Extremely dry where it needs to be, standard where it can be

TNO Compressed air quality - tailored to specific needs

TNO approached Festo with the request to upgrade its existing compressed air system. More compressed air was needed, and also of better quality. Based on a pre-audit, a working group with Royal HaskoningDHV was put together and a proposal was made for two separate systems, each providing its own quality of compressed air. With the additional possibility of linking the systems in case of calamities, TNO has raised the availability, capacity, quality and efficiency of its compressed air supply to a higher level.

Within the field of nanotechnology, TNO's Van Leeuwenhoek Laboratory (VLL) in Delft is one of the largest (cleanroom) research facilities in the Netherlands. Research here includes research into optics and instrumentation for aerospace. One of the challenges here is to create an environment that resembles 'space' outside our atmosphere as much as possible. This means aiming for the highest possible vacuum and very low temperatures of up to -160 °C or colder in large tanks in which the tests are carried out. After these tests, the space is reheated with large quantities (5 to 6 cubic metres) of compressed air.

Franco Brouwer is project leader technology CREF Corporate Real Estate & Facilities) at TNO and in this position, among other things, responsible for maintenance and modifications to the installations. Within CREF, Teun Brussee was responsible for engineering at TNO which supervised this project. He says: 'The compressed air we use to reheat and pressurise the tanks has to be extremely dry. Any water molecule that enters with the compressed air could potentially precipitate on the measurement object. If these are too many molecules, they could firstly interfere with the measurement results of the tests and also cause serious damage to the elements we are testing with.


With increasing demands on compressed air quality, an increasing number of requests for testing and customer requirements regarding the availability of test facilities, TNO decided that the time was right for an upgrade of the compressed air system.

A first step involved Festo conducting a pre-audit. Koen Leeflang is a certified auditor and highly experienced in inspecting and upgrading complete compressed air systems: 'We regularly perform such an audit at companies to map a complete compressed air system. This is done according to ISO11011, which gives us an excellent starting point for determining where changes are necessary. For customers requesting an expansion of capacity, this does not always mean adding a compressor. Sometimes the solution lies in a rearrangement of the piping, larger pipes or another smart solution that avoids the need for large investments. In addition, we can suggest energy-saving measures in practically all cases.'

For TNO, the question was a bit more complicated. On the one hand, there was a desire to increase compressed air quality, and on the other, a capacity expansion was needed. However, the pre-audit showed that by no means all users require the highest quality compressed air. It would therefore become unnecessarily expensive to build a completely new compressed air system to provide all users with the very dry compressed air.

Project group

The pre-audit and TNO's requirements called for serious modification of the compressed air system. It was essential to put together a working group consisting of TNO, Festo and Royal HaskoningDHV. The latter was represented by Annelies Hemmer, Project Manager when it comes to building or remodelling TNO's Delft laboratories. 'In these types of projects, my responsibilities include writing the project plan, associated budgets and assessing its feasibility. For this, the collaboration with Festo and TNO has been of great value.'

She continues: 'In this collaboration, Festo makes the technical proposal for the compressed air system modifications and extensions. TNO has to assess whether this indeed produces the desired result and I look at the financial feasibility of the proposal on this basis. When we are in agreement, Royal HaskoningDHV initiates the realisation where, in consultation with the client, we determine the subcontractors and suppliers. For example, specific fittings and various instruments were supplied by Festo while the air dryers were sourced from a specialist in this specific equipment.'

Redundant at compressor level

Festo's proposal focused on a two-tier compressed air system. Thereby, the first system delivers compressed air in the very high (dry) quality (class 2.1.1 according to ISO8573-1:2010). The second supplies compressed air of normal quality (class 2.4.1 according to ISO8573-1:2010) via its own separate pipeline. A special feature is that a so-called 'calamity valve' is placed between these two systems that can connect them when needed. It prevents tests from failing or having to stop temporarily if there is a threat of too low a pressure in the compressed air system (e.g. due to too many users).

Capacity and quality

To achieve both capacity and quality, one compressor and a new dryer were added to the three existing compressors. Koen Leeflang: 'To start with the latter: the new dryer is a special adsorption dryer with which a pressure dew point lower than -70 °C can be achieved. This pressure dew point is monitored by its own sensor on the dryer and additionally via its own pressure dew point sensor on the outgoing discharge line. This combined with the new compressor provides the extremely dry compressed air needed to pressurise the vacuum tanks. For other users, who have sufficient standard compressed air, the fourth compressor is available. In this way, the compressors are redundant so that TNO can offer its customers maximum availability of its systems.

Teun Brussee: 'This set-up ensures that the right quality compressed air is available at the right place and that we do not use unnecessary energy to generate high quality compressed air in places where it is not needed. A further reduction in energy consumption is possible by lowering the pressures of 9 - 10 bar that we currently use. For example, to 7.5 bar. If it turns out that this is also sufficient, we can take an additional, energy-saving step here.'


The set-up is now running to the full satisfaction of all users. In doing so, the three parties look back with satisfaction on more than a good cooperation. Teun Brussee: 'Thanks to Koen's knowledge and unrelenting enthusiasm, we arrived at a solution that answers all our questions: we have more capacity, higher reliability and the desired quality of compressed air. All with efficient energy consumption. It's great when parties can work together like this.