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Quest for the Perfect Ice: Strategic Ice Making for Curling

By Mary Kate McGowan, Associate Editor, News

Every four years during the Winter Olympic Games, one sport hits its peak popularity—curling.

“It swings in popularity every four years now,” said Daniel Dettmers, Member ASHRAE, a researcher at the University of Wisconsin–Madison.

Dettmers said his curling club in Madison, Wis., has about 600 members during and directly following Winter Olympics years, and he predicted the membership to drop to about 400 in three years.

For those faithful to the sport, their love of curling does not wane during non–Olympics years. When the U.S. men’s curling team took home the gold medal for the first time during the 2018 Games in Pyeongchang, many fans stayed up to watch the game, which was scheduled to start at 3 a.m. EST

The game is strategic, like a chess match. Participants slide 42 lb (19 kg) granite stones down an ice sheet at a bull’s-eye target called “the house” that is about 100 ft (30 m) away.

Like other sports on ice such as hockey and speed skating, curling calls for different parameters for a quality playing surface, said Dettmers.

“Whether it’s hockey or curling or speed skating, everyone wants different temperatures. Everyone wants different conditions,” said Dettmers, a member of TC 10.2, Automatic Ice Making Plants/Skating Rinks.

But curlers are known to be particular about their playing surface. Factors such as heat and humidity can affect the ice in a curling center.

Quality Ice

While curling is popular in parts of the world such as Canada and the northern U.S., the sport is growing elsewhere such as the American west coast, Dettmers said.

Some curling clubs have their own centers, but others convert hockey arenas for the night. The main difference between a hockey playing surface and a curling playing surface is curling requires “pebbling” the ice, he said.

“With curling you have to have that pebble in order for the stone to curl. If it’s just smooth ice, you have no control over the stone, and it’ll just go flying off in one direction or another randomly,” Dettmers said.

Before a curling game, water droplets are dispersed across the ice sheet and rapidly freeze. The pebbles’ peaks are shaved off creating an even top surface with plateaus of different widths, Dettmers wrote in an article that appeared in ASHRAE Journal in 2016.

“The ice makers in curling are closer to artists then engineers. Every morning they scrape off the previous day’s ice and recondition the ice through a series of pebbling and scrapes. For important competitions, like the Olympics, this is often repeated between games,” he said.

The water droplets’ size and temperature and the intensity of the spread of the water spray affect the playing surface.

Likening the conditioning process to waxing bowling lanes, Dettmers said ice makers can make the ice faster or slower and make the stones curl more or less.

Ice deemed “championship quality” is fast and curls the most, which creates the most exciting games, he said. Some of the larger curling clubs have systems that deionize the water, change the pH and monitor the ice.

“Basically, the intention is to make it the fastest ice possible,” he said.

Heat Considerations

Heat recovery strategies can help regulate the ice, he said. There are places throughout hockey arenas and curling centers such as the locker rooms and the bleachers with waste heat, he said.

In curling, eight participants are on a sheet, which can vary in size but is generally 150 ft (46 m) long by 15 ft (4.5 m) wide, according to Dettmers. The participants contribute about 800 Btu/h (235 W) to the curling center’s heat, but the main contributor is often the heat in the air that is usually set to 40°F (4.4°C) to 45°F (7.2°C), he said.

“The big heat loads are either plus or minus whatever is coming through the wall because these things are usually pole sheds or worse,” he said.

With a furnace creating heat that goes into the air, the heat goes into the ice then goes into the refrigeration system, which rejects the heat outside, he said. This can be accomplished by using a coil in the space to the refrigeration system’s condenser. The key is that the condenser is inside the icehouse.

“Traditionally, a natural gas furnace heats the icehouse air for comfort, but that is the refrigeration system’s largest load.  Using the refrigeration system’s heat rejection as primary heat for the icehouse air simply closes that loop to reduce the need for additional heat,” Dettmers said.

In new curling centers, clubs are looking into using water source heat pumps, he said, as opposed to using legacy systems such as R–22 refrigerant systems. 

There is no one set formula on how to create the best ice surface for winter sports. TC 10.2 is working on looking at the interactions among heating, air and the building and their effects on the ice, Dettmers said.