CHICAGO—When it was built in 1927, the Hilton Chicago was the largest hotel in the world. Although it no longer holds that title, today it provides the largest total meeting and event space the Windy City has to offer, according to the company.
Part of that space includes Salon C, a 29,000-sq.-ft.-plus convention facility that recently underwent a renovation. This included upgrading its 80-year-old constant flow air-handling unit to a variable air volume (VAV) system.
The renovation plan included adding new ductwork that would connect to thousands of feet of existing ductwork located in a sub-basement space just below the convention room floor.
Unfortunately, the old ductwork was rife with leaks, and Grumman/Butkus Associates, the engineering firm in charge of the renovation, knew that it would not accommodate the added pressure created by the new VAV system. The team also knew that replacing the ductwork or sealing it using traditional methods would add months to the project schedule and tens of thousands of dollars to the budget.
To solve the problem, the firm turned to local duct-sealing expert Joe St. Pierre and his team at Aeroseal Solutions, who used a duct-sealing technology called Aeroseal that works from the inside of ducts to find and seal leaks.
The sealant was blown into the duct interior via a single entranceway cut into the air handler. Using blocking foam, the team sectioned off and sealed, one by one, six separate sections that made up the entire legacy duct system. It took three days to effectively seal the entire network of underground ducts.
The total duct leakage was reduced by 95% and the new VAV system was ready for operation. “The result was pretty impressive,” said David Schaefer,
project engineer with Grumman/Butkus Associates. “If this new technology didn’t exist, we would have had to rethink the entire project—perhaps replace the entire duct system. This approach not only saved the hotel an unimaginable amount of money in material and labor costs, but it averted the enormous disruption associated with having to tear out and replace the existing ductwork.”
The Aeroseal technology was first developed in 1994 at Lawrence Berkeley National Laboratory. “The technology works from the inside of the ductwork, allowing it to locate and seal leaks without disrupting surrounding structures,” said Neal Walsh, SVP, commercial applications with Aeroseal LLC. “In the Aeroseal process, an aerosol-mist of sealant is blown throughout the interior of the ductwork. The microscopic particles of sealant remain suspended in the air until they reach a leak. Here they cling to the edge of the hole and then to other sealant particles until the leak is completely sealed.”
Leaky ducts can cause a number of problems, from health to energy waste. According to the U.S. Department of Energy, energy loss due to duct leakage costs Americans about $25 billion a year. Others estimate the loss at five to 10 times that amount, according to Walsh. For commercial building owners, duct leakage drives up operating costs several ways: the expense of heating or cooling air that never gets to its intended destination; raised or lowered thermostat settings to compensate for lost air; increased system cycling when the HVAC system simply comes on more often and runs longer; and fan use—leaks in ventilation systems cause the exhaust fans to run harder and longer.
Often overlooked, the cost of running HVAC fans can be substantial, and even a low amount of duct leakage can lead to a substantial increase in fan power consumption. Just a 15% leakage rate leads to an increase in fan power consumption of 25-35%. Higher fan speeds also result in the infiltration of more untreated air from the outside, which requires more energy to heat/cool.
“The American Council for an Energy-Efficient Economy estimates that sealing duct leaks can save building owners an average of 15-30% on their monthly utility bills,” Walsh said.
Leaks in ventilation ducts are responsible for a variety of issues related to health. “Duct leakage was found to be a root cause of the SARS outbreak in 2003 and New York City’s Legionnaires’ disease outbreak in 2015,” said Walsh. “It is a contributing factor in the rise of MRSA infections in U.S. hospitals and has been identified as a key factor in sick building syndrome, a common condition among building occupants that materializes in a variety of health-related symptoms, such as chronic headaches, fatigue, dizziness and nausea. In these types of cases, contaminants are drawn into the duct system via leaks and then spread throughout the building.”
Leaks can also lead to mold and mildew. “Insufficient ventilation (caused by leaks in the exhaust shafts), particularly in bathrooms, kitchens and other areas where moisture collects, can easily create mold,” he said. “This, in turn, can lead to a variety of health-related issues—sometimes quite serious. More disturbing is the fact that the duct leaks not only help create mold and mildew, they can also spread the dangerous spores from one location to others within the facility. Here again, the spores (along with other contaminants) can easily be sucked into the duct system through leaks and then blown throughout the entire building.”
At the Capital Plaza Hotel in Frankfort, KY, the owners estimate that by sealing the ductwork of their 10-story hotel/convention center, they are now saving around $24,000 a year in energy costs.
The work began with a proof-of-concept demo for the hotel where one section of the building’s entire ductwork system was sealed.
“During the demo, we got to see how the Aeroseal technology actually worked,” said Chad Braden, director of facilities at Capital Plaza. “The computer-generated graph follows the sealing process in real time, and we watched as the leaks were sealed and the CFM of lost air went down to practically nothing. There was no other way, short of tearing down and rebuilding the hotel, that we could have gotten anything near these results.”
The success of that demo led to the bigger project of sealing the hotel’s entire system. The sealing process took five days to complete.
The cost of the project was also significantly less than a full overhaul. “I was getting quotes for an overhaul of the HVAC system that ran $1 million to $2 million—it would have taken decades to pay back,” said Jason Delambre, energy consultant, Interdependent Energies LLC. “We opted instead to use Aeroseal for the ductwork. That dramatically improved the efficiency of the current system, allowed us to reduce energy use related to heating and the use of exhaust fans, and it solved a lot of issues related to poor ventilation. We expect payback on the duct sealing to take less than two years. Then it’s simply ongoing savings right off the top of the hotel’s monthly operating expenses.” HB