Hockey Rink Basics
The "Original Six" National Hockey League (NHL) teams plodded along from the '40s to the '60s with no appreciable increase in interest (read on for the answer to the trivia question, "Who are the Original Six?"). These teams played in storied old arenas with qualities similar to the players who pioneered the game: uncomplicated, rough, and at times lacking control.
In the late '60s, the NHL expanded into new markets, and as the interest in the sport grew, the need for neighborhood rinks grew as well. So in cities like St. Louis, Philadelphia, and Los Angeles, existing ice sheets were enclosed in makeshift structures. Needless to say, these facilities were crude, but it didn't take much to satisfy the typical hockey enthusiast.
Bad ice, moldy locker rooms, and carbon-monoxide-(CO)induced headaches not withstanding, the popularity of hockey continued to rise. The Original Six gave way to 30 franchises in such winter game hotbeds as Phoenix, Dallas, and Tampa Bay. Old barns like the Chicago Stadium, Boston Garden, and the Forum in Montreal gave way to multimillion dollar venues.
And it should come as no surprise that this evolution has been duplicated on the community level as well.
Community Rink EvolutionLike many NHL teams, the St. Louis Blues have always had practice facilities that double as community rinks. As a young engineer, I was called in to take a look at their original practice facility. Although the building was steeped in history, the playing environment was terrible. The locker rooms were damp and moldy, the structure was rusting, and worst of all, the ice sheet was less than ideal.
Years later, I was doing some research for a rink design and I visited the Blues' new facility. I assumed that since this was the home of an NHL franchise, it must be state of the art. And sadly, it was. The first thing I noticed as I stepped into the lobby was the unique olfactory cacophony of human odors that is only brewed in the confines of a hockey locker room. Simply put, it stunk.
The rink conditions were certainly better than the old rink, but they were still lacking. The ventilation system was manual and unconditioned outdoor air was introduced into the space; ergo, it was not used very often. There were heat pumps on the rink corners for dehumidification, but the ice was soft and when conditions were just right, fog would creep across the sheet. The rink operator spoke of having to begin each day chiseling away the little ice stalagmites that would form on the ice sheet over night due to dripping from the structure.
Fast-forward to 2003, and it comes as no surprise to learn that the Blues are building a new home, but this time they are employing a state-of-the-art active desiccant dehumidification system. They have recognized that the indoor environmental conditions are critical and have a significant impact on the condition of the ice.
The Modern Hockey Rink: Envelope, Ice, and AirAccording to the International Ice Hockey Federation (IIHF) Ice Rink Manual1, a highly recommended treatise on the topic, the basic technical elements of a well-working facility include a tight, well-insulated structure, mechanical ventilation, an efficient heating system, and air dehumidification.
If moisture problems occur inside the building, the HVAC engineer is reflexively hung out to dry (no pun intended). So it is prudent to advise the architect in such a critical facility. Per the ASHRAE Humidity Control Design Guide2, the following suggestions and cautions should be relayed:
- Build a leak-tight exterior envelope;
- The vapor retarder goes to the outside, and must be continuous;
- Low-e ceilings are useful in reducing the load on the ice sheet;
- Roof insulation need not be excessive;
- Pay attention to the western exposure due to a propensity for high radiant loads; and
- Provide access through a closed lobby or vestibule.
The hallmark of an ice rink that caters primarily to hockey is the ice. Figure skaters and hockey skaters have different ideas of what good ice and bad ice are3. Figure skaters prefer an ice temperature within the range of 24 degrees to 28 degrees F. Ice in that temperature range is softer, so it grips the skate edges better. Hockey players on the other hand prefer ice at 20 degrees to 22 degrees. With many skaters on the ice simultaneously, it is easy for the ice surface to get chewed up at the temperatures preferred by figure skaters. And if the ice is too warm, it may cause players to lose their edge during a crucial play.
Affecting the quality of the ice is the state of the air, and this fact is reflected in the NHL standards4. These call for an air temperature stabilized at 60degrees and an rh level less than 40%, which equates to a 35 degree dewpoint. That is fairly aggressive, but because most rinks are competing to attract league play that generates consistent revenue, this environmental criterion is especially relevant. Why? Because the rink with playing conditions most conducive to hockey, i.e., those that approach the NHL ideal, will have the competitive advantage over other rinks.
Pick Your DewPointIn the simplest terms, there are three major problems that can be addressed via dewpoint control: Fog, dripping, and soft ice. The designer can determine the moisture control level according to which problems are most important to the enduser. Keep in mind that as the humidity level goes down, the cost of equipment often goes up.
At a 45 degrees dewpoint, the simple problem of fog can be eliminated. All that is required to remove fog is to prevent the air above the ice from reaching 100% rh. This can be accomplished using mechanical dehumidifiers. They usually cost less per cfm than desiccant systems, and they can be installed with no ductwork, minimizing installation costs.
To address dripping due to condensation on the ceiling, you must keep the air dewpoint below the coldest surface temperature in the roof structure. A 40 degrees dewpoint will prevent drips in almost any climate, but a surface temperature calculation can show you if the temperature is actually higher than that, possibly making mechanical dehumidifiers viable.
But if hard ice is your goal, and it is if you want hockey revenue, then there is no doubt that a dewpoint well below 45 degrees will be required, and the only equipment that can get you there is active desiccant.
Ventilation - The Five Minute Major of Rink DesignIn hockey, the biggest penalties result in the longest time in the penalty box. A good fight, if it is truly first-class, will always result in a five-minute major. When it comes to the HVAC design of a rink, the biggest punishment by far is meted out by the ventilation requirements.
