Tenure Track Assistant Professor at the EPFL Neuchâtel Branch

Born in 1974

Lives in Bern


Jürg Schiffmann was born in Italy. His parents returned to Switzerland when he was 13 years old. When he left school, he hesitated between going on to study medicine or mechanical engineering. He finally opted for the latter, gaining a degree from the EPFL in 1999, and subsequently spent a year and half in Écublens working for Nextrom. Having lost interest in his work, he launched a start-up with his EPFL professor, Professor Daniel Favrat. Together, they sold and promoted gas-lubricated bearings technology used in mechanical guidance, where a rotating component floats with no solid-to-solid contact on a layer of air generated by the rotating shaft. After five years, the three associates were keen to head in different directions, and the company was liquidated. Jürg remained in close contact with Professor Favrat, and decided to write a thesis on micro-turbocompressors “just for the fun of it”. The concept: to replace the bulky volumetric compressors fitted into heat pumps. While preparing his thesis, he met a former classmate working for Fischer AG, a producer of high-speed machine spindles used to rotate cutting tools. He joined a sister company, “Fischer Engineering Solutions”, the aim of which was to broaden the company’s technological knowledge and transfer this expertise to other markets. In 2008, after completing his thesis and being awarded the “Swiss Electric Research Award”, Jürg expected to spend his career working for this company. But he was contacted by the Massachusetts Institute of Technology, which offered him a postdoctoral research position. He accepted the offer, with his boss approving a year of sabbatical leave. When he returned to Switzerland in 2013 he accepted a professorship at the EPFL, immediately moving to Neuchâtel, to work first in the CSEM’s laboratories and then in the EPFL’s building at the Microcity Innovation Hub. Jürg particularly values being able to collaborate with the region’s microtechnology sub-contractors as it gives him a significant head start with his research projects. These are internationally recognised; he is currently working on assignments with companies based in Germany, Canada and also in Switzerland. Jürg is now a tenure track assistant professor working with around 20 colleagues, including HES engineers, and doctoral and post-doctoral students. Interview.

Why use a turbocompressor instead of a volumetric compressor in a heat pump ?

A volumetric compressor works as follows: a chamber draws in gas by increasing its volume, then shuts. A decrease in volume increases the pressure. Once the system has reached the right pressure, valves open and the gas is forced into the heat pump, which is a closed circuit with a refrigerant. There are two problems with this form of technology:

  1. Oil is used to minimise friction and limit the internal leakage of refrigerant. Yet when the gas is forced out, a small quantity of oil is forced out too. The oil enters this closed loop, sticks to the surfaces and decreases the efficiency of the heat exchangers.
  2. To prevent the compressor from running dry, the outgoing oil needs to be redirected back to the compressor. This leads to load losses in the return pipes and therefore losses in the cycle.

The turbocompressor uses a completely different technology, and one similar to that used in turbo-diesels in cars. Pressure is increased by a wheel formed of ducts and blades. When the wheel turns, the blades transfer work to a fluid, thereby increasing the pressure. By combining this wheel with gas bearings, it is possible to avoid the use of oil, which escapes into the heat pump’s circuit when a volumetric compressor is used. This improves the system’s performance by 20 to 30%.

turbocompresseur neuchâtel epfl

What are the other advantages of using a miniaturised turbocompressor in a heat pump ?

Heat pumps are currently about the same size as a large washing machine. In this machine, there is a 50 cm high x 30 cm diameter compressor that weighs 30 kg. When you use a turbocompressor, the compressor is the size of a can. In addition, a compressor’s characteristics mean it can be adapted to domestic energy requirements. When it gets colder, the compressor turns faster and vice versa, without shutting down, unlike a volumetric compressor. Consequently, the energy consumption associated with restarting the heat pump is reduced.

What other applications have you developed with this technology ?

We are working on a project to recover heat in combustion engines. In a lorry, engines have a yield of around 30%. The rest of the fuel energy escapes into the atmosphere in the form of heat. However, this heat can be recovered by a turbine and converted into energy to pull the lorry, auxiliaries and even power the lorry’s cold unit, thanks to a thermodynamic cycle called the “organic ranking cycle” (ORC). This system has reduced a lorry's diesel consumption by 5 to 10%.

We have also worked with two Swiss companies to replace a car’s engine by a fuel cell with hydrogen storage in the boot. With this type of fuel cell, the air injected into it must be extremely clean, with no hydrocarbons or oil. And a turbocompressor running on gas-lubricated bearings makes this possible. Overall, the car can operate for 200 km using the hydrogen and for another 200 with the fuel cell. It is still in the test phase, but has already been successfully clocked up 50,000 km. The end objective of both these companies is to produce the necessary hydrogen from solar energy. The car would then be mostly powered by renewable energy.

Written by Victoria Barras

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