ICE STATION

Designing an
ice floor is a specialist
task, as BLAKE ELLIS
of Ellerbe Becket
describes.

Right: 
The MCI Center.

ce sports used to be limited to the winter months and played only in northern latitudes. Now people throughout the world enjoy these activities all year round. Operating ice facilities 365 days a year, in warm and humid southern climates, greatly increases the complexity of the systems required to provide a successful environment for an ice floor. Four main factors are involved;

• Ice floor design

• Building design

• Heating, ventilating and air-conditioning (HVAC) system design

• Building and system operation and maintenance

Failure of any one of these components can result in less than satisfactory ice conditions, which can lead to soft ice, fog on the ice surface, injuries to athletes and the consequent unfavourable publicity for the arena.
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Ice Floor Design
To create the ultimate ice floor, we must first look at the ice itself. Proper ice floor design takes into consideration the underfloor drainage, subsoil heating, insulation, piping within the floor, concrete, ice equipment, and snow and ice pits.

The height of the water table under the ice floor influences subsoil drainage. Suitable drainage stops the water from rising high enough to touch the ice floor and freeze, which can crack the surface of the floor when the ice expands. Proper drainage is accomplished through a grid of perforated piping underneath the floor that allows water in, collects it, and then carries it away. 

When an ice floor cracks, it takes cooling away from the ice and instead cools the ground and groundwater, resulting in soft or poor ice. Soft ice has two negative results; reduced glide and increased ice surface flaws. The reduced glide forces athletes to work harder, increasing strain on hockey players and figure skaters. Even more serious is the increase of nicks and cuts in the ice caused by stopping and turning. If the blade of an ice skate catches the flaw at the wrong angle, the skate twists unpredictably and causes injury to even the most experienced athlete.

If the building operator wants to maintain the ice surface for an extended period (greater than nine months, depending on latitude) a subsoil heating system is advisable. This system of piping contains hot water and is buried in the ground underneath the floor. It is regulated to keep the soil above freezing (approximately 40°F/4.4°C) in order to maintain the ice floor above. If the system is not controlled, a perma-frost can develop, causing the soil to expand and move, which will crack the ice surface and possibly the building's foundations.

The selection of the thickness for the insulation under the floor is based on soil temperature. Ellerbe Becket, for example, use a thicker insulation in Florida and a thinner one in Russia. Insulation reduces the amount of energy leaving the floor and being transmitted to the soil. The size of pipe and best configuration for the piping grid in the concrete floor is selected to eliminate soft spots. Typical pipe spacing is 3.5 inches to 4 inches (8.9-10.1mm) between the centres of the pipes. 

Most arenas are multi-purpose, and their floors must be designed and reinforced to handle the weight of large trucks and other loads, such as circus elephants. Even how the concrete is poured is critical -  it must be poured all at once to create a uniform floor without joints (water can work its way into joints, expand when frozen, and crack the floor).

Cooling equipment is selected that will handle making ice under the intense heat of sports lighting. The equipment should operate in the highest outdoor temperatures and humidity during the floors expected use, as well as the coldest temperatures in the winter. Typically, older arenas were properly designed to withstand the freezing environment, but most were not designed to work beyond the month of May in the northern hemisphere. This has caused problems for the National Hockey League's (NHL) Stanley Cup Playoffs, which extend into June. The warm weather reduces the cooling capacity of the ice floor, raising the ice temperature for hockey's most important games of the year. Although some temporary measures are available, an ice arena's systems can also be retrofitted to meet the challenge of summer temperatures.

Many of today's ice floors have a 'quick melt' system that allows hot water to flow through the ice floor piping and break the bond between the ice and the floor. The ice can then be broken apart and removed without fully melting it, which greatly reduces the time spent removing the ice floor - and reduces the mess of fully melting the ice. Ellerbe Becket has designed arenas such as the Ice Palace in Tampa, Florida, Marine-Midland Arena in Buffalo, New York, and the MCI Centre in Washington D.C. all wih ice pits -  holes next to the ice floor in which to place the ice while it melts. A good ice floor design also includes a snow melt pit in which to place shavings from the ice resurfacing machine. The shavings are melted with exhaust and snow-melting systems that minimise the amount of moisture added to the air.
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Building Design
A poor building design for an ice facility can cause less than satisfactory ice conditions through the infiltration of hot, moist air from the exterior. High humidity levels within the building result in the development of fog over the ice and a crust on the ice surface. Fog occurs when the temperature of the air drops below its dewpoint, and the air can no longer hold water vapour. Air with high humidity has more water in it, causing fog to form at higher temperatures. When the humidity or water vapour enters the building, it seeks out the coldest surface on which to condense, which is the ice floor. This causes a crust to build on the ice surface, reducing the slipperiness to the point of unuseability.

The building shell must be designed to control the amount of humidity that enters the facility. This is done by focusing on the vapour barrier, exterior doors and isolation barriers. The vapour barrier is a layer of plastic (or similar substance) placed in the walls along with insulation in order to reduce the amount of moisture that enters the building. The vapour barrier must be discussed from the onset of the building design, to determine its position in the wall and how to maintain the vapour barrier through building components such as soffits. Exterior doors are also essential to humidity control. They must include weather stripping and door sweeps in arenas in all climates.

