Mobile Air Conditioning System Research Articles

Transient thermal model of passenger car's cabin and implementation to saturation cycle with alternative working fluids

A transient thermal model of a passenger car's cabin is developed to investigate the dynamic behavior of cabin thermal conditions. The model is developed based on a lumped-parameter model and solved using integral methods. Solar radiation, engine heat through the firewall, and engine heat to the air ducts are all considered. Using the thermal model, transient temperature profiles of the interior mass and cabin air are obtained. This model is used to investigate the transient behavior of the cabin under various operating conditions: the recirculation mode in the idling state, the fresh air mode in the idling state, the recirculation mode in the driving state, and fresh air mode in the driving state. The developed model is validated by comparing with experimental data and is within 5% of deviation. The validated model is then applied for evaluating the mobile air conditioning system's design. The study found that a saturation cycle concept (four-stage cycle with two-phase refrigerant injection) could improve the system efficiency by 23.9% and reduce the power consumption by 19.3%. Lastly, several alternative refrigerants are applied and their performance is discussed. When the saturation cycle concept is applied, R1234yf MAC (mobile air conditioning) shows the largest COP (coefficient of performance) improvement and power consumption reduction.

HFC152a 대체냉매를 이용한 자동차 냉방장치의 성능 최적화에 관한 연구

This study presents an HFC152a refrigerant air conditioner as an alternative to HFC134a, which is currently used in mobile air conditioning systems. Cool-down performance tests of an HFC152a air conditioning system were conducted and compared to a baseline HFC134a air conditioner. The experimental set-up consisted of a belt-driven compressor, a sub-cooled type condenser, an evaporator, and a block-type thermal expansion valve (TXV). A drop-in test was carried out on the mobile air conditioning system under various vehicle running speeds in a climate-controlled wind tunnel (CWT). Additionally, to optimize the HFC152a air conditioning system, the effects of the TXVs on the performance were studied. The results show that compared to the HFC134a air conditioning system, the refrigerant charge quantity was reduced by approximately 20%, the discharge pressure was reduced by about 350~430 kPa, and the air discharge temperature at vehicle running conditions was lower. In addition, good compressor durability was expected due to the lower compression ratio.

Environmental Impact and Performance Comparison of Refrigerants (R744 and R134a) in a Mobile Air Conditioning System Used for Cooling Buses

Environmental Impact and Performance Comparison of Refrigerants (R744 and R134a) in a Mobile Air Conditioning System Used for Cooling Buses

Performance improvement potentials of R1234yf mobile air conditioning system

In this paper, the performance improvement potentials of R1234yf mobile air conditioning (MAC) system under various operation conditions were studied based on thermodynamic cycle analysis. The effects of superheat at evaporator outlet, subcooling at condenser outlet and compressor efficiencies on system performance were analyzed. It was found that superheat was few benefits for both system coefficient of performance (COP) and cooling capacity. Increasing subcooling from 1K to 10K at condenser outlet, system cooling capacity and COP could be improved by 15% if compressor consumption power was fixed. The isentropic efficiency of the compressor was a key factor in system COP improvement. It was concluded that adding an internal heat exchanger and improving compressor efficiencies would be good options for the future R1234yf MAC system enhancement.

Quick and empirical correlations for refrigerant pressure drop in mobile air conditioning system evaporators

In heat exchanger design and simulation, a precise refrigerant pressure drop prediction is difficult because of limited correlation's accuracy. In the present paper, several quick and accurate empirical correlations for refrigerant pressure drop of the typical evaporators (laminated plate evaporator and minichannel parallel flow (MCPF) evaporator) used in mobile air conditioning (MAC) system were proposed. A factor which was related with the refrigerant mass flow rate, thermodynamic properties and refrigerant status was introduced. The types of evaporator and refrigerant were considered in the correlations which were available under typical MAC evaporator application conditions. The analysis results showed the refrigerant pressure drops were implied in a linear relationship with the proposed factor. The predicted data agreed with the experimental data very well. For laminated palate evaporators, the average deviations were 1.8% and 0.7% for R134a and R1234yf, respectively. For MCPF evaporator, the average deviations were 4.5% and 0.6% for R134a and R1234yf, respectively.

