Article

A Review of Recent Research on Automotive HVAC Systems for EVs

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Abstract

Automotive heating, ventilation, and air-conditioning (HVAC) systems are of particular interest from the viewpoint of improving fuel economy, especially in electric vehicles (EVs) such as hybrid electric vehicles (HEVs), fuel cell electric vehicles (FCEVs), and battery electric vehicles (BEVs). This paper describes recent research on automotive air-conditioning and heating technologies after classifying them into heat pump applications, control and operation, heat exchangers, refrigerants, thermal comfort, localized HVAC systems, and additional energy-saving systems. Even though many researchers have applied the existing concepts and technologies for EVs, significant revamping efforts are necessary owing to the dynamic, transient, and local characteristics of vehicles.

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... The low driving range and battery life are two major hurdles in the development of electric vehicles. The cabin is heated in winter using electric energy of the battery, which results into reduction in driving range of vehicle [2]. The charge-discharge performances of the batteries are degrading significantly as the temperature reduces. ...
... The battery temperature rise rate is calculated using Equation (2). The battery temperature rise rate is presented in °C/min [4]. ...
... The battery temperature rise rate is calculated using Equation (2). The battery temperature rise rate is presented in • C/min [4]. ...
Article
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The objective of the present study is to conduct experiments for investigating heating performances of integrated system with serial and parallel circuits for battery and heating ventilation and air conditioning system (HVAC) of electric vehicles under various operating conditions. In addition, the artificial neural network (ANN) model is proposed to accurately predict the heating performances of integrated system with serial and parallel circuits for battery and HVAC. A test bench of integrated system with serial and parallel circuits has been developed for establishing the trade-off between battery heating and HVAC heating. The heating performances namely, battery out temperature, battery temperature rise rate, battery heating capacity, HVAC heating capacity and total heating capacity are evaluated experimentally for the integrated system with serial and parallel circuits. The behavior of various heating performances is evaluated under influence of flow rate and heater power. Battery out temperature reaches 40 °C within 10 min with rise rate of 2.17 °C/min for the integrated system with serial circuit and that within 20 min with rise rate of 1.22 °C/min for the integrated system with parallel circuit. Integrated system with serial circuit shows higher HVAC heating capacity than integrated system with parallel circuit which are 5726.33 W and 3869.15 W, respectively. ANN model with back-propagation algorithm, Levenberg-Marquardt training variant, Tan-sigmoidal transfer function and 20 hidden neurons presents the accurate prediction of heating performances of the integrated system with serial and parallel circuits for battery and HVAC.
... Heating and air conditioning are essential subsystems in vehicles that maintain cabin comfort levels. Whereas ICEVs use waste heat from the engine to cool and heat the vehicle cabin, engine waste heat in EVs is insufficient and therefore additional electrical energy is necessary to power these systems, which can considerably impact driving mileage [2,3]. In fact, air conditioning and heating account for 33 % of EV energy losses; additionally, 27 % is attributed to rolling resistance, 25 % to electric and mechanical losses, and 15 % to air resistance and other sources [3,4]. ...
... Whereas ICEVs use waste heat from the engine to cool and heat the vehicle cabin, engine waste heat in EVs is insufficient and therefore additional electrical energy is necessary to power these systems, which can considerably impact driving mileage [2,3]. In fact, air conditioning and heating account for 33 % of EV energy losses; additionally, 27 % is attributed to rolling resistance, 25 % to electric and mechanical losses, and 15 % to air resistance and other sources [3,4]. Therefore, efficient design of these subsystems is essential for increasing the mileage range of EVs, especially the heating subsystem, which consumes more energy than does its cooling counterpart. ...
... A greater local thermal comfort increase was seen in the leg region than the thigh region, as illustrated in Fig. 9(c), which in turn improved the overall thermal comfort, as shown in Fig. 9(d). The higher local thermal sensation and comfort in the leg region was likely due to the multi number of heaters (2)(3)(4)(5) surrounding the leg region. Even though an improvement in overall thermal comfort was obtained, the overall thermal comfort model showed an irregular trend. ...
Article
In the global effort to reduce CO2 emissions and mitigate climate change, there is significant interest in replacing internal combustion engine vehicles with electric vehicles. Furthermore, the use of radiant heaters rather than conventional air conditioning systems may reduce the energy consumption in electric vehicles. In this work, a thermal physiology model that includes the effect of local radiant heaters was developed to predict the temperature change in a human body in a cold or warm environment. The developed model indicated an increase in the mean skin temperature when radiant heaters were used in a cold environment. Local and overall thermal sensation and thermal comfort predicted from simulation showed an escalation in the sensation and comfort, thereby suggesting an improvement in passenger comfort with the addition of local radiant heaters. This study might contribute to effective energy saving strategies and passenger comfort in electric vehicles.
... According to the Indian Railways official gazette document [1], the wiring in the railway coaches are done with multiple strand Poly vinyl chloride copper cables insulated with polymer/rubber coatings as per specification. ICF/Elect./857. ...
... Heating and cooling load data of[1], we get the coefficient of performance for an airconditioned railway coach, with special emphasis to the Indian railways. ...
Conference Paper
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Sustaining the proper temperature and proper circulation in an enclosure is necessary for providing better comfort level to the occupants. This process is aided by Heat Ventilation and Air conditioning (HVAC) systems. Any enclosure is susceptible to build up of heat in the presence of occupants and improper eradication of this heat would cause distress. The main objective is to minimize the energy consumption by shifting towards a proposed system using the concept of IOT and mathematical data analysis. The need for automated temperature control is increasing day by day with smart and effective control methods. This project proposes to automate and increase efficiency of temperature control using regression model algorithms in the air-conditioned coaches of the Railways and other enclosed environments to provide optimum temperatures for comfortable travel to passengers.
... From Table 4, it is seen that the energy needed to travel 1 km is 0.91 kWh without considering auxiliary device and air conditioning. The air conditioning and auxiliary load F I G U R E 6 Grid profile for average minimum and maximum load demand and their variations throughout the year location-wise: (a) Residential, (b) Commercial, and (c) Industrial location consume about 33% additional energy to travel 1 km [25], and hence, the total energy required by AC E-bus is equal to 1.36 kWh. Once the energy consumption per km is known, the energy required by a bus to cover the ring road can be determined. ...
Article
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The exponential increase in the number of internal combustion engine vehicles due to rapid urbanization results in traffic congestions and air pollution. A paradigm shift towards public transportation system using an electric vehicle can be a possible solution for this issue. However, for such a system to be effective, it is necessary to study its impact on the electricity grid, and also to size the subsystems appropriately. Hence, in this work, an E‐bus based transportation system with the preliminary sizing of subsystems is proposed. In order to ensure that the proposed transportation system does not overburden the grid, distributed solar energy generation is used as an additional source. The energy required for transportation system is stored in a high capacity storage device from grid and solar. The high capacity storage device is further used to stabilize the grid through peak shaving and valley filling. The systematic energy flow between subsystems is ensured by using a fuzzy logic control algorithm. The feasibility of the proposed system is analysed for Guwahati city, Assam, India, for its driving pattern and different seasonal variations of grid demand and solar irradiation. The results of the analysis show that with proper sizing and energy management, a viable E‐bus based transportation system can be obtained for Indian cities.
... The continuous development of Li-ion batteries with high energy density and high power density is leading to possible accomplishments of high cruising capabilities, high peak power, reduced overall weight, sufficient power supply for automotive heating, ventilation, and air-conditioning (HVAC) [101] and longer travel range. However, this has led to inevitable problem of higher heat generation rates making Li-ion batteries more susceptible to operating temperatures causing capacity fade, aging and power depletion [102]. ...
