Article
Performance Characteristics of a Modularized and Integrated PTC Heating System for an Electric Vehicle Yoon Hyuk Shin 1 , Seungkyu Sim 2 and Sung Chul Kim 3, * Received: 2 November 2015; Accepted: 23 December 2015; Published: 28 December 2015 Academic Editor: Vincent Lemort 1 2 3
*
Green Car Power System R&D Division, Korea Automotive Technology Institute, 74 Yongjung-Ri, Pungse-Myun, Dongnam-Gu, Chonan-Si, Chungnam 330-912, Korea;
[email protected] Donga High Tech Company, Dongtangiheung-Road, Dongtan-Myeon, Hwaseong-Si, Gyunggi-Do 445-813, Korea;
[email protected] School of Mechanical Engineering, Yeungnam University, 280 Daehak-Ro, Gyeongsan, Gyeongbuk 712-749, Korea Correspondence:
[email protected]; Tel.: +82-53-810-2572; Fax: +82-53-810-4627
Abstract: A modularized positive temperature coefficient heating system has controller-integrated heater modules. Such a heating system that uses a high-voltage power of 330 V was developed in the present study for use in electric vehicles. Four heater modules and one controller with an input power of 5.6 kW were integrated in the modularized system, which was designed for improved heating power density and light weight compared to the conventional heating system, in which the controller is separated. We experimentally investigated the performance characteristics, namely, the heating capacity, energy efficiency, and pressure drop, of a prototype of the developed heating system and found it to have satisfactory performance. The findings of this study will contribute to the development of heating systems for electric vehicles. Keywords: PTC heating system; performance characteristics; heating power density; weight reduction; high voltage
1. Introduction There has been a global acceleration in the development of high-efficiency and environmentally friendly vehicles with the goal of solving climate problems such as global warming and addressing the issue of energy depletion. In particular, efforts are being made to increase the use of electric vehicles. Unlike conventional internal combustion engine vehicles, electric vehicles have no gas emissions and their high energy efficiency also reduces considerably the generation of waste heat. An operation strategy for optimal energy management is thus more important in electric vehicles [1–4]. There is particularly the need to develop a new heating system for indoor heating in winter as a replacement for engine waste heat, which is used in conventional vehicles. Because the heating system of an electric vehicle consumes the largest proportion of energy, excluding the actual running of the vehicle, high-efficiency heat pumps have been developed and used to increase the driving range of some vehicles [5–7]. A positive temperature coefficient (PTC) electric heater offers an even more realistic alternative owing to its simple structure and rapid response [8,9]. However, the use of a high-voltage air-heating type of this electric heater, which is mounted on the heating, ventilation, and air conditioning system (HVAC) of the vehicle, requires the development of a heating system with a highly modularized and integrated structure. Unlike a low-voltage electric heater with a heating capacity of about 1 kW, such as that used as an auxiliary heater in a conventional internal combustion engine [10,11], the capacity of the main heating system of an electric vehicle is generally 5 kW or higher. A high-voltage PTC heater (330 V) Energies 2016, 9, 18; doi:10.3390/en9010018
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can supply the same amount of power with a lower current than a low-voltage PTC heater (13.5 V). Further, this results in a reduction in the weight of the power supply cable and an increase in energy efficiency. However, because the system is operated by a high-voltage power supply, the stability of its structure and control technology is essential [12]. Moreover, enhancement of the driving range requires improvement of the power density by increasing the efficiency and decreasing the weight of the heating system. A ceramic PTC thermistor is characterized by fixed-temperature heat generation and is safe for autonomous temperature control within a given limit. It is thus very suitable for use as a heat source for the indoor electric heater of a vehicle. However, the fabrication of the heating element of a high-voltage electric heater requires the development of a sputtering deposition technology for more uniform and denser surface coating of the electrode of a ceramic heating element compared to that achieved by the conventional screen printing process [13]. In the present study, we fabricated a prototype of a high-voltage heating system for electric vehicles. The system has a controller-integrated heater module design and was experimentally tested and analyzed to determine its heating performance and reliability. 2. Design and Analysis 2.1. Heating System Design
Energies 2016, 9 We designed and fabricated a high-voltage modularized and integrated heating system.
