Recent advances on air heating system of cabin for pure electric vehicles: A review

21 Oct.,2022

 

PTC Heater for Bus

PTC Heater for Bus

Heliyon.

2022 Oct; 8(10): e11032.

doi: 

10.1016/j.heliyon.2022.e11032

PMCID:

PMC9568831

PMID: 36254280

Recent advances on air heating system of cabin for pure electric vehicles: A review

,a,b,c,1 ,a,b,1 ,a,b,d ,a,b,d,∗ and a,b

Dazhang Yang

aCollege of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China

bShanghai Professional Technology Service Platform on Cold Chain Equipment Performance and Energy Saving Evaluation, Shanghai Ocean University, Shanghai 201306, China

cNational Experimental Teaching Demonstration Center for Food Science and Engineering, Shanghai 201306, China

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Yilin Huo

aCollege of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China

bShanghai Professional Technology Service Platform on Cold Chain Equipment Performance and Energy Saving Evaluation, Shanghai Ocean University, Shanghai 201306, China

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Qing Zhang

aCollege of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China

bShanghai Professional Technology Service Platform on Cold Chain Equipment Performance and Energy Saving Evaluation, Shanghai Ocean University, Shanghai 201306, China

dQuality Supervision, Inspection and Testing Center for Cold Storage and Refrigeration Equipment, Ministry of Agriculture and Rural Affairs, Shanghai 201306, China

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Jing Xie

aCollege of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China

bShanghai Professional Technology Service Platform on Cold Chain Equipment Performance and Energy Saving Evaluation, Shanghai Ocean University, Shanghai 201306, China

dQuality Supervision, Inspection and Testing Center for Cold Storage and Refrigeration Equipment, Ministry of Agriculture and Rural Affairs, Shanghai 201306, China

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Zhikang Yang

aCollege of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China

bShanghai Professional Technology Service Platform on Cold Chain Equipment Performance and Energy Saving Evaluation, Shanghai Ocean University, Shanghai 201306, China

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Author information Article notes Copyright and License information Disclaimer

aCollege of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China

bShanghai Professional Technology Service Platform on Cold Chain Equipment Performance and Energy Saving Evaluation, Shanghai Ocean University, Shanghai 201306, China

cNational Experimental Teaching Demonstration Center for Food Science and Engineering, Shanghai 201306, China

dQuality Supervision, Inspection and Testing Center for Cold Storage and Refrigeration Equipment, Ministry of Agriculture and Rural Affairs, Shanghai 201306, China

Jing Xie: nc.ude.uohs@eixj

∗Corresponding author.

Corresponding author. nc.ude.uohs@eixj

1Dazhang Yang and Yilin Huo contributed equally to this paper.

Copyright © 2022 The Authors. Published by Elsevier Ltd.

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Associated Data

Data Availability Statement

No data was used for the research described in the article.

Abstract

Due to the environmental protection and energy shortage, the electric vehicles (EV) is gradually replacing traditional fuel vehicles. EV generally use more energy for air conditioning system, especially EV have almost no waste heat from engine to be discharged to the passenger compartment to achieve thermal comfort in heating condition. The energy consumption of the heating system for EV will decrease the maximum mileage. Therefore, the energy saving technology for heating system is developing and applied for EV. The article introduced the advance of conventional and emerging heating system for the EV. The positive temperature coefficient (PTC) heater is a convenient heating method used in EV, but PTC heater has some defects such as low efficiency. The heat pump (HP) system is gradually replacing PTC. However, HP has various problems to be overcome, such as the heating capacity and efficiency in low temperature environment. In addition, other novel technologies are proposed to reduce the energy consumption. This article reviews the literature of novel heating methods for EV, introduces adsorption air conditioning systems (AAC), fuel combustion (FC), heat storage (HS), waste heat recovery (WHR), thermoelectric effect (TE) and magnetocaloric effect (ME).

© 2017 Elsevier Inc. All rights reserved.

