Mechanical system vibration can have a major impact on classroom noise. Equipment placement needs to be carefully considered to prevent unwanted noise, siad Carrier's Ted Cherubim. Equipment such as this rooftop unit installed at Douglas Adams Middle School (Brentwood, Calif.), should be installed over a corridor instead of over a classroom.

In order to understand the future of the school market, you have to look at and understand the past while staying on top of new technologies and codes. About 45 percent of the nation’s schools were built between 1950 and 1969 and about one half of the 115,000 U.S. schools have some connection to an IAQ problem.

“This provides opportunities for contractors to make schools operate the way they should,” said Ted Cherubin, Centurion™ rooftop product manager with Carrier Corp.

According to McGraw-Hill Construction, 242 million square feet of new education construction has been planned this year. “It’s experiencing about a 3 percent compounded annual growth rate,” Cherubin said.

“LEED (Leadership in Energy and Environmental Design) for Schools will be a major driver and a welcome addition to this market,” he said. “Approximately 40 schools are LEED certified, and another 300 are in the application process,” he added, citing engineering sources.


“Energy savings and sustainability are important factors for LEED,” Cherubin pointed out, “but the U.S. Green Building Council and LEED for Schools are making sound levels a major consideration. Carrier, being a rooftop manufacturer, finds that challenging, but we understand that and we see it’s definitely necessary.”

According to studies such as “The Impact of Classroom Acoustics on Scholastic Achievement” (Sutherland and Lubman), “It is clear that excessive noise and reverberation interfere with speech communication and thus present acoustical barriers to learning.” Noise levels can have an even more profound impact on students learning a second language, or those with existing hearing loss or learning impairments.

Mechanical system vibration can have a major effect on classroom noise. “The air distribution system is the avenue between students’ ears and the roof,” Cherubin said. “With good duct design and proper turning vanes and insulation, there are typically no problems.”

“Equipment placement needs to be carefully considered to prevent unwanted noise. Air conditioning units that are installed over a corridor (instead of over a classroom), and properly ducted, are the best for sound control,” Cherubin said.

“Where you get into trouble is placing the unit right over the school room and having short duct runs. That could create a noise issue. Poor ductwork design will take any noise and dump it right into the space.”


According to Cherubin, rooftop units are being applied in a lot of new and existing schools. “One of the main reasons is that it gives you a convenient and easy path to fresh, outdoor air,” he said. “Fresh air can go into the space, in a controlled environment from a temperature, humidity, CO2, and volume standpoint.

“We also have seen our fair share of rooftop units in modular classrooms,” he said. “Districts are asking us to make special provisions to our units for those modular structures.” Weight restrictions, for instance, mean that the unit itself may need to be applied in a position other than on the roof.

“They need air conditioning, and they don’t want to sacrifice on IAQ solutions,” he said. “New rooftop units are equipped to handle the needs of the smaller-sized equipment required for modular schoolrooms.”

“At Carrier, we want an efficient product to create low sound and optimum comfort,” he said. That includes humidity solutions such as the Humidi-Mizer™ Adaptive Dehumidification system. “Energy recovery ventilators also are a big trend because they can deliver more fresh air for the students more efficiently.” CO2 control, he added, can sense occupancy based on carbon dioxide readings and modulate system operation accordingly.

These products all are available on the company’s packaged rooftop products, but they may increase the weight of the unit. The building’s weight restrictions must be factored into the design and handled appropriately, whether that means placing the packaged system elsewhere or reinforcing the roof.


“We at Carrier realize many schools and school districts struggle when looking at initial investments and the ability to provide comfort solutions that meet codes,” Cherubin said. “There are different levels of HVAC systems, from meeting the basic code requirements up to those with more bells and whistles, but what we’ve found nationally is that they try to save money on maintenance,” he said. “Whether it’s with their in-house staff or outside maintenance and service contractors.”

“Both groups, having more influence on what is purchased, are telling administrators, ‘I could reduce my maintenance time and cost with the right product.’ ” Features such as accessible components can increase a system’s maintainability. “The new enhancements not only add to what the market has been asking for, but they also greatly expand the application range for these products while providing justifiable value and comfort.”

The key to convincing administrators of the importance of maintenance, he said, is to prepare a lifecycle analysis. “You have to put maintenance in front of them with energy savings,” Cherubin said. “Their experience with rooftop units in the past may not be favorable, but a lot of newer designs make things easier so they can do more maintenance in-house.” If a contractor is hired, he can cut the amount of time he spends working on the roof. If you make it easy to maintain, they’re going to do it.

“Maintenance has got to be accounted for somewhere,” he continued, “either by the district’s maintenance personnel or outside service contractors. Make sure that it is mentioned. Make sure that the maintenance includes measurable operation values. If you measure things, you can keep a handle on them.”

“There are potential liabilities for not doing maintenance,” he said. “If a school district doesn’t make sure the condensate pans are cleaned, for instance, biological contaminants could enter the airstream, where they are delivered to students and faculty. You could run into some major liability issues.” ASHRAE 62 mandates sloped condensate pans to help minimize the issue and prevent standing water in the condensate pans.

“One of the main benefits of a unit that is truly able to be maintained is lower operating costs. Let’s face it, if it’s easy to perform the maintenance, it gets done and thus the coils are clean, the filters are changed as necessary, and the unit operates efficiently as it’s designed.”


Training staff and administrators are essential to a system’s successful operation. “Our local sales force puts working units on trailers and drives them around to school districts for training. Service and maintenance people want to see how filters come out, how condensate pans are cleaned, and how fan belts are adjusted. That way they know what’s out there, what they’re getting, and they can plan maintenance.”

Training also means making sure maintenance staff and administrators know enough about the equipment’s operation to know when not to shut it off. “An engineer’s study found that problems were occurring because it was a nine-month school year and during those three months off, the unit was shut down.” The maintenance staff changed the system from its designed operation; it was supposed to come on two hours a day to draw the moisture out during those three months. The adverse effects on the IAQ were dramatic.

“Setting the correct parameters from the start and maintaining them are very important,” Cherubin said. “Many people are learning by bad experiences.”

Sidebar: Trend Watch

Thermal displacement in the school market currently is being tested in California, Cherubin said. Thermal displacement supplies conditioned air in the lower portion (occupied) of the building or room, sweeping it across the students instead of pushing it down from ceiling diffusers. It offers energy savings due to the lower required airflow to move the air, a smaller conditioned zone, and also provides a comfort advantage.

“It provides cooling and dehumidification at the spot where students are sitting.” If this trend takes off, it could lead to the development of “a really special rooftop unit.”

Publication Date:08/06/2007