The system circulates a warm, water-and-glycol mixture through PEX tubing buried underground. The intent is to warm the root zone beneath the grass so the playing surface remains soft and forgiving to falling players, even at sub-freezing temperatures. The radiant heating system consists of roughly 28 miles (nearly 150,000 linear feet) of ¾" Wirsbo hePEX™ tubing, that serpentines from end zone to end zone, eight inches on center and ten inches below the 200-foot by 425-foot playing surface. The only connections are at the copper manifolds, positioned at the south end of the field, where each PEX loop begins and ends -- thus removing potential service issues to outside the playing area. The copper headers are fitted with stub-outs at the factory for making the PEX connections, saving substantial time on the job site.
Four Heating Zones
Like the interior of a home or a large office, the field is segmented into four heating zones, also running the length of the field from goal to goal. Each zone contains 42 loops and two temperature sensors that sit within underground boxes connected to one another with plastic conduit. If any underground sensors ever need to be repaired, all eight are on a GPS (Global Positioning System), according to Bennett, enabling service personnel to pinpoint the positions of the underground boxes to within 18 inches. “We also provide a complete photo log of the boxes’ installation, which should also help in locating them,” he says. On sunny days, the demand for warmth varies from zone to zone, depending on the position of the sun. The sensors in each zone communicate an average demand back to a series of control valves, which modulate the flow of warm water in response. The objective is to keep the root system at a consistently comfortable 65°F, says Bennett. “The field is warm and moist enough that it can actually grow grass in December or even January,” he remarks. “The freezing point for the glycol mixture is minus-25 degrees, so the system can be filled with fluid year-round, without the hassle and expense of draining and re-filling it prior to each season.”