- By Bill Harris, Chip Lambert
- May 1st, 2011
It probably would not be easy for an elementary or high school student to hear the teacher in the middle of a downtown construction zone. But that is similar to the challenge that students encounter today in many U.S. classrooms.
Many schools across the country have classrooms that exceed the maximum background noise level of 30 to 35 decibels (dBA) recommended by the Acoustical Society of America (ASA). For example, recent readings taken at several Arizona elementary schools found noise levels of between 55 and 83 dBA in unoccupied classrooms. This is comparable to a typical day-night average rating of 79 dBA at center-city construction sites, according to Environmental Protection Agency (EPA) figures.
Working with the facilities and construction professionals who support them, educators and administrators in school districts across the nation are striving to create high performance schools that use less energy, have a smaller environmental impact and create a safer, more comfortable and more effective learning environment. This includes exploring practical and cost-effective ways to reduce classroom background noise.
In many cases, the process of reducing background noise includes upgrading or replacing old, noisy and inefficient heating, air conditioning and ventilating (HVAC) equipment.
Noisy Classrooms Affect Students, Teachers
Research shows that background noise can have a wide range of negative effects on students’ ability to hear, comprehend and learn. The impact is just as great on teachers who have to hold classes in a noisy environment.
For example, a 2000 study published by the ASA concluded that U.S. classrooms typically have speech intelligibility ratings of 75 percent or less, which means that students cannot understand every fourth word the teacher says. Other studies show that students in noisy classrooms fall behind academically and that talking loudly to be heard over the background noise impacts teachers’ effectiveness and morale.
The effects are compounded for children under age 13, whose listening skills have not yet fully developed. The impact of background noise is even more severe for students with hearing, learning or concentration problems, or those speaking English as a second language.
Recognizing the importance of speech communications to the learning process, the American National Standards Institute (ANSI) and ASA introduced a new standard in 2002 called ANSI/ASA S12.60 Acoustical Performance Criteria, Design Requirements and Guidelines for Schools. The standard, which defines the minimum acoustical requirements for classrooms and other learning spaces, was revised and updated in 2010. It covers both permanent and portable classrooms.
While the standard is currently voluntary, some school districts require compliance in the design of new schools and major renovation projects. Meanwhile, the federal agency responsible for enforcing the Americans with Disabilities Act has initiated rulemaking that would require the standard’s use.
Modern HVAC Systems Are Quieter, More Efficient
ANSI/ASA S12.60 addresses a variety of factors that contribute to the high level of background noise commonly found in today’s classrooms, including traffic noise and other sounds from outside the school building, noise made by classroom occupants and noise from adjacent areas within the school building.
The standard also addresses background noise from school HVAC systems. With close to three-fourths of U.S. public school buildings 30 years old or older, many are still equipped with aging, inefficient and noisy HVAC systems. A significant number are cooled by wall-mounted or ceiling-mounted air conditioning units that put compressors, blowers and other noise-producing components in the classroom itself, magnifying the impact of the noise they generate.
Thanks to technology advancements, modern HVAC systems are designed to keep students and teachers more comfortable, use less energy and are significantly quieter than earlier-generation systems.
To determine whether it is possible to economically meet ANSI/ASA S12.60 requirements, a leading HVAC manufacturer designed and built a classroom mockup on one of its manufacturing campuses. Company engineers designed the mockup to have characteristics comparable to those found in a typical U.S. classroom. They used commercially available, off-the-shelf HVAC systems commonly used in schools, along with industry-standard design and installation techniques.
Engineers tested a packaged rooftop HVAC unit, a zone-level air handler and a high-efficiency heat pump, all installed in typical locations above corridors adjacent to the mockup. Following a rigorous series of tests involving various system combinations and operating modes, the manufacturer’s research team concluded the ANSI/ASA S12.60 limit of 35 dBA can be met by following good equipment selection, design and application processes.
Using benchmark data from the Air Conditioning, Heating and Refrigeration Institute (AHRI), engineers estimated the increase in first costs required to meet the standard to be between 0.7 percent and 1.2 percent. The benefits of creating a quieter, healthier learning environment for students, teachers and administrative staff far outweigh the minor incremental costs.
Research Identifies Key Lessons for K-12 Design Teams
In the process of validating the feasibility of economically meeting the ANSI/ASA S12.60 standards, the HVAC manufacturer captured key lessons that will benefit K-12 design teams looking to adopt the standard in new construction or major remodeling projects.
- Determine the sound-power levels of the HVAC system components to be installed. Sound-power ratings can be determined with the help of an acoustical engineer, HVAC systems supplier or Energy Services Company (ESCO). AHRI Standard 260, which covers sound power ratings, can be found on the AHRI Website.
- Minimize airflow velocity in the ductwork to reduce regenerated noise.
- Use sophisticated acoustical analysis software available from an equipment manufacturer or ESCO to compare system sound levels for alternative systems and predict sound characteristics of a particular classroom.
- Use industry-accepted design and installation methods and look for potential paths that could allow outside noise to enter the classroom.
- Remove or isolate HVAC systems and components from the classroom whenever possible and install them in or above less critical areas, such as corridors, utility areas or mechanical rooms.
- Consider the tradeoff between acquiring quieter HVAC systems and implementing sound control techniques.
These are challenging times for educators and the design, construction and facilities professionals that support them. Enrollments are expanding, demographics are shifting, performance pressures are increasing, class sizes are growing and budgets are shrinking.
School districts are forced to do more with less and still create a better place for students to learn and instructors to teach. Improving acoustics and reducing the background noise in classrooms is an effective and economical strategy for creating a safer, more comfortable, more efficient environment in which students, teachers and administrative staff can do their best work.
Bill Harris is the vertical market leader responsible for the education business segments of Trane, a leading global provider of indoor comfort systems and services and a brand of Ingersoll Rand. Lloyd (Chip) Lambert is the education segment manager for Trane in North America. Lambert has more than 32 years of experience in the HVAC industry with mechanical contractors and major controls companies.