Emissions of halocarbons from mobile vehicle air conditioning system in Hong Kong

During the implementation of Montreal Protocol, emission inventories of halocarbons in different sectors at regional scale are fundamental to the formulation of relevant management strategy and inspection of the implementation efficiency. This study investigated the emission profile of halocarbons used in the mobile vehicle air conditioning system, the leading sector of refrigeration industry in terms of the refrigerant bank, market and emission, in the Hong Kong Special Administrative Region, using a bottom-up approach developed by 2006 IPCC Good Practice Guidance. The results showed that emissions of CFC-12 peaked at 53 tons ODP (Ozone Depletion Potential) in 1992 and then gradually diminished, whereas HFC-134a presented an increasing emission trend since 1990s and the emissions of HFC-134a reached 65,000 tons CO2-equivelant (CO2-eq) by the end of 2011. Uncertainty analysis revealed relatively high levels of uncertainties for special-purpose vehicles and government vehicles. Moreover, greenhouse gas (GHG) abatements under different scenarios indicated that potential emission reduction of HFC-134a ranged from 4.1 to 8.4×105tons CO2-eq. The findings in this study advance our knowledge of halocarbon emissions from mobile vehicle air conditioning system in Hong Kong.

Vehicle Hot Surface Ignition and Mitigation Measures of R-1234yf Refrigerant for MAC Systems

The European Commission (EC) as well as the United States Environmental Protection Agency (EPA) published legislations to regulate or encourage the use of low Global Warming Potential (GWP) refrigerants applied to Mobile Air Conditioning (MAC) systems. Europe mandates a GWP less than 150 of MAC refrigerants for new vehicle types. The thermodynamic refrigerant properties of R-1234yf are slightly different from the properties of R-134a, currently used in MAC systems. Although the basic material data show that R-1234yf is flammable, ignition tests performed for an automotive engine under-hood environment reveal design and packaging influences of its ignition behavior. After extensive collaborative research in 2009, the Society of Automotive Engineers Cooperative Research Team (SAE CRP1234) concluded that R-1234yf is suitable for use in automotive applications. Further ignition risk assessment regarding R-1234yf usage in MAC systems was done by SAE CRP1234-4 in 2013. They concluded that are still very small compared to the risks of a vehicle fire from all causes and well below risks that are commonly viewed as acceptable by the general public. This paper will compare under-hood hot surface ignition behavior of five different vehicles under specific test conditions. Out of these five, two vehicles were further investigated and the engine compartment designs were assessed. A broad range of flammability testing was completed to study release of the R-1234yf and Polyalkylene Glycol (PAG) oil mixture. Both vehicles were equipped with a transverse gas engine, front take down exhaust routing, turbo charger, and single evaporator MAC system. This engine architecture was chosen due to the short distance from a potential condenser leak and the hot exhaust system components in case of a frontal crash. Although the engine architecture was the same for both vehicles, the engine design and packaging were different and were described in this paper. Parameters that were considered include heat shield design, engine packaging, exhaust system surface temperatures during refrigerant release, and the impact on the time to ignition of the R-1234yf/PAG mixture. Mitigation measures were also identified and their potential integration into a vehicle were discussed. As engine coolant will be released in many real-world frontal crash scenarios, the impact of vaporized glycol water mixture on the ignition behavior was assessed. This paper further describes the MAC systems, the test facility used, and the testing procedure applied. Language: en

Crash Test with a Hot Operating Engine and R-1234yf MAC System

As part of the launch of the refrigerant R-1234yf there were a number of studies done regarding the ignition behavior of this new refrigerant in passenger cars. These tests were conducted by a number of automobile manufacturers, component suppliers, and the refrigerant supplier under laboratory conditions at the component and vehicle level. In November 2009 the international automotive industry concluded that the R-1234yf can be used safely in automotive air conditioning systems. Further tests were conducted by different automobile manufacturers, suppliers, and the refrigerant supplier under various laboratory and vehicle operation conditions means hot surfaces in the engine compartment. A number of vehicle manufactures have conducted full vehicle crash tests. In this paper, real world accidents are analyzed using the German In-Depth Accident Study (GIDAS) database as well as the thermal parameters for ignition of R-1234yf, i.e. concentration and surface temperature to create a worst-case scenario. These parameters were considered while conducting a frontal impact test with a hot 1.4 liter turbo gasoline engine with a critical overheated exhaust surface temperature and an operating R-1234yf Mobile Air Conditioning (MAC) system. The test was conducted with an ECE R95 deformable moving barrier at a test speed of 50kph. Language: en

Improved Safety for Automotive Lithium Batteries: An Innovative Approach to include an Emergency Cooling Element

