Using Hydronics to Heat Football Fields

Hydronics systems? Football? While you may not hear those terms in the same breath every day, there’s actually a mind-blowing amount of design and engineering that help keep football field surfaces playable through the cold winter months.

First, some context

With this year’s big game being played in Tampa Bay, frozen ground won’t play a factor, but January's NFC championship game took place at the site of probably the most famous instance of frozen turf in history - historic Lambeau Field.

Green Bay football is known for many things: juicy brats, rabid fans, and some of the coldest temperatures in the entire league. Pair those frigid thermometer readings with Lambeau’s natural grass surface and you’ve got a potential field-sicle on your hands. Pro football fans of a certain age will remember 1967’s “Ice Bowl,” the game that cemented (iced?) Lambeau’s place in football weather lore and inspired its wintertime nickname – The Frozen Tundra.

Believe it or not, Lambeau's entrails were outfitted with an electric heating system at the time. However, they were no match for that day’s freakish weather conditions (-13°F at kickoff), and they failed. Today’s football playing surfaces are highly engineered structures designed with durability, safety, and seasonal weather in mind. This post will focus on the latter, and doing so means we’ll need to head underground to the layer cake of soils and systems that comprise the modern gridiron's foundation.

Lambeau’s system, installed in the late 90s, is considered one of the league’s most advanced and served as the blueprint for systems in other cold weather cities with outdoor stadiums like Kansas City and Pittsburgh.

How it works – system components

We don’t work on heated field systems at SRC, but we know our way around hydronic systems. And, basically, the systems seen in NFL stadiums are just mega-scale versions of the systems used to heat bathroom floors or sidewalks in colder climates. The components that make up these systems are:

• Hot water boilers
• Circulator pumps
• Expansion device
• Mixing valve
• Zone valves
• Controls

System mechanics

Everything starts in a boiler room located beneath the stadium. There, massive boilers heat a glycol solution, which is then pumped out to the field’s subsurface. There, a labyrinth of PEX piping operates similarly to a radiator in an old home, providing radiant heat to the surrounding soil. 

The system must be properly balanced to work efficiently. Balancing is a primary challenge in hydronic systems. This describes the process of achieving and maintaining even distribution of pressure, heat, and working fluid throughout the system. Proper balancing eliminates hot or cold spots and facilitates consistent flow rates, which contributes to improved efficiency.

Design specifics

Piping configuration is one area that impacts system balance. Single-pipe and two pipe systems are some common examples:

Single-pipe

• Single pipe used for both return and supply
• Hot water leaves the boiler and is pumped out to the system’s terminal units (radiators, coils, or PEX in this case). Once it leaves the final terminal unit in the system, it’s pumped back to the boiler and the process starts over.

Two-pipe

• Separate piping loops for supply and returns
• Popular in larger systems

These systems typically make use of reverse return, meaning the first terminal unit that is supplied with glycol will be the last to return to the boiler. This helps to balance the system by ensuring even pressure drop. Since we’re on the topic of football, think of this as being similar to the popular “snake draft” format in fantasy football leagues, designed to promote competitive balance.

Zone control

Another feature of under-field hydronic systems is their ability to disproportionately supply heat to different areas of the field. This is known as zone control, and is used to compensate for changes in the sun’s position throughout the day.

Zone control is achieved via a network of Direct Digital Controls (DDC) zone valves throughout the hydronic system. First, temperature probes throughout the field signal that part of the field needs more or less heating. Then, the zone valve will open or close to adjust flow of the heated glycol mixture through that section of the field. When a section of the field reaches or surpasses the desired temperature, the valve closes allowing the fluid to bypass the loop and continue to other zones that may need it.

So, there you have it, stadium hydronics are the invisible 12^th man that help keep players safe and fields playable. From everyone at SRC, enjoy the game!