Heat2Comfort - Waste Heat-based Air Conditioning of Fuel Cell Multiple Units

In addition to electrification, the decarbonization of railroad transportation also includes the use of alternative power sources such as fuel cells, especially for regional transport lines that cannot be electrified.

In the joint project "Heat2Comfort", the minimum range of fuel cell powered trains is to be increased by 20 % through a new approach to using waste heat for vehicle air conditioning. The aim is to improve passenger comfort from both a thermal and acoustic perspective. The central idea behind this new approach is to effectively utilize the waste heat from the fuel cell to regulate the temperature of the vehicle cabin. A predictive and adaptive air conditioning control is to be implemented in this system, which consists of complex dependencies, in order to achieve the highest possible degree of utilization of the waste heat.

On this basis, the new concept of media-fed thermal activation for railway vehicles can be used for the first time. Heating the medium via the cooling circuit of the fuel cell enables warm surfaces in winter operation with an extremely low supply of electrical energy. Another innovation is the cooling of the medium and thus the thermally active components in summer operation by an absorption cooling machine. Additionally, this system is driven by the cooling circuit of the fuel cell, which means that the waste heat can also be used for interior air conditioning during summer operation. Furthermore, this system does not require a cooling compressor, which results in much quieter operation.

Thermally active interior components (TAIKs) enable significant energy-saving effects while ensuring a high level of thermal comfort. The use of innovative, cellular metallic materials (ZMW, metal fiber structures) is intended to enable uniform and rapid temperature distribution on the surface of the compartment.

The work at Fraunhofer IFAM Dresden includes the thermal investigation of different TAIK variants (including floor elements and ceiling elements) and the design using numerical simulation as well as the construction of several TAIK elements to carry out comfort tests in a mock-up.

The fuel cell serves as the vehicle's primary energy conversion system for traction and ancillary operations. The provision of waste heat can therefore not be primarily matched to the heat requirement of the air conditioning system, which is why the integration of a thermal storage unit is necessary, e.g. to bridge standstill times of the train at stops. A novel approach for this is the integration of a latent heat accumulator in a heat exchanger similar to a hydraulic switch as a thermal switch, which enables high transfer performance with high storage capacity and low installation space requirements.

The work at Fraunhofer IFAM Dresden includes the development of such a thermal switch using innovative, cellular metallic materials (metal fiber structures), the selection of the storage material, the numerical investigation of the heat transfer behavior and the construction and experimental characterization of a demonstrator.