Thesis
The objective of this study is to investigate direct cooling performance characteristics of battery and battery pack for electric vehicles using dielectric fluid immersion cooling technology. This thesis consists of two parts. The first part was on the thermal performance characteristics of a single lithium-ion pouch cell using dielectric fluid immersion cooling assisted with tab cooling. The second part was on the thermal and flow performance characteristics of a 50V lithium-ion battery pack. Firstly, the electrochemical-thermal model for a single lithium ion pouch cell was developed and thermal performance according to cooling conditions and operating conditions were analyzed. The experimental results showed that Li-ion pouch cell immersed in flowing dielectric fluid assisted with tab cooling showed better cooling performance with 46.8% reduction in the maximum temperature at the positive tab compared to natural convection at 3C discharge rate. The electrochemical-thermal model of Li-ion pouch cell immersed in flowing dielectric fluid assisted with tab cooling was developed using Multi-Scale Multi-Domain (MSMD) approach with Newman, Tiedemann, Gu, and Kim (NTGK) model. Thetemperature and voltage predictions of the developed electrochemical-thermal model for the lithium-ion pouch cell were validated within ±5% variation of the experimental data. To analyze thermal performance of the lithium-ion pouch cell, the maximum temperature, temperature difference and heat removal rate were compared. As a result, the dielectric fluid flow direction opposite to the tab end was suggested as the heat removal rate of 6.26W at 3C discharge rate was observed, which was 3.8% higher compared to the case of dielectric fluid flow from the tab end. Subsequently, with developed electrochemical-thermal model the thermal and flow performances of the 50V lithium-ion battery pack using the dielectric fluid immersion cooling assisted with tab cooling technology were evaluated. The results revealed that, the maximum temperature of the 50V lithium-ion battery pack was maintained below 40.0°C at 3C discharge rate with ideal pumping power of 6.52W, however, under high discharge rate condition of 5C, the pumping power increased 12.5 times to 81.5W. With the application of the proposed dielectric fluid immersion cooling assisted with tab cooling technology, the maximum battery pack temperature was 9.3% lower than the indirect cooling method with water-ethylene glycol, confirming the improved cooling performance compared to the conventional cooling method. Under subzero temperature condition of −15°C at 1C discharge rate, the average temperature of the 50V lithium-ion battery pack reached the equilibrium temperature of 25.3°C after 540s for the inlet temperatures of dielectric fluid flow and airflow of 25°C, respectively. Under thermal abuse condition with internal short circuit, the peak temperature of 341.7°C was observed for the battery pack and thermal runaway of battery pack was prevented except the affected cell. To summarize, this study demonstrated the dielectric fluid immersion cooling assisted with tab cooling as a safe and efficient thermal management technology for high-density and high capacity lithium-ion battery and battery pack application in electric vehicles.
... The air conditioning (AC) system has evolved into one of the most significant features of vehicles for enhanced comfort. During the evolution of vehicle technology, modifications to the AC system were made to improve passenger comfort and health, fuel efficiency, and environmental acceptability [1,2]. The vapor compression AC system remains the primary system for commercial vehicles. ...
Article
Full-text available
This paper reports on the experimental investigation of the cooling effect harvested in liquefied petroleum gas (LPG)-fueled vehicles. The heat required to vaporize the LPG in a vaporizer, which was originally transferred by the engine coolant, was replaced by air flow. The fuel line was modified by adding an evaporator equipped with an expansion valve between the LPG tank and regulator. The tests were carried out on a Daihatsu 1945 cc engine at 1000, 2000, and 3000 rpm with three different levels of air mass flow rate obtained through the setting of the electric blower switch. The LPG consumption was determined by the engine load instead of being regulated by an external valve. By considering the air temperature and humidity mixing ratio (X), a cooling effect of 0.89 kJ‧s-1 was achieved at an LPG mass flow rate of 0.407 g‧s-1. This represents the fuel consumption of a 1495 cc engine at 3000 rpm and reduces the temperature to approximately 14 °C. The energy efficiency ratio of the half-cycle refrigeration system in LPG-fueled vehicles was also reported, which ranged from 6.77 to 21.06 for LPG mass flow rates of 0.139–0.407 g‧s-1 and air mass flow rates of 0.049–0.062 kg‧s-1. Although the cooling effect produced is lower than that of the primary air conditioning (AC) system (vapor compression system) in passenger and pick-up vehicles, it has potential as a secondary AC system when combined with the primary AC system through a hybrid system.
... The development of efficient and ecofriendly engines which emit less waste heat is the focus of recent research to overcome the environmental issues of global warming and CO 2 emission [1]. Therefore, in the last decade, the research trend is shifting towards the development of efficient electric vehicles [2]. The challenge associated with full commercialization of electric vehicles is their lower driving range due to high power consumption by the thermal management system. ...
Article
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One of barriers for the present heat pump system’s application in an electric vehicle was decreased performance under cold ambient conditions due to the lack of evaporating heat source. In order to improve the heat pump’s performance, a high-pressure side chiller was additionally installed, and the tested heat pump system was modified with respect to refrigerant flow direction along with operating modes. In the present work, the performance characteristics of the heat pump system with a high-pressure side chiller for light-duty commercial electric vehicles were studied experimentally under hot and cold ambient conditions, reflecting real road driving. The high-pressure side chiller was located after the electric compressor so that the highest refrigerant temperature transferred the heat to the coolant. The controlled coolant with discharged refrigerant from the electric compressor was used to heat up the cabin, transferring heat to the inlet air like the internal combustion engine vehicle’s heating system, except with unused engine waste heat. In the cooling mode, for the exterior air temperature of 35 °C and interior air temperature of 25 °C, cooling performance along with the compressor speed showed that the system efficiency decreased by 16.4% on average, the cooling capacity increased by 8.0% on average and the compressor work increased by 27% on average. In heating mode, at the exterior and interior air temperature of −6.7 °C, compressor speed and coolant temperature variation with steady conditions were tested with respect to heating performance. In transient mode, to increase coolant temperature with a closed loop from −6.7 °C, tested system characteristics were studied along the compressor speed with respect to heating up the cabin. As the inlet air of the HVAC was maintained at −6.7 °C, even though the heat-up rate of the cabin room was a little slow, the cabin temperature reached 20 °C within 50 min and the temperature difference with the ambient air attained 28.7 °C.
... In practice, if there is not enough energy to satisfy the passenger's thermal comfort, the use of the HVAC system should be reduced to reach the final destination or next charging point. In some situations, the speed must be reduced to satisfy the passenger's thermal comfort [3]. ...
Article
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Defining a passenger’s thermal comfort in a car cabin is difficult because of the narrow environment and various parameters. Although passenger comfort is predicted using a thermal-comfort scale in the overall cabin or a local area, the scale’s range of passenger comfort may differ owing to psychological factors and individual preferences. Among the many factors affecting such comfort levels, the temperature of the seat is one of the direct and significant environmental factors. Therefore, it is necessary to predict the cabin environment and seat-related personal thermal comfort. Accordingly, machine learning is used in this research to predict whether a passenger’s seat-heating-operation pattern can be predicted in a winter environment. The experiment measures the ambient factor and collects data on passenger heating-operation patterns using a device in an actual winter environment. The temperature is set as the input parameter in the measured data and the operation pattern is used as the output parameter. Based on the parameters, the predictive accuracy of the heating-operation pattern is investigated using machine learning. The algorithms used in the machine-learning train are Tree, SVM, and kNN. In addition, the predictive accuracy is tested using SVM and kNN, which shows a high validation accuracy based on the prediction results of the algorithm. In this research, the parameters predicting the personal thermal comfort of three passengers are investigated as a combination of input parameters, according to the passengers. As a result, the predictive accuracy of the operation pattern according to the tested input parameter is 0.96, showing the highest accuracy. Considering each passenger, the predictive accuracy has a maximum deviation of 30%. However, we verify that it indicates the level of accuracy in predicting a passenger’s heating-operation pattern. Accordingly, the possibility of operating a heating seat without a switch operation is confirmed through machine learning. The primary-stage research result reveals whether it is possible to predict objective personal thermal comfort using the passenger seat’s heating-operation pattern. Based on the results of this research, it is expected to be utilized for system construction based on the AI prediction of operation patterns according to the passenger through machine learning.
... The cabin heating can be directly related to the positive temperature coefficient (PTC). The increased PTC contributes to the reduction in the range of EV [28,29]. A unified thermal management system that satisfies diverse thermal and design needs of the auxiliary loads in EV's needs to be evolved. ...