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The system contains four heater modules—with each unit comprising heating rods and radiation fins—and an integrated controller, which isare used to regulate power inputmain and operate is shown in Figure 1 and the specifications presented in the Table 1. The featurethe of heater. the system The system is shown in Figure 1 and the specifications are presented in Table 1. The main feature of the is its system proactive production response with respect to the heating capacity, which is afforded by the is its proactive production response with respect to the heating capacity, which is afforded by modular design. Compared to a conventional heating system, in in which and controller controller are the modular design. Compared to a conventional heating system, whichthe theheater heater and are separately configured, the developed system is 20%lighter. lighter. It also advantage of less separately configured, the developed system is 20% alsohas hasthethe advantage of less high-voltage cable work between the controller and heater for its installation inside a vehicle.
high-voltage cable work between the controller and heater for its installation inside a vehicle.
1. Modularized andintegrated integrated high-voltage heating system. FigureFigure 1. Modularized and high-voltage heating system. Table 1. Specifications of the high-voltage heating system.
Table 1. Specifications of the high-voltage heating system. Parameter Parameter 3) Core size3(mm Core size (mm )
Weight (g) Weight Input(g) voltage (V)
Input voltage (V)
Value
Value
200 ˆ 210 ˆ 28 200 × 210 2200 2200 330
× 28
330
Each of the heating rods, which are core components of each heater module unit, consists of a PTC thermistor, terminalrods, assembly, heat rod cover, as shown Figure 2.unit, The configuration Each of the heating whichinsulator, are coreand components of each heaterinmodule consists of a PTC thermistor, terminal assembly, insulator, and heat rod cover, as shown in Figure 2. The configuration of the power terminal structure is based on the shape of the heating rod and fins, as shown in Figure 3. The adopted structure improves the insulation and water resistance of the external surface of the heater, and the positive and negative terminals of the power supply are inserted into the cover
Core size (mm3)
200 × 210 × 28
Weight (g)
2200
Input voltage (V)
330
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11 rods, which are core components of each heater module unit, consists of a3 of PTC thermistor, terminal assembly, insulator, and heat rod cover, as shown in Figure 2. The configuration of the power powerterminal terminalstructure structure is based on shape the shape the heating and fins, asinshown of the is based on the of theofheating rod androd fins, as shown Figure in 3. Figure 3. The structure adopted structure the insulation andresistance water resistance of the external The adopted improvesimproves the insulation and water of the external surfacesurface of the heater, and the and negative terminals of the supply are inserted intointo the the cover of of the heater, andpositive the positive and negative terminals ofpower the power supply are inserted cover the heating rod. To further improve the assembly and enable smooth connection to the controller, of the heating rod. To further improve the assembly and enable smooth connection to controller, receptacle connectors are employed in the power supply section of the heater module. receptacle connectors are employed in the power supply section of the heater module.
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Figure 2. Schematic diagram of a heating rod. Figure 2. Schematic diagram of a heating rod.
Figure 3. Schematic diagram of the heating unit and modules. Figure 3. Schematic diagram of the heating unit and modules.
The heater module unit directly affects the heating performance of the system. Therefore, to The heater module unit directly affects the heating performance of the system. Therefore, to achieve higher performance, the heating rods and fins of the heater modules were varied as indicated achieve theand heating rods and fins ofperformances the heater modules varied as indicated in Tableshigher 2 andperformance, 3 respectively, the corresponding of the were heating system, which in Tables 2 and 3, respectively, and the corresponding performances of the heating system, which contained four heater modules, compared. The heating performance of a heater module was evaluated contained four heater temperature modules, compared. heatingand performance of a of heater module The was based on the maximum of the PTCThe thermistor the conductivity the insulator. fins servedbased as heat withtemperature the environment, thethermistor heater module performance wasofalso evaluated onexchangers the maximum of theand PTC and the conductivity the examined for various thickness and shapes of the fins, as indicated in Table 3. insulator. The fins served as heat exchangers with the environment, and the heater module
performance was also examined for various thickness and shapes of the fins, as indicated in Table 3. Table 2. Experimental results of the heater module performance for varying properties of heating rod.
Table 2. Varying Experimental results of the heater module performance for varying properties of Properties of Heating Rod Heating Capacity of Heater Modules (kW) heating rod. 160 5.1
Maximum temperature of the PTC thermistor (˝ C) @ plate fin thickness of 0.3 mm
170
5.2 Heating Capacity of Heater 5.4 Modules (kW) 1.2 4.9 Conductivity of the insulator (W/m¨ K) @ plate 1.5 5.05.1 160 fin thickness of 0.4of mm Maximum temperature the PTC thermistor 3.0 5.45.2 170 (C) @ plate fin thickness of 0.3 mm ˝ Notes: Standard condition: maximum PTC thermistor temperature 180 of 170 C and insulator 5.4conductivity of 180 Varying Properties of Heating Rod
3.0 W/m¨ K.
Conductivity of the insulator (W/m·K) @ plate fin thickness of 0.4 mm
1.2
4.9
1.5
5.0
3.0
5.4
Notes: Standard condition: maximum PTC thermistor temperature of 170 C and insulator conductivity of 3.0 W/m·K.
