Hat Trick

In the not so distant past, the design of sports arenas was not so complicated. Primarily, they housed events during winter months, so there was little need for air conditioning. Few provisions were made for TV broadcasting, and flexible power distribution systems or event lighting systems were limited considerations.

By Blake Ellis, P.E., Principal, and Wayne Maxwell, P.E., Electrical Engineering Director, Ellerbe Becket, Kansas City, Mo. September 1, 2002

In the not so distant past, the design of sports arenas was not so complicated. Primarily, they housed events during winter months, so there was little need for air conditioning. Few provisions were made for TV broadcasting, and flexible power distribution systems or event lighting systems were limited considerations.

How quickly things have changed. Due to increasing revenues from television broadcasts, longer sports seasons and a multitude of event types, many mechanical and electrical systems must now be specifically tailored to an arena’s unique needs. Important systems now include floodlighting with precision optics, dedicated show and television-broadcast power distribution, ice floors and smoke-control systems.

Event lighting

The development of arena lighting systems has been primarily influenced by increasing television coverage of sporting events. To meet the needs of broadcasters, professional and collegiate officials have developed stringent guidelines for both illumination levels and overall lighting uniformity.

For example, the horizontal illumination requirement for the National Hockey League requires a minimum of 200 footcandles (fc), but National Basketball Association games require 250 fc. In addition, both leagues require significant vertical illumination levels and uniformity to meet the needs of the television network cameras.

To meet these criteria, floodlighting fixtures are designed specifically to illuminate the playing surface—be it a basketball court or hockey ice floor. These fixtures are usually fitted with 1,000-watt metal-halide lamps. To maximize the uniformity of the playing surface, the lamps are aimed at preset locations from catwalks high above the floor. These structures also serve many other lighting and power needs (see “Catwalks: A Special Design Consideration,” p.47).

For professional teams, arenas typically employ about 125 to 150 fixtures for basketball and up to 300 for hockey games. Commonly, shutters or rolling shades are installed over a fixture’s lens to provide remote-controlled temporary “blackout” conditions for player introductions, halftime effects or other special uses.

Seating areas are also affected by league and broadcast requirements. Floodlights, typically with 900-watt quartz lamps, provide adjustable, low-level “house” lighting. Rows of seats adjacent to the event floor are often considered a backdrop to the action. Therefore, these areas can also have specific illumination requirements.

Another seating-area consideration is the aisles, where fans need sufficient light to find their way in and out of the seating bowl. These aisleways are typically illuminated in one of two ways: with small incandescent or LED lamps mounted under seat arms adjacent to aisles, or by catwalk-mounted floodlights with quartz lamps. The latter utilize very narrow beam distributions to minimize “spill” light onto adjacent seating areas.

Aisle lights typically remain on during blackouts—and for many types of shows—but can be turned off for games when they’re not needed. This is acceptable because a portion of the house lights are wired to emergency-power distribution panels in order to fulfill code requirements for egress lighting.

Once the hardware has been chosen, the designer must figure a means for control. Event-lighting fixtures are typically controlled via relay panels located on the catwalk. House lights and theatrical lighting fixtures are controlled by dimmer cabinets, typically installed adjacent to the relay panels. This equipment is often part of a larger, total-building light-control system and is tied into the building’s main lighting control panel (MLCP). Usually, the lighting-control system needs to be programmable via a PC with a touch-screen interface, and compatible with the building-automation system for energy monitoring and management.

Several remote lighting-control panels are also commonly provided. Besides basic on/off and dimming functions, these remote panels can control the blackout systems on event-light fixtures plus control power to advertising panels, TV monitors and suite lighting.

Show power

Decades ago, if a show required power in excess of a building’s spare capacity, promoters were expected to bring in their own generators. When the power demands of rock concerts started to increase, arena managers began to request dedicated equipment to serve these loads, although this primarily took the form of direct-to-bus connections.

Today, it’s not uncommon for a show to require more than 2,500 amps of temporary, 208-volt three-phase power for lighting and sound systems—not to mention the temporary stage lighting, rigging and other special effects—and arena operators are expected to meet these power demands.

Like lighting, the design of power-distribution equipment within stadiums has also evolved. In most modern arenas, show electricians can obtain power from custom-built power panels via a Cam-lok or similar type connector. Additionally, several manufacturers currently produce custom distribution panelboards with a variety of receptacle configurations and ratings to meet even the highest possible load requirements.

Not only are the power demands high, but there is also a need for distribution flexibility. Although the “stage” end of the event floor requires most of the power, show power is also typically needed at the opposite end of the floor, plus up on the crowded catwalk where 800-plus amp panelboards are often specified for the temporary stage lighting, rigging and special effects alone.

Broadcast power

And all that power is just for the show or event itself. The media need their own power feeds, and in medium- and large-sized arenas, it is standard practice to install dedicated cable trays around the event level.