Article
In automobiles, the demand for HVAC has been rising for decades and the key variables that affect the thermal comfort in a car were identified as air velocity, temperature, radiant temperature, and relative humidity. Thermal comfort estimation in a vehicle depends on the transient behavior of the cabin space and boundaries. The predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) are the available methods to describe and optimize thermal comfort in cabin space. In this paper, the cabin thermal comfort of a minivan was analyzed for reduction of energy consumption with the help of experimental and numerical simulation. Using CFD simulation and validation with experimental data, the flow dynamics inside a vehicle cabin is evaluated based on air velocity, temperature, and comfort indices. With some error for the extreme planes, a strong agreement was reached between the experimental values and the CFD model. With the reduction in the air velocity from 2.3 m/s to 1.3 m/s, the average power required to run the blower can be reduced by 43%, providing an advantage of reducing the capacity of the compressor. The higher PPD values were observed on the walls of the cabin and at the outlet of the AC vents.
... In order to decrease the energy consumption for the HVAC systems on electric buses, several solutions have been proposed, as follows [8][9][10][11]: using recovery heat from the traction batteries; an integrated air conditioning and heating system; improved control systems for the heating system; door air curtains/air screened doors to reduce the heat exchange between the inside and outside of the bus [12]; heat pumps; thermal pre-conditioning; complex additional heating equipment. Infrared radiation heating in the vehicle cabin has also been studied for electric vehicles [13,14]. ...
Article
Full-text available
The use of electric buses is increasing all over the world; this is due to the aim of limiting pollution in heavily urbanized areas. Using electric buses is one element of the desire to drop local pollution to zero emissions. The necessary electricity can be generated through centralized production, and in the case of electric buses, the pollution level is directly proportional to the amount of electricity produced. Their limited onboard power needs optimization, both in terms of traction and in auxiliary energy consumption. Heating in electric buses consumes the most energy from the auxiliaries, which can reduce the range of the vehicle up to a half, or more in the coldest days of the winter months. In this context, a precise estimation of heat loss and of the energy necessary for heating electric buses is crucial. Using the heat transfer theory, the heat balance method, and the U-value estimation, this article estimates the heat loss for a typical 12 m electric bus for a harsh winter day. Thermal simulations were made in order to estimate the heat flux through the structure of the bus (windows, walls, roof, and floor). Heat loss components were calculated in order to determine the most affected zones of the bus. The calculated data for the energy necessary to heat the bus were compared with the heating system data from an electric bus. By optimizing the necessary auxiliary energy consumption, the emissions at the source of electricity production will be significantly reduced.
... A surface area (mm 2 ) C 1 model constants C 2 model constants C 3 model constants C p specific heat at constant pressure (J/kg •°C) C μ Constant D H hydraulic diameter (mm) G k generation of turbulence kinetic energy due to the mean velocity gradients G buo generation of turbulence kinetic energy due to buoyancy K T turbulent kinetic energy (J) K 0- 6 linear parameters for open circuit voltage estima- [22] . Recently, there was increased attention towards cold platebased water cooling due to availability of scope for optimizing the cold plate channel configuration and different coolant flow conditions [23][24] , however there is a paucity of studies on the detailed thermal performance of lithium-ion pouch cell with a Uturn type channeled plate on both sides at high discharge rates. ...
... The utilization of air conditioning and heating systems to control passengers' comfort in the automotive industry impacts the fuel consumption and economy, which makes it necessary to improve the fuel efficiency [1][2][3], where the internal temperature of the vehicle's air, as a measurable factor of discomfort, should be controlled between 23 • C and 28 • C [4]. In order to handle this, the development of energy-efficient solutions have been implemented, one of these being Thermal Energy Storage (TES), which is the most efficient in using the available heat resources [5,6]. ...
Article
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The automotive industry is one of the most contaminant; for this reason, solutions in efficient matter has been proposed over the years. This research contributes to this subject by evaluating the thermal comfort in the internal air of a vehicle by using a 20 mm layer of a phase-change material attached to the rooftop interior of a car. The phase-change material selection is based on a list of other materials proposed in previous research and chosen by multicriteria decision methods. In this sense, the material savENRG PCM-HS22P proved to be the best. Moreover, a simulation using the finite elements method showed how the PCM reduced the temperature of the air by 9 °C when heating and by 4 °C when the temperature drops. To conclude, the multicriteria selection methods chose the best material to absorb energy during the charging process and released it during the discharging event in this automotive application.
... For this purpose, alternative "green" technologies are being considered (e.g. [1][2][3][4][5]). Thermoacoustic cooling devices are systems that offer potentially attractive alternatives [6], especially with the rapid development of hybrid and electric vehicles. ...
Article
Thermoacoustic refrigeration technology is a green alternative for the conventional refrigeration system in vehicles. The former uses environmentally friendly inert gases whereas the latter uses chemical refrigerants that can have severe impacts on the environment. In order to apply thermoacoustic technology in the automobile industry, the size and the weight of plausible thermoacoustic refrigerators should be decreased. The design of a new compact thermoacoustic refrigerator is described in this study. This thermoacoustic refrigerator uses two electroacoustic components and one thermoacoustic core. The technical details of design, fabrication, and testing processes are presented. A methodology for thermal design of the heat exchangers is proposed and validated by measurements. The effects of different parameters, such as the driver piston displacement amplitude, the phase shift between the voltage signals applied to the electroacoustic components, and the cold side temperature on the performance indices of the refrigerator are investigated. The performance of the prototype is compared with the performance calculated by the DeltaEC design model. The overall agreement between the calculated and the measured performance parameters is fair, but further insight into the temperature distributions reveals that non-linear effects yield discrepancies between the model and the experiments. A preliminary discussion of the origin of these discrepancies is proposed.
Article
Aluminum, copper, nickel, and stainless steel 304 (SUS304) are widely used to construct heat exchangers. In this work, test specimens made of these metallic materials were irradiated with chromium ions. The static and dynamic contact angles of water droplets on the test specimens were measured to examine changes in the surface characteristics. Condensate behavior was visually observed and condensation heat transfer performance was experimentally measured. Filmwise condensation occurred on the surfaces of all the specimens that had no ion implantation. After these specimens were irradiated with chromium ions, filmwise condensation or dropwise condensation was induced depending on the ion irradiation conditions. When the substrates were irradiated with chromium ions at an ion energy level of 100 keV and an ion dose of 3 × 10¹⁶ ions/cm², dropwise condensation occurred regardless of material. When the specimens were irradiated at an ion energy level of 70 keV, dropwise condensation, filmwise condensation, or both occurred depending on the substrate material. The condensation heat transfer coefficient of the surface where dropwise condensation occurred appeared to be more than 3.2 times larger than the theoretical value according to Nusselt’s film theory in the subcooling region below 9.5 K.
Article
A defrosting control method with differential pressure sensor is suggested in this study for air source heat pump systems. To maintain the performance of the heat pump system under frosting conditions, it is crucial to determine the start time of the defrosting process properly. Thus, this study investigates the feasibility of using the differential pressure sensors for defrosting control and further optimizes the control method. Firstly, the optimum location of the differential pressure sensor for air flow is determined by preliminary experiments. Secondly, a method to deal with various changes in operating conditions and system specification is developed. Lastly, main experiments are conducted under various frosting conditions to validate the suggested control method using differential pressure sensors. To show the reliability of the control method under various frosting conditions, two different error factors are defined; error on a time basis and a capacity basis. As a result, the root mean square of the error for the defrosting time is 6.4% on a time basis and 5.1% on a capacity basis.
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In electrical vehicles, replacing positive temperature coefficient heater as heat source with an air source heat pump could improve the driving range and decrease energy consumption in cold climate. Design of the heating, ventilation, and air-conditioning module for heat pump system has a significant influence on its performance in each working mode. A newly designed heat pump heating, ventilation, and air-conditioning module was introduced in this paper. The air flow characteristics of the heat pump heating, ventilation, and air-conditioning module in four working modes were analyzed, and the air flow rate and wind resistance were obtained by numerical simulation. Experiments were also conducted for validating its airflow rate in each working mode. Results of these experiments show that some unfavorable phenomena such as flow maldistribution and vortex inside the heat pump heating, ventilation, and air-conditioning module exist, which could lead to insufficient utilization of the heat exchange area of heat exchangers and the generation of aerodynamic noise. Furthermore, the air flow rate of the original heating, ventilation, and air-conditioning module was also measured for comparison, and the designed heat pump heating, ventilation, and air-conditioning module shows nearly 15–20% decrease in each working mode.
