Abstract

The aim of this study was to determine if heating a battery pack using a modified electric blanket (MEB) or hot-blowing air from underneath an electric vehicle (EV) extends battery range in a colder climate. Many countries in the world using EVs such as Norway, Sweden, Canada, the United States, and Finland would benefit from increased range during the colder months. A Tesla Model 3 using internal heating with the battery pack provided a model to emulate. The MEB offers a practical means of extending the range in inclement weather with its current layout. The car utilized for this study was a 2021 Hyundai Kona EV Preferred model. Data for this study was obtained during the winter, and all of it was from the Niagara Region in Canada. A total of 39 trials were used, 13 for each of the three options: baseline, MEB, and blowing hot air. There was an increase in range using both the MEB and hot air. Future research should look at adding a permanent add-on aftermarket heating source or an easy-to-connect temporary product that keeps range consistent and increases it during the winter months.

1. Introduction

In recent years, the use of electric vehicles (EVs) has dramatically increased on a global scale. The movement towards green vehicles with no emissions has received a boost from multiple sources over the last couple of years in Canada and the United States. Due to the high price of gas, people are interested in buying EVs. The US has created the National Electric Vehicle Infrastructure (NEVI) program to invest in creating EV infrastructure across all 50 states. Provinces such as Quebec and British Columbia in Canada are offering substantial rebates to residents to encourage EV adoption. These three sources of influence have contributed to the ‘electrification movement.’ In addition, battery ranges have increased with new EVs entering the market, thereby removing a previous obstacle to adoption.

One issue for EV consumers is the lessening range during severe winter conditions compared to other seasons. During winter some EVs lose up to 35% of their range because of the low freezing weather conditions ¹. Northern countries such as Norway, Sweden, and Canada experience cold winters which is detrimental to an EVs range. “Range anxiety” develops in consumers because of a host of variables including cold that effects the overall range from trip-to-trip. One of the key elements effecting the overall range is how the ambient temperature effects charging. There have been multiple methods attempted by manufacturers and consumers to increase the range during charging by limiting impact of temperature on the battery pack.

There are different heating methods that could help a battery achieve an increase in range during colder weather. Popular methods of heating a battery include convective air heating, phase-change materials, alternative current heating, mutual pulse heating, internal self-heating, and liquid heating. A Tesla Model 3 uses an internal self-heating method in certain circumstances which results in less time spent charging on a Supercharger, and lessening battery degradation. The lessened time and battery degradation results should be strived for within all EVs. Convective air heating is the easiest method to heat a battery pack outside of the lab. Circulating heat through blowing air or rising hot air from a source may help the range during the cold winter months. Pre-heating and heating the battery pack can be completed via both methods of convective air heating.

Pre-heating the battery is one such method that could be key to speeding up charging, reducing battery degradation during the winter, and increasing range. To increase battery performance and efficiency, particularly in cold weather, the Tesla Model 3 incorporates battery preheating technology, this is a good model to emulate. Before the Model 3 is driven, the battery preheating system heats the battery pack to an ideal temperature range, which can assist in increasing the battery's charging speed, range, and overall performance. Emulating the battery preheating for all EVs should allow for better charging speed, increased range, and better performance. The battery in a Tesla Model 3 can be preheated in a variety of ways, but the most popular methods include regenerative braking, cabin heating, preconditioning, and supercharger preheating. These techniques demonstrate considerable battery maintenance and can improve the battery's efficiency and performance in cold climates for the Tesla Model 3. Regenerative braking: As the automobile is moving, the regenerative braking system may produce heat in the battery pack, which may aid in warming the battery. Preconditioning: Before stepping into their Tesla, drivers may use the company's mobile app to warm up the interior and battery pack. This may be done by setting a time and desired temperature in the app, and the car will start heating the interior and battery pack on its own at that moment. Driving to a Supercharger: using the built-in navigation in a Tesla Model 3 will begin preconditioning the battery by heating it up via the motors ². Supercharger preheating: while a Tesla Model 3 is being charged at a Supercharger, the charger may also be used to warm up the battery. The battery pack receives electricity from the Supercharger, which can heat the battery before charging starts ³. These preheating techniques are created to assist in maintaining the battery's ideal working temperature, which can aid in increasing its effectiveness and performance, particularly in colder weather situations.

