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Hyundai and Kia’s EV Heat Pumps a Benchmark for Other Brands

2020-07-13

The Hyundai Kona Electric recently received top range marks at a Norwegian test of EVs in frigid conditions, and the secret to its success is the brand’s high-efficiency heat pump technology. We discussed the excellence of Hyundai and Kia’s EV heat pumps, the world’s first of its kind, with the engineers responsible for their development.

You have surely once felt that your smartphone batteries run out faster during winter. This is not just a feeling; scientifically, low temperature increases the lithium-ion battery’s internal resistance, effectively reducing its energy efficiency. The same principle applies to electric car batteries. Come winter, the EV range (distance traveled by car on a single charge) tends to go down sharply from its ordinary levels. The problem is compounded by the fact that winter months also require cabin heating, the energy for which is spent from the battery.

This wintertime shortcoming of EVs was long considered inevitable—until now. Hyundai and Kia’s new high-efficiency heat pump system has managed to drastically reduce the loss of efficiency in low temperatures, and it has been hailed by many experts—including Tesla CEO Elon Musk—as the newest innovation to the modern EV. Currently, many other manufacturers are hastening to adopt the technology themselves.

The Hyundai Kona Electric’s high-efficiency heat pump system allows it to maintain its world-class range even during winter.

Heat pumps help EVs overcome their inherent limitation concerning heating. Internal combustion engine vehicles can use the profuse amount of heat energy produced by the powertrain to heat the cabin; EVs’ electric motors, on the other hand, do not alone produce enough heat for heating, so EVs must extract the electric energy from the battery for the heating purpose. This, consequently, leads to a significant reduction in range during winter. But with the innovative heat pump technology, Hyundai and Kia’s EVs boast an efficient heating system that manages to preserve their normal range during winter. It has significantly improved upon available heating pump technologies by recycling the “waste heat”—the heat released by the EV’s electronic parts.

Seeking more insight into the technology’s excellence, we met the engineers responsible for its development. Advanced Chassis Development Team’s Global R&D Master Kim Jae-Yeon, Cooling Engineering Design Team-1’s Part Leader Park Nam-Ho, and Senior Research Engineer Cho Wan-Jae have joined us for an interview. Here’s what they had to say about their proud creation, the world’s most efficient EV heat pump system.

Kia Motors first introduced the heat pump technology on the Soul EV in 2014.

Q. Heat pumps were first applied to the Soul EV in 2014. What led you to introduce this technology to EVs?

EV consumers’ biggest concern has always been its relatively short range. And these concerns are only amplified during winter months, when turning on the heat reduces the range by 30 to 40%. That’s a lot, right? Heaters use that much energy. We did a survey of EV drivers in 2014, and one major finding was that many were driving in the cold without using heating, worried that the heater may exhaust the battery. We felt this was too large an inconvenience to overlook, so we addressed the issue by developing the heat pump technology and introducing it to the Soul EV in 2014. We don’t know the precise effect of the system because the Ministry of Environment’s EV range measurements were only conducted at room temperature—but the Ionic Electric might serve as a reference point since its motor structure and battery capacity are similar to those of the Soul EV. For the record, the Ionic Electric showed a 19% improvement in wintertime range reduction after being equipped with the heat pump.

The engineers responsible for the heat pump’s development: from left, Senior Research Engineer Cho Wan-Jae, Global R&D Master Kim Jae-Yeon, and Part Leader Park Nam-Ho.

Q. In basic, how does the heat pump work?

The operating principle of the heat pump system is similar to that of an A/C unit—the refrigerant undergoes compressing and condensing to raise its temperature, or undergoes expansion and evaporation to lower its temperature. A/C uses the low-temperature refrigerant to generate the cool airflow, and the heat created by condensers are released via the outdoor unit. This familiar blueprint exists in the heat pump system as well, except that the heat, instead of being released to outside, is being utilized for cabin heating. In summary, the heat pump subjects the refrigerant through a repeating cycle of compression, condensation, expansion, and evaporation, and uses the accompanying high and low temperature for both heating and cooling purposes.

The figure above shows the heat pump system’s operating principle. The “waste heat” originates from the electronic components like the motor, OBC (On board Charger), and EPCU (Electric Power Control Unit), but this heat alone is not hot enough to reach 40℃, a threshold necessary for cabin heating. So it is used, instead, to heat the cooled refrigerant—and in devising this system, we could not only increase the efficiency of the heat pump but also manage to cool the battery as well. This efficiency increase is perhaps better shown through actual numbers—the compressor creates 1 kW of heat, and the cycling refrigerant culls 1.5 kW of heat from external sources. That’s a lot of heat to gain from the small amount of electricity needed to run the heat pump system.

Q. The heat pump system has now become an industry standard—Tesla in the U.S., as well as many Japanese and European EV manufacturers, use it on their cars. What differentiates Hyundai Motor Group’s heat pump from the competitors’ heat pumps?

The heat pump system was actually pioneered by Nissan, who applied it to the Nissan Leaf in 2012. The BMW i3, Volkswagen e-Golf, and Kia Soul EV (1st-gen) and Hyundai Ionic Electric soon followed. But not all heat pump systems are equal—numbers show that Hyundai’s heat pump system outshines the competitors’. The Korean Ministry of Environment has kept track of EVs’ winter range data since 2018, and I’ll refer to its 2020 data here. The winter range of the Ionic Electric, which was equipped with our first-gen heat pump system, boasted 76% of the normal range, compared to 67% of the Nissan Leaf and 64% of the BMW i3. That’s a pretty significant difference in favor of the Ionic Electric.

