When working to improve student and teacher comfort, humidity and temperature are often the most common heating, ventilating and air conditioning (HVAC) issues that school facilities managers address. While humidity and temperature management are essential to providing a healthy and comfortable indoor environment, the acoustical characteristics are commonly overlooked. Classroom acoustics can directly impact students’ and teachers’ ability to concentrate and communicate—thus diminishing the overall learning experience. As U.S. school districts struggle to stretch limited construction funding, classroom acoustics is emerging as a critical consideration in new and existing school building and design.

Schools have earned a D in an assessment of the nation’s infrastructure, according to the American Society of Civil Engineers’ 2005 Report Card for America’s Infrastructure (http://www.asce.org/reportcard/2005/index.cfm). This is hardly the ideal environment in which children, our most precious commodity, should learn. Creating a comfortable, learning- friendly environment for U.S. students can help improve their academic performance. One way to ensure such an environment is through good acoustics in the classroom.

Research has shown that noise and reverberation (the persistence of sound after the source itself stops) adversely affect normally developing young children more than they affect typical adults 1. It is difficult for a typical child below the age of 13 to hear what is being said in a classroom if there is substantial background noise, which can come from internal sources such as the HVAC system, computers, electrical appliances and the children themselves—or external sources such as highway and airport traffic.

Poor classroom acoustics interfere with all students’ learning but pose a particular challenge for those with special needs. This includes  students who are:
• Coping with learning disabilities. According to the U.S. Department of Education, in 2002 approximately 3.9 million children, or 8 percent of those enrolled in public elementary and secondary schools, were classified as having mental retardation, emotional disturbance, or a specific learning disability.
• Learning in a second language. A 1998 U.S. Census Bureau report states that 2.5 million school-aged children had limited proficiency in English. This makes up between five and 11 percent of all school-aged children.
• Having trouble hearing due to ear infections or more permanent conditions like noise damage. Such children may have cochlear implants, which are small, complex electronic devices that can help provide a sense of sound to those who are profoundly deaf or severely hard of hearing. More and more children have these implants, which can, under the appropriate conditions, give a useful auditory understanding of the environment and help them understand speech.

Acoustical Standards
The current standard for classroom acoustical design was developed by the American National Standards Institute (ANSI) and the Acoustical Society of America (ASA). The standard, ANSI/ASA S12.60, Acoustical Performance Criteria, Design Requirements and Guidelines for Schools, was completed and approved in 2002 and is the result of a petition by the parent of a hearing-impaired child. It divides learning spaces into several categories and sets maximum limits for each. The maximum permissible background-sound level for typical classrooms is 35 dBA, with a maximum reverberation time of 0.6 to 0.7 seconds (depending on room volume) 2. These are very low levels that do not match the current acoustical environments in many U.S. classrooms. The challenge is to design classrooms that meet children’s unique needs for sound (as well as lighting, comfort and seating). All sound sources in a room must be considered.

Solutions
Good acoustics in the classroom can be achieved if they are considered at the outset of the design process, and with early collaboration among school planners, architects, contractors and suppliers. The good news is, excessive mechanical noise can be substantially reduced at little or no extra cost if the system is designed properly, according to ASA. Many factors should be considered, including:
• Where the building is situated – coupled with good landscape design, this can help keep outdoor traffic-related noise at a minimum.
• Size and shape of the classroom – building designers should avoid open-plan classroom layouts that provide little opportunity to acoustically isolate one activity area from another.
• Classroom placement relative to other interior spaces – designers should arrange these to minimize the effects of occupancy-, equipment- and environment-related noise that comes from outside the classroom walls.
• Construction of ceilings, walls and floors – designers should select construction materials with the right Sound Transmission Class (STC) ratings for slab, roof and exterior walls, including doors and windows.
• Surface treatment, which determines sound absorption.
• Number, type and location of both internal and external sound sources and the strength of the sounds they produce.

Because an HVAC system is frequently the predominant noise source in a classroom, it must be taken into consideration during the initial building design phase. HVAC equipment can fall into both internal (fans and/or compressors located inside the classroom) and external (rooftop units outside or indoor units in mechanical rooms located away from the classroom). Because the distance between the equipment and the student can play a large role in reducing noise in classrooms, the quietest solutions typically entail placing the HVAC equipment outside of it.

Acoustical prediction and analysis software can help building designers take into account different sound sources, so they can accurately predict what a classroom’s sound level will be. The software allows designers to input specific building requirements along with the type and placement of HVAC equipment, duct configuration, and wall and ceiling type. Something as simple as the size of ductwork or the use of rounded (radiussed) turns as opposed to squared (mitered) turns can make a big difference.

Designers should work closely with HVAC equipment providers to select equipment with low sound levels and to identify system designs that meet their specific acoustical goals. For example, most rooftop equipment has one compressor and a constant-speed fan. The unit fan operates continuously at high speed to satisfy the ventilation requirements. The compressor is cycled on and off based on the need for cooling or heating in the classroom. Sound levels change when the compressor cycles on and off, creating a distraction for children and teachers in the classroom.

One solution is the use of a variable-airflow, multiple compressor unit which sequences on smaller compressors and creates less of a distraction. In addition, the unit supply fan provides only the amount of air needed to meet the ventilation and comfort requirements—thereby reducing sound levels and electrical energy consumption.

While classroom acoustical standards are tougher than ever, building designers today have access to acoustical prediction tools and HVAC equipment application expertise to help them select the right HVAC equipment and system design to meet a school district’s specific acoustical requirements. Improved classroom acoustics contribute to healthier indoor environments to help create high performance schools—facilities that improve the learning environment while saving energy, resources, and money. A well-designed school can enhance student and teacher performance and make education a more enjoyable and rewarding experience.

Written by: Robert L. Johnson, Trane
1 Sound in the Classroom: Why Children Need Quiet, ASHRAE Journal, February 2003
2 Acoustical Society of America (ASA). 2002. ANSI S12.60: Acoustical Performance Criteria, Design Requirements and Guidelines for Schools (Melville, NY: ASA), 5.

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