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The radiation fins of the PTC heater module are the key parts of the heating system that radiate heat directly into the air. The design parameters of a fin are important for achieving lightweight and high PTC heater energy efficiency. As shown in Table 3, heater modules using 0.3- and 0.4-mm-thick comparison models, with the shape fixed as plate, yielded heating capacities of 5.2 and 5.4 kW, respectively. The heat outputs of the heater modules using plate and embossed fin models, with Energies 2016,fixed 9 at 0.3 mm, were 5.2 and 5.4 kW, respectively. Therefore, the optimized design parameter thickness for a radiation fin for the PTC heater was determined to be a thickness of 0.3 m, given the advantage of the 0.3 m model over the 0.4 m model in the tradeoff between weight and capacity, and the embossed Energies 2016, 99 Table 3. Experimental results of the heater module performance for varying fin geometry. 2016, type Energies because of the turbulent effect of the emboss.
Varying Fin Geometry
5 55
Heating Capacity of Heater Modules (kW) 5.2
Table 3. 3. Experimental results of the module performance for varying fin geometry. Table results of the module performance for fin Table 3. Experimental Experimental results ofheater the heater heater module performance for varying varying fin geometry. geometry.
0.3 Thickness of plate fin (mm) Varying Fin Geometry Varying Fin Geometry Varying Fin Geometry 0.4 Thickness of fin Thickness of plate fin (mm) Thickness of plate plate fin (mm) (mm)
Shape of fin @ fin thickness of Shape of @ fin thickness of 0.3 mm 0.3finmm
Shape Shape of of fin fin @ @ fin fin thickness thickness of of 0.3 mm 0.3 mm
Heating Capacity of Heater Modules Heating Capacity of Heater Modules (kW) Heating Capacity of5.4 Heater Modules (kW) (kW) 5.2 5.25.2 5.45.4 5.25.4
0.3 0.3 0.3 0.4 0.4 0.4
Plate
5.25.2
5.2
Plate Plate Plate
5.4
Emboss
5.45.4 5.4 Notes: Standard condition: maximum PTC thermistor temperature of 170 C and insulator conductivity of Emboss Emboss Emboss 3.0 W/m·K. Notes: Standard condition: maximum PTC temperature and conductivity of ˝ C170 Notes: Standard condition: maximum PTC thermistor thermistor temperature of 170 C and insulator insulator conductivity of Notes: Standard condition: maximum PTC thermistor temperature of 170of andC insulator conductivity of 3.0 W/m¨ K. 3.0 3.0 W/m·K. W/m·K.
The printed circuit board (PCB) of the heating system’s controller and other components were The printed circuit board (PCB) of the heating system’s controller and other components were The printed circuit board of the controller and components Theshown printed in circuit board4.(PCB) (PCB) of the heating heating system’s system’s controller and other other componentstowere were configured as Figure The specifications are given in Table 4. Compared the configured as shown in Figure 4.Figure The specifications are given in Table 4. Compared to the conventionalto the configured as shown in 4. The specifications are given in Table 4. Compared configured as shown in Figure 4. The specifications are given in Table 4. Compared to the conventional separated-type heating system, the integrated the developed system and the separated-type heating system, the integrated structure of thestructure developedofsystem and the arrangement conventional separated-type heating system, the integrated structure of the developed system conventional separated-type heating system, the integrated structure of the developed system and and the the of its components afforded compactness. arrangement of its components afforded compactness. arrangement of its components afforded compactness. arrangement of its components afforded compactness.
Figure 4. PCB of the controller and other components of the heating system.
4. PCB of the and other of the heating system. 4. ofcontroller the controller and components other components of the heatingsystem. system. FigureFigure 4.Figure PCB of PCB the controller and other components of the heating Table 4. Specifications of theof of the high-voltage heating system. Table 4. the of heating Table 4. Specifications Specifications ofcontroller the controller controller of the the high-voltage high-voltage heating system. system.