And that difference can be explained by the difference in technological prowess. More specifically, we might discuss the range of heat sources utilized by the system. Our competitors’ heat pump systems merely gather heat from the outside air, but as there isn’t much heat available in the cold wintry air, the whole process is rendered inefficient. On the other hand, Hyundai and Kia’s system additionally uses waste heat from the aforementioned electronic components—that is, the heat generated by simply running the car is recycled for the heat pump’s purpose, contributing to the efficiency increase. Indeed, the “waste” heat isn’t so wasteful when it is given a new purpose.

Global R&D Master Kim Jae-Yeon explains the development process of Hyundai and Kia’s heat pump system.

Q. From the original Soul EV to the present-day Kona Electric, how would you trace the development of the heat pump system?

Largely, it’s been about expanding the sources from which the system gathers heat and making the process of gathering more efficient. As I said, the heat pump system first introduced on the Nissan Leaf in 2012 only gathered heat from the outside air. The 1st-gen Soul EV expanded the heat sources to include the electric motor and inverter, which marked it as the industry’s first multi-source heat pump system. The most recent high-efficiency heat pump on the Kona Electric expanded the sources even further, taking advantage of the waste heat from the battery and the slow-charger.

Of course, we are still improving the heat pump system for our next-gen EVs. For improving heating performance, we are designing it generally to more aggressively utilize the heat from the outside air. For improving the A/C, the condenser is being upgraded to improve both cooling power and efficiency.

The idea for the heat pump system came from a dilemma of excessive heat generation.

Q. Any interesting episodes during the high-efficiency heat pump’s development process?

I suppose it is interesting that we did not actually set out to develop a more efficient heat pump from the beginning. The idea came from thinking outside the box. We were developing the Kona Electric, which had a battery capacity of 64 kWh, a 25.7 kWh increase from the Ionic Electric’s (38.3 kWh). While this did lead to an appreciable range increase, another problem arose—too much heat generated by the larger battery. So we had to come up with a more powerful and efficient way to cool it, and a Eureka moment came while we were in discussion. One team member said, “Couldn’t we use this excess battery heat for our heat pump?” It was a brilliant idea, and we went into the R&D process to realize it. The new high-efficiency heat pump on the Kona Electric is clearly more efficient than our previous heat pumps.

Another aspect that might be interesting is that we were not certain about the technology’s feasibility; put another way, we were uncertain whether the market will care about the winter range metric. Up to 2017, the EV range was exclusively measured in standard room temperatures, and there wasn’t even an index for EV’s winter range—not even for the experts, not to mention the consumers. On top of that, there simply weren’t that many EVs equipped with heat pumps at the time; the Tesla Model S then had the longest range of all EVs, but it didn’t have a heat pump onboard. But considering the Korean weather—with four well-defined seasons—and the diversity of the global market, we thought it worthwhile to keep on developing the heat pump system, even if it meant just serving the niche consumers. But the result wasn’t so niche; it was a wild success. Hyundai and Kia’s EVs have been receiving not just domestic but international plaudits, and EV winter range has become an important metric with which to judge EV performance. We are very proud; we could not have expected more when we were starting out.

The high-efficiency heat pump system, applied to the Kona Electric.

Q. The Tesla Model Y received some attention of late for improving its winter range by applying the heat pump system of its own. What is the difference between the Model Y’s heat pump system and Hyundai and Kia’s?

A precise comparison is difficult, as the Tesla Model Y hasn’t been released yet in Korea. But we could learn some differences upon reviewing Tesla’s patent publication on the technology. The two systems are similar in that they both use the outside air, electronic components, and battery as sources of heat. But the Kona Electric’s heat pumps are smarter in selecting among the sources. Depending on the driving status of the vehicle, the heat generated by the motor, battery, and other electronic components vary; facing this variation, the Kona Electric knows to selects the most efficient source of heat for its heat pump, whereas the Tesla Model Y seems to lack this ability. This difference translates to actual numbers: the Tesla Model Y with the heat pump system improved its winter range by 10% compared to the equivalent model without it. For the Kona Electric, that figure is 18%. It’s quite a bit more efficient than the Model Y in that regard.

The next-gen EVs will, the developers say, be equipped with the next-gen heat pumps.

Q. How will Hyundai and Kia’s heat pump system continue to evolve?

Mainly in two directions. The first direction is increasing the efficiency of the system, in general, to save the electricity it consumes from the battery. We’re investigating various new heat sources and seeking to add some complexity to the refrigerant cycle—all to achieve greater efficiency. The second direction is to modulize the system. Currently, the heat pump components are scattered in different places of the car, depending on the model, but we will ultimately combine those parts into a single module. We’re in the process of developing a one-box module heat pump system, whose efficiency and ease of mass production will allow us to spearhead the movement toward the smart mobility era of the future. These next-gen heat pump technology will be showcased in Hyundai and Kia’s next-gen EVs. For us, and for the consumers, too, that’s something to absolutely look forward to.