Keywords:

Electric vehicle, Heating system, Magnetocaloric, Thermoelectric

1. Introduction

At present, many environmental problems are emerging, and problems such as global warming and resource scarcity are issues that we need to face together. Automobile energy consumption accounts for a large proportion of total oil energy consumption, and has been reached more than 30% in the past few years [1]. Due to the shortage of oil and the pollution of oil on the environment, the United Nations and countries around the world have planned to restrict the production and use of fuel vehicles to achieve sustainable development goals. China has also proposed a project to increase the proportion of new energy and clean energy-powered vehicles to about 40% by 2030. In order to achieve the goal of low carbon and pollution-free, many companies are currently developing products that are more environment-friendly and consume less energy, EV is one of them. Unlike traditional cars, EV have almost no waste heat that needs to be discharged to the passenger compartment to achieve thermal comfort in the cabin. When the heating system of the EV is turned on, the maximum mileage of the EV will be affected. Therefore, how to obtain an efficient and energy-saving EV heating system and improve the vehicle's mileage has become a difficult problem.

In this regard, many previous studies have discussed different heating technologies for EVs from different perspectives. Several articles compare many technologies and discuss their advantages and disadvantages. In 2016, Peng et al. [2] introduced the application of environmentally friendly refrigerants in EVs, and reviewed systems such as multi-source HPs, but the advantages and disadvantages of different HP systems were not compared in the article. In 2018, Zhang et al. [3] reviewed the mileage extension strategy of EVs, but his paper did not mention more novel heating methods to achieve the purpose of making EVs more energy-efficient and improving their range. This paper continues the efforts of previous researchers by comprehensively reviewing different alternative heating techniques and comparing the advantages and disadvantages of different approach techniques.

PTC heating as one of the options has been widely used in commercial EV, but due to its relatively low energy efficiency, it consumes a lot of electricity and sometimes leads to a lack of power [4]. As an alternative, the automotive industry has introduced an ASHP system. ASHP is a excellent method to save energy while meeting climate control requirements [5], it is energy-saving and has both cooling and heating capabilities. However, when the ambient temperature is extremely low, the flow of refrigerant in the ASHP system will be reduced, resulting in poor ASHP system performance [6]. Therefore, it is necessary to improve the efficiency of the ASHP system under low temperature environmental conditions.

The existence of the adsorption air conditioning (AC) system is helpful to solve the problems of heavy heating burden and short battery life of EVs, and also helps to reduce the energy consumption in the heating process. The proposal of the fuel burning system separates the heating system from the battery system, which also greatly saves vehicle mileage. The heat storage system can also achieve a similar purpose through heat storage. In addition, since about half of the energy in the exhaust emissions of EVs is lost in the form of heat, recycling the waste heat can also reduce fuel loss and improve the performance of the heating system. At the same time, the application of magnetocaloric effect and thermoelectric effect technology is booming, and may replace HP systems in the future.

This article introduces the heating systems that can be used in EV and reviews the heating methods of air heating and water heating PTC systems. Secondly, it analyzes the replacement of the refrigerant in the HP system, different options, especially the refrigerator injection systems and the secondary loop systems, and introduces the HP systems with dehumidification and defogging function and the HP systems with novel heat exchanger. This article introduces the principle of adsorption AC, summarized the system composition and application of the fuel combustion system. The application of energy storage heating and different devices are introduced, and the advantages and disadvantages of the waste heat recovery systems and solutions are analyzed. Finally, the emerging technologies such as the application of magnetocaloric and thermoelectric effect in EV heating are summarized.

2. PTC heating systems

In the heating ventilation and air conditioning (HVAC) system of EVs, EVs cannot use the waste heat generated by the engines of fuel-fueled vehicles for heating, many car manufacturers use special heating devices to achieve heating. PTC thermistor is a typical semiconductor resistor with a positive temperature coefficient, and it is one of the most used heating methods in electric air conditioners [7].

PTC heater has the advantages of low thermal resistance, high heat exchange efficiency and low power attenuation for long-term use [8]. There are air heating and water heating in the form of PTC heaters. These two options will be explained in the following sections.