2. Research Questions

Does heating the battery under cold ambient temperatures help increase the range of the EV? Two core questions around the Modified Electric Blanket (MEB) and hot blowing air need to be answered: (1) Will the addition of an MEB or blowing air increase the range of an EV during winter months in Ontario, Canada? (2) Does the charging time decrease when the MEB or hot blowing air is applied?

3. Literature Review

Ji (2014) studied lithium-ion, or Li-ion, batteries under cold conditions. Preheating Li-ion batteries to room temperature, from subzero temperatures as low as minus 20°C, is proposed as a practical method or extending their range ⁴. Three types of heating were tested: self-internal heating from the EV battery itself, convective heating, and mutual pulse heating. The self-internal heating strategy heats the cell solely through internal resistance; heating is done inside the batteries. Convective heating of the cell required a closed system enclosing the flow channel, heater, fan, cell, and other control components; all heating was done within the battery pack. Mutual pulse heating utilizes cell output power and at the same time heats the cell internally, namely, to allow the cells to charge or discharge themselves ⁵. To complete these types of heating, Ji needed access inside the battery pack.

Peng et al. (2019) examined the performance issues of lithium-ion cells under unique conditions, including cold temperatures. While Ji (2014) used three methods of heating, Peng et al. (2019) studied six ways of heating the battery, including convective air heating, phase-change materials, alternative current heating, mutual pulse heating, internal self-heating, and liquid heating. Charging capacity was examined with different voltages. Internal heating methods are quick to heat the battery pack, low cost, and require little maintenance; this is what a Tesla Model 3 uses when going to a Supercharger. Air heating was found to be a poor solution because of a low heating rate and lack of uniformity. Liquid heating was found to be better than air heating because it is more efficient ⁶. One conclusion was that more heating methods should be developed to help lithium-ion batteries operate more optimally in cold conditions. Based on this recommendation, the current study attempted to use two different methods of convective heating to heat the battery pack from underneath.

Lei et al. (2015) reviewed preheating methods for lithium-ion battery packs in cold environments, one method was using a 240V source. A 240V source is equivalent to using a Level 2 EV charger. Their study occurred in a lab environment. One of the trials involved heating a battery pack for 15 minutes within a −40°C battery box with 240 V. Researchers found that the charge performance of the heated battery pack was significantly improved ⁷. A main conclusion was that battery cells should be heated to improve low-temperature performance. One limitation of this study was using constant temperatures for testing, this does not mirror the fluctuating ambient temperatures that apply to EVs owned by consumers.

Like Peng et al. (2019), Vu & Shin (2020) studied pre-heating methods, including heating by mutual pulse strategy. They used a testing temperature of -30°C. Findings indicate that mutual pulse heating using a 1S (second) charge was helpful for a battery to reach its top voltage quickly while not inducing lithium plating within the battery ⁸. A table is used to show how heat is applied, followed by a delay or timing control to obtain a balanced temperature. For example, a temperature of -30 °C is used with 558 seconds of heating followed by 39 seconds of delay to reach a balanced state. Vu & Shin (2020) conclude that pre-heating the battery pack in cold and unpredictable weather conditions is essential.

In a recent study by Recurrentauto.com (2022), a loss of range due to cold weather impacted EVs range. The study was conducted in 2022 and analyzed thousands of EVs in their dataset. Comparisons were made at 70°F versus freezing temperatures of 20–30°F. Findings included the Nissan Leaf SV Plus having a range reduction of 21% and the Ford Mustang Mach-E losing up to 30% of its range. A Hyundai Kona EV, which this study is utilizing, had an estimated 19% reduction in range ⁹. This study seeks to alleviate this reduction through the introduction of different heating sources.

