“Prefabricated mats were the key to staying on schedule. Because we were in the middle of a new stadium project, laydown space was at a premium. Controlling the amount of material on-site, as well as having the material ready when we needed it, was critical to our success. Working with REHAU on the delivery of the prefabricated mats and headers allowed us to complete the installation on time.”
--Adam Grahek, project manager for Harris Mechanical.

Allianz Field, Home of Minnesota United

REHAU REHAU RAUMAT used in hydronic turf conditioning
to extend soccer season for midwestern MLS team

In the spring of 2015, the board of governors of Major League Soccer granted an expansion team spot to Minnesota. Shortly after, the “Land of 10,000 Lakes” announced it would build a state-of-the-art stadium for its Minnesota United FC soccer team, nicknamed “the Loons” after Minnesota’s state bird.

Allianz Field is a $250 million, 346,000-sq-ft (32,144 sq m) facility in St. Paul with seating for 19,400 fans. It offers 25 suites, 38 semiprivate boxes, four club rooms and a 2,300-sq-ft (214-sq-m) retail store.

While fans enjoy the many amenities of the new stadium, what they may not realize is that under the pitch is a system of REHAU RAUPEX O₂ barrier crosslinked polyethylene (PEXa) piping through which a warm water/glycol solution circulates, allowing field managers to control the growing season and the dormancy of the Kentucky Blue Grass turf—with less maintenance. Keeping root zone temperatures steady means healthier, greener grass to withstand the rigors of play.

“The main benefits of turf conditioning are extending the season in the fall and getting a head start on turf management in the spring, especially for a stadium in the northern climates,” explained Mike Day, the turf heating specialist at Denver-based ME Engineers.

“These systems allow athletes to utilize the playing fields sooner in the spring and longer in the fall, especially the natural turf fields,” added Adam Grahek, project manager for Harris Mechanical. The network of embedded RAUPEX pipe extends past the pitch to the warning track. Installed underneath the piping is a drainage system that “acts as a vacuum when it rains by sucking air and water out of the sod and aerates the field by blowing air into the sod,” noted general contractor Mortenson in one of their newsletters regarding the Allianz Field project.

Scoring with prefabbed mats

A typical turf conditioning system consists of a boiler plant that heats a water/glycol solution. Custom-made headers circulate the solution through miles of RAUPEX circuits buried 10 in (25 cm) under the playing field surface. The system controls are set to warm the root zone, so the surface of the field remains in player-friendly condition during the season, regardless of outdoor conditions.

At Allianz Field, the team owners requested the addition of a turf-warming system, Day said. “The biggest challenge was completing the field installation before the brunt of the Minnesota winter hit us,” he added. Grahek noted that the installation challenge was a result of the everchanging
schedule. “We had many rainy days that delayed access to the field,” he said. “This resulted in completing and testing quadrants in lieu of two sections as originally planned.”

With the weather posing a significant concern for the design and installation teams, Harris Mechanical knew the only way to keep to the construction
schedule while coordinating with the other trades (electrical, controls, irrigation, storm utility, concrete and excavators) was to use a radiant mat product. Harris brought REHAU onto the project and worked with account manager Mike East to come up with a solution to speed up the installation:
prefabbed mats.

“Prefabricated mats were the key to staying on schedule. Because we were in the middle of a new stadium project, laydown space was at a premium. Controlling the amount of material on-site, as well as having the material ready when we needed it, was critical to our success. Working with REHAU on the delivery of the prefabricated mats and headers allowed us to complete the installation on time.” Adam Grahek, project manager for Harris Mechanical.

Project:	Allianz Field \| St. Paul, Minnesota
Type of construction:	Athletic field, opened 2019
Scope of project:	96,000 sq ft (8,919 sq m) of heated area
Mechanical engineer:	ME Engineers
General contractor:	Mortenson Construction
Mechanical contractor:	Harris Mechanical
REHAU systems used:	Turf conditioning (RAUMAT^TM radiant mat , RAUPEX^® pipe, custom-fabricated headers

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Prefabrication is a streamlined approach to construction. It saves time on the jobsite, which reduces costs, especially labor costs. Modules constructed in a controlled environment to specific standards are consistent in quality. There is less disruption on the jobsite, which helps everyone stay on schedule.

East had built mats for warehouse projects before, but this was the first prefabbed turf conditioning system for the radiant heating manufacturer.

The prefabbed turf system consists of 86 mats, 136,000 ft (41,453 m) or almost 28 miles of 5/8 in. RAUPEX pipe and 26 prefabricated custom HDPE header assemblies with stainless-steel F2080 outlets—all to heat a 96,000-sq-ft (8,919 sq m) area. The system includes four zones to address shading and ensure an even temperature profile. East coordinated the complete system design with Day; REHAU designer Skip Daugherty completed the pipe layout design. The design target for the root zone temperature was 60˚F (15.6˚C), although the system may typically operate at 55˚F (12.8˚C).

A 4-in. HDPE header delivers the warm water/glycol solution to the radiant piping grid and returns the fluid to the boilers. Headers are custom-fabricated piping manifolds precisely spaced and zoned to match the unique conditioning requirements of the field.

“On this field, we optimized the cost and installation time by shifting the typical orientation,” East explained. “We rotated the headers to run along the end lines of the field and the circuits run to the center and back. The result is longer circuits but a reduced number of headers.”

Once the prefabbed mats were delivered, a five-person crew from Harris installed all the mats and headers in under six weeks, Grahek noted. The Kentucky Blue Grass was then placed on top of the system and “winterized” during the off season. While East and Daugherty lent their expert design services to the project, local REHAU sales manager Jeff Halter provided on-site support to ensure a smooth and successful installation.

The expedited install of the turf conditioning mats “allowed us to start up the system in mid-February and have a great field to play on opening day, even with a few late season snowstorms,” Day said.

Winning the match

“Because of the layout of the heating mains along the perimeter of the field, the residual heat not directly used for the heating mats under the turf allowed for a sort of ‘free’ snow-melt and de-icing system of the concrete track along the west and north parts of the field,” Grahek explained. “All this with no additional heating capacity added to the original design.”

In addition to the radiant heating/turf conditioning system, Harris Mechanical was responsible for the hydronic heating system in the mechanical room on the service level of the stadium, the HDPE mains from the mechanical room to the field, field sub-air rough-in and drainage vaults, and irrigation rough-in from the irrigation room to the field. To help with the site’s sustainability goals, recycled rainwater from the stadium’s canopy supplies the irrigation system.

Support from REHAU helped the mechanical engineering and contracting teams resolve issues before they became problems.

“REHAU support was outstanding,” Grahek recalled. “Having local and national support allowed for fast responses to issues that came up, such as quick product delivery when we needed it. We have used a competitor’s product for similar projects in the past. I believe REHAU exceeded our expectations.”

Day agrees, adding: “Mike East was helpful on this and other projects. He and his team were accommodating in laying out circuiting in the four zones.”

Completed in February 2019, the stadium saw its first MLS game on April 13. “The head groundskeeper, Ryan Moy, is very happy with the system,” Day noted. “With the wireless control technology we provided, he can monitor the system from anywhere.” The state-of-the-art facility has helped revitalize its neighborhood, and Loons fans have virtually scooped up all of the tickets for every game. Visible from a major interstate, Allianz Field is another crown jewel in the Minneapolis-St. Paul sports scene.