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Toronto has more outdoor compressor-cooled rinks than any city in the world – 49, with one more to come in January (the new skating oval at Colonel Sam Smith Park in Etobicoke). But our civic knowledge of the physics of ice maintenance hasn’t kept pace with our collective rink wealth. At Dufferin Rink, after the scheduled City ice maintenance was augmented by 8 late-night volunteer hose-floods, the rink opened for the season on November 22. The ice has been good ever since. Many people seem to find this amazing, even shocking, since the air temperature has been warmer than usual, as high as 11.
What’s the surprise? Collectively, as taxpayers, we spend about $500 a day at Dufferin Rink to fuel the compressors that cool the rink pad. The rink has two compressors of 75 horsepower each – you can hear their noise through the compressor-room doors at the side of the building. These compressors push a brine (salt water) solution through a big tank of cooling ammonia, and then out into the extensive grid of PVC pipes underneath the concrete floor of the rink. This cold liquid brings the entire big concrete slab to well below freezing, so any water that’s put on the rink pads sets up as ice right away. The brine liquid circulates back into a large pipe in the “header trench” right next to the building, underneath where everybody stands when the zamboni is doing ice maintenance. From there the brine gets pushed back into the compressor room, where it passes through the freezing-cold ammonia tank, and out again into the pipes under the concrete, and so on.
The only serious match for this powerful cooling system is the sun, and in the months around the December 21 winter solstice, the sun is very weak. It doesn’t get to spend very much time above the horizon, and that suits the compressors just fine.
The sun begins to gain real power toward the end of February, which is why, on a sunny day on, let’s say, February 25, when the air temperature is minus 8, the ice gets really mushy near the reflective boards, and even a bit soft in the middle. The compressors are losing ground as the sun prepares to bring on spring and summer. But on a low-sun Monday, November 23, at 11 degrees, a thin film of water forms on top of solid ice, and the shinny hockey and pleasure-skating at Dufferin Rink are brilliant.
It’s not only rink users whose rink literacy is in some need of upgrading. The city’s rink staff are also confused. In our travels around the other 48 city rinks, we have often heard zamboni drivers say that they can’t make ice because the temperature is above zero. The city’s Park management blames a multitude of ice-making sins on the temperature, global warming, etc. Convenient – but most of the time, not true. The compressor-cooled rinks can do their job, and having all those rinks can take some of the sting out of the dark months of winter for Torontontians.