Dr Michael Leinweber is the product manager for temperature and climate chambers at Weiss Technik and project manager for the introduction of CO2 at the Balingen site. In the interview, he speaks openly about the use of CO2 as a refrigerant in compact test chambers and the possible concerns of test engineers and companies.
Mr Leinweber, you have spoken to over 300 users, including in seminars. What do test engineers and lab operators think about the use of CO2 as a refrigerant?
First of all, I have to say that most of customers have a somewhat limited interest in the refrigerant itself. They have a testing task that they have to complete safely and reliably and they need a technically secure solution that meets the statutory requirements and at the same time reduces the costs involved in testing. However, the F-gas regulation has now forced them to switch from a system that often functions reliably over many years. This leads to uncertainty, especially since a practical solution has thus far failed to present itself. Many positive results come from simulations or lab studies without test specimens in the test space or proof-of-concept systems. We have now changed all of that.
What is Weiss Technik offering more than a proof-of-concept
When we were at the Automotive Testing Expo in Stuttgart at the beginning of 2024, we had a functioning CO2 system but didn’t yet have a series product. We have changed that: since August we have had near-production CO2 test chambers with customers in the field and have been able to accumulate thousands of operating hours with them already. Not in our lab under perfect conditions and an empty test space, but in real customer use and in continuous operation. We will take a very close look at the data collected here to get a detailed picture of the behaviour of the chambers in the field and to incorporate the feedback into the roadmap for further development. Because one thing is clear: no matter how intensively we test the different temperature and humidity combinations in our testing environment, the suitability of the systems for the tough everyday testing only becomes clear once they are in use on site.
What questions do laboratory operators and test engineers have for you?
Many questions initially revolve around the legal framework and the specific effects on the lab: “What do I have to change by when and how can I ensure the operational safety of my lab?”. Once these questions have been clarified, questions often arise that pertain to a certain respect or even fear of using CO2 as a refrigerant – for one thing with regard to the operating pressure, and for another because CO2 is wrongly perceived as toxic.
Why is CO2 not toxic?
CO2 is a non-toxic gas. However, CO2, like R449A and other refrigerants commonly used in environmental simulation, displaces oxygen and is invisible. With a practical limit value of 0.07 kg/m3 according to DIN EN 378, this is higher for CO2 than it is for other refrigerants. But this is of little consequence in laboratory practice. Let’s take an example: in a 10 x 10 m room with a ceiling height of 2.5 metres, a maximum of 17.5 kg CO2 per system can be present without a CO2 alarm having to be installed. Only customers with very large test chambers in the range of several cubic metres will have refrigerant volumes of this magnitude. In the reach-in range, i.e. up to 2000 litres of test space volume, we are at less than 3 kg and therefore very far from this limit value. This means that, even in the unlikely event of a leak, the risk is extremely low.
How do you eliminate customers’ fear of the high operating pressure?
Transcritical CO2 systems like our CO2 test chambers require a high operating pressure of up to 120 bar. To make these permanently safe, we have already taken appropriate measures at the design and construction stages. Of course, all components used are approved by the manufacturers for the pressure range. To be on the safe side, we employ specially trained staff in the production and have further intensified our quality controls. We carry out tests in accordance with the pressure equipment directive before the systems are installed and again in the overall system. During development, we overstressed possible weak spots to such an extent that accidents occurred. These were then reinforced accordingly where necessary to be on the safe side.
Do you see CO2 as being the refrigerant of the future?
Yes. Of course, there are still applications for which the sheer power or the low temperatures of a cascade are needed. This is the case in the aerospace sector, for example, where testing is regularly carried out at temperatures below -50°C. But in most other fields of application, CO2 is definitely the future. After all, CO2 is a natural refrigerant with GWP 1. That means that it is available and has no negative impact on the climate, fulfils many test requirements at lower sound pressure levels and often with lower energy consumption. It’s a win-win all round, which can come into play now that the appropriate components are available and we have mastered the transcritical CO2 technology. With our new generation of devices, we have confidently solved the technical challenges that arise when using CO2 as a refrigerant. The practical tests that we have been conducting since last August demonstrate this impressively.
What specific support were you able to offer customers during the transition?
First of all by providing technically safe, economical and reliable solutions with our CO2 systems. Moreover, we also advise our customers on sensible scenarios and applications for their own test environment. For example, in a larger test laboratory, it may be advisable to convert only part of the systems to CO2 and to continue to operate another part with cascade in order to be able to meet all possible requirements in a future-proof way. We are also currently developing simulation software that can be used to specifically simulate applications. This increases investment security for customers because they are aware in advance which tests they can conduct afterwards and with which results.