The NEKKA project set out to create a new vehicle climate control system that relies on the elastocaloric effect instead of conventional vapor‑compression cycles. The main technical goal was to achieve higher energy efficiency, measured by the coefficient of performance (COP), while also reducing the system’s size, weight and cost. To reach this, the project focused on four key areas: development of corrosion‑resistant, long‑term stable nickel‑titanium shape‑memory alloys; simulation‑driven design of the elastocaloric subsystem and the complete prototype; creation of a dedicated test rig and measurement infrastructure; and, originally, validation of the system in a real vehicle.
The alloy development produced a functional material that can be integrated into a hub element, the core of the elastocaloric unit. The material’s thermomechanical properties were characterized and fed into a Modelica/Dymola model that represents a conventional mobile climate and heating system using R‑744 as the working fluid. This reference model provided baseline values for cooling and heating power as well as COP across a range of ambient temperatures and humidities. Statistical analysis of German and European weather data, combined with typical vehicle usage patterns, yielded a temperature cluster that covers 99 % of German and 96 % of European trips between –10 °C and 30 °C. Using these data, the project estimated the total energy consumption of the reference system over a 15 000‑hour life cycle, assuming 11 000 hours of driving and 4 000 hours of charging. Two performance scenarios were examined: a minimal power case of 2–3 kW and a maximal case of 3.2–7.5 kW. For a 300 000‑km vehicle with a consumption of 19.3 kWh per 100 km, the total energy use of the heating and cooling system was calculated to be 57 900 kWh. This represents roughly 14–24 % of the vehicle’s overall energy consumption in Germany, a figure that is comparable or lower than that of conventional systems.
Parallel to the material and simulation work, the team designed a test bench that incorporates the elastocaloric unit as a functional model unit (FMU) within the overall climate system model. Sensors and measurement devices were selected to capture temperature, pressure, and power flows, enabling a first control strategy to be implemented and evaluated in simulation. The simulation results confirmed that the elastocaloric subsystem can deliver the required heating and cooling loads while maintaining a COP that is competitive with, or superior to, the reference R‑744 system.
The project was carried out by TLK‑Thermo GmbH, headquartered in Braunschweig, under a grant from the German Federal Ministry of Economic Affairs and Climate Action. The project ran until September 2023, with the final report published in February 2024. While the original plan included installing the prototype in a test vehicle for on‑road validation, the final report focuses on the laboratory and simulation achievements. The outcomes provide a solid basis for further development toward a production‑ready elastocaloric climate system that could offer significant environmental and economic benefits for electric vehicles.