ZF Friedrichshafen image of vibration damper blanks
ZF Friedrichshafen AG

More air, more savings for ZF shock absorbers

More air, more savings for ZF shock absorbers – thanks to heat recovery

An inefficient compressed air station and plenty of untapped energy – reason enough for Manuel Baumgarten of ZF Friedrichshafen in Eitorf to replace his old compressed air system. A little patience and a tailor-made solution from KAESER helped him to cut costs and make good use of recovered process heat.

You can't get more efficient than that. The printouts meticulously affixed to the boiler of the KAESER air station speak for themselves. Placed there personally by Manuel Baumgarten, the head of maintenance at the Eitorf plant, where ZF Friedrichshafen AG manufactures shock absorbers, no one who enters the room overlooks the detailed data proving the system's efficiency and cost-effectiveness – or the pictures of how things looked here before installing the yellow and black KAESER equipment. It is soon quite clear that the system is Baumgarten's baby.

Old compressed air station at ZF Friedrichshafen

 In 2010, this space – packed with outdated compressed air equipment – looked more like the engine room of a Mississippi steamer. It was a hodgepodge of mismatched components, added piecemeal over a 35-year period. The machinery was still serving its purpose, but Baumgarten knew that it had to go. It was obsolete and enormously wasteful. But how does one go about convincing management to invest an estimated six-figure sum? The only way is to make sure it will pay for itself.

It was so loud that you had to shout to be heard. And it was hot. Even in winter you couldn't stand it in here for long.
Manuel Baumgarten, ZF Friedrichshafen AG
Whatever happens – no downtime!

In Eitorf, three continuously operating ZF Friedrichshafen production lines that never stop running churn out 30,000 shock absorbers per day and seven million per year. They stop for weekends but roar back to life on Sunday evening. As a result, the costs for any down time add up very quickly. Production manager Andreas Adolphs wasn't the only one with doubts – was it possible to replace the compressor during normal plant operations? But there was no other alternative to this calculated risk unless Friedrichshafen planned to carry on as before.

ZF Friedrichshafen employees in a meeting
But who would be up to the challenge?

After deciding to replace the system, it was time to find a service provider with the necessary skills and experience – a perfect job for KAESER. Norbert Hages, a technical consultant with KAESER in Bochum, rose to the occasion. After exploratory meetings and consultations with Baumgarten, Hages mapped out the reasons that set KAESER apart from the competition and offered clear benefits to the customer.

The SIGMA AIR UTILITY operator model that he offered had the flexibility and risk control so urgently needed by ZF Friedrichshafen AG. In addition, the proposal ensured a secure supply and minimal downtime. “That was a good start,” recalls the KAESER engineer. But the customer wanted more. Was there perhaps a way of harnessing the exhaust heat? Norbert Hages gave the matter some thought.

ZF Friedrichshafen employee Baumgarten shows the weekly compressed air demand profile
Heat recovery – energy for nothing

The KAESER proposal was a hit. Heat recovery is not only good for the environment – we shouldn’t underestimate the economic benefits. But would the process heat be sufficient to maintain Baumgarten's target temperature of 60°C in the shock absorber cleaning bath?

It was impossible to avoid implanting such a good idea. But it required a decision.

Kaeser Kompressoren engineer Hages and ZF Friedrichshafen employee Baumgarten discussing the compressed air station plans
A complete overhaul – with no downtime.

Finally, the call came from Eitorf: “Mr. Hages, we want to do this project with KAESER.”

But simply dismantling and installing the compressed air equipment would not be enough. ZF Friedrichshafen gutted and refurbished the entire room from the ground up. KAESER installed five compressors and four refrigeration dryers. There were hoses and stainless steel pipes to carry the hot water to the cleaning bath. A specialized firm performed the hydraulic balancing, calibrated the pump and temperature sensors, and adjusted the heat meter.

The project included installation of a control unit and a three-way valve keep the temperature in the cleaning bath at a constant 60°C. And in case of problems with the hot water supply, the gas heating system would be at the ready. That was the plan.

After installation, it all worked perfectly with just one hitch: the heat recovery performance was not quite up to scratch. Baumgarten and Hages were disappointed. Instead of meeting the maximum expected recovery quota of 76% of the electrical energy input, just 45% was reusable. Nothing new turned up even after taking measurements over an extended period. Regardless of the system settings or fine-tuning, the performance showed no improvement. Were the results perhaps inaccurate? And if so, why?

Kaeser engineer Hages and ZF Friedrichshafen employee Baumgarten in a meeting
Error spotted – and eliminated

After a few weeks of wondering what to do, the solution appeared. The system was taking measurements next to a bend in a pipe where hot water was mixing with cold. This was causing disruptive turbulence in the flow, which was falsifying the readings. Troubleshooting mission accomplished! “You never stop learning,” says Norbert Hages. “It's not enough just to install a system. All of our installations are tailor-made solutions. Excellent results cannot be had off the rack.”

The hard work paid off.

Now the measurements are showing the right results, and the system is achieving an optimal level of heat recovery “that is very respectable,” says Mr Hages. And Baumgarten, who wears a manager's hat along with that of an engineer, is delighted: “We're saving $141,000 a year on our energy bills simply because the system is so efficient. On top of that, we gain $42,000 from heat recovery. That's enough to heat 40 single-family homes for a whole year. Plus $31,000 in maintenance costs.” Although the compressors restart half an hour earlier on Sunday evenings to pre-heat the cleaning bath, Friedrichshafen is saving a substantial sum through this measure alone.

ZF Friedrichshafen in Eitorf enjoys annual cost savings of €172,000 thanks to the Kaeser compressed air station

No less impressive are the savings in CO2 emissions. Assuming a conversion factor of approximately 1,667 KWh per ton of CO2, the electric power savings (760,000 KWh) combined with the process heat recovery (960 000,KWh) represents an annual reduction of about 1,000 tons of CO2 emissions.

CO2 emissions saving

That is an exemplary achievement. The investments, long since fully amortized, are a fact of which Manuel Baumgarten is justly proud, not least of all because the challenging project required considerable staying power from everyone involved. “Five years! Quite a few compressed air suppliers would certainly have jumped ship,” he concludes, and then he smiles: 

“But we never gave up. Luckily for us – and for KAESER.”

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