCs and HCFCs can also split and release the ozone destructive chlorine atoms, which can add the harmful ultraviolet radiation for the earth. Thus, they are gradually reduced and eventually phased out in the Montreal Protocol. Currently, most refrigerants in the refrigeration systems are the HFCs family. However, they are still presenting a high-GWP values up to 4000.
Life cycle climate performance From Section 2.2, it can be observed that the TEWI has not consider the indirect emissions resulting from manufacturing, delivery and recycling of refrigerants aspects. Then LCCP has developed. It extends the concept of TEWI, with the consideration of the environmental impact associated with the energy consumed to manufacture both the refrigerant and the raw materials used for the manufacturing of the refrigerant, and the direct warming impact of any fugitive greenhouse gases emitted during the refrigerant manufacture [19]. Currently the LCCP can be regarded as a more complete and complex index to evaluate the global warming performance of a technology, and there are several tools for study: ORNL LCCP Excel Tool for various stationary refrigeration systems [7], the AHRTI LCCP model for residential heat pumps [8], and GREEN-MAC-LCCP for only automotive air conditioning application [14]. The LCCP is calculated from the Eq. (2) [7]. It can be found that the complexity for the LCCP can enhance the grades of freedom of the applicant and can be more flexible and applicable to various input parameter settings.
Emtotal ¼ Emdirect; ref leak þ Emdirect; ref acci þ Emdirect; ref service þ Emdirect; ref EOF þ Emdirect; ref prod transport þ Emdirect; ref; other þ Emindirect; consumption þ Emindirect; manufacture þ Emindirect; EOF þ Emindirect; transport
TEWI ¼ GWPðL n þ mð1 CÞÞ þ ðn E bÞ
ð1Þ
where: GWP – Global Warming Potential; L – Annual amount of the refrigerant emissions (leakage) [kg/year]; n – Lifetime of the refrigeration system [year]; m – Refrigerant charge [kg]; C – Recovery factor/refrigerant recycling [between 0 and 1]; E – Annual energy consumption of the refrigeration system [kWh/year]; b – The amount of the CO2 equivalent mass emissions for 1 kWh energy generation, kg/kWh.
ð2Þ
Emdirect, ref leak – Emission due to refrigerant leakage; Emdirect, ref acci – Irregular emission due to such things as accidents; Emdirect, ref service – Emission due to leakage of refrigerant from servicing; Emdirect, ref EOF -Emission due to end-of-life of system where refrigerant is lost; Emdirect, ref prod transport- Emission due to leakage from refrigerant production and transportation; Emdirect, ref other -Reaction byproducts from the atmospheric breakdown of refrigerant emissions; Emindirect, consumption– Emission due to energy consumption during system’s lifetime; Emindirect, manufacture–Emission due to energy used to manufacture refrigerant and components; Emindirect, EOF–Emission due to energy used for end of life of components and refrigerants; Emindirect, transport–Emission due to energy used to transport equipment
Total equivalent warming impact Section 2.1 mainly discusses the GWP from the refrigerant aspects. In fact, during the system operation in its lifetime, the emissions is not only caused by refrigerant leakage into the atmosphere, but also affected by the system energy consumption. Thus, the new concept/tool-TEWI has developed, which includes of direct emissions (refrigerant leakages) and indirect emissions (emissions resulting from electricity production that is consumed by the refrigeration system, as shown in Eq. (1) [18]. It can be found that the direct emissions depend on the refrigerant GWP, the amount of refrigerant leakage, the equipment running time, etc. While the indirect emissions depend on the energy consumption during operation and the emissions per unit energy generation:
35
Life Cycle Assessment The Life Cycle Assessment (LCA), which is the cradle-to-grave analysis for environmental impact valuation of a given product or service caused by its existence, can extend the LCCP approach to the other relevant aspects, such as the eutrophisation potential, acidification potential, ozone depletion potential, etc. The main advantage for the LCA present in relation to LCCP is in its standardization: LCA is ruled under ISO 14000 Standards. The emissions are resulting from the whole lifecycle of refrigerant and the devices that supports it (i.e. the entire components of a refrigeration system [20]):
Design and development of technologies; Row material acquisition and transformation; Production of system devices components and refrigerant; Process of assembly; Operation (includes servicing);
36