Table 4. Specifications of the controller of the high-voltage heating system. Item
Item Item
Item Operating voltage (V) Operatingvoltage voltage(V) (V) Operating Operating Communication voltage (V) Communication Communication Output Communication Output Output Output Protection
Protection Protection
Protection 2.2. Heater Module Analysis
Specification
Specification Specification
Specification voltage: 9–16 High voltage: High220–460/Low voltage: 220–460/Low 220–460/Low voltage: 9–16 High voltage: voltage: 9–16 High voltage: 220–460/Low voltage: 9–16 CAN 2.0 CAN 2.0 CAN 2.0 PWM (Pulse Width Modulation) CAN 2.0 Modulation) PWM (Pulse Width Modulation) PWM (Pulse Width Over protection Over current protection PWMcurrent (Pulse Width Over currentModulation) protection Over/under voltage protection Over/under voltage protection Over/under voltage protection Over current protection Command fail Command fail Command fail Interlock detection Over/under voltage protection Interlock SoftCommand start Interlock detection detection fail Soft Maximum power consumption Soft start start Interlock detection Maximum Maximum power power consumption consumption Soft start Maximum power consumption
2.2. Heater Analysis 2.2. HeateraModule Module Analysis Assuming symmetrical shape with respect to the PTC heater cross-section, we applied a 1/16
model and ignored the heat radiation error stemming from the power source terminal. The boundary
Assuming aa symmetrical 2.2. Heater Module Analysis Assuming symmetrical shape shape with with respect respect to to the the PTC PTC heater heater cross-section, cross-section, we we applied applied aa 1/16 1/16 model model and and ignored ignored the the heat heat radiation radiation error error stemming stemming from from the the power power source source terminal. terminal. The The boundary boundary conditions conditions used analyze performance of the PTC of air 500 kg/h, Assuming symmetrical shape respect to heater cross-section, we applied 1/16 usedato to analyze the the heating heatingwith performance of the the PTC PTC heater heater consisted consisted of an an inlet inlet air flow flowaof of 500model kg/h, inlet temperature 00 C, and capacity the element of W. The of and ignored theair radiationof the of power source terminal. The conditions inlet airheat temperature oferror C,stemming and heating heatingfrom capacity of the PTC PTC element of 312.2 312.2 W.boundary The heat heat value value of the the PTC element was calculated by applying a PTC heater module heating capacity of 5 kW to the analysis PTC element was calculated by applying PTC heater heating capacity of 5flow kW toofthe analysis used to analyze the heating performance of thea PTC heatermodule consisted of an inlet air 500 kg/h,
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conditions to analyze heating of ten the million PTC heater of an inlet air flow component intoused the model. Thethe number ofperformance mesh is about andconsisted the computational time required of 500 kg/h, inlet air temperature of 0 ˝ C, and heating capacity of the PTC element of 312.2 W. The to produce a converged solution was about 1 or 2 days on average. The analysis program that was used heat value of the PTC element was calculated by applying a PTC heater module heating capacity of in this5 kW study utilizes themodel. grid-quality check method, and its analysis a by method that checks the to the analysis A thermal analysis of the heater was also involves performed substituting the convergence eachforiteration, confirming the gridThe independency is highly reliable. propertyfor values each component intothat the model. number of mesh is about ten million and themass, computational timeand required to produce a converged solution about 1 orgoverning 2 days on average. The momentum, energy conservation equations werewas used as the equations for The analysis program that was used in this study utilizes the grid-quality check method, and its the simulation of the heater. The turbulence model was used to calculate the turbulent flow with constants analysis involves a method that checks the convergence for each iteration, confirming that the grid obtained via empirical and reliable. theoretical methods. The modified production (MP) k-ε equation known as independency is highly the Kato-Launder was usedconservation for the turbulence [14]. heat flowequations analysis was The mass, modification momentum, and energy equationsmodel were used as The the governing for the using simulation of thebuilt heater. turbulence model was used todiscretization calculate the turbulent with performed SC-tetra onThe a node-based finite-volume method,flow a commercial constants obtained via empirical and theoretical methods. The modified production (MP) k-ε equation analysis program [15], and the analysis results were organized with respect to the heater’s temperature known as the Kato-Launder modification was used for the turbulence model [14]. The heat flow distribution a pressureusing dropSC-tetra to below a value corresponding to an air flow of 500 kg/h, which analysisusing