However, how can you control the entry of exterior moisture when one event is leaving the arena and another is setting up, leaving the loading dock open? Ellerbe Becket build isolation barriers between the ice floor and these spaces to create a zone within the building that can handle the higher humidity levels. The isolation doors that Ellerbe Becket designed for the National Car Rental Centre in Sunrise, Florida, for instance, gives building operators the ability to open the loading dock doors and close the isolation doors, keeping the ice floor separated from the area. This allows event staff to load and unload their equipment at their leisure, while the building staff are still able to maintain high ice quality.

HVAC System Design
In recent years HVAC systems in ice arenas have experienced many changes. The United States has seen a trend towards lower and more standardised indoor temperatures and humidity levels. By lowering the air temperature in arenas, you reduce the chance of fog forming over the ice. Ellerbe Becket has recently designed arenas at 70°F (21.1°C) with 50% relative humidity, while the National Car Rental Centre is designed to maintain 65°F (18.3°C) with 50% relative humidity -  even during the tropical 
Florida summers. These lower temperatures increase the required system performance from HVAC systems. A solid HVAC design takes into account a variety of factors, which include chilled water temperature, air handling unit design, desiccant dehumidification, and also control systems.

To achieve the required conditions at the National Car Rental Centre, the arena was designed to use both low temperature chilled water (36°F/2.2°C, with typical temperatures in the 42° to 46ø°F/5.6° to 7.8°C range) in conjunction with desiccant dehumidification systems - the first NHL arena to use this system. The desiccant dehumidification system uses the property of a substance (a desiccant) that attracts moisture at room temperature and gives off moisture at high temperatures (250°F+/120°C+). Air is passed over the desiccant to reduce humidity. Then the desiccant is heated, which dispels moisture to the outside. 

When use low temperature chilled water is used, special care must be paid to the design of the air handling unit components to ensure they can accommodate lower temperatures. If they cannot, the exterior of the air handling unit and piping could form condensation and 'sweat'. Ellerbe Becket evaluate each installation independently to determine whether low temperature chilled water, desiccants or other options provide the best design for the project. For example, Indiana's Conseco Fieldhouse utilises slightly cooler chilled water (40°F/4.4°C) in conjunction with an increased air flow rate to maintain proper design conditions for the space.

HVAC systems also need to be designed for many changing conditions that the building experiences. First, not all events completely fill the seating bowl with people. For many small events, the upper deck of seats is closed off. Therefore a HVAC system that also can be partially closed off will reduce the building's energy use and lower building operating costs. Second, the arena's systems may be designed to keep air from blowing over the ice in order to keep it from melting. However, when the arena is used for a non-ice event, like a concert, the system would blow air to the centre of the arena. HVAC systems that offer this type of flexibility increase the comfort level of patrons, which encourages them to return for future events.

Regardless of the HVAC components used, Ellerbe Becket design the control system to allow the operator to maintain the space temperature and humidity during a full ice event, a partial ice event, and during off-hours.
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Building/System Operation and Maintenance
After all of the ideal components have been designed into an arena, proper operation and maintenance provides the final link to a successful ice floor.

Primarily, operations and maintenance personnel must keep the ice surface itself at the correct temperature and with a uniform thickness. A typical ice temperature for hockey is 18°F (-7.8°C), while the normal temperature for figure skating is 20°F (–6.7°C) or higher. Both sports commonly require an ice thickness of between 0.75 inch and one inch (19 to 25mm). The lower ice temperature for hockey increases the players' speed by increasing the glide they get from each stride, whereas figure skaters like a slightly softer surface that allows them to dig into the ice for jumps and tight circles.

Building operation and maintenance personnel must also:

• Remove any nicks and cuts in the surface caused by skates or other objects, to prevent injuries.

• Operate HVAC systems to maintain the correct temperature and humidity at all times, while not turning the system off during unoccupied periods (this is where the flexibility of the HVAC system is vital).

• Thoroughly cover the ice surface when the arena is used for non-ice events like basketball and concerts, in order to reduce the negative effects of higher space temperatures. When the floor of the arena needs to be covered with dirt for a circus or a motor event, the ice floor should be removed so the dirt does not get into the ice itself.

• Give the appropriate time (eight to 12 hours) to recreate the ice surface if it is removed. An ice floor can be flooded in five hours, but the super-cold floor temperature (0° F/-17.8° C) required to freeze the water in the short timeframe usually results in a brittle ice surface that cracks easily.

To create the ultimate ice floor a design team evaluates a great number of factors beyond the design of the ice floor itself. The HVAC system design, building design, and the operation and maintenance all play important roles. If any one of these components is ignored, it will hinder the success of the design. A successful project will incorporate all of these elements from an early stage in the design process.

Blake Ellis, PE, is Mechanical Engineering Director at Ellerbe Becket. He and his engineering team have created ten ice floors in the last five years for the NHL and other sports facilities around the world. 

E-mail address: Blake_Ellis@ellerbebecket.com.