May 3, 2021 | Blog
With an air-borne virus threatening lives around the world, indoor air quality in schools is under closer scrutiny more than ever before. There are no mitigation codes to follow because the CDC and ASHRAE engineers are still actively developing safety standards as they study the ways the virus spreads. In this time of uncertainty, SMACNA contractors are finding ways to help schools meet rapidly evolving recommendations and build parent confidence.
“I don’t think that any one thing we do will resolve the pandemic,” cautions Christopher Yacu, senior vice president of International Test and Balance (ITB) in Northbrook, Ill. “But each of us can address our own areas of expertise. TAB services improve air flow, mechanical contractors add ionization treatments, and management enforces masking and social distancing measures. Together we complete the whole picture and improve safety.”
New Construction in Montana
Population density across Montana is generally low. Many rural school districts are fully open while population centers like Helena and Billings follow hybrid schedules.
Norpac Sheet Metal in Billings, Mont., recently completed a new $93 million high school in Bozeman, Montana, which will serve 1,500 students. “We bid the contract for Gallatin High School in May 2018, and construction duration was about eighteen months,” said Brooke Logan, project manager and estimator.
Covid-19 hit just as Norpac was finishing up the 304,000 square foot facility, but the school’s modern HVAC design already meets CDC and ASHSRAE recommendations for ventilation. “Large heat-recovery air handlers provide ventilation air to the building,” said Stewart Brown, vice president of estimating. “They bring in cold air through the heat-recovery wheel, and the warm inside air passes through the wheel on its way to exhaust outside. The air streams in the heat recovery units don’t cross, so the supply air is virus-free.”
Gallatin High stands on 57 acres of land, so a VRF system with a well field was a natural choice for the school. Norpac handled the project downstream from the heat pumps, installing 191,700 pounds of metal. Piping runs from the mechanical rooms out to the branch provider box, which uses hard copper piping and R-410A refrigerant. Fan coil units are hung for every zone, and ductwork and diffusers come off the fan coil units.
At 80 by 54 inches, the biggest ducts are in the mechanical rooms. “The air handling units in the mechanical rooms are the size of a Volkswagen,” Logan says. Norpac fabricated the ductwork at their inhouse shop in Billings, Mont., and shipped it 144 miles to Bozeman every week.
Most Montana schools use older technologies. School districts are purchasing air scrubbers and UV light units to supplement existing HVAC equipment. “You can install UV lights wherever there’s a coil,” Brown says. “On the remodel projects we’ve seen so far, schools are asking contractors to add UV lights to their air handlers.”
Air Testing and Balancing in Illinois
Public schools in and around Chicago, Ill., planned to start in-person classes in the fall of 2020, but switched to distance-learning due to rising COVID-19 cases. Many schools are continuing remote education, while other districts allow some students on campus. Since Chicago-area school facilities tend to be older, they generally avoid capital outlays by keeping their current equipment. Even a change in air filters can pile on costs. “When schools upgrade to MERV 13, they experience a static pressure drop because the bigger filters restrict air flow,” Yacu explained. “To compensate, they must increase fan size and speed, which can be prohibitively expensive.”
Testing and balancing helps schools maximize performance with careful adjustments, like ensuring that air flows through the entire filter. “We don’t want 90% of the air flowing through a small part of the filter,” said Yacu.
One cost-control strategy is to break large projects down into manageable steps by updating one section of the system at a time. ITB recently did a test and rebalance for the auditorium at Victor J Andrew High School in Tinley Park, Ill. For just $3,600, ITB increased the auditorium’s outside air intake to 30 percent.
Portable Air Purification Units in Minnesota
Public schools in St. Paul, Minn., opened early this fall, but closed in mid-November as local COVID-19 cases rose. Area schools are currently hybrid or fully remote.
ASHRAE’s “Reopening Schools and Universities” publication suggests that schools introduce “terminal or portable, all electric HEPA/UV Machines in each classroom.”
Albers Mechanical Contractors in St. Paul, Minn., has already designed medical-grade air purification units for a respected area health care provider and finds that schools want to adopt the same technology.
The core of the ISO-Aire purifier is a medical-grade HEPA filter with bipolar ionization and optional UV features to destroy viral DNA. Air enters the units at the bottom and exits from the top.
“The air does not flow across the student’s faces. We don’t want to spread air from someone who’s sick to the next person, but to quickly move particles out of the breathing zone,” says Kevin Albers, manager of marketing and sales. “These units push high and pull low to create proper circulation.”
“Their existing rooftop units cannot handle filtration higher than MERV 11, and adding UVC to the roof is difficult because you have to slow the air down to give the light time to destroy the virus,” said Chuck Albers. “The problem is where the people are, so the school district decided on an in-room solution. An engineer advised them to place purifiers in critical areas, such as the cafeteria.” So far, Anoka–Hennepin has invested more than $2 million in updates, including air purification.
An Alternate View of COVID Mitigation in California
Schools in Alameda, Calif., are currently restricted to distance learning. Elementary school students may return to the classroom in early 2021.
Steve Taylor of Taylor Engineering in Alameda, Calif., agrees on the value of air purification. “In some cases, existing buildings may not have mechanical ventilation systems because building codes used to allow operable windows to be the sole source of ventilation,” he said. “Schools are a good example. In that case, portable air cleaners may be the only practical way to provide effective ventilation.”
However, Taylor’s preferred approach is different from many contractors. Taylor believes that MERV 13 gives the best value for the operating cost. He is also cautious about ionization, citing the ASHRAE Building Readiness Guide.
“Relative to many other air cleaning or disinfection technologies, needlepoint bipolar ionization has a less-documented track record in regard to cleaning/disinfecting large and fast volumes of moving air within heating, ventilation, and air conditioning systems. This is not to imply that the technology doesn’t work as advertised, only that in the absence of an established body of evidence reflecting proven efficacy under as-used conditions, the technology is still considered by many to be an ‘emerging technology.’”
Given the current state of knowledge, Taylor advises clients to use purifiers with MERV 13 filters without ionization or UV. Whatever filtration system clients choose, he stresses that “the first and most important mitigation is source control.
If portable air cleaners are employed, then reminders should be posted in the vicinity warning that their use does not mean any other safety protocols, such as social distancing and wearing masks, may be relaxed.”
The Bottom Line
Whatever HVAC upgrades they request, clients must continue to follow good hygiene. “Infection from aerosols is not the predominant transmission, and it’s the only path that HVAC systems can mitigate,” Taylor emphasizes. “We do need to address HVAC mitigation measures and aerosol transmission, but HVAC measures can never be the only mitigation. They do literally nothing to reduce the risk of short-range (large- and medium-sized) droplet transmission that the CDC and WHO say are the dominant paths.”
This story originally appeared in SMACNews.