was performed built on a node-based finite-volume discretization method, a was commercialflow analysis program [15], andcross-sectional the analysis results were organized with respect to the the maximum of the blower. The temperature distribution around theheater’s heating rods temperature distribution a pressure to below a value corresponding to an airairflow of and is and fins of the PTC heater isusing shown in Figuredrop 5a. The distribution reflects the pertinent flow 500 kg/h, which was the maximum flow of the blower. The cross-sectional temperature distribution shown in a manner that enables comparison of the different heat transfer paths from the PTC element to around the heating rods and fins of the PTC heater is shown in Figure 5a. The distribution reflects the fins. In the heat transfer path from PTC that element surface to theoffins, the heatheat resistance the pertinent air flow and is shown in athe manner enables comparison the different transfer of the pathspad, from which the PTCserves elementastoan the insulator, fins. In the accounted heat transferfor path from 75% the PTC surface the radiation about of element the total heat toresistance. fins, heat resistance of the radiation pad, which an insulator, for about 75% of Figure 5bthe shows the pressure distribution in the fin serves at the as same position accounted of the temperature distribution the total heat resistance. Figure 5b shows the pressure distribution in the fin at the same position of shown in Figure 5a. A relatively high flow resistance was observed at the point where the heat rods and the temperature distribution shown in Figure 5a. A relatively high flow resistance was observed at fins of PTC heater curve. temperature pressure of temperature each component of theofPTC thethe point where the heat rods The and fins of the PTCand heater curve. The and pressure each heater component of the PTC heater determined by the analysis be used to improve the fin design. determined by the analysis can be used to improve the fin can design.
(a)
(b)
Figure 5. Temperature and pressure distribution of the high-voltage PTC heater modules. (a) Temperature
Figure 5. Temperature anddistribution pressure (Pa). distribution of the high-voltage PTC heater modules. distribution (˝ C); (b) Pressure (a) Temperature distribution (°C); (b) Pressure distribution (Pa). 2.3. Heat Interference Analysis of the Controller
2.3. Heat The Interference Analysis of the Controller integration of the controller and the heater modules, which are conventionally separated, causes the radiation performance of the controller to decline due to heat interference with the heater in
The of the and the heater modules, whichdesign are conventionally theintegration limited space. By acontroller heat flow analysis, we considered possible alternatives forseparated, addressingcauses this issue. The employed analysis model of the controller-integrated PTC heating system shown in the the radiation performance of the controller to decline due to heat interference with theis heater in Figure The contains an insulated gate bipolar mode transistor (IGBT), which as a this limited space.6.By a model heat flow analysis, we considered possible design alternatives forserves addressing heat source and is a core component of the controller. It was developed using a scale of 1/12. The flow issue.region The of employed analysis model of the controller-integrated PTC heating system is shown in the analysis was set to ensure flux uniformity. Figure 6. The model contains an insulated gate bipolar mode transistor (IGBT), which serves as a heat source and is a core component of the controller. It was developed using a scale of 1/12. The flow region of the analysis was set to ensure flux uniformity.
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The boundary conditions were divided into basic and severe conditions as indicated in Table 5 to The boundary conditions were divided into basic and severe conditions as indicated 5 compare the radiation performance of the controller with respect to the operation conditioninofTable the system. to compare the radiation performance of the controller with respect to the operation condition of the The analysis was performed by switching between operation and non-operation of the heater and various system. The analysis was performed by switching between operation and non-operation of the heater flow conditions of the blower. The basic flow condition was 300 kg/h and the severe condition and various flow conditions of the blower. The basic flow condition was 300 kg/h and the severe corresponded reduction oftothe air flowofby 2/3, constitutes a severe operation environment conditionto corresponded reduction theabout air flow bywhich about 2/3, which constitutes a severe operation controller a real vehicle environment [16]. Theproperty physical property each for theenvironment controller for in athereal vehicleinenvironment [16]. The physical value forvalue eachforcomponent component including the IGBT was used for the analysis. including the IGBT was used for the analysis.