This paper describes a concept for an independent and redundant safety concept for Lithium batteries in Electric and Hybrid Electric Vehicles. This concept includes an emergency cooling system based on pressurized carbon dioxide (CO2). Since carbon dioxide (CO2) is a possible medium of future mobile air conditioning (MAC) systems, the MAC system can be utilized for the one-time emergency cooling described in this paper. In the first part of the paper, some major safety aspects of automotive Li batteries are highlighted. In the second section, the paper describes a technical approach, how these batteries can be made safer. Pressurized CO2, which is a promising candidate for cooling liquids used in future mobile air conditioning (MAC) systems, is used to effectively cool down an overheating or up-heating battery in a critical state. The safety system thereby is not based on an electrical effect, but on a direct and fast-reacting thermal conduction, avoiding a thermal runaway of individual cells. The application of the proposed system is to act preventively just before the thermal runaway gets uncontrollable. In this case, the limited amount of CO2, which is available in the MAC system, fulfils the emergency cooling requirements. The combination of standard car components for the concept leads to an only moderate increase of the total weight and the additional system costs. Therefore, the described system might be of interest for car, battery and air conditioning system producers. This paper explains that the synergetic combination of CO2-based MAC systems and Li-based batteries is an innovative approach to improve environmental compatibility in future vehicles. The concept is proven experimentally on a lab scale with battery cells and battery packs consisting of four serially connected cells, respectively.

Molecular Simulation Studies on the Thermophysical Properties of the Refrigerant Blend R-445A

The ternary mixture of CO2, the tetrafluoroethane R-134a, and the trans-1,3,3,3-tetrafluoro-1-propene (R-1234ze(E)) has recently been proposed as refrigerant blend R-445A for mobile air conditioning (MAC) systems. However, the lack of experimental data for the thermophysical properties of this refrigerant blend hampers studies on its performance in MAC systems or other potential technical applications. In our earlier work [Raabe, G.; Maginn, E. J., J. Phys. Chem. B 2010, 114, 10133–10142; Raabe, G. J. Phys. Chem. B. 2012, 116, 5744–5751], we have introduced a force field model for different fluoropropenes. In this work, we employ the molecular model for Gibbs ensemble simulation studies on the vapor–liquid equilibrium (VLE) properties of the ternary refrigerant blend R-445A in the temperature range from T = (260 to 330) K. In addition, we present predictions from molecular dynamics simulations for the densities and viscosities of the mixture in the liquid phase at temperatures from T = (270 to 315) K and pressures up to 1.6 MPa. All simulation results are compared to calculations by REFPROP 9.1 Agreement between simulation and correlation is in general good, which attests the predictive capability of the molecular simulation studies.

Rainwater trifluoroacetic acid (TFA) in Guangzhou, South China: Levels, wet deposition fluxes and source implication

The origin of trifluoroacetic acid (TFA) occurring in hydrosphere has long been a controversial issue. Hydrochlorofluorocarbons and hydrofluorocarbons (HCFCs/HFCs) as replacements of chlorofluorocarbons (CFCs) are precursors of TFA in the atmosphere, their contribution to rainwater TFA is a concern as their ambient mixing ratios are continually growing. Here we present rainwater TFA monitored from April 2007 to March 2008 in urban Guangzhou, a central city in south China's highly industrialized and densely populated Pearl River Delta region. Rainwater TFA levels ranged 45.8–974ngL−1 with a median of 166ngL−1. TFA levels negatively correlated with rainfall amount, the yearly rainfall-weighted average for TFA was 152ngL−1. The annual TFA wet deposition flux was estimated to be 229gkm−2yr−1, and the total wet deposition of TFA reached ~1.7tyr−1 in Guangzhou. The Two-Box model was applied to estimate attributions of HCFCs/HFCs and fluoropolymers to rainwater TFA assuming TFA generated was proportional to gross domestic product (GDP), gross industrial product (GIP) or number of private cars. The results revealed that the degradation of HCFCs/HFCs and fluoropolymers could explain 131.5–152.4ngL−1 rainwater TFA, quite near the observed rainfall-weighted annual mean of 152ngL−1, suggesting rainwater TFA in Guangzhou was predominantly originated from these anthropogenic precursors. HCFCs/HFCs accounted for 83.3–96.5% of rainwater TFA observed, while fluoropolymers' contributions were minor (~5%). HFC-134a alone could explain 55.9–90.0% of rainwater TFA, and its contribution would be greatly enhanced with its wide use in mobile air conditioning systems and rapid increase in ambient mixing ratios.

