Schwalmstadt, Germany-based Konvekta, a global manufacturer of bus air conditioning and heating systems, has reported energy savings and emission reduction from an articulated electric bus in Nuremburg, Germany, which features two CO2 heat pumps, in the front and rear sections, for heating and air conditioning.

The articulated electric bus – which comprises two or more rigid sections linked by a pivoting joint – has operated on German public transport routes since that start of 2020, according to a Konvekta press release. Konvekta describes this as the world’s first installation of CO2 heat pumps in an articulated electric bus.

Its two UltraLight 500 CO2 heat pumps 2.0 include “two energy carrier modules for hot and cold water, and both systems run on the refrigerant CO2,” according Konvekta..

Savings and Emission Reduction

The two heat pumps have reduced costs and emissions for the operator, VAG Nuremberg transport company, said Konvekta. Annual costs for heating and cooling using the CO2 heat pump are slightly less than €1,500 (US$1,695). By comparison, the annual cost of running a heat pump with R134a refrigerant (plus electric heater) is slightly less than €3000 (US$3,390.33).

Likewise, the CO2 heat pump produces just over 4,000kg of CO2e emissions, compared with more than 9,000kg of CO2e emissions  for a heat pump featuring R134a plus electric heater.

The heating energy is “sourced from the ambient air and not from fuel or electricity,” said Konvekta. “To obtain 100% heat, the Konvekta CO2 heat pump needs at best only 25% operating power (current) from the battery.” The thermodynamic cycle from the ambient air supplies the rest of the necessary energy.

At -10°C (14°F), the CO2 heat pump consumes “45 kWh electric energy per 100km (62.13miles) in contrast to conventional electric heating components that consume more than 100kWh for the same distance,” Konvekta said.

Meeting the Challenge of an Articulated Bus

Due to the approximate 18m (59.05ft) length of articulated buses, thermal regulation in the entire space is a challenge.

To meet the challenge, the batteries’ temperature control was integrated into the thermal management system, “because batteries need an optimal operation temperature frame to reach the maximum range and lifetime,” said Konvekta.

Networking between heat pump systems is also necessary to ensure optimal temperature control.

“The brain of the CO2 heat pump system is a specially developed intelligent control unit,” said Konvekta’s Head of Marketing, Claudia Mittelstaedt. The control unit within the bus responds to the environment around it rather than operating by fixed parameters. “Air quality, battery temperature, outdoor temperature and other influencing factors are acquired, evaluated and the air conditioning unit is adapted optimally.” 

This avoids energy loss and results in efficient and demand-based air conditioning, according to Mittelstaedt.

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