Optimal heating in e-buses: the role of high-voltage heaters

As the electrification of larger vehicles advances, thermo management becomes crucial. Traditional vehicles utilized engine heat for temperature regulation. However, this mechanism is absent in pure electric variants, like the e-bus. To ensure a frost-free windshield, a cozy interior, and a well-regulated battery temperature, HVHs are essential. Given the larger mass to heat compared to regular cars, the technical challenge lies in developing highly efficient HVHs, aiming to keep energy consumption minimal. 

Depending on the vehicle requirements, Webasto offers high-voltage heaters with voltages of 400 V or 800 V. "Especially commercial vehicles such as buses, trucks, or construction machinery have high energy consumption. Higher voltages are the key here, as they allow for lower currents," explains product manager Ulrich Vohrer. Webasto was the first company in the industry to introduce high-voltage heaters with 800 V into serial production to optimize power consumption.

Integration of high-voltage heaters in e-buses

Correct placement and integration of HVHs are pivotal for the efficiency and electric thermo management of an e-bus. Medium-sized e-buses, for instance, use up to three HVHs, while articulated buses may use up to five. They are often located where traditionally the engine was. Batteries are typically housed in these areas.

“There are various ways to integrate HVHs in e-buses,” Vohrer points out. “Through specific circuits, they can heat different bus zones. HVHs use coolants to regulate convectors or front boxes. The resulting warm air then flows either actively or passively into the bus interior.”

Beyond interior heating, high-voltage heaters are crucial for battery and power electronics conditioning. “The battery and its associated wiring operate most efficiently at an optimal temperature of around 25 degrees,” emphasizes Vohrer. “Using heat exchanger and precise control electronics, consistent battery temperature can be assured.”

What makes a high-voltage heater efficient?

What makes a good HVH (High Voltage Heater)? A key factor is efficiency: "In the cold months, heating e-buses can account for up to 30-40 percent of energy consumption and significantly reduce the range. An inefficient conversion process exacerbates this problem even further," explains Vohrer. Webasto has developed an innovative heating technology for this: "By directly spraying the heating element onto the heat exchanger, we convert almost 100 percent of the energy into heating performance. Combined with precise control electronics, we achieve significantly higher efficiency than other technologies. Our customers benefit from this as energy consumption is minimized, and thus the range is increased."

Since HVHs heat immediately without start-up currents, they can also convert recuperation energy directly into heating performance. "Some of our customers 'overheat' the coolant while charging and can thus heat the first kilometers without battery energy," says Vohrer.

In addition to efficiency, safety plays a central role, especially when dealing with high voltage and in the context of cybersecurity. "Our HVHs are equipped with sensors that monitor various parameters, such as temperature, voltage, and currents. The Webasto HVHs are certified according to ASIL (Automotive Safety Integrity Level), with the HVH 120 even achieving the highest safety level ASIL D. This ensures safe operation even when sleeping in the vehicle. Furthermore, all hardware and software components are often designed redundantly." Referring to cybersecurity, Vohrer adds: "Our latest HVH generation meets the highest security standards and ensures that the system neither poses a threat to the vehicle nor can be externally manipulated."

Applications of HVHs and new developments

The high-voltage heaters from Webasto are already in use in various electric buses, trucks, construction vehicles, ambulances, fire trucks, and electric airport vehicles. At Busworld Europe in October 2023 in Brussels, Webasto unveils the next generation of its high-voltage heaters. “The new HVHs are more compact and powerful. Moreover, LIN and CAN expand communication options with the vehicle,” reports Vohrer. The HVH 120 model surpasses the standard HVH 100 model with an additional 2 kW performance at 12 kW and also boasts an extended lifespan: “Our heating elements are highly durable - we guarantee a lifespan of 15,000 hours, but our goal is 25,000 hours.”

Even though high-voltage heaters mostly operate invisibly in the background, they remain an essential component in the world of electric vehicles. Concealed yet powerful, they play a significant role in making the electrification of large vehicles feasible and comfortable. These foundational technologies are what differentiate and shape the electromobility of tomorrow.