Iron Range Engineering

Target Field Tour

On Friday October 2, 2009 a group from Iron Range Engineering toured the new Minnesota Twins stadium, Target Field, located in downtown Minneapolis. The tour was led by Kyle Fritze, a Mechanical Engineer from M-E Engineers. Kyle acts as a consultant engineer, providing the link between the architecture firm Populous Architecture and the general contractor Mortenson Construction. Kyle would interpret the problems the contractor had with the design and relay the information to provide options for the architect. His title is Representative Engineer of the Mechanical and Electrical Processes. These processes are used in the building of the stadium, his specialty, however, is HVAC systems.

Design and Layout
The stadium location was selected from one of two spots. The chosen location was downtown Minneapolis, near the Target Center. The stadium has a very small footprint, as this was all the location allowed. The stadium was designed and built to fit around interstate 394 by the right field plaza. On the other side, a set of railroad tracks runs parallel to the third base line. Traffic will be an issue, and the light rail and public transportation options will be highly recommended. A passenger train will be added to act as a shuttle service to long distance locations. The field contains three main gates for the general public. The fan capacity is reduced by 15,000 from the 55,000 provided by the HHH Metrodome. Target Field has a sellout capacity of 40,000 fans.

Building and Construction
The building of the stadium was constructed by four main cranes that were centered inside the walls of the structure. They started building in right field, home of Target Plaza, in August 2007. Construction continued to work its way around home plate and into left field, ending near the service gate located in center field where the cranes were removed. The field was laid out using GPS, which allowed maximization of the space and precision in the location of design. In right field, the bleachers come within two feet of the Parking Ramp, and a large ad- panel was constructed to keep onlookers from peering in. Six levels make up the stadium: service, service mezzanine, main concourse, club, suite, and terrace concourse. It also is home to the largest canopy in MLB. The canopy is designed with the Minnesota winters in mind. There are four large legs and a main truss that support each section of canopy. This heavy support structure will be adequate for bearing the weight of the numerous lights, speakers, and snow that will accumulate during the winter.
During the early stages of development, there were up to 1,000 employees working on the jobsite at any given time. Now, as the construction process wraps up, they have reduced the number of employees down to about 300. On any given day, Kyle would have an average of three problems brought to his attention. These problems often included conflicts with designs and layouts that were not physically feasible for the construction crews to build. Kyle commented on the fact that engineers and architects don’t always agree, but spend long hours coming up with solutions that are both functional and aesthetically pleasing.

Technical Design
There are many different engineering aspects included in the operation of the stadium. These include, but are not limited to: heating, plumbing, electrical, environmental, and economical processes. The stadium contains four 400 ton air cooled chiller units that are in operational use. Each cooling unit contains 10 to 12 condensers. To improve efficiency of the heating system, exhaust air from the locker rooms is used to preheat incoming air. The exhaust air is blown over a heat wheel that rotates and heats the input air; therefore increasing efficiency and reducing cost. Believe it or not, one of the hardest things to configure in the construction of the interior design was the grease ducts. This was because of the 1/8 inch per foot slope from horizontal, required for the drainage of the steam and grease splatter given off while cooking. To keep all of the beer cold for the 12 bars and concession areas, 26 keg coolers were installed.
With all of the electrical needs of the building, two backup generators are required for emergency use. Both of the generators are diesel powered, one produces 1000 KVA while the other produces 800 KVA. NFPA Code requires them to run for a period of 30 minutes per month to maintain reliability and performance. Exhaust from the generators is routed out to interstate 394 to prevent it from blowing back into the stadium. For the lighting of the field, the canopy contains a light bar, on the outer face, that projects out on the field. The positioning of the lights will be done at night on a 10’ x 10’ grid. Each square foot of field is required to have 225-350 foot-candles of light intensity according to Major League Baseball.
The plumbing that ran exterior was surrounded by heat trace. Heat trace is a wrap that surrounds the exterior of the pipes. It is activated by a thermostat to maintain a pipe surface temperature above 32 F to prevent freezing in cold weather. The original design had only planned for 6,000 lineal feet of the heat trace; the actual stadium required 18,000 lineal feet. The domestic water enters the building at 50 psi from the city. Once it has entered, the water is pumped up to 100 psi to maintain the required 80 psi at the upper levels after head loss is taken into account. Below the surface of the field, 38 miles of heated water tubing runs throughout placed on six inch centers to keep the playing conditions of the field ideal. The water that flows through the pipes is heated by steam from a city garbage incinerator located near the third baseline next to the stadium.
Now that the Twins are going back to an outdoor stadium, there are many design features needed to make outdoor baseball possible in Minnesota. The field was cored out six feet deep and layered with six different levels of rock and soil to maximize the runoff of water. Underneath the playing surface, several miles of drain tile was laid out to handle up to a four inch per hour rain, which is required by Minnesota State Code. The sod for the field came from Colorado. During the winter months, a special, heavy duty, breathable tarp covers the field. It is designed to sit on the grass to minimize compaction due to heavy snow. The field will be heated during cold months by 38 miles of hot water pipe to prevent the problems that come with freezing. The stadium has many aesthetic features to provide a good experience to the fans while also being player friendly. One of these features is the big green backdrop built in center field to allow the batters to better locate the ball coming from the pitcher. The backdrop includes spruce trees to break up the design of the plain wall, while also giving the stadium some character. The seats of the stadium were also chosen to be green to give the fielders a better chance of picking up the balls in play. Because of the layout of the field and positioning of the stadium, the Twins are taking the first baseline dugout to utilize the sun and rain protection.
Target Field is an impressive engineering feat. As of right now, the field is right on schedule to be ready for play in the upcoming 2010 season. The cost to build the stadium was around 450 million dollars. The stadium is also on track to becoming Silver LEED Certified; this takes into account the efficiency and environmental impact. The stadium includes twelve bars, numerous suites, multiple seating levels, a large plaza in right field, and year round administrative offices for the Twins executives.