Climate-friendly technologies in the mobile air-conditioning sector: a patent citation analysis

The development of climate-friendly technologies and its diffusion across countries is of key importance to slow climate change. This paper considers technologies in the mobile air-conditioning (MAC) sector which is a major contributor of fluorinated greenhouse gas emissions. Using patents as an indicator of innovations and patent citations as a proxy for knowledge flows, the inducement of new environmental and non-environmental technologies and knowledge diffusion within and across countries are analysed. The focus is on direct abatement of fluorinated greenhouse gases excluding energy efficiency improvements. We find that most environmental MAC patents originate from the US and Germany. Most knowledge flows take place within countries. Regarding cross-country flows most environmental knowledge diffuses from French and German patents, which is likely to be a result of regulatory activities in Europe and intensified research on environmentally benign MAC systems. Yet, this exchange of knowledge is not very intensive and stable so that the impact of EU regulations on US and Japanese patenting behaviour seems to be fairly weak.

Carbon footprint model for evaluating the global warming impact of food transport refrigeration systems

Abstract This paper presents a model for assessing the carbon footprint of food transport refrigeration systems. The model considers all the impacts of the refrigerators and refrigerants in each process, including production, transport, use, repair and recycling, on greenhouse gas emissions expressed as the CO2 equivalent emissions in total. The carbon footprint can be divided into direct emissions which are the greenhouse effect caused by various greenhouse gas emissions and leakage in each process, and indirect emissions which are the CO2 equivalent emissions due to the energy consumption in each process. This model was used to evaluate the carbon footprint of food transport refrigeration systems with three refrigerants, R404A and the environmentally benign refrigerants R744 (CO2) and R410A for various ambient temperatures, refrigeration temperatures, lifetimes and refrigerator drive modes. The results show that the carbon footprint of food transport refrigeration systems with R404A is larger than for R744 and R410A. Although the Global Warming Potential (GWP) of R744 is the lowest, the carbon footprint of food transport refrigeration systems with R744 is not always the smallest, but may exceed that of R410A in high temperature areas. The CO2 emissions caused by the energy consumption are a large part of the total CO2 emissions, with the energy consumption to power the refrigerator and to carry the refrigeration unit weight resulting in the largest proportions; thus increasing the coefficient of performance (COP) of the refrigerator and the efficiencies of other equipments can significantly reduce the energy consumption and CO2 emissions. Higher ambient temperatures and lower refrigeration temperatures lead to more CO2 emissions. Refrigerators driven by auxiliary engines have higher CO2 emissions than refrigeration systems driven by the main vehicle engine or electricity. The carbon footprint evaluation model developed in this paper can also be used to evaluate the carbon footprint of mobile air conditioning and other systems.

Periodic Reverse Flow and Boiling Fluctuations in a Microchannel Evaporator of an R134a Mobile Air-Conditioning System

Periodic Reverse Flow and Boiling Fluctuations in a Microchannel Evaporator of an R134a Mobile Air-Conditioning System

Application of Magnetocaloric Heat Pumps in Mobile Air-Conditioning

Air-conditioning (AC) is an important sub-system in electric vehicles (EVs). AC is responsible for the highest energy consumption among all the auxiliary systems. As the energy is delivered by the batteries, the power consumption for air-conditioning can imply a significant reduction of the vehicle autonomy. Given the actual state of the art and the temperature and power requirements, electrically driven compressors are the most feasible solution. However, vapour-compression systems are reaching their maximum efficiency. Using innovative technologies can improve the performance of standard systems and hereby increase the vehicle autonomy. This paper presents the first steps in the design of a magnetocaloric air-conditioner for an electric minibus. The system will include two reversible magnetocaloric heat pumps, one in the front part of a minibus and one on the rear. The heat rejection system of the power electronics will be coupled to the air-conditioning system. In order to assist the design of the system, a dynamic model has been developed for the cabin, the hydraulic loops and heat exchangers, and the magnetocaloric units. An integrated design of the complete system is necessary, as it will work under dynamic conditions which depend on the thermal load in the cabin. In this paper, the operation conditions of the magnetocaloric units are presented and the design of the magnetocaloric air-conditioner is discussed. This work has been developed under the frame of the European Project ICE which aims to develop an innovative mobile air-conditioning system for EVs based on a magnetocaloric heat pump.

