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Toronto has more outdoor mechanically-cooled rinks than any city in the world - 53. But our civic knowledge of the physics of ice maintenance hasn't kept pace with our collective rink wealth. Many people seem to find it amazing, even shocking, that outdoor rinks can be skateable when the air temperature is above freezing, as high as 11 or even 15 - during the low-sun months.
What's the surprise? Collectively, as taxpayers, we spend about $500 a day at each rink to fuel the machinery that cools the rink pad. The rink compressors vary between 100 and 200 horsepower each. You can hear their noise through the compressor-room doors at the sides of the buildings. A brine (salt water) or glycol solution is pushed through a big tank of cooling ammonia, and then out into the extensive grid of PVC pipes underneath the concrete floor of the rink. The cold liquid brings the entire big concrete slab to well below freezing, so any water that's put on the surface of the rink pads sets up as ice right away. The brine liquid in the pipe grid 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 machinery room, where it passes through the freezing-cold ammonia tank, and out again into the pipes under the concrete, and so on.
The angle of the sun: The only serious match for this powerful cooling system is the sun. In the months on either side of 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 machinery just fine. By March, though, the sun is getting much higher in the sky, and the machinery often has trouble keeping the ice frozen at minus 4.
Even on a sunny day at the end of February, when the air temperature is minus 8, the ice gets really mushy near the reflective boards, and a bit soft in the middle. The ice-making plant is losing ground as the sun prepares to bring on spring and summer. But on a low-sun Monday in November, even at 11 degrees, a thin film of water forms on top of solid ice, and the shinny hockey and pleasure-skating are brilliant.
Ice thickness: Many rinks are often closed for parts of days for "ice conditions" from mid-February on, even though above-zero temperatures don't shut them in early winter. Not only is the sun much stronger in February than in the November-January low-sun time, but also, by now, many of the rinks have ice so thick that it insulates the cooling pipes underneath, and the rinks are essentially natural ice rinks.
The remedy for too much ice is for the ice maintenance staff to zamboni the rain off the ice surface as it's raining, throughout the winter. Then the rain doesn't freeze onto the ice surface and the ice stays thin enough to let the cold of the pipes come through.
It's not only rink users whose rink literacy is in some need of upgrading. Over the years, some of the city's rink staff have also shown confusion. In our travels around the city's outdoor rinks, we have heard some zamboni drivers say in low-sun November that they can't make ice because the temperature is above zero. And there are still some staff who maintain that the thicker the ice is, the better -- on the same principle as natural ice on a pond. But it's not the same principle.
Over the years, the city's Parks management has blamed a multitude of ice-making sins on the temperature, global warming, etc. Convenient - but most of the time, not true. The mechanically-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 Torontonians. But if the zamboni staff tell you that their zamboni sinks into the mush in early March, you'd better believe them -- or just take a look yourself.
Here's an interesting history of mechanically-cooled ice rinks, written in 2004 by Ted Martin, then the general manager, Ontario Operations, with Cimco Refrigeration in Toronto.
Read about better ways of stewarding our mechanically-cooled outdoor rinks here.
Parks and Rec Master Plan, 2019 - 2038: outdoor rinks
Rink information log
shovelling by skaters
Rink-related injury claims against the City of Toronto, 2010 to 2014
Strollers on outdoor rinks correspondence and pilot
A History of Toronto's outdoor ice rinks, by Jutta Mason
An excerpt from Jutta's rink history: the issue of turf struggles
Many of Toronto's 52 compressor-cooled municipal outdoor rinks are bare-bones sports facilities, but some are also important wintertime social spaces for their neighbourhoods. People expect to meet acquaintances there, to chat and catch up on news as well as skating together. Double-pad rinks are more likely to have this function, since pleasure-skating is anytime there, not only in restricted time slots. A few single-pad rinks have also become social spaces, either because of a particular location in a neighbourhood or because of programs (such as a weekly community supper) that maximize the friendship possibilities of the rink.
Double-pad rinks that are also neighbourhood social spaces (to widely varying degrees): Rennie, High Park, Dufferin, Wallace, Harry Gairey, Otter Creek, North Toronto Memorial, Hodgson, Ramsden, Dieppe, Greenwood.
Harbourfront's Natrel Rink (not municipal) is both an entertainment venue and a social space where friends often arrange to meet.
The wintertime social meeting-up function of rinks needs to be better recognized, and fostered, than it is at present.
The science is there, the history is there (pre-amalgamation), professionals say it can be done, Harbourfront is doing it, even volunteers have done it. This list supplies the fundamentals of ice making.