Wang et al. (2018) examined how plug-in hybrid electric vehicles (PHEVs) functioned when battery pre-heating occurred via the engine or grid under low temperature conditions. Their study took place in China and used buses for testing. Convection heating was used for preheating. To determine success or failure, Wang et al. (2018) examined four areas, including the operating cost of a PHEV, including fuel cost, electricity cost, battery pre-heating cost, and battery degradation cost. Pre-heating helped reduce operating costs by up to 22.3% ¹⁰. All four areas benefited from applying a battery pre-heating process as the environment's temperature lowered.

A similar study to the current one, Wang et al. (2021) looked at an immersing preheating system (IPS) using a heat transfer fluid (HTF) between the batteries. Their goal was to optimize the battery lifetime and performance in cold weather. The study was completed using a simulator and does require access inside the battery pack. The battery pack was cooled down to − 28°C. Findings include that the IPS can achieve a high rate of temperature increase, which is up to 4.18°C/min, and a small temperature difference in the battery pack, which is less than 4°C ¹¹. Their experiment demonstrated and concluded it would take 11.0 minutes to preheat the battery pack from − 28°C to 25°C using the HTF in an IPS ¹².

As part of the Ferrier & Appiah-Kubi (2020) study on the optimization of an EV, hot air was forced under a 2017 Nissan Leaf EV to help increase range during trials. A regular electric dryer was used as the heating source for one hour per recharging cycle. The study took place in the springtime when moderate ambient temperatures were present. From 2016–17, Nissan Leafs employed a 30 Kwh battery pack, considerably smaller than those used in today’s EVs. They concluded that heating the battery during charging was beneficial to the operating range of the EV ¹³. Therefore, one conclusion was that future research should focus on adding an air flow heating source under an EV while recharging for multiple hours (using a Level 2 charger) to examine if it extends range under colder winter conditions.

4. Methodology

The data for this study was gathered throughout the winter months of February 6 to March 29, 2023. All data collected is from the Niagara Region of Ontario, Canada. The principal researcher owns the vehicle used in this study, a 2021 Hyundai Kona EV Preferred model. At the time of data collection, the EV had travelled roughly 51,000 kilometers (31,689.93 miles). Data gathering began outside on an asphalt driveway after 6 p.m., when the vehicle was plugged in. Each night, a ChargePoint Level 2 (J1772) home charger was used to recharge the battery to a State of Charge (SOC) of 90%. Before recharging began, ambient temperature was measured in Fahrenheit using the EV gauges as shown on the instrument panel. Data regarding the length of time to charge was recorded from the ChargePoint smartphone application on an Android phone.

The first part of this study relied on 13 trials of collecting baseline data and 13 trials of using the modified electric blanket (MEB). Thirteen were chosen based on the length of ‘colder’ temperatures in the geographical area. A minimum of 39 days were needed to complete the trials. Due to winter storm days and delays getting materials, a total of 46 days were required to complete the trials. The MEB is twin size 62"x 84" and has 4 heat settings (95-113°F) (see Figure 1). Only the highest setting of 113°F was applied during the trials. The MEB was purchased from Amazon. Prior to and during the entire charging process, the MEB was applied. Application of the MEB commenced after turning it on and waiting for 10 minutes (four trials), 15 minutes (three trials), and 30 minutes (six trials). Three trials of 15 minutes were attempted instead of four due to winter storms and time constraints. Six heavy duty muslin clamps, 4.6 inches long, or 11.43 cm, were used to attach the MEB to the EV. The end clamps were attached to the small mudflaps on the EV. Middle clamps were attached to small holes underneath the outer frame of the EV. Clamps held the blanket in place underneath the vehicle, slack was attempted to be removed, thereby keeping it close to the EV battery pack. Slack in the middle of the blanket was removed by adding a metal frame from a baby stroller with wheels.