6. Analysis model of the heat interference with the controller. FigureFigure 6. Analysis model of the heat interference with the controller. Table 5. Boundary conditions for heat flow analysis of the controller-integrated high-voltage PTC
Table 5. Boundary conditions for heat flow analysis of the controller-integrated high-voltage heating system. PTC heating system. Operating Condition
Operating Condition Inlet air flow (kg/h) Air temperature (˝ C) Heat of IGBT (W) Inletvalue air flow (kg/h) Heat value of PTC (W)
Air temperature (°C)
Heater Not Operated
Heater Not Operated Basic Conditions
Heater Operated
Basic Conditions Heater
Basic Conditions 35.9 (300 kg/h at fullBasic mode) Conditions 0
35.9 416.7at(Heating capacity of 5 kW) (300 kg/h full mode) -
Operated Severe Conditions Conditions 12.0Severe (100 kg/h at full mode)
0 8
12.0 250(100 (Heating 3 kW) kg/hcapacity at fullofmode)
0
summarizes attained by the components as determined by the analysis. HeatTable value6of IGBT (W)the temperatures 8 The temperature of the IGBT under operation conditions without the heater was determined to be 416.7 250 about 59.6 ˝ C, while the operation of the heater increased it to about 77.9 ˝ C. Under the severe condition Heat value of PTC (W) 0 (Heating capacity of (Heating capacity of involving decreased air flow, the temperature increased to a maximum of 101.4 ˝ C. Because this was 5 kW) 3 appropriate. kW) within the allowed range for the controller, the radiation design was determined to be heat flow analysis of the controller-integrated high-voltage PTC heating system. 6. Results of Table 6Table summarizes thethetemperatures attained by the components as determined by the analysis. The temperature of the IGBT under operation conditions without theHeater heater was determined to be about Heater Not Operated Operated Component 59.6 °C, while the operation of the Basic heater increased it Basic to about 77.9 °C.Severe Under the severe condition Condition Condition Condition involving decreased air(˝flow, the temperature maximum of 101.4 °C. Because this was IGBT C) 59.5 increased to a 77.9 101.4 ˝ C) PTC element ( 92.8 113.2 within the allowed range for the controller, the radiation design was determined to be appropriate. Radiation fin (˝ C) 80.0 105.6 Figure 7 compares the cross-sectional temperature distributions of the PTC heater with and without operation of the heat source under the basic operation condition, and also quantitatively shows the heat Figure 7 compares the cross-sectional temperature distributions of the PTC heater with and transfer paths operation through the IGBT constitutes a considerable portion of without of the heatcomponents. source underRadiation the basic apparently operation condition, and also quantitatively shows the heatintransfer pathsabout through theofIGBT components. Radiation apparently constitutes the heat produced the IGBT; 71% the heat is transferred to the controller housing acover, considerable portion of the heat produced in the IGBT; about 71% of the heat is transferred the which functions as a heat sink. Figure 8 shows the air flow line through the heat sink of thetocontroller. controller housing cover, which functions as a heat sink. Figure 8 shows the air flow line through the It was observed that about 5% of the total air flow into the radiator entered the cooling hole of the heat
Table Table 6. 6. Results Results of of the the heat heat flow flow analysis analysis of of the the controller-integrated controller-integrated high-voltage high-voltage PTC PTC heating heating system. system. Component Energies Component 2016, 9, 18
Heater Heater Not Not Operated Operated Basic Basic Condition Condition
IGBT IGBT (°C) (°C)
59.5 59.5
Heater Heater Operated Operated 7 of 11 Basic Severe Basic Condition Condition Severe Condition Condition 77.9 77.9
101.4 101.4
heatPTC sink of the controller. It was observed that about 5% of the total air flow into the radiator entered -92.8 113.2 PTC element element (°C) (°C) 92.8 113.2 the cooling hole of the heat sink. This flow proportion indicates a correlation between the heating Radiation (°C) -80.0 105.6 Radiationoffin fin 105.6 performance the(°C) system and the heat interference with the 80.0 controller.
(a) (b) (a) (b) Figure 7. Figure 7. Comparison Comparison of of the the temperature temperature distributions distributions in in the the PTC PTC heater heater under under the the basic basic Figure 7. Comparison of the temperature distributions in the PTC heater under the basic condition condition with and without operation the (C). (a) operation the condition with andoperation without of operation of the(a)heater heater (C). (a) Without Without operation of the heater; heater; with and without the heaterof (˝ C). Without operation of the heater; (b) Withof operation of the operation heater. (b) (b) With With operation of of the the heater. heater.
8. Flow at heatsink sink hole the heating system controller. Figure 8. line at hole the heating system controller. FigureFigure 8. Flow Flow lineline at the thetheheat heat sink holeofof of the heating system controller.