2.1. Air heating

There are two types of air heating: high-voltage air heating and low-voltage air heating. Low-voltage air heating system adds water pumps, water pipes, three-way valves and heating cores, motors, and radiator water tanks to form a closed water circulation system. At the same time, low-voltage air heating heaters are added to the HVAC system. The system structure of the high-voltage air heating method removes the water inlet and outlet pipes and the heater core of the original car, and replaces the heater core with an air heating PTC of the same size and the same installation method as the car heater core, and then changes the related control circuit. Thermal insulation measures should be taken for the core [9]. During operation, the PTC heating device provides a heat source to heat the water in the radiator water tank, and then the hot water enters the heater core to directly heat the air.

High-voltage air heating heaters can provide higher power output and efficiency heating than low-voltage air-heating heaters. At the same time, the method directly heats the air, which makes the cab have a faster temperature rise rate. Park et al. [10] constructed a PTC air heating system with a closed-loop device as shown in , analyzed the efficiency of the heater and adjusted the geometric variables. The efficiency of the system is as high as 98%, and the output density has been increased. To make the air conditioning and heating system meet the defrosting and defogging regulations and heating requirements, the heating power of the PTC needs to be at least 3 kW or more. This power is a huge consumer relative to the total battery capacity, which leads to a dramatic drop in the mileage of pure EVs.

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2.2. Water heating

Compared with air heating, the water heating PTC system has a more compact structure, a lighter weight, and a higher heating efficiency. Bohlender and Reiss [11] has developed a PTC water heating system, the system contains of a continuous flow heater and an integrated high-pressure controller. The electronic water pump and the PTC heating system are integrated in the design. The design reduces the space size and weight of the system, and significantly improves the heating efficiency. Huang [12] also disclosed a new type of water PTC heater, which enhances heat transfer and improves safety. The equipment also solves the problem that the tube wall and the internal heating element cannot be closely attached, which reduces the heat transfer effect and affects the service life.

However, the electric power of the PTC heater for water heating is about 5.5 kW, which is a huge consumption relative to the total battery capacity. Due to the limitation of battery power, the PTC system will adversely affect the cruising range when it is running [13]. Reduce cruising range. In addition, the problem of poor cooling performance of PTC heaters also needs to be solved.

4. Adsorption air conditioning systems

Even though the vapor compression heat pump AC system seems to be able to meet the heating requirements in most cases, its heating performance will be affected by the environment and significantly decrease when the ambient temperature is extremely low. In addition, same as PTC heating, the use of vapor compression heat pump air-conditioning systems will also produce additional power loss, but AAC can avoid this problem [42]. In the AAC system, the compressor is replaced by a adsorption reactor, and the system structure is shown in . During the charging process of the EV, the adsorption reactor absorbs heat, and the refrigerant flows from the adsorption reactor into the liquid storage tank. During the heating process, the refrigerant flows from the liquid storage tank into the evaporator, the adsorption reactor heats the cold air in the cabin, and at the same time absorbs the steam in the evaporator to complete the heating process. This system usually uses NH3 as the refrigerant because it is well matched to the adsorbent to form a working pair and will not freeze at low temperatures.

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Jiang et al. [44] proposed a new type of AAC using expanded natural graphite as a sorbent for heating the cabin of an EV, and evaluated its impact in terms of energy density, energy efficiency, extra mass, and mileage savings. The results show that the additional mass has a limited effect on the EV's driving range. During the experiment, the EVs of the selected models can save nearly 100 km of driving range when heated by AAC, which can significantly reduce the energy consumption of EVs. At the same time, the energy density and efficiency of the system are positively correlated with the changing trend of refrigerant vaporization temperature, and the range of COP is from 0.34 to 0.82 under different vaporization temperatures and mass ratios. Wajid et al. [45] provided a solar AAC and confirmed its feasibility.

An et al. [43] studied the influence of ambient temperature on EVs using AAC, and determined the best solid adsorption working fluid in different temperature regions. Because the adsorption process progresses smoothly and the adsorption effect is better when the temperature difference between the adsorption reactor and the evaporator is small, the results show that MnCl2 is recommended as the adsorption in severe cold areas, CaCl2 is recommended as the adsorption in warm areas, and other places can use a mixture of MnCl2 and CaCl2. Shabir et al. [46] also tested different sorbents and determined the most suitable sorbent for different systems.