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Plate heat exchangers (PHEs) have been suggested for use in secondary loop air conditioning systems in automobiles operated with flammable refrigerants, such as R1234yf. In this study, the evaporation heat transfer coefficient (HTC) and two-phase frictional pressure drop (FPD) of R1234yf in a brazed PHE with offset strip fins were investigated. The mass flux in the experiment was 40–80 kg m−2 s−1, heat flux was 4–10 kW m−2, vapor quality at the inlet was 0.1–0.8, and saturation temperature was 5–15°C. Prior to the primary analysis, a coolant-to-coolant test was performed using a modified Wilson plot approach to estimate the multiplier (C) and the Reynolds number exponential (n). The observed C and n values were 0.868 and -0.496, respectively, with an R2 value of 0.977. The main results demonstrated an increase in the evaporation HTC with an increase in vapor quality in the initial stages, followed by a subsequent decrease, forming a peak at a mean vapor quality of 0.35–0.41. The nucleate and convective heat transfer regimes were dominant during the evaporation of R1234yf at lower and higher mean vapor qualities, respectively. Evidently, the evaporation HTC was significantly influenced by the mass flux and vapor quality compared with the heat flux and saturation temperature. Furthermore, the two-phase FPD continuously increased with the mass flux, vapor quality, and heat flux, although it decreased with the saturation temperature. As a result, new correlations are proposed herein for forecasting the Nusselt number and friction factor of R1234yf with average absolute errors of ±12% and ±15%, respectively.
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Catering to the growing demand for urban mobility and emphasis on reducing air pollution in towns and cities are mutually conflicting objectives. One solution is a paradigm shift of the transportation policies from personal vehicles to public transportation system using electric buses. Using electric bus fleets for public transportation is not straightforward in Indian cities for two reasons, viz., weak electricity grid and predominantly coal‐based power generation. In this work, a novel transportation system, that uses solar PV generation and large capacity batteries, is analyzed for its impact on air pollution and environmental sustainability. A detailed well to wheel analysis of the system, for various power generation scenarios, is presented and also compared with the existing ones. The analysis done in this work answers the question: "Can the electric bus‐based public transportation contribute towards emission reduction in transportation?" The results also elaborate that to reach the target under the Paris Protocol, India has to take drastic majors like phasing out of coal by 2030. To phase out Coal, India has to reduce its contribution by 5% each year from now and use renewable energy sources extensively. This article is protected by copyright. All rights reserved.
Article
Vapor injection heat pumps have been proposed for cabin heating in electric vehicles (EVs) to improve the performance and reliability under severe weather conditions. However, the geometric optimizations of the injection-port and internal heat exchanger (IHX) in vapor injection heat pumps designed for EVs have rarely been investigated. The objective of this study is to investigate the effects of the injection-port angle and IHX length in a vapor injection heat pump for use in EVs at various startup conditions. The heating performance of a vapor injection heat pump with R134a is measured by varying the IHX length from 100 to 400 mm and injection-port angle from 320° to 440° at various cabin temperatures. The effects of the IHX length and injection-port angle are analyzed in terms of coefficient of performance (COP) and heating capacity. The optimum IHX length and injection-port angle for the maximum COP are determined to be 300 mm and 400°, respectively.
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Thermal comfort of occupants in conventional vehicles driven by an internal combustion engine is controlled by heating, ventilation, and air conditioning (HVAC) system. However, the operation of a conventional HVAC system decreases the mileage of electric vehicle (EV) in the heating mode by nearly 50%. Thus, local radiant heating was proposed as a heating strategy to reduce electric energy consumption while providing reasonable thermal comfort. In this work, we developed a personalized overall thermal sensation (OS) model using machine learning to evaluate the thermopsychological effect of local radiant heating and simulate the OS of occupants in EVs. Data were obtained from a real EV that went through a cold environmental chamber and were evaluated using random forest algorithm. By considering individual thermal preferences of occupants, we predicted the OS for each subject with higher accuracy by a factor of 2.6 compared with the prediction performed using the weighted average method. Total energy consumption was reduced by approximately 10% in the EV equipped with local infrared radiant warmers while providing OS that was comparable with that of the HVAC system.
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The driving ranges of electric vehicles (EVs) will decrease greatly with increased use of the vehicle heating system in a cold climate. Air conditioning heat pump (ACHP) systems, which convert energy stored in the ambient environment into heat, represent a promising approach for increasing the EV driving range. In this work, the performance of an ACHP system in an EV under extremely cold conditions is investigated experimentally. The requirements of an ACHP system for EVs at various ambient temperatures are determined using our capacity matching strategy. A prototype system designed based on these requirements is evaluated. Data collected from experiments performed at a full-scale facility under extreme temperature conditions are analyzed. The results show that the ACHP system proposed for EV applications can satisfy both the cooling and heating requirements for the passenger compartment. The system increased the driving range by 23% when compared with that of an EV using a positive-temperature-coefficient (PTC) heater at −10 °C.
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The use of vehicles is a daily matter worldwide, however, they remain parked most of the time and commonly under the heating sun, leading to a rise in the internal temperature that provokes heating discomfort, and when the temperature drops this discomfort to the user is felt as cold. In this way, to reduce the distress drivers use air-conditioners in the first case and heaters in the second event as needed, making the consumption of energy a common activity. This research method takes a list of phase change materials used in some applications and makes a novel selection of the best material to be implemented on a vehicle's rooftop, which is done by Multicriteria Decision Methods means. The weighting is done by the Entropy weighting method compared with the new method based on the removal effect of criteria (MEREC), the decision-making methods VIKOR, COPRAS and TOPSIS choose the best material and the Spearman's correlation verify its agreement. The best material selected unanimously is the savENRG PCM-HS22P, which latter was simulated by finite elements methods, resulting in the reduction of 9 °C in the internal air when heating and conservation of 4 °C in the cooling with an increasing Phase Change Material layer.
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Automotive air‐conditioning heat pump systems are particular interest worldwide in energy conservation and emission reduction for electric vehicles, hybrid electric vehicles, and fuel cell electric vehicles. Refrigerant charge amount is a key factor for the air‐conditioning heat pump system optimization affecting the condensing pressure and subcooling in both heating and cooling modes. In this paper, the influence of the refrigerant charge on system performances was investigated using the experiment method on a secondary loop air‐conditioning heat pump system. The typical heat transfer and flow parameters were recorded, and both cooling and heating performances of the system were investigated and illustrated by pressure‐enthalpy diagrams. The critical refrigerant charges were determined in both heating and cooling modes. Three typical void fraction correlation models were also applied for the refrigerant charge determination modeling as a system off‐design method. Results show that the Hughmark void fraction correlation method has the best prediction of the critical refrigerant charge in both cooling and heating modes.
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This manuscript analyzes the sub-systems of evaporative cooler (EC) combined with desiccant dehumidification and regeneration for automotive air conditioning purpose. The thermodynamic and psychometric were conducted to design all evaporative cooling system components in terms of desiccant selection, regeneration process, compact heat exchanger and evaporative cooler. Moreover, the effect of the desiccant, heat exchanger and evaporative performances on the mass flow rate and water sprayed required for evaporative cooling system were investigated. The results show that the theoretical evaporative cooling design will achieve two main objectives: lower fuel consumption and less environmental pollutants. However, it has the two drawbacks in terms of increase weight and reduces the coefficient of performance (COP). The main remark is that evaporating cooling system is more efficient than the conventional air conditioning when the gasoline price is more than 0.34 $/liter.