3. Performance Reliability Experiments 3. and Reliability Experiments 3. Performance Performance andand Reliability Experiments 3.1. Test Facility and Method
3.1. 3.1. Test Test Facility Facility and and Method Method
A wind tunnel device was configured inside the constant-temperature chamber, as shown in Figure 9a, to measure the heating capacity, efficiency, and pressure drop of the high-voltage heating A A wind wind tunnel tunnel device device was was configured configured inside inside the the constant-temperature constant-temperature chamber, chamber, as as shown shown in in system. A T-type thermocouple and twenty four-point thermocouples with a resolution of ˘0.1 ˝ C were Figure 9a, to measure the heating capacity, efficiency, pressure drop of heating Figure 9a,to tomeasure measure the heating capacity, efficiency, and pressure drop of the the high-voltage heating used the inlet and outlet air temperatures ofand the wind tunnel device. Allhigh-voltage the temperature system. T-type thermocouple and twenty thermocouples with of ±0.1 andA were collected a Gantner data logger. The experimental conditions system. Apressure T-typemeasurements thermocouple and twentybyfour-point four-point thermocouples with aa resolution resolution of for ±0.1 °C °C measuring the heating performance of the vehicle heating system comprised an input power voltage were were used used to to measure measure the the inlet inlet and and outlet outlet air air temperatures temperatures of of the the wind wind tunnel tunnel device. device. All All the the of 330 V, inlet air temperature of 0 ˝ C, and inlet air flow rate of 300 kg/h. This was used to replicate the air flow from the HVAC system blower of a vehicle under outdoor winter temperature conditions. To assess the reliability of the high-voltage heating system, we evaluated the heating performance after conducting impact and dust tests. The target was to achieve less than 10% change in the heating performance. The impact and dust test conditions are given in Tables 7 and 8 respectively.
conditions for measuring the heating performance of the vehicle heating system comprised an input power voltage of 330 V, inlet air temperature of 0 C, and inlet air flow rate of 300 kg/h. This was used to replicate the air flow from the HVAC system blower of a vehicle under outdoor winter Energies 2016, 9, 18 8 of 11 temperature conditions.
(a)
(b)
Figure 9. Schematic diagram of the test facility and prototype heating system used to evaluate the Figure 9. Schematic diagram of the test facility and prototype heating system used to heating performance. (a) Schematic diagram of the test facility; (b) Installation of the prototype evaluate heating performance. (a) Schematic diagram of the test facility; heatingthe system. (b) Installation of the prototype heating system. Table 7. Impact test conditions.
To assess the reliability of the high-voltage heating system, we evaluated the heating performance Waveform Type Half Sine after conducting impact and dust tests. The target was to achieve less than 10% change in the heating Peak acceleration (g) 100 performance. The impact and dust test conditions are given 6in Tables 7 and 8, respectively. Pulse duration (ms) Impact direction Number of impacts
X, Y, Z ˘10
Table 7. Impact test conditions. WaveformTable Type8. Dust test conditions. Half Sine Peak acceleration (g) 100 Test temperature (˝ C)
Pulse duration Dust (ms) type
Concentration Impact direction(mg/m3 ) Humidity (%)
Number of impacts Dust spreading time Test time
Unspreading time (pause time) Repetition time
20 6 Portland cement 3000 X, Y, Z 45–85 ±10 5 s 15 min 8h
Table 8. Dust test conditions.
TestResults temperature (C) 3.2. Performance and Reliability
20 Portland cement
Dust type
The air-side heat transfer, power consumption, and pressure drop of the developed high-voltage 3 Concentration ) 3000 to evaluate the heating system were measured using four(mg/m final prototypes and the results were used heating performances and efficiencies of the heating capacity to Humidity (%)systems. Efficiency is the ratio of the45–85 the power consumption of the system, and isDust calculated using Equation (1). Table spreading time 59ssummarizes the results for the four high-voltage heating systems. The average heating capacity and efficiency were Test time Unspreading time (pause time) 15 min about 5.4 kW and 0.95, respectively, which met the target performance. The average pressure drop was Repetition time 8h determined to be about 40.5 Pa, which is also adequate: .
C ˆ m ˆ pTo ´ Ti q η“ P VˆI
(1)
drop was determined to be about 40.5 Pa, which is also adequate:
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C P m (T o T i ) V I
(1) 9 of 11
Table 9. Experimental results of heating performance.