5. Fuel combustion systems

If a system separate from the battery system can be used for heating alone, it can also achieve the purpose of reducing battery loss and reducing vehicle mileage. A thermally efficient heating system with fuel burners is proposed to achieve this possibility by directly heating the air in the passenger cabin by exothermic combustion of the fuel. At the same time, it should be noted that an independent heating system means a larger footprint and heavier weight, which means that the combustion system is more used in extremely cold areas to reduce mileage, and is not suitable in colder areas [47].

Cho et al. [48] proposed the use of FC system as an auxiliary heating method for EVs to heat the air in the cabin and at the same time control the flow of high-temperature exhaust gas to the heat exchanger. The results show that based on this system, the mileage of the EV can be reduced to 40% of the mileage when the original heating system is used when heating at an ambient temperature of 0 °C. Seo et al. [49] proposed a system with a fuel burner that can be used to heat the car battery in an electric car cabin at the same time. The structure is shown in , and its heating characteristics have been measured, which further confirms its feasibility.

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Burners that use biological materials as fuel are also full of prospects, and bioethanol is a good choice. Carbon dioxide emissions when burning ethanol for heating are much lower than those when burning gasoline, while the energy density of ethanol is higher than that of gasoline, which makes it popular. Kohle et al. [50] proposed a FC heating system based on ethanol combustion. Compared with electric heating, its mileage has been significantly reduced, which shows that it is very effective to combine environmentally friendly fuels with FC burners. Riess et al. [51] also proposed a heating system that uses ethanol as fuel, and reached a similar conclusion that the independent combustion heating system can significantly optimize the battery when the EV is driving in a very cold environment. I believe that more efficient and energy-saving fuels and burners will be appeared in the future.

6. Heat storage heating systems

As the current heating system, especially PTC heating, will reduce the mileage of EVs. In addition, EV heating is intermittent, in order to reduce energy consumption, HS systems have become more and more important [52]. Replacing the original heating system of the EV with a heat storage device can reduce the burden of heating on the car battery, break the air conditioner's dependence on electricity, make car batteries last longer and protect the environment [53].

Phase change energy storage is a good choice for reducing energy consumption, which usually chooses beeswax or paraffin as the phase change material (PCM), and its requirements for motor output are extremely low. The performance of different PCM was evaluated by Putra et al. [54]. The results show that the thermal conductivity of beeswax is low, but it has large sensible and latent heat, which can store a large amount of thermal energy. At the same time, when the melting temperature of RT44HC is within the recommended range of battery operating temperature, RT44HC is also a good choice.

Xia et al. [55] proposed a phase change energy storage design using paraffin as the phase change material combined with heat pipe heat exchange. The system stores heat in the heat storage device when the EV is not working, releases the stored heat during operation, and uses the phase change of the working liquid in the heat pipe to deliver heat to the vehicle. The system mainly includes four parts: heating device, heat storage device, heat transfer device and control device. The PTC heater is selected as the heating device, and the device uses the cross arrangement of the PTC heating plate and the heat pipe to improve efficiency. The heat storage box is wrapped with nano-aerogel composite thermal insulation material to reduce heat dissipation loss. Tests show that the device can continue to provide heat for 2 h.

7. Waste heat recovery heating systems

During the operation of EVs, a large amount of energy is lost in the form of heat energy through various channels such as batteries and electrical equipment. If the waste heat can be recovered and the heat extracted from it and reused in the vehicle propulsion system, fuel consumption can be reduced, thereby improving battery performance [56]. In the waste heat recovery heating system, the air with waste heat exchanges heat with the refrigerant in the heat exchanger, and the refrigerant evaporated by the waste heat enters the compressor and is compressed to release heat to the air in the EV to convert the waste heat into heat capacity.

Under normal circumstances, WHR will have a positive impact on the COP of the system. Tian et al. [57] proposed an EV thermal management system with motor and controller unit WHR, and analyzed its performance. The results show that under the best working conditions, using the WHR system, the COP of the vehicle is between 2.05 and 4.71 under different condensation temperatures, which is a maximum increase of 13.2% and a mileage increase of 33.64% compared with the traditional system without it.