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Recovery, recycling or destruction of refrigerant and system devices. If only the GHG emissions are taken account, the LCA and LCCP should lead to same results with existing known energy consumption inputs. However, in the case of refrigeration, it is not so flexible for the LCA inputs under the various operating conditions, such as high/low ambient conditions and location information for heat pumps, etc. Thus, for a specific refrigeration system emissions during its lifetime, the LCCP is more powerful and reliable to evaluate and minimize the environmental performance impact. Transport LCCP modeling methodology In this section, the fuel consumption modeling tool (FCMT), which is the Thermo King Fuel Simulator, together with the transport LCCP tool are introduced for the transport LCCP modeling methodology. The FCMT can facilitate calculation of indirect emissions due to unit energy or fuel consumption in the LCCP tool, which is capable of analyzing a wide range of transport product lines. Since the transport LCCP comprehensive investigation under various influencing factors has not been investigated in detail and it is different from the LCCP for the stationary refrigeration systems, for the convenience of readers, the modeling methodology is shown here. Thermo King Fuel Simulator Prior to the LCCP simulation tool, the FCMT, is used to calculate the most important indirect emission caused by the energy or fuel consumption. Fig. 1 shows three Simulink models: box model, control model and plant model. The box model can calculate the cooling load required by the system to maintain the box at a pre-set temperature. It can be decided and influenced by the box dimensions, insulation material, ambient temperature, and box temperature, and such factors can be used to calculate the heat loss through the box walls with knowing the thermal conductivity of the insulating material. Ref. [15] also mentioned that, alternatively, the box loss may be known directly if it is tested experimentally following TTMA RP38-07 [21]. Either method (specifying materials or entering know loss values) for the box loss calculation can be used in the FCMT. A solar load is computed and factored into the box model to account for the actual skin temperature of the box exterior in relation to the ambient temperature, vehicle speed, and location [15]. Door openings during the refrigeration system
operation is also accounted as part of the heat loss for in the box model. The plant model can predict the system energy efficiency and capacity under environmental boundary conditions. The control model, with the aid of the specific refrigeration control valves in response to coded temperature control algorithms, is used to control the engine speed, fan speed, and refrigeration capacity. The plant model is affected by the control model. The control model and plant model are hence proprietary models based on the Thermo King’s specific design and control architecture. The three models work together to predict energy/fuel consumption for any given operating route and conditions. Then the Simulink model can be converted to the standalone dynamic link library (DLL) file via the MATLABÒ platform. Then the fuel consumption can be calculated and the DLL file (FCMT_win32.dll and FCMT_Engine.dll) can run with Excel with worksheet input and VBA programs, thus the energy or fuel consumption can be calculated. Transport LCCP calculation This section introduces the transport LCCP calculation, as shown in Fig. 2 and Eq. (3).
X TransportLCCP ¼ ðR þ RP ÞfYðL þ LSA Þ þ Eg þ Y ðC F F þ C K KÞ X X X CM M þ C M MR þY FT CF þ
ð3Þ
RP – Atmospheric reaction products from the atmospheric breakdown of HFCs; R – Refrigerant Global Warming Potential (GWP); Y – Lifetime, in years L – Annual regular emissions due to refrigerant leaks from the system during operation; LSA– Annual regular emissions due to leakage in assembly plants, irregular emissions due to accidents and service emissions from servicing operations; E – Refrigerant loss at the End-of-Life (EOL) of the unit; K – Annual energy consumption from the refrigeration or AC unit operation; MR, M– Mass of refrigerants and components for manufacturing and EOL energy purpose; M– Energy from additional fuel consumption to transport the refrigeration or AC unit mass on board the vehicle during its lifetime. FT– Annual energy from additional fuel consumption to transport the refrigeration or AC unit mass on board the vehicle during its lifetime;
Fig. 1. Flow chart of the Thermo King Fuel Simulator.
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
37
Fig. 2. Transport LCCP composition.
CF – Equivalent CO2 kg/kg Fuel; CK – Equivalent CO2 kg/kWh; CM – Equivalent CO2 kg/kg material of refrigerants or components for manufacturing and EOL energy purpose; The Microsoft Excel-based LCCP tool architecture flowchart is shown in Fig. 3. The DLL file created from the MATLABÒ based FCMT and a series of VBA macros were implemented with the LCCP Excel program for the energy calculation. All direct or indirect emissions are computed with the VBA program. To start for the LCCP calculation process, the pre-set inputs should be provided in the ‘‘main” worksheet for refrigerant, fuel type, name of the refrigeration system information sheet. Then the vehicle models and types (trailer, truck, bus A/C, etc.), box dimensions, insulation conditions, ambient conditions, control modes, product pre-set points, etc., should set for the fuel consumption input worksheet from FCMT. Once all input data are provided and click the ‘‘Run” button, the program can read in climate data from a typical meteorological year (TMY3) database, conducts annual energy or fuel consumption calculations from the defined vehicle running schedule, and computes all indirect and direct emissions. The ‘‘Results” sheet displays the detailed calculation results including direct and indirect emissions, etc. The transport tool can beneficial for easy implementation of updated versions of the accompanying FCMT. Transport refrigeration LCCP results and discussion In this section, various influencing factors are investigated to assess the LCCP to minimize the total environmental impacts.