These mobile broadcasting units require power as follows:

  • Network production (TV) trucks. These are semi-tractor/trailers-size vehicles that contain all equipment for complete remote broadcasting requirements, such as video/audio editing and production directing. Consequently, these vehicles require extensive power feeds, usually 208-volt, three-phase power at 200 to 400 amps. To meet these power needs, dedicated panelboards, or power pedestals if floor-mounted, are typically provided near the rear of the trailers.

  • Portable satellite-uplink trucks. Commonly called satellite news vehicles (SNVs), these custom-built trucks for national television networks come complete with large, collapsible transmitters for uplinking broadcast signals to a network’s satellites. Although usually fitted with built-in generators, they require power for basics like air conditioning and lighting. Often referred to as “shore” power, 60 to 100 amps of power will typically meet these needs, and it is usually provided via pin and sleeve receptacles or by Cam-lok connectors.

  • Portable microwave trucks. Commonly called electronic news gathering (ENG) trucks, these full-size vans are modified for use by local TV stations for their uplinks. They also require shore power, although not as much as SNVs.

SNV and ENG trucks park outside the arena because they require a direct southern path facing orbiting communications satellites. Due to the trucks’ remote locations, a custom-built panel is necessary, with dedicated feeder circuits serving either one or two of these vehicles.

Ice floor systems

Fans of basketball and hockey know that arena crews must switch out the floors to accommodate either sport, but may not realize how important it is to a multi-purpose arena’s bottom line to conduct this transition quickly. This, of course, allows the building owner to maintain a nearly continuous event calendar. Appropriately, ice-floor systems are one of the most challenging items in an arena—both from a design and operational point of view.

The ice floor is basically a single, refrigerated concrete slab without construction joints. Because fully loaded semi trailers will travel across it—and elephants may sit on it—the floor must handle these loads and still meet stringent criteria for flatness, which ensures consistent ice thickness and temperature.

Concrete ice floors are designed with a quick-melting system that heats fluid running through in-floor piping. The heated floor breaks the bond between the ice and concrete, allowing partially melted ice to be broken apart and removed to an ice-melt pit. The piping, itself, is typically constructed from either Schedule 40 black steel or polyethylene. While polyethylene is much less expensive, its temperature limits result in higher melting and removal times.

When determining the quantity and size of compressors needed for the refrigeration system, the designer needs to know:

  • Heat/mass loads placed on the ice from lights, people and the air itself.

  • How the ice floor will be operated.

  • How much equipment and power redundancy is desired.

Heat rejection is another consideration, and several options are available: reusing the same cooling tower employed for the facility’s HVAC system; using a separate cooling tower; or even employing an evaporative condenser.

Drainage must also be addressed. Specifically, a subsoil system is required to prevent moisture from coming in contact with the ice surface and forming ice underneath (see Figure 1). Along with being properly drained, the soil must be heated to approximately 40°F, and insulation must be placed between the slab and the soil to eliminate any possibility of permafrost—which would cause the floor to heave.

The air moisture levels in the arena must also be held in check. Air distribution itself must circulate in a pattern that doesn’t create soft spots on the ice. In southern climates, to prevent fog from forming over the ice, the building envelope design and moisture barrier must be brought into play to control humidity within the arena.

Smoke control system

One final arena design consideration is life safety, specifically smoke control. Such measures serve two primary functions: first, they help clear a path for people to get out of a building in case of fire; and second, they can reduce the number of exits required. This is the case, because many building codes allow the overall exit width to be reduced—and therefore the number of exit doors—if the facility is smoke-protected. While a reduction in exit width isn’t much for a 250-seat auditorium, in a space with around 20,000 people, the difference is tremendous. With a smoke-control system, the ratio of seats to exit paths can be increased while the number of exterior openings is decreased. Without this flexibility arenas would have doors around the entire building perimeter.

If these systems are designed incorrectly—or if local code officials are not engaged properly—these systems can greatly increase project costs. They may also delay completion of the building if the system doesn’t pass the acceptance test.

So creating smoke-control zones is a matter of deciding which concourses and public areas—and also which parts of the seating bowl—would benefit from an exit-width reduction. There are many options: They may operate simultaneously, by level, by quadrant or some combination thereof. The general rule is that more zones mean greater complexity for firefighters and an increased first cost.

In concourses and other public areas, the smoke-control zones should be designed with the sprinkler systems in mind, so that sprinkler flow switches activate the smoke-control system. In the seating bowl, sprinklers are often omitted, as the high roof structure would place them so far from any fire that either the heads would not activate or would be ineffective. Thus, for seating bowls, firefighters will activate smoke controls manually at the fire-control panel, or controls can be activated automatically by a network of beam detectors that monitor the event floor.

Exhaust and make-up air must be provided to each zone for a fully functioning smoke-control system. In deciding where to locate exhaust air ducts, it is important to remember that code minimums must be maintained for the above-floor heights of the exhaust opening bottoms. The next steps are to locate the make-up air intake, identify the flow patterns, choose the size of fire and calculate an exhaust rate. With this information, you can determine the amount of make-up air to provide mechanically, while keeping the force to open an egress door below 30 lbs., and leaving enough differential pressure to control the smoke’s movement. At this point, these determinations must be reviewed with the authority having jurisdiction. This is also the time to discuss the test method to determine code compliance.

