© Anna Schroll

Getting rid of heat

The cooling water in a gas power plant in Dresden releases its heat through heat exchangers on the roof. But they were terrible for the overall effi­ciency. Then the oper­a­tors took a radical step resulting in a cut of nearly 90 percent in energy consump­tion.


The high-tech heart of Dresden beats far outside the baroque city center on a feeder route to the A4 auto­bahn. On a field in the middle of nowhere is a hulking factory building surrounded by parking lots. The noise of departing airplanes drifts over from the nearby airport. Glob­al­foundries makes ultra-tiny tran­sis­tors on semi­con­duc­tors here. Next to the chip factory, two chim­neys rise into the sky from a power plant. Andreas Büttner from Zeppelin Power Systems, the head service tech­ni­cian here, says “We provide elec­tricity and process heat for the chip factory.”

A company called EVC oper­ates the exclu­sive gas power plant, and the service tech­ni­cians from Zeppelin Power Systems make sure that the systems work flaw­lessly day in and day out. “Chip produc­tion requires an extremely stable power supply with the highest possible voltage and frequency stability, at a level that the public grids can’t provide. And we can also deliver when there’s a blackout all around us. That’s why this gas power plant is here.”

Two hori­zontal condensers per engine

druckluft_pruefung

Safety first: Andreas Büttner checks the compressed air tanks regu­larly. (Photo | Anna Schroll)

The gas engines roar in the cellar-like rooms, with 16 cylin­ders per engine driving the crank­shaft of a gener­ator and deliv­ering output of four megawatts in full-load oper­a­tion. Red cables lead from the gener­ator into the floor, conducting the produced elec­tricity. The power plant also supplies water in two temper­a­tures — 32 and 80 degrees Celsius — and steam for EVC’s absorbers. The oper­a­tors use the immense amount of waste heat from the engines and gener­a­tors, which they carry off through a cooling water circuit. Every minute, 65,000 liters of water rush by the hot engine parts.

The cooling water starts at a temper­a­ture of 75 degrees Celsius; after­wards it has reached about 96 degrees Celsius. “After we’ve decou­pled the heat for the chip factory with heat exchangers, the water is still at around 90 degrees, much too hot to reuse for cooling the engine. So even more heat needs to be extracted from the water. For that we have two hori­zontal condensers on the roof for each engine,” says Büttner and heads up the stairs.

“The EC fans need 89 percent less elec­tricity. At first I thought I’d done the math wrong.”
Andreas Büttner Head Service tech­ni­cian with Zeppelin power systems

On the roof, the hot cooling water flows through pipes with tiny aluminum ribs in the hori­zontal condensers. Above them, axial fans suck up the ambient air from below and blow the heat up into the sky. The air above the fans shim­mers with heat. Büttner leans over a fan and says “Two years ago, you would hardly have been able to talk up here. There were 192 old, unreg­u­lated fans, always running flat out and eating up huge amounts of elec­tricity. Every month we had to repair ten of them because their elec­tronics couldn’t take the heat. We knew some­thing had to be done.”

Büttner had two hori­zontal condensers refitted with EC fans with Flow­Grid air-inlet guards and AxiTop diffusers as a test. A fan’s EC motor adjusts itself depending on the temper­a­ture of the ambient air and the output of the gas engine so that on typical warm days, 25 percent of motor capacity is enough. After a few months, Büttner checked the results. “The EC fans needed 89 percent less elec­tricity. At first I thought I’d done the math wrong, but it was true. Of the savings, 30 percent was due to the more effi­cient fan motor and 70 percent to the adjustable speed.”

The envi­ron­ment likes it

A year later, Büttner had the other 168 fans replaced. They’ve been humming quietly and problem-free ever since. Büttner is still leaning on an AxiTop as he says, “We’re saving over 1.1 million kilo­watt-hours every year, elec­tricity we don’t have to produce in the first place. For the climate and the envi­ron­ment, that means less natural gas, less exhaust and a total of 613 fewer tons of carbon dioxide.” Büttner looks over the roof into the distance. “At Zeppelin Power Systems, we’re serious about protecting the envi­ron­ment. I always say we want to leave some­thing for our chil­dren.” Two kilo­me­ters away, an airplane takes off. Even with 192 fans at work, it can still be heard.

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