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Energy efficient HVAC system is becoming increasingly important as higher Corporate Average Fuel Economy (CAFE) standards are required for future vehicle products. The present study is a preliminary attempt at designing energy efficient HVAC system by introducing localized heating/cooling concepts without compromising occupant thermal comfort. In order to achieve this goal of reduced energy consumption while maintaining thermal comfort it is imperative that we use an analytical model capable of predicting thermal comfort with reasonable accuracy in a non-homogenous enclosed thermal environment such as a vehicle's passenger cabin. This study will primarily focus on two aspects: (a) energy efficiency improvements in an HVAC system through micro-cooling/heating strategies and (b) validation of an analytical approach developed in GM that would support the above effort. The paper will discuss the analytical approach adopted in this study, its application in predicting overall comfort and sensation levels for various micro-cooling strategies, and subsequently comparing these predicted results with the real human subject test. The combination of the present CFD work coupled with the thermal comfort simulations will allow for the exploration of different microclimate control strategies as they relate to occupant thermal comfort for an "Energy Efficient HVAC System".
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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.
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The objective of this study is to provide the numerical model for prediction of the frost growth of the round plate fin for the purpose of using it as a round plate fin-tube heat exchanger (evaporator) under frosting conditions. In this study, numerical model was considering the frost density change with time, and it showed better agreement with experimental data of Sahin (1994) than that of the Kim model (2004) and the Jonse and Parker model (1975). This is because the prediction on the frost height with time was improved by using the frost thermal conductivity reflecting the void fraction and density of ice crystal with frost growth. Therefore, the developed numerical model could be used for frosting performance prediction of the round plate fin-tube heat exchanger.
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The objective of this study is to investigate the performance characteristics of a stack coolant source heat pump using R744 with a stack coolant heat source for fuel cell electric vehicles under cold weather conditions. Electric heaters are currently used in fuel cell electric vehicles, and the high levels of energy consumption involved lead to lower fuel efficiency and a reduction in the vehicle’s driving range. In order to improve the efficiency of the fuel cell electric vehicles in this study, a heat pump using R744 as a refrigerant and making use of wasted heat from the stacks is developed to cover the heating capacity. This heat pump is tested and performance optimized for stack coolant heat recovery under the compressor speeds, air temperatures, and flow rates of the interior heat exchanger, as well as the coolant flow rates of the CO2-coolant heat exchanger. In addition, the heating capacity of the tested system was sufficiently attained over 5.0 kW at the coolant flow rate of 5.0 l/min under extremely cold weather conditions of −20°C.
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This manuscript investigates the analysis and modeling of vehicular thermal comfort parameters using a set of designed experiments aided by thermography measurements. The experiments are conducted using a full size climatic chamber to host the test vehicle, to accurately assess the transient and steady state temperature distributions of the test vehicle cabin. Further investigate the thermal sensation (overall and local) and the human comfort states under artificially created relative humidity scenarios. The thermal images are calibrated through a thermocouples network, while the outside temperature and relative humidity are manipulated through the climatic environmental chamber with controlled soaking periods to guarantee the steady state conditions for each test scenario. The relative humidity inside the passenger cabin is controlled using a Total Humidity Controller (THC). The simulation uses the experimentally extracted boundary conditions via a 3-D Berkeley model that is set to be fully transient to account for the interactions in the velocity and temperature fields in the passenger compartment, which included interactions from turbulent flow, thermal buoyancy and the three modes of heat transfer conduction, convection and radiation. The model investigates the human comfort by analyzing the effect of the in-cabin relative humidity from two specific perspectives; firstly its effect on the body temporal variation of temperature within the cabin. Secondly, the Local Sensation (LS) and Comfort (LC) are analyzed for the different body segments in addition to the Overall Sensation (OS) and the Overall Comfort (OC). Furthermore, the human sensation is computed using the Fanger model in terms of the Predicted Mean Value (PMV) and the Predicted Percentage Dissatisfied (PPD) indices. The experimental and simulation results show that controlling the RH levels during the heating and the cooling processes (winter and summer conditions respectively) aid the A/C system to achieve the human comfort zone faster than the case if the RH value is not controlled. Also, the measured and predicted transient temperatures are compared and found to be in good agreement.
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The objective of this study is to investigate heating performance characteristics of a coolant source heat pump using the wasted heat from electric devices for an electric bus. The heat pump, using R-134a, is designed for heating a passengers' compartment by using discharged energy from the coolant of electric devices, such as motors and inverters of the electric bus. The heating performance of the heat pump was tested by varying the operating parameters, such as outdoor temperature and volume flow rate of the coolant water of the electrical devices. Heating capacity, compressor work, and heating COP were measured; their behaviors with regard to the parameters were observed. Experimental results showed that heating COP increased with decrease of outdoor temperature, from 20.0 °C to 0 °C, and it observed to be 3.0 in the case of 0 °C outdoor temperature. The observed characteristics of the heating COP suggest that the heat pump is applicable as the cabin heater of an electric vehicle, which is limited by short driving range.
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In this paper, a comparative study of the second law of thermodynamics is presented to determine the possibility of using HFO-1234yf, an environmentally friendly refrigerant, as a drop-in replacement of HFC-134a in automotive air conditioning system. For the thermodynamic analysis, a computer program is written to simulate the operating conditions of automobile air conditioning system. The thermodynamic properties of the refrigerants are extracted from the REFPROP 8.0 software. For calculating the coefficient of performance (COP), exergy destruction, exergy efficiency and entropy generation, computational models are used to evaluate the effects of different parameters on their changes. It is found that using HFO-1234yf as the air conditioning refrigerant leads to higher exergy efficiency compared to HFC-134a. Also, maximum entropy generation and exergy destruction occur in the compressor. The exergy destruction and entropy generation of the cycle components are less in the case of using HFO-1234yf refrigerant instead of HFC-134a.
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A DHP (dehumidifying heat pump) has been proposed to save energy consumption in electric vehicles during the dehumidifying and heating operation. Since the mean occupancy rate in a vehicle is less than two people, it is required to optimize the performance of the DHP at low occupancy for an effective operation. The objective of this study is to investigate the performance improvement of a DHP by using the additional waste heat source in electric vehicles with low occupancy. The experiments on the DHP were conducted by varying operating modes, according to various numbers of passengers. Even though the air source DHP in an AL (alternating) mode showed 7.6% lower heating capacity on average, compared to that in the DH (dehumidifying and heating) mode, the COP improvement of the air source DHP in the AL mode against the DH mode was approximately 31% for one passenger. In addition, the dual source DHP in the AL mode showed 15.8% higher heating capacity and 5.2% higher COP on average, compared to the air source DHP in the AL mode.
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In recent years fuel consumption of passenger vehicles has received increased attention by customers, the automotive industry, regulatory agencies and academia. One area which affect the fuel consumption is climate control systems. Twenty-one energy saving measures were evaluated regarding the total energy use for vehicle interior climate using simulation. Evaluated properties were heat flow into the passenger compartment, electrical and mechanical work. The simulation model included sub models of the passenger compartment, air-handling unit, Air Conditioning (AC) system, engine and engine cooling system. A real-world representative test cycle, which included tests in cold, intermediate and warm conditions, was used for evaluation. In general, few single energy saving measures could reduce the energy use significantly. The measures with most potential were increased blower efficiency with a reduction of 46% of the electrical work and increased AC-system disengage temperature with a reduction of 27% of the mechanical work. These results show that the operation of the climate control system had a large effect on the energy use, especially compared to the required heating and cooling of the passenger compartment. As a result energy saving measures need to address how heating and cooling is generated before reducing the heat flow into the passenger compartment.
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In this paper, condensation and evaporation characteristics of low global warming potential (GWP) refrigerants such as R-1234yf and R-1234ze series are reviewed. This review focuses on heat transfer and pressure drop in plate heat exchangers. Mass flux is considered as an important factor while saturation temperature is not for condensation and evaporation process in plate heat exchangers. The dryout phenomenon occurs occasionally and gives greatly harmful impact on evaporation heat transfer. It is found that R-1234yf and R-1234ze(E) give slightly lower heat transfer performance than R-134a for both condensation and evaporation processes. Generally, low GWP refrigerants presented in this review give lower heat transfer coefficient and higher frictional pressure drop than the conventional refrigerants. Nevertheless, R-1234ze(Z) gives superior heat transfer performance than other refrigerants in condensation. R-32 gives remarkable performance in evaporation, but it gives relatively high GWP compared to other low GWP refrigerants.
