Ice arena HVAC and dehumidification

Canada has thousands of indoor ice arenas, many owned by municipalities and run on tight operating budgets. An arena is an unusual building: a sheet of ice kept well below freezing sits inside an enclosure where spectators expect to be reasonably warm, players generate heat and moisture, and the roof structure above is exposed to cold radiation from the ice. Getting the HVAC right is mostly a matter of controlling moisture.

When arena humidity is not controlled, the results are obvious: fog over the ice, condensation dripping from the roof deck onto the playing surface, soft or bumpy ice, rusting steel and mould in the roof assembly.

Why arenas have moisture problems

Three things combine in an arena:

1. A very cold surface. The ice surface is typically maintained around -4 to -7 C (19 to 25 F) depending on the use, with hockey ice generally kept colder and harder than figure skating ice.
2. Moisture sources. Outdoor air brought in for ventilation, people (spectators and players), and the flood water laid down by the ice resurfacer, which is often hot water.
3. Cold building surfaces. The roof structure radiates heat to the cold ice, so the underside of the roof deck can drop below the dew point of the arena air even when the air itself is above freezing.

Whenever the air's dew point is higher than the temperature of a surface, moisture condenses on that surface. Over the ice, warm humid air cooled near the surface becomes fog. On the roof deck, it forms condensation that drips onto the ice or freezes into frost that later melts. A good grounding in psychrometrics makes the relationships clear.

Design conditions

Typical design targets for community arenas are:

The key number is dew point, not relative humidity. Holding the arena's dew point a few degrees below the coldest surface temperature, including the underside of the roof and any structural steel, prevents condensation. The ASHRAE Handbook (Refrigeration volume, chapter on ice rinks) gives detailed guidance on these loads.

Dehumidification methods

Desiccant dehumidifiers are widely used in Canadian arenas because they can achieve the low dew points needed and work well at cold air temperatures where cooling coils would frost. The regeneration heat can come from gas, electricity, or heat recovered from the ice plant.

In winter in much of Canada, outdoor air is very dry and ventilation alone may control humidity. The problem months are spring, summer and fall, especially for arenas that keep ice in year-round. Our guide to dehumidification strategies compares the methods in more depth.

Low-emissivity ceilings

A low-emissivity (low-e) ceiling, usually a reflective aluminum-faced fabric or panel installed below the roof structure, is one of the most effective upgrades in an existing arena. It does two things:

• Reduces radiant heat transfer from the warm roof to the ice, lowering the refrigeration load.
• Keeps the ceiling surface warmer, because it reflects rather than radiates to the cold ice, which reduces condensation risk.

Low-e ceilings also improve lighting by reflecting light downward. They must be installed with attention to fire ratings, sprinkler coverage and access to the space above.

Air quality: resurfacers and combustion

Fuel-powered ice resurfacers and edgers, using propane, natural gas or gasoline, have historically caused carbon monoxide and nitrogen dioxide poisoning incidents in arenas. Several provinces and health authorities have published arena air quality guidelines that set monitoring and ventilation requirements. Requirements vary by province, so arena operators should check with their provincial health and occupational safety authorities.

Good practice includes:

• Continuous CO and NO2 monitoring with alarms and automatic ventilation response.
• Regular emissions testing and tune-ups of fuel-powered resurfacers.
• Ventilating the resurfacer room and ensuring resurfacers are not idled indoors.
• Switching to battery-electric resurfacers, which many municipalities have now done, eliminating the combustion source entirely.

The ice plant and refrigeration safety

Most Canadian arenas use either an ammonia primary system with a secondary brine or glycol loop, or a direct or indirect synthetic refrigerant system. Increasingly, CO2 is used as a refrigerant in new arenas.

Ammonia refrigeration in arenas is governed by CSA B52 and provincial pressure equipment and operating engineer regulations. Requirements include machinery room ventilation, refrigerant detection, alarms, emergency shutoff and, for ammonia, limits on locating machinery near occupied areas. Following the fatal ammonia leak at a Fernie, BC arena in 2017, provinces and operators renewed focus on inspection, brine-side leak detection, chiller condition and operator training. See CSA B52 mechanical refrigeration code.

Heat recovery

An arena refrigeration plant rejects a large amount of heat, much of which can be reused. Common uses include:

• Heating the flood water for the resurfacer.
• Under-slab heating to prevent permafrost heaving beneath the rink floor.
• Snow melt pits for resurfacer snow.
• Desiccant regeneration.
• Space heating for lobbies, change rooms and spectator areas.
• Domestic hot water preheating.

Well-designed heat recovery can supply a large fraction of an arena's heating needs. Arenas in multi-sport complexes can share recovered heat with pools, which need heat year-round. See heat recovery strategies in commercial HVAC.

Spectator and support areas

Spectator seating is often heated with radiant heaters to keep people comfortable without warming the air near the ice. Change rooms need generous exhaust and heating, since they are warm and humid after games. Lobbies and concessions are usually served by separate rooftop units or air handlers.

Diagnosing problems in existing arenas

Infrared thermography is a useful tool for finding cold spots on the roof structure, wet insulation and air leakage paths that lead to condensation. Infrared thermography surveys are particularly useful before planning roof or ceiling upgrades.

Key takeaways

• Humidity control, expressed as dew point, is the central HVAC challenge in ice arenas.
• Keep the arena dew point below the coldest building surface to prevent fog and dripping.
• Desiccant dehumidification is common because it achieves low dew points at cold temperatures.
• Low-emissivity ceilings reduce both refrigeration load and condensation risk.
• CO and NO2 from fuel-powered resurfacers require monitoring, and electric resurfacers eliminate the source.
• The ice plant must comply with CSA B52, and its rejected heat is a valuable resource for heat recovery.