However, when the temperature is higher, the situation changes. Han et al. [58] proposed an air source HP system with WHR for electric buses to improve heating performance. Experiments have found that when the outside temperature is below −5 °C, recovering waste heat can improve system performance. However, when the temperature rises, the pressure drop of the waste heat exchanger becomes larger, and the recovery of the waste heat will adversely affect the performance of the system.

In order to solve the negative impact of temperature on the WHR system, Ahn et al. [59] proposed to investigate the feasibility of dual-source heat pumps using air and waste heat in EVs, and compared the system performance of the three cases of air source only, waste heat only and dual heat source. The study found that the heating performance of the dual heat source mode is higher than that of the pure air source and pure waste heat mode, and at the same time, good results can be obtained by operating in the mode at higher temperatures.

Due to the limited capacity of EV batteries, in order to balance the supply and demand relationship between EV power demand and waste heat recovery, Merhy et al. [60] proposed an energy strategy based on a multi-objective and multi-criteria optimization algorithm, which can be based on power supply and demand conditions. Control the energy flow of the EV and decide whether to recover the waste heat. The reliability of this strategy is verified by simulation, and it provides a reliable solution for the optimization of vehicle energy flow of waste heat recovery system.

8. Magnetocaloric effect

Active magnetic regeneration (AMR) as a reversible thermal cycle technology that can be used for heating, cooling and mechanical power generation, and can even reach 60% Carnot efficiency it is one of the most promising alternative technologies for the development of heat pumps [61]. The magnetic HP system is based on the AMR principle. It uses the magnetocaloric effect (ME), which is a characteristic of certain magnetocaloric materials. When the applied magnetic field changes, it heats or cools, so that it can use the heat dissipated by the magnetocaloric material when it is applied by an external magnetic field to heat the refrigerant and then supply heat through the heat sink. Since the heat transfer process of magnetic heat pumps does not require liquid phase change, fluid heat transfer liquids can be used without the need for fluorinated refrigerants or other gaseous refrigerants, which reduces the possibility of impacting environmental benefits. In addition, since the working medium of the magnetocaloric system is a solid with a high entropy density instead of a gas, the system can be easily miniaturized to reduce the burden on operation due to the volume and weight of the system.

Zimm et al. [62] proposed an AMR-based active magnetic regenerator cycle, and the system principle is shown in , and made some progress. Plait et al. [63] Proposed a heat pump technology based on ME and applied it to the cabin heating system of automobile to replace the traditional heating system. They modeled the ME system and evaluated its implementation in EV. The results show that the ME system can meet the heating demand of cabin space, and the heating power can be higher than that when using batteries, which shows that it is possible to use ME system for heating in the future. Lyskawinski et al. [64] also revealed that the magnetic heating method was compared with the traditional method, which confirmed its feasibility. However, it should be noted that the energy efficiency of the magnetocaloric cycle is low, the temperature span caused by each cycle is limited, and its current heating capacity depends heavily on the cycle efficiency. Therefore, the search for magnetocaloric materials with better performance is still the future topics to discuss.

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9. Thermoelectric effect

TE can realize the conversion between heat and electricity. A thermoelectric module based on this principle converts voltage into temperature difference. The thermoelectric heating module is composed of a group of semiconductor thermocouples of different materials. When a certain voltage is applied to the junction of the thermocouple connection, one side of the thermocouple pair will absorb heat, while the other side will release heat. The heat is transferred to the air inside the EV through the radiator. Compared with the traditional vapor compression cycle, thermoelectric modules are less efficient, but they are small in size, light in weight, fast in heating, require no refrigerant, and have a high COP [65]. Cosnier et al. [66] proposed the heating system model using thermoelectric module, the COP can reach about 2 during heating, and the temperature difference between the cold side and the hot side can even reach 70 °C, confirmed the feasibility of heating air with thermoelectric modules.

The heating system using the thermoelectric module is relatively safe and stable when working, directly converts electrical energy into heat energy, and its power changes with the current value and voltage value acting on the system, which can accurately control the temperature, so it is very suitable for the adjustment of local thermal environment.

Wan et al. [67] proposed and tested a local air-conditioning system for trucks using TE, with six thermoelectric modules placed at different locations around the driver. The results show that the system can obtain better cop and reduce operating energy consumption under the current of 3–6 A, and it can meet the driver's thermal comfort requirements.