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This paper presents an experimental performance investigation and exergy analysis using R1234yf in an automotive air conditioning system. The R1234yf system with an internal heat exchanger (IHX) was compared with an R1234yf system without the IHX and an R134a system. The R1234yf system had 4.0–7.0% smaller cooling capacity and 3.6–4.5% lower COP compared to the R134a system. With the IHX, the R1234yf system showed almost equivalent cooling capacity to the R134a system. The COP of the R1234yf system with the IHX is lower than that of the R134a system by 0.3–2.9% for a compressor speed of 800–1800 rpm. The COP increased by 0.9% at a compressor speed of 2500 rpm. The second law efficiency of the R1234yf system was 3.4–4.6% lower than that of the R134a system at all compressor speeds. The second law efficiency of R1234yf with the IHX was improved by 1.5–4.6% compared to the R1234yf system without the IHX. The EDR of the R1234yf system was 0.5–3.3% higher than that of the R134a system in the range of 800–1800 rpm. However, the R1234yf system with the IHX had 1.2% lower EDR than the R134a system at a compressor speed of 2500 rpm.
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A new refrigerant is needed because the GWP of the R404A and R134a that are used in existing refrigerated trucks and automotive air conditioners is so high. This study predicts cooling performance by using an analytical model, for refrigeration systems using R404A and R134a. Furthermore, the performances of those systems were compared with those of alternative refrigeration systems using R1234yf and R744. The performance data of the analytical model had a trend similar to that of the experimental data: the average error between the analytical and experimental results was within 5.4%. The frost thickness of the R404A system for all operating conditions was about 2.4–3.7% larger than that of other systems because the evaporating temperature of the R404A system was lower than that for other refrigerants. For various operating conditions, the coefficient of performance (COP) of the R134a system was higher than that of other systems, while the R744 system showed the lowest performance. However, the COP reduction of the R744 system with operating time was the smallest because the thermodynamic properties of R744 were very superior. In addition, the frost thickness was seriously affected by the variations of indoor air temperature and compressor rotation speeds, and the system performance decreased significantly for severe operating conditions.
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This study presents a simulation model of a heat pump air conditioning system with a variable capacity compressor and variable speeds fans for electric bus. An experimental sample has been developed in order to check results from the model. Effects on system performance of such working conditions as compressor speed, evaporator fans speeds and the condenser fans speeds have been simulated by means of developed model. The results show that the three speeds can be adjusted simultaneously according to actual working condition so that the AC system can operate under the optimum state which the control objects want to achieve. It would be a good and simple solution to extend the driving ranges of EVs because of the highest efficiency and the lowest energy consumption of AC system.
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This paper demonstrates that the implementation of Flash Gas Bypass method can improve the performance of conventional direct expansion R134a mobile air-conditioning system with a microchannel evaporator. This method uses flash gas tank after expansion valve to separate and bypass flash refrigerant vapor around the evaporator, and feed the evaporator with only liquid refrigerant. Pressure drop is reduced and refrigerant distribution is significantly improved, resulting in higher evaporator effectiveness and evaporation pressure. Both lower pressure drop and lifted evaporation pressure allows the compressor to work with lower pressure ratio, saving required compressor work. An experimental comparison of the direct expansion system shows that Flash Gas Bypass method increases the cooling capacity and COP at the same time by up to 16% and 11%, respectively. Thus, the implementation of this method is very promising for the system using a microchannel evaporator which is especially very sensitive to the refrigerant side maldistribution.
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The thermal management system for electric vehicles is developed. Called the Thermal Link System, it consists of a heat-pump air conditioner, a system recovering waste heat from the electric power train, and a heat exchanger between the air-conditioner refrigerant and the power-train coolant water. The recovered heat is used for interior heating, so the amount of power consumed by the heat-pump air conditioner can be reduced. In this system the refrigerant for the heat-pump air conditioner and the coolant water for electric power trains are thermally linked by the heat exchanger, which can reduce the temperature of the coolant water to less than that of the surrounding air. This enhanced cooling function increases the power of electric power trains, or extends the amount of time at full power operation. Here we describe the Thermal Link System's mechanism and effects on energy efficiency.
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The Unitary HPAC (Heat Pump Air Conditioner) System has been developed to enable a heat pump system in passenger vehicles. Unitary HPAC uses technology of reversing the coolant instead of refrigerant to distribute heat from where it is generated to where it is needed. Integrating this system in a plug-in hybrid vehicle reduces the energy required by the heating and air conditioning system, reducing the grams of CO 2 per mile by up to 25%. Although this system can be applied to any passenger vehicle, it is most beneficial to hybrid and electric vehicles, because it provides an additional source of hot coolant. These vehicles provide less waste heat than conventional internal combustion engine vehicles so they must rely on electric heaters to provide the heat needed for comfort. The electric heaters are an energy draw that reduces the electric drive range. The Unitary HPAC system will extend the electric range significantly. In addition to maintaining passenger comfort in cooling mode, heat can be removed from the battery, inverter, and electronics with coolant and directed to the passenger compartment. This paper will use a plug-in hybrid vehicle to demonstrate the operation of the Unitary HPAC. It will show how the Unitary HPAC can significantly reduce refrigerant charge and provide passenger comfort with less energy.
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"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.
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Efficient performance of a vehicle Air Conditioning (AC) can be affected by uncertain factors such as road conditions, environmental conditions and driver behaviour. Recent study shows that prediction of road power demands (look-ahead) for AC system can provide the optimum comfort temperature with air quality as well as a reduction of energy consumption. The new energy management system features comprise recent research over and above making adaptive the intelligent AC controller to ensure proper operation under different road load conditions. For making an adaptive fuzzy controller, the following important issues must be considered: the size of the membership functions of the fuzzy sets, the position of the membership functions, the rule weights and/or the link values. The adaptive intelligent air conditioning system was able to control the operation of AC, blower, fresh-air and recirculation gates for providing the desired comfort temperature and indoor air quality under various environment conditions. The simulation results of the adaptive intelligent air conditioning system demonstrate around 1% more energy saving compared to fuzzy air conditioning enhanced with look-ahead system.
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In this study, performance was assessed by charging the same automotive refrigeration systems with the refrigerants R134a and R1234yf, respectively, to compare the characteristics of the refrigeration cycle of the two refrigerants. The internal heat exchanger was installed in order to improve cooling performance of R1234yf and to investigate the level of performance improvement in comparison with conventional R134a system. Performance test by using R1234yf and R134a in the same system showed low power consumption and cooling capacity for using R1234yf, that is, up to 4% and 7%. In particular, performance comparison between the R1234yf and R134a for automotive air conditioning revealed that cooling capacity and COP of the 1234yf system without the IHX decreased by up to 7% and 4.5%, respectively, but those with the IHX decreased by up to 1.8% and 2.9%, respectively. Crown Copyright
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Electric vehicles (EVs) are vehicles that are propelled by electric motors powered by rechargeable battery. They are generally asserted to have GHG emissions, driveability and life cycle cost benefits over conventional vehicles. Despite this, EVs face significant challenges due to their limited on-board energy storage capacity. In addition to providing energy for traction, the energy storage device operates HVAC systems for cabin conditioning. This results in reduced driving range. The factors such as local ambient temperature, local solar radiation, local humidity, duration and thermal soak have been identified to affect the cabin conditions. In this paper, the development of a detailed system-level approach to HVAC energy consumption in EVs as a function of transient environmental parameters is described. The resulting vehicle thermal comfort model is used to address several questions such as 1) How does day to day environmental conditions affect EV range? 2) How does frequency of EV range change geographically? 3) How does trip start time affect EV range? 4) Under what conditions does cabin preconditioning assist in increasing the EV range? 5) What percentage increase in EV range can be expected due to cabin preconditioning at a given location?