ASHRAE 62 requires 0.5 cfm/sq ft of ice sheet and 7.5 cfm/person or spectator if they are in the arena for less than three hours5. For a small rink with no seating, the minimum air quantity then is 8,250 cfm (0.5 cfm/sq ft x 16,500 sq ft). Add 400 spectators, and all of the sudden you are up to 11,250 cfm (8,250 cfm + (7.5 cfm/sq ft x 400 people)).
Since it is commonly held that the 0.5 cfm/sq ft of rink outdoor air requirement is due to concerns regarding CO buildup from resurfacing operations using propane-fueled resurfacers, some jurisdictions will allow this quantity to be handled by an emergency ventilation system tied to a CO monitor.
The drawback to this approach is that even though you are saving money on the installation, if the system goes off, unconditioned air will be introduced into the space, condensation and fog will likely form, and the ice will be compromised. I personally have nightmares about such systems popping off during some inopportune time, like during a midsummer thunderstorm for example. Yeesh!
Concerning the ventilation for the spectators, recall the need to maintain the dewpoint at or near 40 degrees to avoid dripping. With mechanical refrigeration makeup air units, you are limited to about a 45-degree dewpoint supply temperature, so "you can't get there from here" with such equipment. That isn't to say that such equipment is ruled out completely in every case, but the author's opinion is that DX is not appropriate for a competitive rink makeup air system.
HVAC Hat TrickIn many areas, building codes will require that the installation have sufficient capacity to handle the entire ventilation load continuously under full load conditions. In this worst-case scenario the best solution may be found in the active desiccant dehumidification, demand controlled ventilation plus passive desiccant energy recovery hat trick.
The single system would consist of a nominal 10,000 cfm two-wheel desiccant dehumidification system (TWDS) air handler with an active desiccant wheel, supply fan, a passive desiccant energy wheel, regeneration heater, exhaust fan, and, if needed, a post cooling ( Figure 1).
During unoccupied periods the unit would run in recirculation mode, bypassing the energy recovery wheel. During low occupancy times, the unit would operate at a reduced ventilation quantity, perhaps 15% to 20% of the amount suggested by ASHRAE 62. During full rink operations, the unit would provide the full ventilation quantity as required.
In all modes the system would maintain the dewpoint of the air, not its rh. By operating based on dewpoint, the system will not over dry the space when the air temperature is cold nor under dry when the air temperature rises. For example, at the NHL conditions of 60 degrees and 40% rh there is no benefit to drying the air below the 35-degree dewpoint. But when air in the building cools at night, a humidistat at 40% rh will be calling for dehumidification even though the dewpoint falls way below 35 degrees.
The ventilation mode would be controlled based on the signal from a CO2 monitor located at the seating area and a CO monitor at the rink. Regardless of which sensor triggers the change, the system would only go into full ventilation during peak periods and the cost associated with drying the ventilation air at all times would be avoided.
Last, the energy wheel can reduce the cost of the system by as much as 30% to 50%. For example, if the outdoor condition in Atlanta (home of the Thrashers) is 83 degrees, 133 grains/lb; and the indoor condition is 60 degrees, 30 grains/lb; then 66 lb/hr of water must be removed from every 1,000 cfm of ventilation air brought into the building. With a passive wheel, that incoming load drops to approximately 20 lb/hr!
When it comes to energy use and utility bills many designers dismiss active desiccant systems out of hand, claiming it is too expensive to operate. But the I believe that the DOE's Federal Energy Management Program debunked this myth when they stated "While it is difficult to generalize the cost effectiveness of (active desiccant) systems, there are a few applications where cost-effectiveness is so well established that detailed analysis is not necessary. These include ... ice arenas that operate in summer ...7."
Pressure Relationships, Heating, and CoolingThis article has focused on the unique requirements of the rink, but the basics covered in a previous article regarding recreation center needs for proper air balance and control of odor migration apply in rinks as well6. The only exception, and it is a biggie, is that the rink should be net positive to all surrounding spaces and the outdoors.
Trying to heat a building with a massive radiant cooling source as its primary feature is a waste of energy and money. Instead, provide infrared heaters over the seating areas. With a desiccant unit, the supply air will be hot more often than not, so ipso facto, it becomes a heating source. Direct the supply air high and toward the roof peak rather than downward. This not only avoids soft spots on the ice, but it kicks up the ceiling temperature, alleviating the dripping concern. The best location for the return is near the ground level, which keeps the air mass moving in a circular pattern from high to low, which increases ventilation efficiency.
Regarding cooling, consider these two extremes on the possibility continuum. The net effect of the ice sheet is difficult to determine with any accuracy, but manufacturers claim that the credit from the ice sheet may be as much as 50 tons, in which case post cooling is never actually required even when it is installed.
Secondly, if the space might ever be used for another purpose - perhaps the ice is covered with thermal panels and basketball or indoor soccer is played - then providing a separate DX cooling system for such an activity may be prudent. Your reality will likely fall somewhere between the two.
SummaryIce rinks and facility expectations have evolved since the early days of the Original Six (trivia question answer: Detroit Red Wings, Toronto Maple Leafs, Chicago Blackhawks, New York Rangers, and the Montreal Canadiens).
Rink construction, air temperature, and ice conditions are critical. Because revenue is closely tied to the quality of ice, in many cases the ideal dewpoint of 35 degrees can only be reached and maintained with active desiccant systems.
Ventilation can be a back breaker, but the incorporation of demand control and passive energy recovery can make for a viable solution. A positive pressure relationship between the rink and other spaces must be maintained. And heating and cooling should be kept as simple as possible, always considering the impact of the ice.
And most importantly ... Go Blues! ES