CO2 (R744) mobile heat pumps are making inroads in the European electric-bus markets, with German manufacturer Konvekta expecting to have 1,000 units installed by the end of 2021.

That was the message from Björn Kern, Head of Konvekta’s Technical Application Department, who participated in the transport and MAC session at the 2021 ATMOsphere Europe Summit, which took place online on September 28-29.

“Customers are happy, and we expect it to go forward also next year,” Kern said. “I think that by the end of 2022, we will have at least 1,800, and if we are lucky, 2,000 units, in the field.”

The main market for CO2 heat pumps in e-buses is Germany, with cities like Berlin (122 installations) and Hamburg (43) being major customers. Countries such as the Netherlands and Luxemburg are also starting to join in. The ambient- temperature range of the Konvekta units encompasses -20°C to 43°C (-4°F to 109.4°F).

Konvekta is also installing its heat pumps in traditional diesel buses.

The CO2 heat pumps from Konvekta can switch from heating to cooling, and consist of an air-to-air circuit and an air-to-water circuit.

Increasing driving range

Konvekta’s control system is “complicated,” with 12-15 sensors placed around the vehicle, Kern noted. This allows temperature control to be “very efficient.” In addition, the sensors enable the system to calculate power values, giving information about compressor speed, and determining whether the demand is high or low. The system is optimized to constantly deliver the best possible coefficient of performance (COP), Kern said.

In other words, the control system “becomes very, very important, and is one key point of success to have a good range of the electric vehicle,” he noted.

A test conducted in February this year compared two e-buses in Berlin, one with the Konvekta system installed, and one with a regular AC unit and an electrical heater. The bus with the Konvekta system used 0.38kWh/km (0.61kWh/mi) for the heating system, while the bus with the traditional system employed 0.9kWh/km, Kern said.

For these two e-buses, the difference meant that the bus with the Konvekta unit had a range of 151km (94mi) on a charge, whereas the traditional bus managed a range of 114km (71mi). Konvekta is still working to improve the efficiency even further.


Together with one of the company’s big customers, the city of Berlin, Konvekta is also looking into pre-conditioning, a system that will enable bus companies to power up the system remotely to create a comfortable environment in the bus from the beginning of the day.

The idea is that “they are monitoring the weather forecast, saying, ‘ok, tomorrow morning we are starting at 6 am and the weather will be 5°C (41°F).’ That means we need to start pre-conditioning at 4:30 am, and then we send out a signal from the control center to all buses to start up the system at that time,” Kern explained.

“This sounds like science fiction, but this will become a thing in the next two years,” Kern said. “It’s always about energy management and charging.”

“I think that by the end of 2022, we will have at least 1,800, and if we are lucky, 2,000 units, in the field.”

Björn Kern, Konvekta

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