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A localized air-conditioning system is expected to decrease energy consumption by avoiding extra cooling on the vacant seats. However, the energy saving of the localized air-conditioning system with satisfactory thermal comfort has seldom been quantified. In this study, both thermal comfort in the vehicle compartment and energy saving of the localized air-conditioning system with the front and ceiling vents were investigated. Thermal comfort in the vehicle compartment with the front and ceiling vents was analyzed using computational fluid dynamics with empirical correlations for thermal indices. In addition, the performance of the air-conditioning unit was measured at various air flow rates and air temperatures. The energy consumption of the localized air-conditioning system with the optimized front and ceiling vents decreased by 20.8% and 30.2%, respectively, against the baseline, while satisfying the neutral thermal comfort at the vent air temperature of 9 °C.
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In this study, the energy and exergy performance of secondary loop systems (2LPs) using HFC-152a and HC-290 was investigated. These 2LPs were compared with a HFC-134a direct expansion system as a baseline system. As compared with the baseline, tested refrigerant charge amount was reduced by 28% for the HFC-152a 2LP and 60% for the HC-290 2LP. Under typical 35 C ambient temperature condition, the coefficient of performance (COP) of the HFC-152a 2LP was increased by 5% for highway driving conditions and 10% for idling conditions. Regarding the HC-290 2LP, the COP was increased by 8% underhighway driving conditions and was decreased by 15% under idling conditions. As for the exergy per-formance, the total exergy destruction was reduced by roughly 9.6% for the HFC-152a 2LP and 14.3% forthe HC-290 2LP as compared with HFC-134a baseline during highway driving conditions. A theoretical potential of HC-290 2LP idling performance is that its idling COP would be approximately 15% higher and its exergy destruction would be 12.5% lower than those of the HFC-134a baseline.
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A heat pump has been considered as an alternative to an electric heater to increase the efficiency of the heating unit in electric vehicles. However, the heating performance of a single source heat pump has yet to be improved at low outdoor temperatures. This study investigates the feasibility of a dual source heat pump using both air and waste heat in electric vehicles. The performance of the dual source heat pump was measured at various operation modes: air source-only, waste heat-only and dual heat source. The heating performance of the dual source heat pump was higher than those of the single source heat pumps. In addition, an alternating single mode operation of air source-only and waste heat-only modes was proposed to improve performance at low outdoor air temperatures.
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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.
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For a space heating air source heat pump (ASHP) unit, when its outdoor coil surface temperature is below both the air dew point temperature and the freezing point of water, frost will form on its outdoor coil surface. Frosting affects its operational performance and energy efficiency. Therefore, periodic defrosting is necessary. Currently, the most widely used standard defrosting method for ASHP units is reverse cycle defrost. The energy that should have been used for space heating is used to melt frost, vaporize the melted frost off outdoor coil surface and heat ambient air during defrosting. It is therefore necessary to study the sources of heat supplies and the end-uses of the heat supplied during a reverse cycle defrost operation. In this paper, firstly, an experimental setup is described and experimental procedures are detailed. This is followed by reporting the experimental results and the evaluation of defrosting efficiency for the experimental ASHP unit. Finally, an evaluation of defrosting heat supplies and energy consumptions during a revere cycle defrost operation for the experimental ASHP unit is presented. The experimental and evaluation results indicated that the heat supply from indoor air contributed to 71.8% of the total heat supplied for defrosting and 59.4% of the supplied energy was used for melting frost. The maximum defrosting efficiency could be up to 60.1%.
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The performance of personalized ventilation with seat headrest-mounted air supply terminal devices (ATD), named seat headrest personalized ventilation (SHPV), was studied. Physical measurements using a breathing thermal manikin were taken to identify its ability to provide clean air to inhalation depending on design, shape, size and positioning of the ATD, flow rate and temperature of personalized air, room temperature, clothing thermal insulation of the manikin, etc. Tracer gas was mixed with the room air. The air supplied by the SHPV was free of tracer gas. Tracer gas concentration in the air inhaled by the manikin was measured and used to assess the clean air supply efficiency of the SHPV. The response of 35 subjects was collected to examine thermal comfort with the SHPV. The subjects participated in 3 experiments at personalized air temperature and room air temperature of 22/20 °C, 23/23 °C and 26/26 °C, respectively. Questionnaires were used to collect human responses. Personal exposure effectiveness (the portion of the clean personalized air in inhalation) of up to 99% was measured during the manikin experiments. The results suggest a dramatic improvement of inhaled air quality and a decreased risk of airborne cross-infection when SHPV is used. Subjects assessed the air movement and the cooling provided by the SHPV as acceptable. Acceptability was unchanged over in time and increased with the increase of the air temperature. No draught was reported. The SHPV can be used in spaces where occupants are seated most of the time, e.g. theatres, vehicle compartments, etc.
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Battery electric vehicles (BEVs) are promising candidates to replace cars including ICE drive trains in the coming years especially in urban regions in order to contribute to a reduced exhaust and noise emission. Up to now the BEV’s bottleneck is the battery system which is able to store only a very limited amount of energy on board. Hence, it is necessary to use the rare energy in the most efficient way. In this work a simple method is presented to reduce the electric losses during operation through an adaptive control of the HVAC power input, depending on the driving situation. It is shown that the proposed method enables an energy saving and therefore a range extension about more than 1% without any additional hardware effort. This basically does not seem to be much but can be an important step contributing to BEVs’ final breakthrough.
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In this study, ‘drop-in’ performance of HFC134a, HFO1234yf and HFO1234yf/HFC134a mixture at three compositions of 5%, 10%, and 15% HFC134a is measured in a heat pump bench tester under summer and winter conditions. Test results show that the COP, capacity, discharge temperature of HFO1234yf and HFO1234yf/HFC134a mixture are similar to those of HFC134a. For HFO1234yf/HFC134a mixture, flammability decreases as more HFC134a is added and at compositions of more than 10% of HFC134a, the mixture becomes non-flammable. The amount of charge for HFO1234yf and HFO1234yf/HFC134a mixture is up to 11% lower than that of HFC134a. Since HFO1234yf/HFC134a mixture with 10–11% HFC134a is virtually non-flammable and azeotropic and has no ODP and GWP of less than 150 meeting the requirement of European mobile air-conditioner directive, it can be used as an environmentally friendly solution for various HFC134a applications including mobile air-conditioners with minor modifications.
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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.
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Taking a novel hybrid-power gas engine heat pump as an example, fuel-consumed rate, fuel-consumed flow, fuel conversion efficiency and life cycle assessment were used to analyze energy-saving effect and natural gas environmental benefits on human health, ecosystem quality and resource consumption through contrast with electric power consumption model. The test results show that the fuel conversion efficiency under different operating conditions of HPGHP is higher than conventional GHP under the same load. Besides, from the total indicator, scores on resource consumption is the highest. Gaseous product is mainly CO2 and other carbon or sulfur oxide gases are discharged in form of negative or water body, which means the use of natural gas effectively control the pollution gas emissions. At last, concept of environmental benefit time was established; the result shows that HPGHP can embody better environmental benefits than gas heat pump when running more than 1778 h.
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In this paper, the mixture of HFC-161/HFC-134a (0.6/0.4 in mass fraction), named ‘M5’, is proposed as a substitution of HFC-134a used in automotive air conditioning systems. The theoretical and experimental cycle performances for M5 and HFC-134a were conducted at the condensation temperature from 50 °C–65 °C, evaporation temperature from −5 °C–10 °C. Theoretical results show that COP of M5 is very close to that of HFC-134a, the specific refrigeration capacity and volumetric refrigeration capacity of M5 are much higher than those of HFC-134a. Experimental results show that COP of M5 is a bit higher than that of HFC-134a, the refrigeration capacity and compressor power of M5 are about 32% and 30% higher than those of HFC-134a, respectively, the compressor discharge temperature and pressure ratio of M5 are about 15% higher and 10.9% lower than those of HFC-134a, respectively. Considering the good performance and compatibility with the existing system, M5 is a potential alternative refrigerant for HFC-134a.
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Whilst air conditioning systems increase thermal comfortableness in vehicles, they also raise the energy consumption of vehicles. Achieving thermal comfort in an energy-efficient way is a difficult task requiring good coordination between engine and the air conditioning system. This paper presents a coordinated energy management system to reduce the energy consumption of the vehicle air conditioning system while maintaining the thermal comfortableness. The system coordinates and manages the operation of evaporator, blower, and fresh air and recirculation gates to provide the desired comfort temperature and indoor air quality, under the various ambient and vehicle conditions, the energy consumption can then be optimized. Three simulations of the developed coordinated energy management system are performed to demonstrate its energy saving capacity.
