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Healthcare acoustic environments a concern for HVAC technicians

The “Acoustics in Healthcare Environments” white paper from CISCA explores tools architects, interior designers, and HVAC technicians can use to create a safe and comfortable acoustic indoor environment.

Many sounds are present in hospital environments, including those from beepers, alarms, machines, rolling carts, conversations, and HVAC systems, among other sources. These can be severely irritating and at times harmful to patients, depending on their current conditions. Acoustics in healthcare environments are complex and require a careful, strategic design.

The following information is derived from the Ceilings & Interior Systems Construction Association’s “Acoustics in Healthcare Environments” white paper. The information here focuses on the ways HVAC systems can be improved to accommodate the lower acoustic requirements of healthcare environments. [Note: The full white paper addressed additional steps that can be taken to improve the indoor acoustic environment beyond the HVAC system.]

Understanding the primary acoustic issues
Sound can be transmitted to a person’s ear directly from a source (direct sound), after reflecting off of one or more surfaces (reflected sound), after passing through a shared, solid, structural component like a wall or ceiling (transmitted sound), or after bending over and around partitions (diffracted sound).

The main acoustic properties that need to be addressed in healthcare settings are sound pressure level; reverberation time; and, most important to HVAC systems, background noise. Background noise is defined as “all direct and indirect sound that is audible to the human ear that has the potential to interfere with wanted (such as medical equipment warnings) or unwanted (such as private conversations) sound signals.”

Background noise levels should meet the criteria set by established standards such as those developed by ASHRAE and should be identified at the onset of a project. Certain specialized healthcare environments (such as, spaces where audiometric testing is conducted, sleep disorder clinics) require minimal background noise and distractions. The continuous background noise levels created by building services such as HVAC systems are typically calculated as specified by the manufacturer.

Minimizing mechanical equipment noise
Mechanical equipment noise enters spaces through interior partitions and the façade of the building, through ventilation ducts, and as a result of vibration from mechanical equipment. Mitigating the impact of each requires specific design solutions. To address noise issues related to mechanical systems HVAC engineers should consider the following:

  • Specify quieter equipment, acoustic silencers, louvers, barriers and vibration isolators;
  • Analyze filter performance, partition construction and detailing, air flow velocities, façade design, site planning, and potential cross-talk issues (such as situations where sound from one room may be transmitted to another via ducts);
  • Consider the noise impact of terminal boxes and how performance is affected when sound attenuators are used;
  • Consider alternatives to standard duct attenuation strategies, which are usually prohibited in hospitals due to the potential indoor air quality and hygiene problems they create;
  • Insulate pneumatic tubes and ice machines to reduce noise levels;
  • Determine elevator type, location, and surrounding structure with knowledge of their vibration and structure-borne sound impacts (such as vibration transmitted from one location to another through the building structure);
  • Understand that noise from building services can impact other sensitive spaces within the building through windows. Consider façade design, site planning, and acoustic control to mitigate these impacts; and
  • Understand that when designing partitions that enclose mechanical equipment it is important to understand that the noise generated by the equipment, in most cases, extends beyond the sound frequencies in which STC tests are run. This implies that designing around STC ratings alone will not assure acoustical privacy. Specifically, STC testing stops at 125 Hz, whereas mechanical equipment can generate noise down to 20 Hz.

Several healthcare design guidelines released in recent years have emphasized the importance of acoustics in the design of healthcare environments. Healthcare environments should be designed to meet published standards. Among these are the Sound and Vibration Design Guidelines for Hospital and Healthcare Settings, HIPAA, 2010 FGI/ASHE Guidelines for Design and Construction for Health Care Facilities, and the Green Guide for Health Care.

Additionally, LEED for Healthcare is currently in draft form. The new LEED for Healthcare rating system responds to design issues that are under unique conditions in the healthcare industry. The five main areas of the traditional LEED rating systems (sustainable sites; water efficiency; energy and atmosphere; materials and resources; and indoor environmental quality) include new considerations especially for healthcare. A credit is included for acoustic environment improvement.

"Acoustics in Healthcare Environments" is a free tool for architects, interior designers, and other design professionals who work to improve healthcare environments for all users. It is an introduction to the acoustical issues commonly confronted on healthcare projects. The full white paper explores additional ways HVAC systems can be integrated with proper ceiling and flooring materials, along with other factors, to full integrate the indoor acoustic environment.

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