UNF experiment tests claims of heat reduction under glass roof.
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JACKSONVILLE, Fla. — It's the most expensive building project in Jacksonville's history.
The Jacksonville Jaguars have plans to renovate Everbank Stadium into what they're calling "The Stadium of the Future". The price tag on the renovation and surrounding neighborhood development is $2 billion and one of the key pieces of this project is a glass roof.
The Jaguars and their architecture firm, HOK, say that the glass roof will actually reduce the heat inside the stadium. But will that be the case?
By now we've all seen renderings of "The Stadium of the Future" and its glass roof. We've also heard the claim of a reduced heat factor from Peter Broeder, Design Principal for HOK, the architecture firm that will install the roof.
"The chrome reflective quality of it is going to shield heat on the fans, solar heat, so it's going to reduce the solar heat gain for the fans by about 70%," Broeder said on June 7 when renovation plans were announced.
That's a huge claim for a massive problem at Jaguars games. Many fans stay away from games early in the season because of the heat and lack of shade.
"Anyone who's been seated on the eastside of the stadium for a 1 o'clock kickoff on a hot September day knows it's almost unbearable," said Jaguars President Mark Lamping when the stadium renovation plans were released.
That's one of the reasons why the Jaguars want to invest in ETFE technology for the roof. But will it work? And how will the Jaguars avoid turning their stadium into a greenhouse?
For that answer we went to the University of North Florida. The Physics and Engineering departments at UNF joined in an interdisciplinary effort to test the claims of heat reduction for the fans under the special type of glass.
UNF physics professors Dr. Greg Wurtz and Dr. Dan Santavicca created a special film coating that they believe is close to the type of glass that the Jaguars hope to use in their renovations.
UNF engineering associate professors Dr. Steve Stagon and Dr. John Nuszkowski designed, built and tested the experiment. Dr. Nuszkowski demonstrated the effect different types of glass would have on temperature inside of 4 different "mini-stadiums".
One mini-stadium was covered with glass, one was open-air like the Jags current stadium, one has window tinting and the fourth is covered with a material that Dr. Nuszkowski believes is close to what the Jaguars roof will be.
"Basically an aluminum coated acrylic glass to give it a mirror-like finish so it has a coating that is 0.1% the thickness of a human hair, so it's 100 nanometers is the coating on the glass," said Dr. Nuszkowski.
The boxes were placed in the sun shortly before 1 p.m. on a day that was 88 degrees in Jacksonville. After 4 minutes, the open air Jags replica stadium read 100 degrees because it was in direct sunlight.
"You can see the temperature is going way up because of it," said Dr. Nuszkowski.
The Jags proposed glass mini-stadium temperature gauge read 86 degrees after 4 minutes.
More time elapsed as the experiment continued and the mini-stadiums baked under the Florida sun.
15 minutes went by, consider our mini-stadiums midway through the 1st half of a regular season game. The mini-stadium with a normal glass roof read 138 degrees; that's the greenhouse effect.
"Over here with no glass, so more like the current Jags stadium we have 124, 126 degrees Fahrenheit," said Dr. Nuszkowski.
The inside of the normal window tinting mini-stadium was 130 degrees.
"And over here with the full reflective mirror like finish at the tip we have 102 degrees Fahrenheit," said Dr. Nuszkowski, "by far our coolest."
That's a difference of more than 20 degrees between the current open-air model and the custom glass. But how does it work?
"From the sun you have solar energy coming in, which is the energy the people in the stadium would feel," said Dr. Nuszkowski, "so the glass itself with the reflective coating reflects most of that solar energy back out into the atmosphere."
In this experiment the replica of the Jags proposed glass was the most effective way to keep temperatures from skyrocketing by reflecting solar rays away from the mini-stadium. Simply being in direct sunlight will make you feel warmer than the air temperature, but the more solar rays reflected back into the atmosphere means the more comfortable the conditions will be for fans in the stands, assuming the city and the Jaguars agree to terms on "The Stadium of the Future," but that's a conversation for a different day.
Below are some extra notes from Dr. John Nuszkowski about the science behind solar heat gain, heat factor as well as the physics behind reflective glass.