The second part of this study used hot air from a standard electric dryer forced underneath the 2021 Kona EV Preferred. All trials were completed on a standard asphalt driveway on the end unit of a subdivision. For trials one through five, air was pumped under the vehicle for two hours while the vehicle charged using a Level 2 charger. For trials six through thirteen, fifteen minutes of pre-heating were used, followed by 45 minutes of heating, no heat applied for one hour, and then one more hour of heating. Figure 2 shows the four-inch diameter tube that was attached to the dryer; it is a total of eighteen feet. Figure 3 contains an overview of the tube. The tube was purchased from Amazon. No funding from any outside sources was provided; the principal researcher provided all funds.

5. Results and Discussion

Although the MEB and blowing hot air create a low heat transfer rate, their application had positive results. The result of the trials is that heating a battery pack from underneath will result in significant improvements in range. Heating the battery pack using the MEB and blowing hot air resulted in increased EV range. It also helps in creating a consistent starting range. The MEB is a good way to mimic the pre-heating of the battery pack found in a Tesla M3.

6. Descriptive Statistics

Table 1 illustrates relevant information gathered from February 5 to February 19, 2023, a total of 13 trials were completed. A balanced design was used throughout the study. The standard deviation of the starting temperature during baseline gathering is the largest amongst the three samples, thereby displaying a large fluctuation from night to night during this time of year.

Table 2 was created based on the first independent variable, the MEB. The charge time was reduced by 11.11% by using the pre-heated MEB; this is one benefit of using it. A much lower standard deviation of 4.77 ̊F (or 12.79%) for the starting ambient temperature occurred in a second set of trials while using the MEB. Based on a colder ambient temperature, Ending KM should be lower, not higher, based on how batteries react negatively to colder weather. A strong negative correlation occurs when ambient temperature is colder, and the Ending KM is reduced with no additional independent variable. The MEB increased the Ending KM even though the ambient temperature had lowered during trials. These results suggest that the process of introducing the MEB creates an increase in starting range.

Descriptive statistics for Table 3 are based on the second independent variable of blowing hot air underneath the EV, where the battery pack resides. Like Table 2, Table 3 provides a much lower standard deviation from the baseline temperature. The mean temperature in this sample was higher than previous trials. Ending KM is higher in a third sample than in the previous two trials. The charge time comparison from baseline to blowing hot air is one minute better for the latter, not a substantial difference.

As denoted in Table 4, there were an equal number of trials used for each of the factors. Within the table, the baseline is represented by 0, 1 is the MEB, and 2 is blowing hot air. All trials were grouped according to their independent variable, no differentiation was made for alterations in timing. Only differences between factors are shown (within subjects are shown in Tables 9 and 10). This study was conducted outside of the lab, and the colder weather was diminishing as springtime neared, thereby removing the ability to continually conduct trials. (See Methodology for more details.)

Table 5 indicates the initial comparison between subjects. A between-subjects analysis was conducted to examine if there were significant differences for each of the independent variables. The dependent variable is the Ending KM or starting range. There were significant differences found at the .001 confidence level, which created the need for a post hoc comparison test; a Tukey test was completed.

In Table 6, results from a Tukey test are shown. A Tukey test was completed to examine the significant results between the trials. A confidence interval of 95% was used for significance. As noted below, both blowing hot air and the MEB had significant differences from the baseline. However, there was no significant difference between blowing hot air and MEB. Both the MEB and blowing hot air increase the temperature surrounding the battery pack, which improves the range, just in different ways.

As shown in Table 7, a one-way ANOVA was conducted to examine if charge time was impacted by the MEB or blowing hot air. The charging time did not significantly decrease at the .01 confidence interval when the MEB, or hot blowing air, was applied to the battery pack. Also, significance could not be found at the .10 or .05 confidence intervals. There are multiple explanations as to why it did not decrease, including: (a) application of a heating source for the entire duration of charging did not occur, (b) there was not a wide range of temperatures during trials; (c) the amount of energy lost to heat during AC to DC processing may be lessened with the pre-heating of the battery pack, and (d) a level of 90% SOC was used as the limit, which lessens charging time.

