ATEX-WP

Based on the results of the earlier German Invest BW project “Sol2Power” (grant number BW1_2080), a prototype of a refrigerant-free heat pump, thermodynamically based on the innovative ATEX cycle, is to be developed and tested.

The ATEX cycle is a pure compressed air process, which is based on the total expansion of compressed air (Air Total Expansion).

Compressed air processes are already deployed for the air conditioning of aircraft and trains, where turbines are exclusively used for compression and expansion. However, for application in a heat pump, the efficiency of turbines is too low.

The innovation of the ATEX heat pump lies in implementing the thermodynamic process – fundamentally identical in heat pumps and refrigeration systems – by means of reciprocating piston machines. This requires for a thermal power of around 3 kW compressing volumetric air flow rates of approximately 10 cubic meters per minute to about 1 bar overpressure and subsequently expanding them back to ambient pressure (total expansion of the compressed air). Conventional compressed-air motors reach very low efficiencies at low pressures and high volumetric flows, and they are not suitable for expanding compressed air down to ambient pressure. The pre-developed membrane piston machine has been specifically designed for this purpose and, for the first time, enables the realization of a compression heat pump without typical refrigerants. This technology has the potential to compete with, or even surpass, conventional refrigerant-based heat pumps, particularly when high output temperatures are required.

All available refrigerants for compression heat pumps are climate-active and/or flammable, require high pressures in the refrigerant cycle and the installation of the heat pump or evaporator outdoors. The development of a competitive heat pump without typical refrigerants would lead to a new era in heat pump technology and additionally open up new market segments where heat pumps with outdoor units cannot currently be used such as for the retrofit of buildings in urban areas.

09/2025 - 08/2027

Scientific project partner: 

Institute for Building Energetics, Thermotechnology and Energy Storage (IGTE) at the University of Stuttgart, Germany

Industrial project partner: 

Alfred Hermann GmbH & Co. KG

The project “ATEX-WP” is funded by the Ministry of Economic Affairs, Labour and Tourism of the State of Baden-Württemberg through the project management agency VDI/VDE Innovation + Technik GmbH under the grant number BW7_2149. The authors express their gratitude for the support and take full responsibility for the content of this publication.