Obviously, a fire of the size used in calculating exhaust needs cannot be ignited for testing the system without destruction of property, so an alternate method must be used. Even though cold smoke is often proposed as a substitute, it does not have the buoyancy of hot smoke and therefore is not a good acceptance test. A better test is to run the smoke-control system through its various modes, making sure dampers are in the right positions, the proper fans have turned on and off and, most importantly, that exhaust fans are removing the desired amount of air. This method of verifying exhaust volumes ensures that the design attains proper exhaust rates and meets the intent of the code.

Take the SBC Center system…

The smoke-control system at the new SBC Center in San Antonio, Texas, is an example of successful interaction with code officials during design. Several meetings resolved concerns about the fire size that was being modeled as well as many other issues. The result is a system that operates as follows:

In the bowl exhaust mode, two exhaust fans in each quadrant are engaged and exhaust 580,000 cfm of exhaust air. Mechanical make-up air is provided by two bowl air-handling units and one concourse air-handling unit per quadrant bringing in 100% outside air for 520,000 cfm total. The remainder is infiltrated through the exterior walls and doors. (See Figure 2 above for airflow patterns.)

The concourse is zoned by quadrant and by level, creating a complex system, but allowing the fire department to exhaust only a small area of the concourse, if desired. The system runs in the opposite direction from the bowl exhaust mode, shown in the diagram above.

Putting it all together

The number and complexity of systems in multipurpose arenas seems to expand with each new facility that’s drawn up. For example, there are improved mechanical shop-air systems, dust collectors, hoods to remove diesel exhaust and so on. Furthermore, many arenas now feature complex audio/visual, telecommunications and security systems.

Some of these systems help arena operators better understand their event costs so they can pass them on to promoters, producers and organizers. Other technology, such as the quick-melting ice floor system, allows a concert to be held the day after a hockey game, increasing the operating efficiency of the facility.

There are intriguing challenges in designing a modern multipurpose arena. For the engineer or engineering firm, the real challenge lies in meeting the needs of a myriad of event operators, sports leagues and media—all while ensuring the safety and entertainment value for fans.

Catwalks: A Special Arena Design Consideration

Essential to major arena systems design, catwalks are narrow walkways, typically suspended from the roof structure, that serve as the primary location for event lighting fixtures and show power panels.

Besides event, house and, occasionally, aisle light fixtures, other catwalk-mounted systems include:

Bowl work lights. These are floodlights of similar wattage, but are simpler in design and smaller in number. They are used during event setup and removal only.

Catwalk work lights. For show electricians, maintenance workers and others who must regularly navigate the catwalks, fixtures with compact fluorescent lamps are typically mounted on one side of the catwalk structure or overhead at appropriate intervals to provide sufficient safety illumination.

Photographic strobe lights. Professional photographers line up, inches from participants, along the event floor. But even with the event and house lighting systems in operation, strobe light trigger boxes are required to ensure pictures with even illumination on the players or performers. Their cameras plug into a “trigger” box in one of several locations on the event floor, and activation of the camera shutter signals numerous strobes mounted along the front edge of each catwalk to provide the additional light needed to capture the fast action.

Spotlights. Power for eight or more spotlights is typically provided along the perimeter of the arena bowl, usually on dedicated areas of the catwalk.

Memphis’ new arena

With such a multitude of purposes, the design and positioning of catwalks is key to an arena’s design. At a minimum, catwalks run parallel to both the sides and ends of the event floor and around the perimeter of the seating bowl. To accommodate event lighting for professional sports, a second row of catwalks is often required along the side.

For example, catwalks for the new multipurpose arena in Memphis, Tenn., will be suspended from the roof structure (see figure below). In addition to serving event lighting systems, the catwalks will permit access to spotlight and scoreboard platforms. Two rows of catwalks will be installed parallel to the court’s sidelines to meet the NBA’s illumination levels and uniformity requirements. An additional catwalk will encircle the bowl perimeter to meet vertical illumination requirements of baseline TV cameras and for access to spotlight platforms.

The angle of light incidence to the playing surface is an important consideration for both broadcasters and fans. To minimize glare at TV camera positions, the Illuminating Engineering Society indicates an optimal 45° angle from the event lighting fixtures to the playing surface. If this angle is much higher than 45°, the vertical light level will be insufficient for the cameras. If much below 45°, then fans seated across from the floodlights in rows near the playing surface will receive excessive glare.

To meet this criteria, yet integrate with the building structure, catwalks were positioned horizontally to achieve angles of incidence between 35° and 49°.

The NBA also has recommendations: The angle between the “inner” catwalk and the centerline of the court should be in a 20° to 30° range. The angle between the “outer” catwalk and centerline should be in the 45° to 50° range.