Table 8 is a breakdown of the trials based on pre-heating and heating conditions using the MEB and forced hot air. Zero represents the baseline with no time applied from either of the independent variables. A one represents ten minutes of pre-heating with the MEB, followed by charging until a 90% SOC. As noted, all trials were completed at a final level of 90% SOC. A two represents 15 minutes, and a three had 30 minutes of pre-heating time with the MEB. The final two entries, 4 and 5, had 2 hours of continual heating and 1 hour of heating, 1 hour break, and 1 additional hour of heating, respectively. All 39 trials are represented.

Table 9 examines heating under five different timing scenarios versus the baseline. A comparison of five different timings with the MEB and hot air, as outlined in Table 9, led to significant differences. The dependent variable was the Ending KM or range.

A Tukey post hoc test, as shown in Table 100, was completed after significance was found in comparing different elements of time with the MEB and hot air blowing. Based on the Tukey test, significance was found between the baseline and 10 minutes of pre-heating using the MEB. No significant deviations were noted at the .05 CI between 15 and 30 minutes of pre-heating compared to the baseline. These findings could be explained by the limited trials of 3 and 4, respectively, plus the vast temperature fluctuations with the baseline trials.

Blowing hot air for an hour followed by a break, and then another hour of hot air created a significant difference from the baseline, 15- and 30-minute pre-heating, and continuous heating. This strategy appears to have had the best results. Results can be explained by how charging speed slows as the battery nears 90% SOC. Range is expanded at the end of charging due to the application of heat; it isn’t aided by the continuous heat because it’s terminated before the final stage of charging is reached. This finding was consistent with the Ferrier & Appiah-Kubi (2020) study. Like blowing heat with an interval in-between, the MEB heats until the end of charging. Although 15 and 30 minutes of MEB pre-heating did not show significance at the <.001 confidence interval, it was significant at the .05 level. Again, the lack of trials can explain the varied results after 15 and 30 minutes of pre-heating.

7. Conclusions

To increase the range of the EV, two additional external heating sources were used and found effective. These methods can be used when charging at home, as opposed to using power from the EV battery itself to heat the battery while driving to a Supercharger, as is the case with the Tesla Model 3. Charging at home and adding an external heat source will not affect range while driving but will increase starting range and reduce the need to recharge. Using an MEB or blowing hot air helps in creating a consistent starting range each day and is not adversely affected by plummeting temperatures.

Blowing hot air for an hour followed by a break (break method), and then another hour of hot air does increase the range of the Kona EV used in this study. Applying blowing air in a continuous manner for two hours does not increase range. Like the hot air with a break, pre-heating using the MEB is an effective way to increase the range during colder weather in winter months. It is advantageous to add an external heating source for added range if it is done in the break method or pre-heating option.

Charging time is an important factor related to the operation of EVs. The charging time did decrease when using the pre-heated MEB, but not significantly. As noted, the charge time comparison from baseline to blowing hot air is one minute better for the latter, not a substantial difference. Applying the MEB and blowing hot air did not decrease charge time in this case study.

The results from this study are generalizable to countries with colder climates. The MEB, with its current design, is a useful way to increase range in winter weather. However, re-engineering the MEB is needed to create a permanent solution for binding to an EV. An MEB with a tighter fit should aid in increasing heat closer to the battery pack and add uniformity to where heat is applied, thereby adding range to the EV. Additionally, it will limit air flow between the MEB and EV, which will increase direct heat to the pack. Engineering an MEB prototype to be used with various EVs will be a follow-up task for this study.

There were significant results from adding hot, blowing air underneath, but there is little control when conducted outside in a driveway. Uniformity in the applied heat would be more useful for consumers to predict future range. Blowing hot air affects a small portion of the battery pack in a mid-size SUV such as a Kona EV. A larger diffusion of the heat at the tube's exit point may help increase heating in larger EVs.

There are three recommendations for future research based on the above findings. Although untested, the study results could possibly apply to plug-in hybrids too; this is the first recommendation for future research. Another is to apply hot air in a confined or controlled environment, such as a garage, to limit cross winds. A final idea to help understand the impact of hot, blowing air is to try it out on both smaller EVs, such as a Nissan Leaf, and larger EVs, like a Tesla Model X.

References