The vehicle, which is a single compartment diesel-driven tractor trailer with swing type doors, has exterior dimensions of 53.1 feet (16.2 m) length, 8.5 feet (2.6 m) width, and 9.5 feet (2.9 m) height with a box loss of 180 Btu/h/R (0.53 W/K), a life expectancy of 15 years with a 15 percent nominal leak rate. The charge amount for refrigerants is set to be 13.0 lbs (5.9 kg) even though a small change may be produced with an alternative refrigerant. The daily distribution used for the study represents the fresh products at setpoint 30 °F (1 °C) or frozen products at set-point 10 °F (23 °C). Application conditions are short haul daily distribution runs of 5 days/week for 50 weeks. The haul load was 40,000 lbs (14,930 kg) for both cases. Operation of fresh/frozen conditions is a 1-h pull-down followed by 14 h of operation. Operation includes six door openings of 20 min each. The road condition is the rural with sunny condition with Cycle Sentry running mode. The values of mass of various system components with different materials from Ingersoll Rand product windchill database are incorporated into the transport LCCP tool for calculation. The components are frame, bulkhead, engine, generator, compressor, refrigeration heat exchangers, tubing and VCS components, air flow components, control box & harness, skins-covers & nameplate and fluids. The material emission factor is shown in Table 1. Effect of low GWP alternative R452A for LCCP investigation The pressures to control climate change and to minimize the environmental impacts are driving the development of new regulatory policies to restrict and lower the direct GWP impact of Fgases. The R404A (GWP = 3943) is commonly used in current air cooled application types, and specifically in transport refrigeration.
Fig. 3. Transport LCCP flowchart.
38
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49 Table 1 Material emission factor. Material
Emission factor CO2-eq. (kg/kg)
Aluminum Copper Plastics Steel Cast Iron Brass Engine Oil Rubber Lead
1.6 3.3 3.0 2.3 1.6 2.5 3.3 3.1 2.1
Thermo-King, is the first and only provider that offers its customers an entire portfolio of truck and trailer refrigeration units that use the new, lower GWP refrigerant R452A (GWP = 1945) for a better environmental performance. This gives companies a choice to reduce their emissions and maintain the same high performance of their refrigerated fleet. R452A is an ASHRAE 34 newly classified A1 refrigerant (lower toxicity/non-flammable) that is developed to be nearly design-compatible to replace R404A specifically in transport refrigeration. It is a blend of R32/R125/R1234yf at a composition of 11%/59%/30% by weight. As shown in Fig. 4 and Fig. 5, R452A was designed compositionally to best match R404A’s pressure enthalpy and temperature entropy characteristics, indicating the transport refrigeration units compatible with next generation R452A refrigerant. Based on the two industry accepted transport refrigeration equipment standards-AHRI Standard 1110 2013 [22] and ATP Standard [23]), the laboratory testing reveals that R452A can achieve acceptable and equivalent system performance when it is substituted in R404A transport refrigeration equipment. The expansion valve was set to get maximal cooling capacity and this setting was maintained under other temperature conditions. Under close refrigerant charge amount, R452A has the down 5.5% net cooling capacity relative to R404A at ambient temperature 100 °F (38 °C) (AHRI rating condition) at low return air temperature (20 °F, 29 °C) and at compressor high speed. R452A has comparable cooling capacity practically to R404A at higher return air temperatures (35°F, 1.7 °C). Same trend can be achieved at ambient temperature 86 °F (30 °C) (ATP rating condition), but the capacity difference is smaller in this case. In addition, for ATP rating condition, the R-452A performance of coefficient of performance (COP) and fuel efficiency ratio relative to R-404A is within 1%. It has been
Fig. 4. Pressure-Enthalpy comparison for R404A and R452A.
Fig. 5. Temperature-Entropy comparison for R404A and R452A.
