Overview of Noise Control and HVAC Acoustics in Buildings

Overview of Noise Control and HVAC Acoustics in Buildings

Course Outline

An acceptable acoustical environment is important for human comfort. In a classroom, noise can hinder the learning process. In offices and meeting rooms, it can strain communication; in multi-purpose rooms, it can reduce the enjoyment of a gathering; and in an auditorium, it can devastate a performance. In summary, noisy spaces can lead to stress and ineffective communication.

This 4-hour online course provides a basic understanding of noise control fundamentals and summarizes few design tips on HVAC system design.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

Upon completing the course, you will be able to:

Describe the key terminology used in building acoustics;
Differentiate between dB and dB (A);
Differentiate between sound power and sound pressure;
Ascertain the net sound effect from various sources;
Describe the A-weighing, NC and NR ratings;
Evaluate the techniques used in noise control situations;
Understand the concept of reverberation, absorption coefficient & sound transmission loss;
Describe the noise reduction coefficient (NRC) and sound transmission loss (STL);
Identify the noise points in the HVAC systems;
Apply the acoustic features to HVAC design & specifications;
Understand Do's and Don'ts of equipment selection and installation; and
Identify the right codes and standards.

Intended Audience

This course is aimed at students, mechanical and HVAC engineers, architects, building designers, interior designers, contractors, civil estimators, facility managers and general audience.

Course Introduction

When the sound is at acceptable levels, then the requirements for acoustical comfort are satisfied. There are many sources of sound in buildings: voices, human activities, utility equipments and external noises such as traffic and machinery. Building services such as plumbing, elevators, lighting, or heating, ventilation, and air conditioning (HVAC) systems can generate excessive noise inside the building. HVAC equipment may constitute a major noise source which may include the boiler or mechanical room, as a result of the component operation (i.e. air handling unit fans, pumps, and compressors), the distribution pipes and air ducts (especially for central air ventilation systems the sound travels with the air flow inside the air ducts to the air supply outlets) and the indoor air-conditioning units (i.e. heat exchanger components water-air, fan coils). The goal of noise control in buildings is to achieve an appropriate sound level for different rooms. What is appropriate depends on the type of activities expected to occur within the room and the level of speech intelligibility or acoustical privacy required.

The best way to avert noise problems is to review the mechanical system plans and building layout drawings with a qualified acoustical consultant before installation. This would help spot trouble and trigger a more thorough analysis to prescribe noise control treatment.

This course attempts to cover these aspects.

Course Content

The course content is in a PDF file Overview of Noise Control and HVAC Acoustics in Buildings. You need to open or download this document to study this course.

Course Summary

Theoretically, it takes a difference of 10 decibels to double the loudness. Also it takes approximately 3 decibels for the average human ear to discern any difference in loudness at all. In many cases, the sound rating isn't as significant a determiner of sound difference to listeners as is the sound characteristics or quality. One type of sound with a lower sound power rating may be more offensive than another with a higher sound power rating. There are other important considerations, such as location, when considering the effects of sound.

The noise in HVAC systems comes primarily from the main fans, flow of air through the system, VAV boxes, and flow through diffusers. Both the noise coming out the diffusers and that leaking through ceilings from ducts and components above must be considered. Sometimes there are problems with turbulence causing duct vibration, or improper vibration isolation of fans or other equipment. Potential sources and means of noise and vibration transfer from a central ventilation or/and air-conditioning system inside a building: (1) noise from fans inside the air ducts; (2) through the floor in the mechanical room; (3) noise from ventilation outlets/inlets; (4) noise from the building envelope; (5) noise transmitted through the building envelope; (6) noise from air flow and mixing from ventilation ducts.

Some basic considerations for a quiet design of HVAC systems include: minimizing pressure loss within ducts, selecting of fans that operate at maximum efficiency on performance curves while providing necessary ventilation, and designing ductwork leading to fans to minimize turbulence. If the sound power of a fan is too large, attenuation must be introduced immediately after the fan to prevent unacceptable noise passing along the system. Attenuation can be provided by vibration isolation, lining the ducts with absorptive material or by the attenuator units. Flow-related noise concerns require optimizing the duct velocities. Retrofitting ventilation with silencers, insulation within ducts and active noise control also has been successful for noise abatement. The list is almost endless and it takes a lot of experience and knowledge to be able to judge what would work best in a given situation. While the building designer must determine the optimum criteria for each room, the support of mechanical and acoustical consultants will be required to ensure that an acoustically successful design is achieved.

Noise control is not an exact science; however there are numerous ways the noise can be reduced from a particular source. The most desirable way to control excessive noise levels is by using engineering controls such as application of absorption materials, isolation techniques, installing barriers or acoustic dampening materials, design modification and using special equipments. The design of engineering controls considers the sound pressure levels, type of noise (continuous or impact noise) and frequency of the noise. The advantage of applying an engineering control directly to a tool is that the one does not have to determine how to modify a room so that the noise levels can be controlled. The HVAC system is only part of the overall story, a quiet system can go a long way toward promoting comfort and productivity.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.