Test bench for refrigeration and air-conditioning systems

Fresh air for a healthier climate

© Udo Geisler

16 May 2019

It’s a well-known fact that we’re all pumping too much CO2 into the atmosphere. And this isn’t caused just by the daily commute or holiday travel: residential and office buildings are among the biggest contributors to climate-damaging CO2 emissions. Alongside better thermal insulation, more efficient ventilation systems should also reduce energy consumption, thereby protecting the environment. Whether such systems deliver what they promise is tested by TÜV NORD experts on the test bench for refrigeration, air conditioning and ventilation technology in Essen.

If you want to get from Essen’s main railway station to the Technology Park, you either have to take the A40 motorway for a while or catch the 146 bus towards Kray – a guided bus that uses special rail-mounted rollers to trundle along the central reservation of the motorway, passing the commuter traffic as it does so. The notion that has driven this invention is efficiency. Which is also the defining idea once you get to the destination: at the main site of TÜV NORD, Timo Reisner and his colleagues work in a large hall to determine how efficient refrigeration, air-conditioning and ventilation equipment really is.

In addition to thermal insulation and draught­proof windows, modern ventilation systems are considered a key element in the quest to make residential and office buildings more energy efficient. The idea is not just to save heating costs but above all to reduce energy demand, which is still mainly met by climate-damaging fossil fuels and results in green­house gas emissions. “In large buildings, a central ventilation system is essential because building technology can provide more efficient ventilation than an individual person would be able to in practice," explains Timo Reisner, deputy Head of Laboratory. After all, ventilation systems do more than just supply fresh air with the windows closed. They are also designed to ensure that the heat emitted in winter by heating systems, electrical appliances and human bodies isn’t released into the atmosphere unused. “When I open the window in an office, the heat energy just escapes,” Reisner says. Which is why it has been illegal since 2016 to sell central ventilation systems without built-in heat recovery technology, adds Reisner's colleague Marius Ciucas. This is stipulated in the amended version of the Ecodesign Directive (ErP), with which the EU has sought to reduce energy consumption and green­house gas emissions since 2009.

And the more effectively a building is sealed by modern windows and thermal insulation, the more essential a ventilation system becomes. This is because, unlike in conventional buildings, the used, moisture-laden air can’t automatically escape, for instance through gaps in the windows. “The fact that a ventilation system repeatedly blows fresh air into the room and removes old air prevents the build-up of mould. For kids and asthmatics, this is a win-win situation,” Ciucas says. Allergy sufferers can also benefit from a ventilation system: special filters intercept the pollen before it gets inside.

Larger ventilation systems for lower energy demand

Every two years, the requirements on the energy efficiency of ventilation equipment become more rigorous. This also means that the systems are getting bigger and bigger, Timo Reisner reports. “In 2018, the next stage of the Ecodesign Directive came into force. To comply with its provisions, you have to reduce air speeds in these central air conditioning units.” This is because the faster the air particles whizz through the devices, the more forcefully they get churned up on impact with obstacles such as coolers, heaters or filters. Such turbulence generates pressure losses, so the fans have to work harder, consuming more electricity. “In order to transport the same volume of air at a lower speed, the cross-sectional area of my unit needs to be bigger,” explains the trained geophysicist, who also has a doctorate in engineering.

You gain an impression of the scale involved in the large multifunctional hall, in which the imposing ventilation devices are waiting for their tests. “The larger the diameter of the air channel, the smaller its surface area relative to the volume of the airflow. As a result, there is also relatively less surface area for friction to slow the air down,” Reisner says by way of explanation of an additional effect of the larger devices. After all, the less motion energy the air particles lose as they make their way through the ventilation system, the less power the fans need to pump fresh air into the offices.

Lower speeds dramatically reduce energy consumption

“Another advantage of the larger is that you can also use bigger fans,” says Marius Ciucas. Alongside cooling and heating equipment, they are responsible for much of the energy consumption of a unit. And with larger fans, which are now powered by significantly more energy-efficient EC motors, you can transport the same amount of air at lower speed – resulting in a significant dip in electricity demand. “The increase and decrease in energy demand are raised to the third power of the rotational speed. That means, if I double the speed, I'll have eight times the energy consumption,” Reisner observes.

Reisner, Ciucas and their colleagues are well prepared for this burgeoning technology. In mid-2016, they moved from the old test bench on Essen's Langemarckstrasse to the new site “Am TÜV”. Here, the two significantly larger test chambers mean that they now have considerably more space and, with it, the flexibility required to test devices for IT cooling, rooftops, split air conditioners, control cabinet coolers, but above all the powerful indoor air-conditioning devices that they are most frequently called on to test.