proved that the R452A can achieve the equivalent and acceptable capacity and efficiency to R404A Fig. 5. There are 3 scenarios for the LCCP comparison. R404A Baseline is from the early Thermo King product SB series and the refrigerant is R404A. R404A Precedent is from the Thermo King series of Precedent transport refrigeration units (TRU) and it is at the forefront of green energy, delivering double-digit fuel savings, best-in-class performance and lower life cycle costs. R452A Low-GWP represents the new, lower GWP R452A as standard in the vehicle powered range of units. Field tests indicate that it has equivalent capacity and efficiency to R404A Precedent. The R452A product of trailers and other vehicle-powered refrigeration units is available in Europe in Jan.1, 2016. To have a deep understanding about the product LCCP, the CO2eq. emission contributors are revealed, as shown in Fig. 6, Fig. 7 and Table 2. The direct emission is the refrigerant leakage emission, including manufacturing leakage emission, service leakage emission, annual regular leakage, EOL leakage emission, accident leakage emission and decomposition leakage emission. The direct emission includes emissions caused by the energy for equipment manufacturing, installation, maintenance, and the emissions from the all fuel consumptions by the system operation. Three product categories are compared for the fresh product condition (30 °F set-point) and frozen product condition (10 °F set-point). Basically, in the case of the fresh product, as shown in Fig. 6, the fuel consumption, services as the main indirect emission and consumes approximately 70–80% of the total emissions. While the regular refrigerant leakage, services as the main direct emission and consumes 15–25% of the total emissions. Direct emissions from refrigerant service leakage and loss end of life (EOL) produce 2–3% and 1–2% total emissions, respectively. The total indirect emission is appropriately 69–82% for the fresh case. Fig. 6 indicates that R404A Precedent lifetime emission can give a 19% emission reduction compared with R404A Baseline for the fresh product and the two scenarios have the same direct emissions. This is because the Precedent platform utilizes an all-new and advanced Diesel Direct Electric (DDE) architecture to drive optimum efficiencies. It’s a smarter approach and it can already meet much stricter Tier 4 final emissions certification by the Environmental Protection Agency (EPA) and California Air Resources Board (CARB). Further, it can comply with CARB’s Ultra-Low-Emission Transport Refrigeration Unit In-Use Performance Standards (ULETRU). In addition, the superior temperature control is also used. The laboratory tests
39
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49 Table 2 LCCP evaluation for 3 scenarios (kg CO2-Eq.) Fresh/frozen condition
Fresh product (30 °F)
Frozen product (10 °F)
Scenario
R404A Baseline
R404A Precedent
R452A Low-GWP
R404A Baseline
R404A Precedent
R452A Low-GWP
Total lifetime emission Total direct emission Emission Manufacturing Emission Service Emission Leakage Emission EOL Total indirect emission Emission equipment Mfg Emission equipment installation Emission fuel consumption Emission maintenance Emission equipment EOL
257,908 63,765 444.7 6670.1 52026.5 4624.6 194,142 1693.2 105.5 192,119 99.5 124.9
208,635 63,765 444.7 6670.1 52026.5 4624.6 144,869 1693.2 105.5 142,846 99.5 124.9
176,410 31,541 219.9 3299.3 25734.6 2287.5 144,869 1693.2 105.5 192,119 99.5 124.9
736577.1 63765.9 444.7 6670.1 52026.5 4624.6 672,811 1693.2 105.5 670,788 99.5 124.9
642267.5 63765.9 444.7 6670.1 52026.5 4624.6 578,501 1693.2 105.5 576,478 99.5 124.9
610,043 31541.5 220.0 3299.3 25734.7 2287.5 578,501 1693.2 105.5 576,478 99.5 124.9
Fig. 6. Effect of refrigerants on LCCP for fresh products.
40
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 7. Effect of refrigerants on LCCP for frozen products.
Fig. 8. Effect of ambient temperature on LCCP.
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 9. System operating performance metrics under various ambient temperatures.
41
42
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 10. Effect of US cities on LCCP.
Fig. 11. Effect of US cities on LCCP.
Fig. 12. Effect of annual refrigerant leakage rate on LCCP.
including both the fresh Cycle Sentry test and frozen Cycle Sentry hill test both indicate double-digit fuel savings can be achieved. The R452A Low-GWP type leads to a 15% emission reduction compared to the R404A Precedent. The Kyoto Protocol recognizes HFCs
as one of the potent GHG that most developed countries have agreed to restrict. European Union (EU) and Japan are already developing HFC regulations as part of their Kyoto compliance scheme. The EU 2014 F-Gas Regulation caps and phases-down
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
43
Fig. 13. Effect of food product refrigerating temperature set-point on LCCP.
HFCs refrigerants in most applications including stationary and mobile refrigeration based on their GWP. EU has also implemented product bans based on refrigerant and several European countries have, or are planning GWP-based taxes on HFCs. In response to such changes and environmental needs, the industry are pushed to exploit lower GWP refrigerants. R452A and R404A have the equivalent capacity and efficiency, but the former has half the GWP of the latter. Thus, the former has more environmental benefits. As for the case of frozen product in Fig. 7, R404A Precedent can achieve a 13% CO2-eq. reduction compared with the R404A Baseline and R452A has a 5% CO2-eq. reduction compared with the R404A Precedent type. While the comparison between the fresh product case and frozen indicates the fuel consumption of the later is larger. This is because a lower food evaporating temperature (from 30 °F set-point for the fresh products to the 10 °F setpoint for the frozen) can result in a lower energy efficiency. This section indicates enough attentions should be paid for low GWP refrigerant utilization as well as energy efficiency enhancements.
