Introduction

There is widespread use of heating ventilation and air‐conditioning (HVAC) systems in a variety of small and large buildings. The main consideration facing the designer of such systems is to ensure that the plant provides the required amount of heated or cooled air throughout the building and does not create objectionable noise or vibration either in the areas served by the system or in adjacent areas. Because air must be supplied (and in many cases extracted) by a fan of some kind (either axial, centrifugal, or mixed‐flow), it is inevitable that some noise and vibration are generated. It is becoming common practice to use systems with very high airflow velocities which introduce additional problems due to noise generated by the turbulent airflow, which is created. However, despite the many difficulties that may be encountered, the noise produced by the system can be controlled if the system is correctly sized and care is taken to ensure that all elements of the system are properly installed. Air‐conditioning also makes it possible to use sealed windows, thus giving good sound isolation from most of the outdoor noise. This can be important with buildings situated close to airports, railroads, and highways.

Once a completed HVAC system has been installed in a building, it is often very difficult and expensive to correct noise and vibration problems. Thus, great care should be taken at the design stage of a system to select all of the equipment items carefully and to minimize all possible sources of noise and vibration. A successful design can be obtained only by careful cooperation between the architect, ventilation engineer, and acoustical consultant.

The primary considerations in selecting the mechanical equipment necessary for cooling, heating, and ventilating a building are related to (i) satisfying its intended use, and (ii) providing acceptable sound and vibration conditions in occupied spaces in the building. In critical cases such as conference rooms, auditoria, bedrooms in homes and hotels and lightweight buildings, the sound and vibration produced by the equipment must be minimized. In order to meet these mechanical and acoustical requirements, it is important to use the source‐path‐receiver concept discussed in Chapter 9 and throughout this book. The major chapter topics include

• Noise level criteria
• General features of HVAC systems
• Errors in system installations
• Fans and fan noise
• Space planning
• Mechanical room noise and vibration
• Ductwork and duct attenuation
• Sound attenuators (plenums and silencers)
• Sound generation by flow
• Air terminal devices (grilles and diffusers)
• Duct breakout and breakin noise
• Sound radiation from mixing boxes and plenum walls
• Prediction of room sound pressure level from sound power level

This chapter concentrates on the acoustical aspects of HVAC systems, although these are intimately related to each part of the mechanical systems installed. Useful reviews on HVAC noise and vibration control can be found as chapters in several books [1–17]. The ASHRAE Handbooks on HVAC applications, updated periodically, contain valuable chapters on noise and vibration control.