Maintaining a frozen sheet of ice inside a climate-controlled building requires specialized engineering. This complex, multi-layered system is designed to manage heat transfer with precision. The entire process relies on mechanically removing heat from the floor faster than the environment introduces it. This paradox of keeping ice frozen indoors involves careful infrastructure design, heavy-duty refrigeration, and continuous surface maintenance.
The Substructure and Chilling System
The ice surface rests on a substructure designed for continuous cooling. At the base is a massive concrete slab that acts as a thermal mass to hold the cold temperature. This slab sits atop layers of insulation and often a heated concrete layer below it. The heated layer prevents the ground underneath the rink from freezing and expanding, which could cause structural damage.
Embedded within the concrete slab is a dense network of piping, typically made from durable polyethylene or steel. These pipes circulate a secondary refrigerant, usually a chilled solution of brine or glycol, cooled to about 16°F (-9°C). This fluid is pumped through the pipes, drawing heat away from the concrete slab and the ice. This indirect refrigeration method safely keeps the primary, more hazardous refrigerant contained in a dedicated mechanical room.
The Refrigeration Plant
The actual generation of the required cold temperature occurs in the refrigeration plant, which operates on the principles of the vapor-compression cycle. This system relies on a primary refrigerant, frequently ammonia, known for its excellent thermodynamic properties for absorbing and shedding heat. The cycle begins in the chiller (evaporator), where cold liquid ammonia absorbs heat from the warmer secondary refrigerant returning from the rink floor. As the ammonia absorbs this heat, it boils and transforms into a low-pressure gas.
The refrigerant gas then moves to the compressor, which drastically increases its pressure and temperature. This superheated, high-pressure gas is sent to the condenser, where it rejects its heat to the outside environment, often using a cooling tower or large fans. Once cooled, the gas condenses back into a high-pressure liquid. This liquid passes through an expansion valve, which rapidly drops the pressure and temperature before the refrigerant returns to the chiller to repeat the cooling process.
Building the Ice Layers
Once the concrete floor is chilled to the correct temperature, typically around 19°F to 24°F, the process of building the ice sheet begins. The ice is not created by flooding the floor all at once, which would result in cloudy ice with trapped air bubbles. Instead, a special spray boom applies many thin layers of fine water mist, or “fogging,” directly onto the cold slab. Each layer freezes nearly instantly, creating a smooth, strong bond with the floor and preventing the formation of air pockets.
After a thin base layer is established, the ice surface is painted white using a water-based paint mixture. This white base increases visibility and reflects light, minimizing heat absorption from above. Rink markings, including lines, circles, and logos, are then measured and painted onto this white layer. Finally, additional thin layers of water are applied to seal the paint and build the ice to its final thickness, usually measuring only about one to one and a quarter inches deep.
Maintaining the Ice Surface
The ice surface is under constant thermal attack from multiple sources, known collectively as the heat load. This load includes heat transfer from warm air, friction from skaters, radiant heat from lighting, and audience body heat. The refrigeration plant continuously compensates for this energy input, maintaining the ice temperature between 24°F and 28°F to ensure a hard, fast surface.
A significant part of maintenance involves using the ice resurfacer, commonly known as a Zamboni machine, to address wear and tear from skating. The machine’s conditioner uses a sharp blade to shave off a thin layer of scraped, grooved, and damaged ice. This snow-like residue is collected into a tank via augers.
The machine then washes the surface and spreads a thin layer of fresh water, often heated to 140°F. Hot water is used because its lower dissolved gas content allows it to melt the top layer of remaining ice, filling grooves and bonding effectively with the old ice to create a clearer surface upon refreezing. Environmental control, particularly managing humidity, is also important. Specialized dehumidification systems keep the arena air dry to prevent moist air from condensing and releasing heat onto the cold ice, which causes “snowing.”