Effect of climates for LCCP investigation Fig. 8 shows that in the R452A system, reducing the ambient temperature from 90 °F (32 °C) to 60 °F (15.5 °C) can produce up to 60% emission reduction for the fresh product case while 39% reduction for the frozen. The direct emissions remain constant. A higher ambient temperature indicates a larger product heat load, which needs more fuel sources. To reveal the heat load more clearly, Fig. 9 displays the system operating performance metrics under various ambient temperatures with 1 h pre-cooling and 14 route hours for one day. In the case of fresh product, reducing the ambient temperature from 90 °F to 60 °F can decrease the food heating load and thus shorten the engine running time (from 3.91 h to 1.25 h per day). Fig. 9(a)– (d) show that reducing R452A system ambient temperature can shorten the engine high speed and low speed duration percentage by 17.7% (from 26% to 8.3% of the total engine on percentage). In addition, during the pull-down test period with 1 h pre-cooling, a higher ambient temperature indicates a longer high-speed engine duration time. Fig. 9(d) and (e) show a comparison between the fresh product and frozen product with the ambient temperature 60 °F. It can be observed that a huge amount of engine on duration percentage (up to 51%) can be achieved for the frozen product while it is only 8.3% for fresh. Thus a massive energy consumption can be produced in the frozen case.
Six cities, Minneapolis, Boston, Richmond, Los Angeles, San Antonio, Phoenix, from cold areas to hot areas, are conducted to investigate the LCCP, as shown in Fig. 10. The maximum and minimum weather data source is collected from 1981 to 2010 by the NOAA Notational Climatic Data Center of the United States. In Fig. 10 the variation from the cold area of Minneapolis to the scorching hot area of Phoenix give a 66% emission reduction for the fresh product case while 53% for frozen. In addition, Fig. 11 shows the effect of sunny/cloudy conditions, which have different solar heat fluxes, for the lifetime emissions. The sunny/cloudy condition has much less effect than the ambient conditions on the LCCP. A switch from sunny condition to the night condition produces a 7% emission reduction for the fresh product case while less than 4% for frozen. Effect of annual refrigerant leakage rate for LCCP investigation Most transport refrigeration/air conditioning equipments utilize the open-shaft compressors, which could have a higher regular leakage rate than the hermetic systems. In this section, the annual leak rate range from 25% to 10% has been chosen to investigate the LCCP, as shown in Fig. 12. It can be noticed that only the emission from the regular leakage varies while others remain constant. Decreasing the R452A annual leak rate from 25% to 10% can give a 13% emission reduction for the fresh product case while 4% reduction for the frozen. R404A products produce more emissions since R404 has approximately double GWP values than R452A. Effect of food product refrigerating temperature set-point for LCCP investigation Fig. 13 shows the effect of food product refrigerating temperature (i.e. the evaporating temperature) set-point on the LCCP. Increasing the R452A system set-point from 10 °F (23 °C) to 50 °F (10 °C) can lead to more than 80% emission reduction. A lower evaporating temperature indicates a lower energy efficiency, leading to a higher fuel consumption. To explore more detail for the effect of the food product set-point, Fig. 14 shows detail about the system operating performance metrics with 1 h pre-cooling and 14 route hours for one day. Increasing the R452A system setpoint from 10 °F to 50 °F gives a 9.1 engine running time reduction per day (from 10.7 h to 1.6 h per day). Fig. 14(a)–(d) indicates increasing the set-point results in 60.5% engine duration percentage reduction (from 71.5% to 11% of the total engine on percentage). A significant emission reduction can be achieved as the
44
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 14. System operating performance metrics under various food product refrigerating temperature set-points.
food product set-point temperature increases. It can be noticed that the food product set-point has even higher effect on the LCCP than the climate condition.
less heat loss to the ambient, thus leading a lower fuel source energy consumption. The food box insulation condition has less effect on the LCCP than the climate condition and food product temperature set-point.
Effect of box insulation condition for LCCP investigation Effect of system operation control condition for LCCP investigation Fig. 15 shows the effect of food box insulation condition on the LCCP. A 15% R452A annual insulation degrade rate can provide a 13% emission reduction for the fresh and 14% for the frozen. Only the emission from the fuel consumption varies while other items remain constant. A lower annual insulation degrade rate indicates
There are two running modes supported in this version–Cycle Sentry and Continuous. When Cycle-Sentry mode is selected the unit will start and stop automatically to maintain the set-point, keep the engine warm, and keep the battery charged. When
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
45
Fig. 15. Effect of annual insulation degrade rate on LCCP.
Fig. 16. Effect of system control-running mode on LCCP.
