isoSTORRetrofit: Increasing the efficiency of industrial compressed air systems

Isobaric storage of compressed air leads to optimized compressor cycling and reduced electricity costs

© shutterstock

Compressed air receiver in the industry

Compressed air receivers can be constructed and operated in different ways. An important element is the compressed air tank, which influences the efficiency of the station.

© Fraunhofer UMSICHT

Laboratory plant

Investigations on the pressure compensating modules are carried out in the laboratory plant specially designed for this purpose.

© Fraunhofer UMSICHT

Pilot plant

The pilot plant demonstrates that the pressure compensation modules can reduce the compressor's cycle frequency, thereby lowering energy costs..

Project aims

The energy efficiency of commercial and industrial compressed air generation can be considerably increased by isobaric storage in the compressed air receiver and the resulting optimized compressor cycling. In the isoSTORRetrofit project, Fraunhofer UMSICHT is investigating a new concept that, with the aid of a phase-changing cushion gas, should enable almost isobaric storage in existing compressed air systems. To this end, the scientists are developing and investigating so-called pressure compensating modules that can be retrofitted into conventional compressed air recievers via existing inspection and maintenance openings.


Compressed air is an important energy source for trade and industry. In Europe alone, more than 1.4 million air compressors are in operation. In Germany, seven percent of industrial power consumption is attributable to the generation of compressed air. So even a small increase in energy efficiency in compressed air production means a large savings potential.

This is where the retrofittable pressure compensating modules that are created in the isoSTORRetrofit project come into play. They are inserted into the already installed compressed air reciever via existing inspection and maintenance openings – without any structural measures at the existing compressed air station. A compressed air reciever retrofitted in this way provides up to six times more buffer volume. At the same time, electricity costs are reduced by up to 20 percent through optimized compressor cycling.

A further advantage: Because the stored, usable compressed air volume is considerably larger when operating with pressure compensating modules than with conventional storage, the pressure compensating modules can alternatively be used to dimension the compressed air reciever significantly smaller for the compressed air system with the same performance. This is particularly interesting for applications where space is limited.

Interim result

For the development and investigation of the pressure compensating modules, a laboratory plant was constructed as a storage tank. Here, various parameters such as temperature and pressure can be varied and their influence on the performance of the pressure compensating modules can be analyzed.

In addition, the first pressure compensating modules have already been developed and tested in the laboratory plant. One of the results: The capacity of a storage tank equipped with the pressure compensating modules increases in comparison to pure isochoric operation.

Furthermore, a pilot plant was put into operation. The purpose of the pilot plant is to demonstrate that the cycle frequency can be reduced and thus energy costs saved. The pilot plant consists of a 4 kW air compressor with downstream compressed air dryer and a 250 l compressed air receiver. Large numbers of pressure compensation modules are placed in the compressed air receiver. A consumer station simulates real compressed air systems in order to allow an evaluation of the energy consumption and energy savings, respectively, under different load conditions.

Duration: July 2018 to December 2021
Funding code: MEF 602230