Heating System 9. Experimental results of heating performance. Performance Table Parameter A B C Heating Input current (A) 17.1 17.3 System 17.3 Performance Parameter A B D Power consumption (kW) 5.66 5.62 C 5.72 Input current 17.3 16.9 Temperature difference (C) (A) 64.217.1 65.3 17.3 65.1 Power consumption (kW) 5.66 5.62 5.72 5.59 Heating capacity (kW) 5.44 65.1 5.43 Temperature difference (˝ C) 5.3564.2 65.3 64.9 Heating capacity (kW) 5.35 5.44 5.40 Pressure drop (Pa) 40.9 40.3 5.43 40.1 Pressure drop (Pa) 40.9 40.3 40.1 39.9 Energy efficiency 0.945 0.968 0.949 0.949 Energy efficiency 0.945 0.968 0.966
D 16.9 5.59 64.9 5.40 39.9 0.966
AsAs can bebe observed from was no no abnormality abnormality in in the the external externalappearance appearance can observed fromFigures Figures10 10and and11, 11 there there was of the heating heating system system after after the the impact impact and and dust dust tests. tests. The The results results of ofthe theheating heating of the the final final prototypes prototypes of of the performances of the prototypes after the tests are also summarized in Table 10. The decrease inthe the performances of the prototypes after the tests are also summarized in Table 10. The decrease in heating performance performance after after the the impact impact test test ranged ranged between between 7% 7% and and 10%, 10%, while heating while the the decrease decreaseafter afterthe the dust test was about 2%. The changes of not more than 10% confirmed the reliability of the high-voltage dust test was about 2%. The changes of not more than 10% confirmed the reliability of the heating system. high-voltage heating system.
Figure 10. appearance of a prototype of the heating system before andbefore after anand impact Energies 2016, 9External Figure 10. External appearance of a prototype of the heating system aftertest. an impact test.
Figure External appearanceof ofaa prototype prototype of before andand after a dust test. test. Figure 11.11. External appearance ofthe theheating heatingsystem system before after a dust Table 10.Results Results of of heating Table 10. heatingperformance performanceexperiments. experiments. Heating System Heating System Performance Parameter Performance Parameter
After Impact Test
After Impact Test A
Input current (A) InputPower current (A) consumption (kW) Heating capacity (kW) Power consumption (kW) Pressure drop (Pa) Energy (kW) efficiency Heating capacity
A
16.4 16.4 5.43 4.84 5.43 39.2 0.891 4.84
B
B
16.9 16.9 5.59 5.06 5.59 39.9 0.905 5.06
After Dust Test
After Dust Test
C 17.3 5.72 5.42 40.7 0.947
C
D
D
16.5 17.35.45 5.26 5.7240.1 5.420.965
5.26
16.5 5.45
Pressure drop (Pa)
39.2
39.9
40.7
40.1
Energy efficiency
0.891
0.905
0.947
0.965
4. Conclusions
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4. Conclusions In this study, a high-voltage heating system containing heater modules with an integrated controller was developed for electric vehicles. Further, the performance and reliability of prototypes developed were experimentally evaluated. The study and findings can be summarized as follows: (1)
(2)
(3)
A modularized controller-integrated high-voltage heating system was fabricated and compared with a conventional controller-separated heating system, and was observed to afford a 20% weight reduction. The heating performance of the heating system was verified via experiments using various design parameters of the heat rods and fins, which are the main components of the heating modules. In addition, heat flow analysis of the system revealed improved performance and reduced heat interference with the controller. The performance test of the high-voltage heating system indicated heating performance, efficiency, and pressure drop of about 5.4 kW, 0.95, and 40.5 Pa, respectively. A reliability evaluation involving impact and dust tests also yielded satisfactory results.
Hence, by integration and modularization, we successfully developed a lighter-weight and more productive high-voltage heating system for electric vehicles and exhibited its reliability. Further study is planned to verify and improve the reliability of various components of the system for commercialization. This is expected to increase the application of heating systems in electric vehicles. Acknowledgments: This study was conducted as part of the Energy Technology Development project sponsored by the Ministry of Trade, Industry and Energy. The additional support received from the Donga High Tech-Company is greatly appreciated. Author Contributions: Sung Chul Kim and Yoon Hyuk Shin organized the overall numerical analysis and experimental evaluations. Seungkyu Sim commented on the results and conclusions. All the authors also reviewed the manuscript. Conflicts of Interest: The authors declare no conflict of interest.
Nomenclature Cp I . m Ti To V η
specific heat of air (J/kg¨ K) current (A) mass flow rate of air (kg/s) inlet air temperature (˝ C) outlet air temperature (˝ C) input voltage (V) energy efficiency
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