Workers from the E.M. Duggan Co. unroll PEX tubing during the construction phase of Gillette Stadium in Foxboro, MA.

“The condition of the field can be our worst nightmare, or an answer to our dreams,” said one sports turf professional.

There’s a trend afoot today that has the artificial turf makers on edge — real grass. Lush, living, carefully nurtured turf is all the rage, and now that turf can be hydronically conditioned. According to some experts, what gives real turf an advantage, and players the best surface going, lies hidden in the soil where roots receive warmth from miles of pipe that circulate heated fluids.

Workers connect the irrigation mains with great care.

GILLETTE’S FIELD

The Patriots’ new radiant heating/turf warming system, manufactured by Watts Radiant (Springfield, MO), uses 153,000 lineal feet of PEX tubing that warms the soil. The manufacturer has installed similar systems for other sports facilities, including Safeco Field, the Arizona Diamondbacks’ field, and the Chicago Bear’s practice field.

Even with new developments in irrigation and soil management, the ability to grow turf is directly related to the root zone temperature. Constant root zone temperature helps to accelerate turf growth, allowing for faster repair of damaged areas. It also helps to maintain a more pliable soil condition.

With a turf conditioning system in place and doing its job, the result is a healthy grass playing surface that’s better cushioned, causes fewer skin abrasions, results in fewer serious injuries, and plays well.

In all, the system used 29 miles of PEX tubing.

DOES IT MELT SNOW?

“To do this we need a surface temperature greater than 32 degrees. In a turf system, our target isn’t the surface, but rather an area 6 to 10 inches down, where the root zone is. This layer is designed to maintain anywhere between 50- and 60-degree temperatures, depending on the turf, soil conditions, and climatic conditions.”

There will be times when a turf system will melt snow, though it’s really not designed to do this. According to Marshall, most turf systems aren’t operational during the weekends, when most games are played.

“The underground pipes are usually moving fluids [in this case, a water/glycol antifreeze mix] Monday through Friday,” said Marshall. “Typically, the radiant system in the field is turned off a few days before game day — just the opposite of what you’d think. If it did snow, and the system was on, there’s a chance that slush would form, becoming a real problem, endangering both players and field.”

A worker crimps PEX tubing to a large manifold. Note the protective collars used where the tubing intersects different layers of the field.

IT’S A GRASS ROOTS THING

Before a radiant design can be done, several factors must first be determined. “Among these,” said Dennis Brolin, the Patriots’ field superintendent, “are the actual soil conditions. Most professional fields are multi-layered, beginning with a solid base of compacted earth.”

Aeration of the soil is a key consideration, he said. Different fields will require different aeration techniques, but one thing is the same: something must penetrate the field in the aeration process. The radiant tubing, and any irrigation equipment, needs to be deep enough to avoid being damaged.

According to Marshall, once the physical properties of the material and conditions and the tubing depth are determined, a preliminary radiant design is begun. This phase of the design process determines the amount of tubing required to cover the field, the BTU load, supply water/glycol temperature, and flow rates.

“Our soil temperature tests have been perfect,” said Brolin. “We’re seeing very uniform heat at the 9-inch-deep root zone mix. There’s minimal temperature variance throughout the whole zone.”

NO TWO ARE ALIKE

For the Patriots, a six-zone system was created with three zones on either side of the 50-yard line. Tubing runs parallel to the sidelines, from the end zones to midfield and back. Four-inch manifolds were installed along each end zone to connect the 3/4-inch PEX pipes.

According to Marshall, supply and return manifolds were installed in trenches along each end zone. Main supply and return lines were placed in trenches that ran along the sideline. The mechanical access is located in the corner of one of the end zones. Twelve 4-inch black iron supply/return lines access the mechanical room at one point. PEX tubing lengths were 425 feet, which allowed for the tubing to go from the manifolds to the 50-yard line and back.

Special factory-produced elbows were made to accommodate the curvature of the field.

The tubing is secured to the field with the use of Watts Radiant RailWays and is spaced 8 inches on center. While the system was under the pressure test, sensors were installed in the field.

The mechanical system consisted of six Taco zone circulators and a DDC temperature control system. The DDC allowed for remote access to the system, remote monitoring, and history tracking. The zone load is approximately 10.5 million BTUs and the total system load is nearly 12 million BTUs. This load is supplied by an Alfa-Laval heat exchanger interfaced with the venue’s power plant located in the stadium.

“Nothing will ever replace grass,” concluded Brolin. “But you’ve got to have the system in place to support it. Every detail has to fall in place. It all comes down to quality control — the right plan, the right installers, and the right materials, manufactured to perfection. Watts Radiant and Emerson Swan helped us design and install what I’m confident will be a near-perfect system. So, stay tuned and watch us take another Super Bowl victory.”

THE WINNING TEAM

Publication date: 11/11/2002