Sound Remedies For Medical Facilities

Controlling noise emitted by modern HEALTH CARE TECHNOLOGIES as well as protecting patient privacy while speaking is essential for hospitals and clinics

How close to the emergency generators can the new microsurgery suite be?

In today's medical facilities, the only constant is change. It is important to be on the lookout for conflicting needs when siting a new MRI suite or cooling tower. Avoiding the transfer of airborne sound or structure-borne vibration between various adjacencies requires thoughtful planning.

Areas where images are magnified for diagnosis or treatment are potentially susceptible to vibration. The most common areas of concern include microsurgery and lab microscopes. Quantitative criteria for acceptable levels of floor vibration are often provided by system manufacturers or acoustical consultants. This allows for an engineering assessment of what measures are needed to meet the criteria.

On renovation projects, field measurements can be made of existing levels of floor vibration and, if needed, sources of building vibration can be identified through frequency analysis or ON/OFF tests. A major university hospital recently commissioned such tests during planning and expansion to accommodate lab microscopes with 40OX magnification. To prevent image blurring, steps were taken to stiffen the building structure and isolate vibration of rotating equipment in a new mechanical penthouse. Ophthalmologic surgery suites and even standard operating rooms all require vibration-free environments to varying degrees.
The proliferation of MRI machines has also caused acoustical problems. The concern here is more "outbound" - that is, sound and vibration generated by the MRI process intruding into nearby waiting and treatment rooms, adjacent horizontally or vertically. With the use of progressively larger magnets, airborne noise and structure-borne sound levels are increasing, requiring better planning and more aggressive measures for control.

Noise and vibration problems can be anticipated. If mitigation measures are planned during the design phase, costly and extraordinary construction techniques can be avoided. Good planning can make it possible to avoid the kinds of steps that are necessary to make building occupants satisfied if, for example, the chiller room is located next to a meeting room. With available expertise, the costs and benefits of various options can be explored while the project is still on paper.

COMMUNITY NOISE CONCERNS

Many jurisdictions now have regulations covering the sound that may be emitted from building service equipment. The most common noise sources for medical facilities are cooling towers, air-cooled HVAC equipment (usually rooftop units) and emergency generators. While generators may be exempt from community noise regulations during emergencies, there is customarily no exemption for the noise produced during weekly generator tests. So it is wise to test during the day and to meet the daytime noise limit requirements. Nighttime regulatory limits are usually lower. For example, in New Jersey, levels emitted to residential properties are limited to 65 dB(A) during the day and 5OdB(A) at night.

Where lowest first cost is an overriding concern, the trend is to use aircooled, packaged or custom rooftop air handlers to serve building additions or new facilities. The sound radiated to the community is highest during the summer when cooling demand is highest, and noise is produced by the compressors and condenser fans. Unfortunately, it is difficult to mitigate the noise from such equipment, both during the design stage and after the fact, except by introducing shielding with acoustical barriers. The difficulty of mitigation is all the more reason to ensure good planning occurs.

At one hospital, a new rooftop aircooled chiller was contributing to noise levels far above allowable nighttime limits. Because the roof could not support the wind load and weight of the needed noise control barrier, the only solution was to use this rooftop unit in the daytime hours and to provide supplemental cooling with additional equipment, selected and located to meet nighttime cooling needs while meeting sound-emission requirements.

Although water-cooled systems relying on cooling towers require greater up-front investment, there are many more options available during equipment selection for controlling sound emissions to the extent required. Options include:

* Equipment style: Centrifugal fan cooling towers and propeller fan towers have different acoustical characteristics and directivity - the way sound emissions differ from position to position around a noise source.

* Fan speed: Because towers are custom-designed for thermal demand, oversizing the tower and slowing the fans can often meet acoustical and thermal needs simultaneously.