ASHRAE publishes revised standard on ventilation in health care facilities

ASHRAE Standard 170 has been updated to include updates, changes, and clarifications dealing with humidity, ducted returns, recirculating rooms units, and duct lining.


In some sense, designers of health care facilities must follow the same creed as health care professionals: to first do no harm. A newly revised standard for ventilation of health care facilities, ANSI/ASHRAE/ASHE Standard 170-2013: Ventilation of Health Care Facilities can help designers by providing the minimum requirements for the design of ventilation systems for health care facilities to provide environmental control for comfort, as well as infection and odor control.

ANSI/ASHRAE/ASHE Standard 170-2013: Ventilation of Health Care Facilities was written by ASHRAE and the American Society for Healthcare Engineering (ASHE). When the standard was first published in 2008, it was the first American National Standards Institute (ANSI) standard in the nation to specifically address ventilation in health care facilities.

“Without high-quality ventilation in health care facilities, patients, health care workers, and visitors can become exposed to contaminants through normal respiration of particles in the air,” Paul Ninomura, chair of the 170 committee, said. “Ventilation systems and designs for health care facilities are intended to provide a comfortable environment for patients, health care workers, and visitors while diluting, capturing, and exhausting airborne contaminants including potentially infectious airborne agents.”

Standard 170 has been in constant maintenance since 2008 and the past five years have provided an opportunity to review and further improve it. The revised standard features updates, changes, and clarifications dealing with humidity, ducted returns, recirculating rooms units, and duct lining, to name just a few refinements.

One trend that almost all classes of buildings have seen on the rise lately has been energy efficiency. Health care facilities can be energy extensive buildings and energy recovery can provide significant savings. Provisions for the application of energy recovery are now specifically addressed in 170-2013. However, as the standard stipulates, if energy recovery systems are utilized, the systems cannot allow for any cross-contamination of exhaust air back to the supply airstream. Run around coils are just one example of a system that is permitted, according to Ninomura.

The standard also addresses some issues that may reduce costs to build and operate health care facilities. Standard 170 allows relative humidities as low of 20% for some rooms. This may result in smaller capacity of humidification equipment, lower operating costs, and reduced maintenance costs. The standard permits some use of plenum returns in outpatient facilities, which in turn may result in lower construction cost and operating costs.       

Additionally, some hospitals are interested in utilizing displacement ventilation to reduce operating costs. The standard addresses the application of displacement ventilation within patient rooms. 

Poorly ventilated health care facilities may increase the concentration of airborne contaminants including fungi or mold, which may cause allergic responses in even healthy workers and occupants. Considering the various occupancies and patient populations, great care must be taken in the design of health care ventilation systems.

Tony , Non-US/Not Applicable, Saudi Arabia, 01/08/14 07:20 AM:

For optimum energy recovery by heat exchange between exhaust air and incoming fresh air, the many separate small exhaust air flows found in a typical medical facility should be collected together. This is best achieved by deciding at an early stage of the project to replace the usual multitude of individual exhaust fans (with their associated proliferation of drive belts, other spare parts and power supplies) by a few central units which pass the collected flow from the various exhaust ducts to one large, more efficient heat exchanger.
The central exhaust unit consists of a large plenum box in which a constant negative pressure is maintained by a set of variable-speed fans (n duty + 1 standby), the air flows in the various individual ducts being set by means of BAS-controlled motorized dampers. The constant plenum pressure of this configuration ensures that no individual duct flow is affected by a change in any other. It thus permits all necessary TAB airflow adjustments and "on-the-fly" adjustment of relative pressurization between adjacent spaces to be made from the BAS Operator Station.
Anonymous , 01/16/14 12:54 PM:

In reply to Tony (Saudi Arabia): Would there not be any issue of mixing the wet and dry exhausts if all exhausts ere centralized ?
Anonymous , 01/22/14 02:16 PM:

Also, it is assumed that exhausts from infectious isolation rooms are excluded from this Plenum box.
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