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Experiments were conducted for a typical R134a compact European automotive air conditioning system equipped with an internally controlled variable displacement compressor, minichannel condenser, TXV, and minichannel evaporator. A “drop-in” R1234yf system was tested together with two modified R1234yf systems with the primary goal to document some laboratory results and their analyses which could prove useful in aiding manufacturers and researchers by indicating “minor” system modifications which could be implemented in existing air conditioning systems, with the aim to achieve with R1234yf similar capacity and efficiency as modern R134a systems. Since the experimental results indicate that, for a given cooling capacity, R1234yf systems present lower performance than the baseline R134a, numerical simulations were used to investigate the effects of “major” system modifications, such as, the use of an enhanced condenser and/or an enhanced evaporator.
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This paper deals with the effects of the operating parameters on the cooling performance that can be applied for a transcritical CO2 automotive air conditioning system. The experimental conditions of the performance tests for a CO2 system and components such as a gas cooler and an evaporator were suggested to compare with the performance of each at the standardized test conditions. This research presents experimental results for the performance characteristics of a CO2 automotive air conditioning system with various operating conditions such as different gas cooler inlet pressures, compressor speeds and frontal air temperatures/flow rates passing through the evaporator and the gas cooler. Experimental results show that the cooling capacity was more than 4.9kW and coefficient of performance (COP) was more than 2.4, at each optimum pressure of gas cooler inlet during idling condition. Also, the cooling capacity was about 7.5kW and COP was about 1.7 at the optimum pressure of gas cooler inlet during driving condition when air inlet temperatures of gas cooler and evaporator were 45°C and 35°C, respectively. Therefore, we concluded that the automotive air conditioning system using CO2 refrigerant has good performance. This paper also deals with the development of optimum high pressure control algorithm for the transcritical CO2 cycle to achieve the maximum COP.
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Air conditioning systems (A/C) significantly increase the energy consumption of a vehicle and negatively influence its performance. A/C can be considered the main auxiliary load on a vehicle engine when it is operating. Thus, there are significant savings to be made by operating an A/C system smartly, both in terms of running costs and the effect on the environment. This paper presents an intelligent energy management system that is able to reduce the energy consumption of a vehicle with an air conditioning system and improve its efficiency by using the look-ahead system uses information from various information systems to make intelligent decisions. The new energy management system features: a prediction of road power demand by using look-ahead control of vehicle systems, an intelligent control strategy to manage the operation of the A/C, the blower, and the gates, to provide the optimum comfort temperature with the consideration of the in cabin air quality while minimizing energy consumption. Two simulations are performed by using the developed fuzzy air conditioning enhanced look-ahead System and ordinary fuzzy air conditioning and then the results are compared together with the results from Coordinated Energy Management System (CEMS). The results of fuzzy air conditioning enhanced with look-ahead system demonstrate it is capable of saving 12% and 3% more energy comparing with CEMS and ordinary fuzzy air conditioning system respectively. © 2011 Elsevier Ltd.
Article
Frost build-up blocks the gap between fins and decreases the airflow rate, and the heating capacity and COP of air-source heat pump become lower. The reverse-cycle defrosting (RCD) and hot-gas bypass defrosting HGBD are the two common methods of frost removal. The comparison between the RCD and HGBD methods on one heat pump were not found by authors up to now. This paper compared the dynamic characteristics during the RCD and HGBD periods on one medium air-to-water heat pump of 55Â kW. The feasibility of the HGBD method without heat provided to evaporate the liquid refrigerant after melting frost, which was supposed in the danger of the compressor liquid slugging, was especially discussed. The results showed the liquid refrigerant leaving the air cooled coils for the HGBD method was trapped in the suction accumulator and flashed into the saturated gas by the compressor pumping action, and no compressor liquid slugging happened in our tests. The HGBD time was much longer than the RCD time. The amenity for the HGBD method was better than that for the RCD method, due to lower refrigerant noise, smaller indoor temperature fluctuation, and no cold blowing. The suction superheat and discharge superheat for the HGBD method were lower than those for the RCD method. The HGBD could overcome the main disadvantages of the RCD method and deserved the further investigation.
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This study deals with the performance characteristics of an R134a automotive air conditioning system capable of operating as an air-to-air heat pump using ambient air as a heat source. For this aim, an experimental analysis has been performed on a plant made up of original components from an automobile air conditioning system and some extra equipment employed to operate the system in the reverse direction. The system has been tested in the air conditioning and heat pump modes by varying the compressor speed and air temperatures at the inlets of the indoor and outdoor coils. Evaluation of the data gathered in steady state test runs has shown the effects of the operating conditions on the capacity, coefficient of performance, compressor discharge temperature and the rate of exergy destroyed by each component of the system for both operation modes. It has been observed that the heat pump operation provides adequate heating only in mild weather conditions, and the heating capacity drops sharply with decreasing outdoor temperature. However, compared with the air conditioning operation, the heat pump operation usually yields a higher coefficient of performance and a lower rate of exergy destruction per unit capacity. It is also possible to improve the heating mode performance of the system by redesigning the indoor coil, using another refrigerant with a higher heat rejection rate in the condenser and employing a better heat source such as the engine coolant or exhaust gases.
Article
A CO2 heat pump system using recovered heat from the stack coolant was provided for use in fuel cell vehicles, where the high temperature heat source like in internal combustion engine vehicles is not available. The refrigerant loop consists of an electric drive compressor, a cabin heater, an outdoor evaporator, an internal heat exchanger, an expansion valve and an accumulator. The performance characteristics of the heat pump system were investigated and analyzed by experiments. The results of heating experiments were discussed for the purpose of the development and efficiency improvement of a CO2 heat pump system, when recovering stack exhaust heat in fuel cell vehicles. A heater core using stack coolant was placed upstream of a cabin heater to preheat incoming air to the cabin heater. The performance of the heat pump system with heater core was compared with that of the conventional heating system with heater core and that of the heat pump system without heater core, and the heat pump system with heater core showed the best performance of the selected heating systems. Furthermore, the coolant to air heat pump system with heater core showed a significantly better performance than the air to air heat pump system with heater core.
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Subjective experiments involving 12 different conditions were conducted to investigate the effects of heated seats and foot heaters in vehicles on thermal sensation and thermal comfort. The experimental conditions involved various combinations of the operative temperature in the test room (10 or 20°C), a heated seat (on/off) and a foot heater (room operative temperature +10 or +20°C). The heated seat and foot heater improved the occupant's thermal sensation and comfort in cool environments. The room operative temperature at which the occupants felt a 'neutral' overall thermal sensation was decreased by about 3°C by using the heated seat or foot heater and by about 6°C when both devices were used. Moreover, the effects of these devices on vehicle heater energy consumption were investigated using simulations. As a result, it was revealed that heated seats and foot heaters can reduce the total heater energy consumption of vehicles. Statement of Relevance: Subjective experiments were conducted to investigate the effects of heated seats and foot heaters in vehicles on thermal comfort. The heated seat and foot heater improved the occupant's thermal sensation and comfort in cool environments. These devices can reduce the total heater energy consumption in vehicles.
Article
Eight subjects participated in a subjective experiment of eight conditions to investigate the effects of heated seats in vehicles on skin temperature, thermal sensation and thermal comfort during the initial warm-up period. The experimental conditions were designed as a combination of air temperature in the test room (5, 10, 15, or 20 °C) and heated seat (on/off). The heated seat was effective for improving thermal comfort during the initial warm-up period when air temperature was lower than 15 °C. Use of heated seats prevented decreases in or increased toe skin temperature. Heated seats also increased foot thermal sensation at 15 and 20 °C. Optimal thermal sensation in contact with the seat was higher when air temperature was lower. Optimal skin temperature in contact with the seat back was higher than that with the seat cushion. Moreover, these optimal skin temperatures were higher when air temperature was lower.