The new multipurpose facility at the Central Wyoming Fair Grounds in Casper, WY, was a longtime dream for the residents of Natrona County and fair manager Tom Jones. That dream became a reality during June of 2000 when the “Arena” hosted the College National Finals Rodeo. The Arena is now host to everything from indoor soccer matches to trade shows, and has already booked a return engagement for the 2001 Rodeo Finals.

Being an agricultural community, having an indoor facility in which to ride, rope, and train was important to the local culture. Having an hvac system that could handle the dust, smell, and humidity was also important to the patrons who paid for the Arena through private donations and a 1% county sales tax increase. The 95.5-acre fairground is the largest in Wyoming.

The 76,875-sq-ft facility posed some unique mechanical system design problems. The Arena’s permanent dirt floor is 275-ft long and 148-ft wide. A temporary overlay is available for other events that need a hard floor. The side walls are 32-ft high. Permanent aluminum seating with back rests totals 2,094, and portable seats can accommodate another 1,350 people. About 60,000 sq ft is utilized for the primary event hall. The balance of the facility is composed of four concession areas, three 25- by 25-ft classrooms, and administrative offices.

The primary hvac design challenges were to keep the dust, humidity, and smell away from the seating area during livestock events, while providing a good level of comfort in the stands and on the arena floor for the wide range of events that would be held in the facility.

Meeting Project Parameters

After the funds were raised for the project, the team of Casper, WY-based designers and contractors was selected through an interview process. Tim Schenk with Gorder South Group was the architect. Gary Kloefkorn with Kloefkorn/Ballard Construction & Development Co. was the general contractor. Dave Woodward with the Casper Tin Shop and Kevin Schilling with PWA Consulting made up the mechanical-design team.

An initial search for any facility having similar hvac requirements was unsuccessful. The group then decided to establish its own project parameters and mechanical specifications. An air turnover of three times per hour led to a ventilation rate of 105,000 cfm for the arena portion of the building.

Working With Modine

Airsystems representative Joshua Marklowitz of MJM Associates (Englewood, CO) the group selected three Modine Airsystems (Racine, WI) Model QR225 direct-fired, makeup air units. These rooftop, natural-gas units are rated 35,000 cfm each and have an 80/20 return-air option.

Providing 80% of the return air compared to the 75/25 ratio offered by some others was a key difference. The design and specification assistance provided by MJM Associates and Modine Airsystems’ also contributed to the final decision. Each unit has a maximum output in excess of 5.7 MMBtuh. The 100% thermal efficiency results in lower fuel bills.

Building Pressurization System

Part of the mechanical installation involved a carefully planned, building-pressurization system. It uses a photohelic pressure control that opens or closes the makeup air unit’s outside-air, burner-bypass dampers to maintain a constant building pressure. This is an important feature in relation to the nine stages of exhaust ventilation. A two-speed Cook wall-prop exhaust is installed across from each Modine Airsystems unit.

The low speed is energized to match the minimum ventilation rate of each direct-fired burner. The high speed for the three fans plus a fourth wall-prop unit can be energized manually to set the desired ventilation for the space. The photohelic pressure sensor matches the outside air volume to the exhaust rate.

A Maxitrol sensor maintains the desired discharge air temperature during cold-weather operation. The three makeup air units are evenly spaced above the seating area. Each unit is connected to a 54-in. exposed spiral duct installed below. Air is distributed from the ducts with Metalaire drum diffusers. Large return-air ducts with 2 in. of lining return up to 80% of total volume to each unit. The sound attenuation above the seating area is excellent. All of the supply air either moves towards the seating area or towards the exhaust fans. In both cases, the air is always moving away from the spectators, so the seating-area air stays fresh and clean.

The Modine Airsystems QR225 direct-fired, makeup air units are very easy to maintain. Easy access enables the Arena maintenance staff to handle routine filter changes and fan bearing lubrication in minutes. No other maintenance has been required to date.

The first major event held in the new facility was the National College Finals Rodeo. The system was tested with a full house on the six days of competition involving contestants from all over the United States. The air movement was quiet, and there was no noise associated with equipment operation. Since the rodeo, the mechanical system has been well tested by other events and crowds of varying size. Overall, the system has exceeded the expectations of the design team and the building managers. After handling the dust, smell, and humidity from the rodeo, there was no doubt that the hvac system could handle the lesser challenges posed by various other groups and organizations that utilize the Arena throughout the year.