10. Conclusion

In this article, a comprehensive review of the latest technology of EV heating systems, analysis of existing systems, technologies and challenges in this field, the conclusion is as follows: The PTC system was once the most popular heating system, with the advantages of low thermal resistance and high efficiency. However, due to its poor fuel economy, it is gradually replaced by HP system. The HP system has strong heating capacity and higher economy. The replacement of refrigerants used in HP systems and new circulation methods are being actively discussed. However, the HP system still has the problems of poor low-temperature performance and surface frosting, which need to be solved urgently. But these problems can be solved by coming up with better performance mixed or natural refrigerants, better systems such as refrigerant injection systems and secondary loop systems, innovative dehumidification and defogging methods, special materials for heat exchangers, and this is also the future research needs to be considered.

In addition, other novel technologies are investigated and proposed to reduce the energy consumption of EV's heating system. The adsorption heating system can reduce battery consumption and save the mileage of EVs. Fuel combustion heating with a separate heating system can significantly increase vehicle mileage with high heating efficiency. The development of heat storage and waste heat recovery systems can make use of heat from environment or the EV themselves in order to reduce the burden on batteries and extend the life of car batteries. The application of magnetocaloric effect and thermoelectric effect also makes the EV heating system more environmentally friendly.

shows a brief comparison between the previous major EV heating technologies, including advantages and disadvantages. It helps design engineers understand and select specific available technologies for practical applications.

Table 3

System typeAdvantagesDisadvantagesPTC heating systemsDirectly heats the air with fast heating speed; high system efficiency.High energy consumption, seriously affecting vehicle mileage; complex structure, many parts and components; high cost.Vapor compression heat pump systemsHigh system efficiency and good economy; good adaptability; slightly higher mileage than PTC.Poor performance at low temperature, limited by temperature range; high cost.Adsorption air conditioning systemsLower battery capacity requirements, significantly reducing battery weight and operating costs; longer mileage.Finding the best adsorbent-adsorbate pair is challenging; initial investment is higher; efficiency is lower than heat pumps.Fuel combustion systemsNo dependence on the main battery of EVs; increased cruising range; high efficiency.Heaters require space and additional refueling burden; high cost.Heat storage heating systemsLow demand for batteries; greatly prolongs the mileage of the EV and the service life of the battery; energy saving and environmental protection; takes up less space in EVs.The continuous heat supply time is short; low efficiency.Waste heat recovery heating systemsLow energy consumption; improved battery performance; great savings in tram mileage; moderate efficiency and high efficiency.Energy efficiency is heavily dependent on waste heat; at lower temperatures there is insufficient heat supply and can only be used as auxiliary heating.Magnetocaloric heating systemsSmall size, light weight, no pollution; few moving parts, low vibration and noise; high reliability, long life, and easy maintenance.The temperature difference produced by each cycle is small; the heat exchange rate is slow.Thermoelectric heating systemsNo refrigerant and moving parts; compact structure; precise temperature control, suitable for local thermal environment regulation.Low efficiency, low heat production; the issue of developing higher performance TE materials remains to be resolved.Open in a separate window

From the perspective of energy saving and environmental protection, the above technologies are likely to be used as a supplement or alternative to the vapor compression heat pump technology in the future. However, the problems that still need to be solved are to find a better matching adsorption working pair, a system with more reasonable structure, a phase change material and a magnetocaloric material with a better performance, a better combination of the waste heat recovery system and the optimization of the whole vehicle energy flow, and the more reasonably distribution of thermoelectric modules should be arranged in the case of local heating. The pursuit of more efficient and energy-saving EV heating systems is a permanent theme of exploration, and only the joint efforts of all researchers can promote its continuous development.

Declarations

Author contribution statement

All authors listed have significantly contributed to the development and the writing of this article.

Funding statement

Dazhang Yang was supported by Shanghai Professional Technology Service Platform on Cold Chain Equipment Performance and Energy Saving Testing Evaluation [20DZ2292200].

Data availability statement

No data was used for the research described in the article.

Declaration of interest’s statement

The authors declare no conflict of interest.

Additional information

No additional information is available for this paper.