Subterranean sunshine

6/30/2013 | Words: Marcel Rothmund | Pictures: Nicole Maskus-Trippel

combined heat and power plant, swimming pool

The water in an open-air swimming pool has to be warm even on less sunny days – after all, who wants to swim in cold water? At the Hockermühlbad pool in Amberg, Bavaria, a modular combined heat and power plant supplied by MTU Onsite Energy provides the necessary heat. In the winter, the CHP module heats a school building via a district heating pipeline.

The thermometer is showing 36°C as the roofs of the idyllic old town of Amberg shimmer in the heat of the midday sun. At the Hockermühlbad lido, an elderly man in blue shorts is sitting on a wooden bench near the showers. With his portly figure and bald head, he has something of the look of a Buddha figure. Leaning back in relaxed fashion, he suns himself in the heat. Behind him, boys and girls in swimming gear sit on the edge of the pool, looking upwards expectantly. Standing on the five-meter diving board is a young lad in black-and-white swimming shorts. He takes a short run-up and jumps. As he descends he performs a somersault before plunging into the refreshingly cool water, which is maintained at 24°C – the ideal temperature for hot days. But even when it is cooler, the water in the Hockermühlbad pool should not be lower than 24°C. A modular combined heat and power (CHP) plant supplied by MTU Onsite Energy makes sure of that. Away from all the splashing about in the pool and the games on the grass, it is hidden from the swimmers in an underground room.

First CHP module for swimming pool
Near the turnstiles at the lido entrance there is a flight of steps leading down behind a mesh gate. A man with a white shirt, black trousers and short gray hair unlocks the gate. He is Günter Schwarzer, the bathing amenities manager for the Amberg municipal utility company, which runs the swimming pool. Together with his colleague Wolfgang Hüttner he descends the staircase into the basement. Wolfgang Hüttner is a works engineer with the Amberg utility company. In the underground room it is oppressively humid and a ventilation shaft in the basement ceiling hums incessantly. “Here’s the prize possession!” says Wolfgang Hüttner. He points to a modular CHP plant supplied by MTU Onsite Energy. The natural-gas fueled generator set with a twelve-cylinder Series 400 engine its uncovered in pride of place in the center of the room. “We didn’t want a soundproof enclosure because servicing is much easier for us without it,” Wolfgang Hüttner explains.

The CHP module in the generator room heats the swimming pool water to a pleasant 24°C. Wolfgang Hüttner (le#) and Günter Schwarzer in front of the CHP plant.?
The CHP module in the generator room heats the swimming pool
water to a pleasant 24°C. Wolfgang Hüttner (left) and Günter
Schwarzer in front of the CHP plant.

The Amberg municipal utility company bought the CHP module for the Hockermühlbad pool in 2011. It generates 232 kW of electricity, which as well as covering the lido’s own power requirements can also be fed into the local power grid. A particularly important feature is the heat produced as a by-product of electricity generation. The generator set recovers the heat from its exhaust system, enabling it to supply up to 358 kW of thermal output to a watercirculation heating system. The heating system in turn heats the water in the swimming pools via heat exchangers. “Twenty-four degrees is the ideal water temperature for most pool users,” said Günter Schwarzer, speaking from experience. If the temperature drops just a single degree on less sunny days, there are very soon complaints from swimmers. “We’ve even had people come to us saying the water temperature had dropped by 0.2°C! We checked it straightaway and were flabbergasted to find out they were right!” Günter Schwarzer recounted. As soon as the water temperature in the pools drops below 24°C or the water tank for the showers is empty, the CHP module springs into action. It takes about a day to heat the pool water by one degree. Exactly how long depends on the wind and the outside temperature. Before the start of the open-air season in May each year, it takes a whole week to heat up the pools. Last April the CHP unit had to generate around 210,000 kWh of heat to do so.

Underground heat
The swimming pools are not just kept warm by heating the water; they are also heated from below by a sort of underfloor heating system. The CHP plant supplied by MTU Onsite Energy plays its part here too. In the basement next to the generator room you can see the concrete swimming pools from underneath and walk around them. Some of the recovered heat is blown into this large room as hot air and so heats the swimming pools from the outside. While Wolfgang Hüttner and Günter Schwarzer chat below ground, above them the swimmers do their turns in the large pool. There is one section specially for aquajoggers and slow swimmers.

Pensioner Peter Bachmann acts as pool supervisor. He stands in front of the lifeguard’s glass cubicle in beige sandals, blue shorts and a white polo shirt keeping an eye on the swimmers. “The CHP plant is a great thing because it keeps the water warm in the swimming pools in the season and heats the grammar school in the winter,” says Peter Bachmann, gesturing over the lido fence. Over there you can see Amberg’s Erasmus Grammar School, which is heated day and night in the winter by a district heating pipeline from the CHP module. As he is talking, two elderly ladies are having a go at aquajogging. One of them is stumbling rather awkwardly in the water. Peter Bachmann observes the scene from above with a slight shake of the head.

Gas-fired in the past
Before the Amberg municipal utility company acquired the CHP module, they used a conventional gas-fired heating system at the Hockermühlbad lido. “In the past we used large quantities of gas just to heat the water in the pools, but the gas heating never worked reliably,” relates Wolfgang Hüttner. Today, the CHP plant provides electricity, hot water and district heating, and produces much lower carbon dioxide emissions. Wolfgang Hüttner is standing in the underground room facing a pumping station with pipes going in all directions. This is the district heating out-feed point to the grammar school. “The output of the CHP module is so great that we could even connect a couple more large buildings,” he said. As well as the CHP plant at the open-air pool, the Amberg municipal utility also operates two other MTU generator sets.

Solar collectors are no alternative
On average, around 2,000 swimmers visit the Hockermühlbad lido every day. To maintain the water quality, roughly 30 liters of fresh water a day per swimmer is fed into the pool water. And, of course, it has to be warm. So it is first heated to 24°C by the CHP module. Theoretically, the pool water could also be heated by collector-type solar panels using the energy from the sun. “They do that at other outdoor pools in the Amberg-Sulzbach district,” said amenities manager, Günter Schwarzer. But that would require too much space. Although the Hockermühlbad facility has as much as 50,000 square meters of open space, as things are it can be used as a sunbathing area for the benefit of pool users. “Apart from that, the water temperature can very quickly drop to 18°C with solar collectors if there is no sunshine,” added Günter Schwarzer. And that is something he would rather avoid with his very temperature-sensitive bathers.

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