As an independent testing laboratory, they have, for example, been working for French certifier Eurovent Certita Certification (ECC) for 20 years. What’s more, they also monitor the systems for the future operators of office buildings. After all, you can’t simply order large ventilation systems from a catalogue. “Such indoor air-conditioning equipment is always tailor-made,” explains Timo Reisner. Building planners turn to their choice of manufacturer with their specific requirements. “And these all have their own design software. They enter the framework conditions required by the planner, and the device is then put together and turned over to the client,” adds Marius Ciucas. Whether the equipment conjured up by the software actually meets the client’s requirements is investigated by the TÜV NORD experts in what are known as witness tests.

Tests in tropical temperatures

Before each test, the device is set up in the indoor air chamber and connected by means of air ducts to the adjacent outdoor air chamber. The technician then starts to fit the system with temperature sensors and hoses for air pressure measurement. Finally, the indoor and outdoor air chambers are brought to the required temperature and humidity. "We can simulate a scenario in which the device is directly connected to the outer wall of a building,” Reisner says. And because the systems are tailor-made, they must of course be able to withstand the temperatures and conditions that obtain at the sites in question. Last year, the experts more frequently found themselves testing equipment for Saudi Arabia and the United Arab Emirates. “In those cases, we had external conditions of 36 degrees Celsius and 74 percent humidity. When you opened the door to the test chamber, it really felt as though you were running into a wall,” Reisner relates with a laugh.

During the test, the outside air is directed into the device, and the air volume flow, humidity, temperature and air pressure are measured. The pressure loss is determined for every single component in the system: from the filter and the heat recovery system and the cooler for the summer and the heater for the winter, all the way through to the fan. When these are taken together, it becomes possible to determine how well the device and its components are actually performing. In the case of the fan, the cooler, the heater and the heat recovery system, the temperature is measured as well – both upstream and down­stream of the component. “In the case of heat recovery systems, we can determine energy efficiency, in other words how much of the energy in the exhaust air the device can recover,” explains Reisner. Ten temperature sensors are generally used per measurement level, before and after each component. This not only makes the measurement particularly precise but also allows the experts to check the quality and accuracy of their own measurements.

To enable them to go on to check electrical safety, filtration technology, hygienic suitability or sound emissions after the performance test, they work with experts from other areas. After all, even the most efficient system will be of little use if the noise it makes gets on the nerves of the office workers.

Getting new ideas off the ground

So what do the experts particularly like about their work? “The diversity you get with it,” Marius Ciucas replies. “Because every device is configured for one particular operator, the requirements in the testing process are always a bit different." In general, the team constantly has to adapt to different testing procedures and to try to get new ideas off the ground. "In our fairly young team, we’re all really keen to question and improve old methods to enhance the quality and efficiency of our work,” says Timo Reisner.

They are also developing and pursuing new approaches and ideas in collaboration with TÜV NORD's own Corporate Centre Innovation, whose experts also support them as they move on to the implementation phase. This is a promising approach: in the future, it might be possible to send the measurement data collected during the witness tests directly via the Internet to the end customers of the manufacturers. “They would then no longer need to come to us from all over the world for the tests, saving time and money and cutting CO2 emissions,” says Marius Ciucas. As a possible project for the more distant future, they have also envisaged the development of an augmented reality application that could, for instance, visualise the measurements of temperature sensors in a colour scale. This would enable the experts to see at a glance whether the temperature distribution on the measuring level is plausible or whether a single sensor might perhaps have failed during the test. “We humans are visual beings, after all. If we visualise this kind of central information, we will of course be able to record it much more quickly and draw the necessary conclusions from it,” explains Timo Reisner.

They have already brought other workflows in line with the latest state of the art of digital technology. For example, Marius Ciucas has developed a programme on his own initiative to automate the transmission of the measurement data. These no longer need to be entered by hand and inserted into the calculation tables. The engineer doesn’t of course want to make himself redundant by generating a test report at the touch of a button. “We can now put the time we used to have to spend entering the data to good use in technical issues,” Ciucas explains. When it comes to the actual evaluation of the measurement results, however, they can still rely on the in-depth work carried out by their predecessors. “For the physical mathematics which feature in the evaluation, we draw, for example, on what my office neighbour Helge Uhlig has developed and refined over decades,” reports Timo Reisner. “His work has been incredibly well verified because it’s been examined and reviewed by a wide range of co-workers over the years.”