Continuous mode is selected, the unit will start automatically and run continuously to maintain the set-point and provide the constant airflow. Three product set-point temperatures: 0 °F (17.8 °C), 5 °F (15 °C) and 10 °F (12 °C) are selected to investigate for two running modes. Fig. 16 shows that the Cycle Sentry has a 14 21% emission saving than the Continuous. To reveal the mechanism in more detail, Fig. 17 shows the system operating performance metrics with 1 h pre-cooling, 14 route hours for one day, and 10 °F food product set-point. The switch from Continuous mode to Cycle-Sentry gives a 6.8 h engine running time reduction per day. Fig. 17(a) and (b) indicates the switch shows 45.5% engine duration percentage reduction (from 86% to 40.5%). Usually the Continuous mode has the more accurate temperature control and run continuously to maintain set-point, which can be seen from the comparison for the return air temperature curve between the two modes, but at the cost of a higher energy consumption. Thus, a reasonable selection for the two options should be performed to maintain the quality of the food products while minimize the environmental impact at the same time. Effect of system efficiency improvement for LCCP investigation Fig. 18 shows the effect of system efficiency improvements on the LCCP. Energy efficiency, can be enhanced via the utilization of more reliable and efficient compressors, optimized coil design,
reduced heat loss with ambient, etc. Increasing the R452A system efficiency improvement rate from baseline 0% to 15% produces the 11% emission reduction for the fresh products and 12% for the frozen. The emission due to the fuel consumption varies while other items remain constant. Effect of alternative transport refrigeration technologies for LCCP investigation As for the food transport refrigeration systems, although the vapour compression cycle is well established for system operation, the rising cost of fuel/electricity and pressure to reduce the environmental impacts have renewed the interest in other alternative transport refrigeration technologies. The thermally driven technologies and other innovative technologies could offer the environmental advantages over the conventional vapour compression cycle in the near future. R404A, the predominant high-GWP refrigerant, and other HFC refrigerants, are extensively unemployed with the alternative technologies. This section discusses various alternative technologies for LCCP comparison with existing vapour compression cycle technology. (1) Adsorption technology Adsorption technology is shown in Fig. 19(a). The ‘thermal compressor’ (desorption/adsorption bed) is used to replace
46
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 17. System operating performance metrics under two running modes.
Fig. 18. Effect of system efficiency improvement on LCCP.
the conventional vapour compression cycle mechanical compressor and the sorbent/low-GWP refrigerant serves as the working fair. This is beneficial for the system to achieve the lower environmental impact. In addition, it can utilize the low grade waste heat for better thermal integration of transport refrigeration processes. A study was performed to design, model, built and test a trailer refrigeration and bus air-conditioning air cooled adsorption system with activated carbon sorbent beds as the sorbents and ammonia (R717) as a refrigerant [24]. The theoretically characterization for the system was for the purpose of being capable of maintaining temperatures in the range 18 to 4.5 °C for transport refrigeration. It mentioned that the heat available
from diesel engines in the power range 225–525 hp was determined to be 40–60 kW from the engine cooling circuit and 40–140 kW from the exhaust gases. It also mentioned that the practical COP used for system design was in the range 0.6–1 and specific cooling power rates were considered to be around 614 W per kilogram of carbon for ammonia (R717) refrigerant and 198 W per kilogram of carbon for R134a refrigerant. (2) Air cycle technology Air cycle technology is shown in Fig. 19(b). The environmentally friendly gaseous refrigerant (air) is the working fluid. The air in the cycle can produce cold with a sequence of processes comprising compression, followed by constant
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
pressure cooling, and then expansion to the original pressure to achieve a final temperature lower than at the start of compression. A study [25] was conducted to accommodate the air cycle system within the physical envelope of an existing conventional R404A vapour compression refrigeration trailer unit to achieve an equivalent refrigeration capacity
47
(specified as 12 kW at 0 °C trailer temperature and 7.2 kW at 20 °C trailer temperature, both at 30 °C ambient). The commercially available or existing parts, including the diesel engine prime mover and air circulation fans of the vapour compression system were utilized for the air cycle system. The standard exhaust turbocharger components were selected for the two compressor stages and the modified turbine for the air cycle. It could achieve a full-load capacity of 7.8 kW at 20 °C (8% higher than the existing unit), but at 0 °C the cooling capacity was 9.5 kW (21% lower than the existing unit). Based on the test results of the demonstrator unit, an optimised air cycle unit with thermodynamic model employing state of the art technology predicted overall COP to be 0.53 at 20 °C and 7.8 kW refrigeration capacity, which was only 7% lower than the corresponding COP for the vapour compression unit [26]. (3) Ejector technology Ejector refrigeration is shown in Fig. 19(c). It is a thermally driven technology and has the benefits of the simplicity of structure, no moving parts, more environmental free working fluids, low grade heat source above 80 °C. However, it has lower COPs, 0.2–0.3, compared with vapour compression cycle or other thermally driven technologies. Currently there are no commercially available off the shelf for the ejector food transport refrigeration system. The water can be used as a refrigerant in the design and application of bespoke steam ejector systems for cooling applications above 0 °C. In general, the rising energy costs can encourage more effective utilization of waste heat for better thermal integration of refrigerant transport processes. Thus, it is expected that the ejector technology is beneficial for the transport environmental impact and deserves the further investigation for efficient steady flow ejectors in the near future. Here the alternative transport refrigeration technologies are integrated for the investigation of LCCP. The ejector technology is not employed since it has very low energy efficiencies. In addition, for the convenience of readers, the fuel source of gasoline is also compared for the LCCP, as shown in Fig. 20. It is noticed that with R452A, gasoline gives an 11–13% emission reduction compared with diesel. As for the adsorption cycle, it can utilize the free available waste heat or renewable energy as the load driving source, and such driving source can emit few emissions. In addition, the main fuel consumption can be caused due to the weight of the adsorption system. Thus, considerable emission reduction can be achieved for the adsorption cycle. As for the air cycle, it has the benefit that the working fluid air is environmental friendly media. The emission reduction can be obtained for the fresh product case while not for the frozen since the direct emission takes a less percentage for the latter. While it should be noted that the air cycle technology should be investigated further to achieve a higher system efficiency performance. In addition, the thermal energy storage with phase change materials (PCMs) can also be integrated in the food transport system to minimize the environmental impact if the PCMs are charged with the renewable energy. Conclusion
Fig. 19. Alternative transport refrigeration technologies.
