The project investigated how the waste heat generated during ultra‑fast charging of battery electric vehicles can be captured and reused, while simultaneously ensuring reliable and comfortable battery cooling. A detailed process simulation was carried out with the IPSEpro software, integrating a compression refrigeration cycle that supplies the cooling required for the vehicle battery. The refrigeration system was designed in close coordination with the CoolEV project partners, who supplied the specifications for the required cooling capacity and the electrical power available for the charging station.
The simulation considered two cooling concepts. In the first, a conventional free‑cooling scheme uses ambient air to condense the refrigerant, with the resulting heat being expelled through a forced‑air condenser driven by fans. This approach is highly dependent on the ambient temperature and the charging power; higher summer temperatures increase the temperature differential between evaporator and condenser, thereby raising the energy needed for cooling. In the second concept, the refrigeration machine is operated as a heat pump. The heat extracted from the battery is transferred to a low‑temperature heat sink, which can then be used for domestic hot water, space heating or feeding a district heating network. This dual‑function approach allows the same electrical energy to provide both cooling and useful heat, improving overall energy efficiency.
To evaluate the feasibility of the heat‑pump concept, a heat buffer was introduced into the external vehicle cooling loop. The buffer decouples the instantaneous heat removal from the battery from the heat extraction by the heat pump, allowing the system to store excess heat and release it when the demand for low‑temperature heat rises. The simulation also explored a bypass of the evaporator, whereby a portion of the refrigerant stream is diverted before the evaporator and mixed with the superheated vapor after the evaporator. Although this bypass reduces the heat absorbed in the evaporator, the results showed that it does not provide adequate control over the cooling capacity, and therefore was not adopted in the final design.
The choice of refrigerant and compressor was guided by the need for low global warming potential (GWP) and suitable pressure ranges. R410a and R454B, while common, require pressures above 30 bar, demanding large compressors. Natural refrigerants such as R290 (propane) and R600a (isobutane) were considered, but suitable scroll compressors were only available for R290 from Emerson. Because variable‑speed compressor data were not available, the simulations used fixed‑speed scroll compressors, which deliver a constant volumetric flow and a fixed cooling capacity. A generalized polynomial model for compressor efficiency was developed to capture the performance across the operating range.
The project also integrated traffic data to estimate the number and timing of charging events at a simulated charging park over a one‑year horizon. This allowed the simulation to account for realistic load profiles and to assess the cumulative amount of waste heat that could be harvested. The results indicate that the waste heat from ultra‑fast charging can contribute significantly to local heating demands, potentially offsetting a portion of the energy required for domestic hot water or space heating.
The work was carried out from 1 January 2020 to 30 June 2023 under a grant from the Baden‑Württemberg Ministry of Science and Research (ZSW, grant number 01MV19005D). The project team, led by Dennis Huschenhöfer (contact dennis.huschenhoefer@zsw-bw.de), collaborated with the CoolEV partners to define the technical requirements and to validate the simulation results. The findings provide a quantitative basis for integrating waste‑heat recovery into future fast‑charging infrastructure, supporting the development of more sustainable electric mobility solutions.