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Quest for Perfect Ice: Ice Making for Curling

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©2016 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 58, no. 2, February 2016

By Daniel J. Dettmers, Member ASHRAE

About the Author
Daniel J. Dettmers is a researcher with the Industrial Refrigeration Consortium at University of Wisconsin–Madison. He is past chair of ASHRAE TC 10.5, Refrigerated Processing and Storage.

Ice is seemingly simple—just bring water to a temperature below 32°F (0°C), and you are done. Unfortunately, a number of sporting enthusiasts would respectfully disagree. Just think about those sports whose performance relies on “perfect” ice: hockey, figure skating, and curling. Each has a different definition of “perfect” ice, and curlers are often considered the biggest divas of the bunch, possibly for good reason.

Curling, a sport whose popularity peaks during the Winter Olympic Games, is often described as chess on ice. It’s a sport particularly well-suited to individuals who are strategy-minded, detail-oriented, and enjoy the cold. For a description of the basics of the game, see the sidebar “The Game of Curling.”

A single curling game’s ice sheet varies in size but is generally 150 ft (46 m) long by 15 ft (4.5 m) wide, as shown in Figure 1. A small club will have two to three sheets, while larger U.S. clubs run six to eight sheets. Thus, a standard six-sheet club will have an ice surface around 150 ft (46 m) long by 90 ft (27 m) wide. Typical refrigeration load averages 6 tons to 8 tons (21 kWT to 28 kWT) per sheet. Part of the refrigeration load arises from the participants, but the bulk is from heating the air for comfort and improved ice conditions.

The ice sheet for curling is not flat, but a surface littered with “pebbles” of ice. Prior to the start of any game, a shower of water droplets is dispersed across the playing surface (ice sheet), as shown in Photo 1. As the water droplets rapidly freeze, they create an uneven surface. In proper preparation of the ice sheet, the pebbling would then be “broken,” or have the peaks shaved off, to give an even top surface of plateaus with a variation of gaps below. The size of the water droplet, temperature of water applied, and the intensity of the spread of water spray all affect the profile of the surface. The variables are chosen based on the experience and preference of the club’s head ice maker. It seems that no two ice makers can agree on all three variables, as each has his own methods.

 

The Curl

Part of the phenomena of curling comes from the shape and size of the stone. It is an approximately 42 lb (19 kg) piece of 3 ft (1 m) circumference granite that has a handle on top, similar to a teakettle (see photo in sidebar, The Game of Curling). It contacts the ice on a 5 in. (130 mm) diameter circle of stone that is 0.25 in. to 0.5 in. (6 mm to 13 mm) wide called a running band. The running band surface area coupled with the stone’s weight results in a contact pressure of ~1,500 lb/ft2 (72 kPa). This heavy weight on top of a small contact surface on the ice is sufficient to reduce the friction of the ice, possibly by melting, allowing the stone to move easily down the sheet.

The exact mechanics of how the curl (rotation) of the stone affects the stone’s path of travel is still up for debate. But, the stone will move in a lateral direction to the path of travel in the same direction as its rotation. In other words, if the curler twists the stone in a clockwise fashion, it will curl to the right with the bulk of the sideways distance covered at the end, as the velocity of the stone slows.

 

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Comments

  • 17 Feb 2016 | Peter Christiansen
  • As an avid curler, I was thrilled to see my sport represented on the cover of the ASHRAE Journal. The author describes curling as being "well suited to individuals who are strategy-minded, detail-oriented, and enjoy the cold." This is an apt description of Canadian engineers like me who are over-represented in the general curling population up here. This was one of the most enjoyable articles I have ever read in the ASHRAE Journal.
  • Reply

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