The LCCP is used to evaluate the total lifetime emissions for the food transport refrigeration system under various influencing factors. The low GWP R452A (GWP = 1945), is investigated to provide an improved environmental performance. The switch from R404A Baseline to R404A Precedent gives 13–19% emission reduction. This is mainly because the Precedent platform can drive optimum efficiencies and achieve double-digit fuel savings across real-world applications. As for R404A
48
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49
Fig. 20. Effect of alternative transport refrigeration technologies on LCCP.
Precedent, when the R404A is replaced with R452A, a 5–15% emission reduction can be achieved since R452A has around half GWP of existing R404A. In the R452A system, reducing the ambient temperature from 90 °F (32 °C) to 60 °F (15.5 °C) can produce up to 60% emission reduction for the fresh product case while 39% reduction for the frozen. The direct emissions remain constant. A higher ambient temperature indicates a larger product heat load, which needs more fuel sources. A switch from sunny condition to the night condition produces a 7% emission reduction for the fresh product case while less than 4% for frozen. Decreasing the R452A annual leak rate from 25% to 10% can give a 13% emission reduction for the fresh product case while 4% reduction for the frozen. Increasing the R452A system food product refrigerating temperature (i.e. the evaporating temperature) setpoint from 10 °F (23 °C) to 50 °F (10 °C) can lead to more than 80% emission reduction. A lower evaporating temperature indicates a lower energy efficiency, leading to a higher fuel consumption. A 15% R452A annual insulation degrade rate can provide a 13% emission reduction for the fresh and 14% for the frozen. Only the emission from the fuel consumption varies while other items remain constant. A lower annual insulation degrade rate indicates less heat loss to the ambient, thus leading a lower fuel source energy consumption. The food box insulation condition has less effect on the LCCP than the climate condition and food product temperature set-point. Two running modes Cycle Sentry and Continuous are compared. The comparison shows that the Cycle Sentry can lead to a 14–21% emission saving than the Continuous. This is because the Continuous, which has the more accurate temperature control and run continuously to maintain set-point, has the higher duration percentage for both the engine on high speed and low speed. A reasonable selection for the two options should be performed to maintain the quality of the food products while minimize the environmental impact at the same time. Increasing the R452A system efficiency improvement rate from baseline 0% to 15% produces the 11% emission reduction for the fresh products and 12% for the frozen. The emission due to the fuel consumption varies while other items remain constant. The alternative transport refrigeration technologies may also have the environmental benefits than the conventional HFC based vapour compression refrigeration systems. This aspect deserves further investigation. As for the adsorption technology, it can utilize the free available waste heat or renewable energy as the cooling load driving source, and the main fuel consumption can be caused due to the weight of the adsorption system. Thus, considerable emission reduction can be achieved. As for the air cycle, it has
the benefit that the working fluid air is environmental friendly media. While both the adsorption technologies and the air cycle technologies should be investigated further to achieve a higher system efficiency performance. Acknowledgement No funding support. The author would like to express the deepest appreciation to Z.Li and P.Li for their endless love, support, and encouragement during the uncertainty of career path. References [1] Intergovernmental Panel on Climate Change (IPCC), 2007. IPCC Fourth Assessment Report, the Physical Science Basis. http://www.ipcc.ch/ ipccreports/ar4-wg1.htm (accessed May 2013.). [2] LuAnn Dahlman. Climate Change: Global Temperature. https:// www.climate.gov/news-features/understanding-climate/climate-changeglobal-temperature (accessed June 2016.). [3] Billiard F. Refrigerating equipment, energy efficiency and