Experimental study on evaporator performance in mobile air conditioning system using HFO-1234yf as working fluid

The widely used evaporators with two different type were experimentally studied in psychrometric calorimeter room using HFO-1234yf as working fluids. The evaporators types are laminated plate and microchannel parallel flow (PF) type. The experimental results compared with R134a system show that cooling capacity has different features in laminated plate evaporator and microchannel PF evaporator under different refrigerant pressure at expansion valve inlet. In general, cooling capacity of laminated plate evaporator of HFO-1234yf is reduced up to 8.0%. But in microchannel PF evaporator, cooling capacity is comparable and/or larger than that of R134a up to 6.5%. The HFO-1234yf evaporator air off temperature deviation is larger than that of R134a evaporator. The air side pressure drop is very close for both evaporators and refrigerants. HFO-1234yf refrigerant side pressure drop is larger than that of R134a for both evaporators.

Cooling Performance Characteristics on Mobile Air-Conditioning System for Hybrid Electric Vehicles

This study investigates the cooling performance characteristics of the mobile air-conditioning system using R744 (CO2) for the hybrid electric vehicle as an alternative to both the R-134a and the conventional air-conditioning system. The developed air-conditioning system is operated with an electric driven compressor in the battery driving mode and a belt driven compressor in the engine driving mode. The cooling performance characteristics of the developed system have been analyzed by experiments under various operating conditions of inlet air temperature, air flow rates for the gas cooler side and evaporator side, and electric compressor revolution respectively. As a result, cooling performances of the tested air-conditioning system for the EDC driving mode (electricity driven compressor) were better than those for the BDC driving mode (belt driven compressor). The cooling capacity and cooling COP of the tested air-conditioning system for both driving modes were over 5.0 kW and 2.0, respectively. The observed cooling performance of the tested air-conditioning system may be sufficient for the cabin cooling of hybrid electric vehicles.

Comparative experimental study of an open piston compressor working with R-1234yf, R-134a and R-290

Among the different alternatives proposed in the automotive field to replace R-134a and R-1234yf is a new generation fluid which has recently gained great importance for MAC (Mobile Air Conditioning) systems. This fluid has the advantage of having a low GWP (Global Warming potential) and thermodynamic properties similar to R-134a. But there is some criticism regarding the non-natural origin of the fluid and its possible long-term effects on the environment have not been studied. In that sense, hydrocarbons and particularly R-290 can be considered as alternatives. This paper presents a comparative study between R-1234yf, R-134a and R-290 for an open piston compressor at different operating conditions. The text matrix comprised two compressor speeds, evaporation temperatures from −15 °C to 15 °C and condensation temperatures from 40 °C to 65 °C. From these tests, the compressor behavior with these refrigerants has systematically been analyzed in terms of compressor efficiency, volumetric efficiency, losses to the ambient and oil-refrigerant properties.

PERFORMANCE OF R-1234YF IN MOBILE AIR CONDITIONING SYSTEM UNDER DIFFERENT HEAT LOAD CONDITIONS

"Drop-in" tests of R-1234yf in a mobile air conditioning (MAC) system were conducted, and the system performance results were compared with those of the same system using R-134a. The performance tests were performed in a psychrometric calorimeter test facility based on enthalpy-difference method. The system performance was investigated under low-, middle- and high-load conditions. The results showed that the optimum refrigerant charge of R-1234yf was approximately 90% compared with that of R-134a under the same MAC system. When operated under optimum refrigerant charge, the system cooling capacity and COP of R-1234yf was 11% and 8.3% lower than that of the R-134a system, respectively. When wind tunnel test was conducted on a practical vehicle, the result showed that the carriage temperature in the vehicle with the R-1234yf system dropped slower. The average carriage temperature and blower outlet temperature were 2°C higher than those of the R-134a system during the test.

Flash gas bypass in mobile air conditioning system with R134a

This paper demonstrates that the performance of a mobile air conditioning system (with a microchannel evaporator modified to be single pass) operating normally with R134a in direct expansion mode can be significantly improved when switched to flash gas bypass (FGB) mode. When operated at the same compressor speed, the system in FGB mode produces about 13%–18% more cooling capacity at 4%–7% higher COP than DX mode. When the compressor speed was adjusted to maintain the same cooling capacity, the COP improved 37%–55%. Two main reasons are identified and discussed: 1) improved refrigerant distribution and 2) reduction of refrigerant pressure drop.