refrigerants. Bulletin of the IIR [2005-1]; 2005. [4] Estrada-Flores S. Chain of thought [Vol. 1, No. 2, April 2008]. http://www.foodchain.com.au/FCI_enews2.pdf; 2008. [5] AEA Technology. The validity of food miles as an indicator of sustainable development – Final report for DEFRA. Didcot: AEA Technology, UK; 2005. [6] Department for Environment, Food and Rural Affairs (defra). The validity of food miles as an indicator of sustainable development. London: Defra, UK; 2005. [7] Life Cycle Climate Performance, V1.0, 2014. Available at: http://lccp. umd.edu/ ornllccp/. [8] Zhang M. and Muehlbauer J. Life Cycle Climate Performance Model for Residential Heat Pump Systems, 14th International Refrigeration and Air Conditioning Conference, Purdue University, West Lafayette, Indiana, USA; 2012. [9] IIR LCCP WP: http://www.iifiir.org/medias/medias.aspx?INSTANCE= EXPLOITATION&PORTAL_ID=portal_model_instance__WP_LCCP_Evaluation. xml. [10] Beshr M, Aute V, Sharma V, Abdelaziz O, Fricke B, Radermacher R. A comparative study on the environmental impact of supermarket refrigeration systems using low GWP refrigerants. Int J Refrig 2015;56:154–64. [11] Li G. Investigations of life cycle climate performance and material life cycle assessment of packaged air conditioners for residential application. Sustainable Energy Technol Assess 2015;11:114–25. [12] Li G. Comprehensive investigations of life cycle climate performance of packaged air source heat pumps for residential application. Renew Sustain Energy Rev 2015;43:702–10. [13] Li G, Alabdulkarem A, Hwang Y, Radermacher R. Drop in life cycle climate performance of low GWP R-410A alternatives for heat pumps. 11th IIR-Gustav Lorentzen Conference on Natural Refrigerants – GL2014; 2014. [14] Papasavva S, Hill W, Andersen S. GREEN-MAC-LCCP: A Tool for Assessing the Life Cycle Climate Performance of MAC Systems. J Environ Sci Technol 2010;44:7666–72. [15] Nasuta D, Srichai R, Zhang M, Martin C, Muehlbauer J. Life Cycle Climate Performance Model for Transport Refrigeration/Air Conditioning Systems, ASHRAE Annual Conference, Seattle, WA; 2014.
G. Li / Sustainable Energy Technologies and Assessments 21 (2017) 33–49 [16] World Meteorological Organization (WMO). Scientific assessment of stratospheric ozone. Report no 44. In: Presented at the WMO Global Ozone Research and Monitoring Project; 1999. [17] United Nations Framework Convention on Climate Change (UNFCCC), 1998. Kyoto protocol to the United Nations framework convention on climate change. http://unfccc.int/essential_background/kyoto_protocol/items/1678. php (accessed June 2012.). [18] Orfeo S.R. A history of the TEWI process. In: Presented at the Proceedings of International Conference on Ozone Protection Technologies, Washington DC, USA; 1996. [19] Little A. Global Comparative Analysis of HFC and Alternative Technologies for Refrigeration, Air Conditioning, Foam, Solvent, Aerosol Propellant, and Fire Protection. Arthur D. Little, Inc, Cambridge, Massachusetts; 2002. [20] Rebitzer G, Ekvall T, Frischknecht R, Hunkeler D, Norris G, Rydberg T, et al. Life cycle assessment: Part 1: Framework, goal and scope definition, inventory analysis, and applications. Environ Int 2004;30(5):701–20.
49
[21] TTMA RP 38-07, 2007, Method of Testing and Rating Heat Transmission of Controlled Temperature Vehicle/Domestic Containers. [22] ANSI/AHRI Standard 1110 2013 Standard for Performance Rating of Mechanical Transport Refrigeration Units, Air-Conditioning, Heating, & Refrigeration Institute, Arlington VA, 22201. [23] Agreement on the International Carriage of Perishable Foodstuffs and on the Special Equipment to be used for Such Carriage (ATP). UNECE Transport Division publication ECE/TRANS/219. [24] Christy C, Toossi R. Adsorption Air-Conditioning for Containerships and Vehicles. Available from: http://www.metrans.org/research/final/99-19_ Final.pdf/#search=%22C%20Christy%2C%20R%20Toossi.%20Adsorption%20AirConditioning%20for%20Containerships%20and%20Vehicles%22; 2004. [25] Spence SWT, Doran WJ, Artt DW. Design, construction and testing of an aircycle refrigeration system for road transport. Int J Refrig 2004;27:503–10. [26] Spence SWT, Doran WJ, Artt DW, McCullough G. Performance analysis of a feasible air-cycle refrigeration system for road transport. Int J Refrig 2005;27:381–8.