Almost without exception, North American hospitals are mechanically cooled and ventilated—but change is in the air. At the annual conference of the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) in June, the society’s natural ventilation task group presented recommendations from its three-year review of the ASHRAE standard for ventilation in healthcare facilities. In a significant shift, the task group suggests that natural ventilation—which it defines as the transport of fresh air through non-mechanical means—should be allowed in most spaces outside of operating rooms and other critical care areas. “We should open the door to this,” says Travis English, chief design engineer for Kaiser Permanente (Anaheim, Calif.) and a member of the task group. “We should have the option to evaluate it case by case.”

ASHRAE standards define conventional industry practices for engineers in the U.S. Many jurisdictions have adopted the current ASHRAE Standard 170: Ventilation of Health Care Facilities, in whole or in part, that requires that “all air provided to a space shall be filtered,” and that “the entire minimum outdoor air changes per hour…shall meet the filtration requirements.” While this wording may have been intended to apply only to ducted air, it’s widely understood to preclude natural ventilation anywhere in a healthcare facility.

The group’s recommendation reflects North American design culture’s growing interest in natural ventilation, which is being driven by research on the benefit of fresh air to patients, the need for more energy-efficient and resilient buildings, and increasing awareness of naturally ventilated healthcare facilities internationally. “Some have seen the models of natural ventilation used in hospitals in the U.K., and asked, ‘Why not consider this for the U.S.?’” says Paul Ninomura, a design engineer with the Indian Health Service (Seattle) and primary author of the Standard 170 task group’s position paper. (In addition to the U.K., the paper also refers to German, Norwegian, and World Health Organization standards allowing or encouraging the adoption of natural ventilation in modern healthcare facilities.)

In Singapore, Ng Teng Fong General Hospital incorporates operable windows and a unique fan-shaped ward layout so that more than 80 percent of the inpatient areas receive natural ventilation. (For more on the project, read “Breath of Fresh Air” on page 38.) In awarding a 2017 AIA COTE Top Ten Award to the project, the awards jury noted that its passive design strategies are a model for hospitals around the world.

In North America, a handful of early adopters have navigated existing technical and cultural obstacles to natural ventilation in healthcare facilities. Spaulding Rehabilitation Hospital, a 132-bed post-acute-care hospital in Boston that opened in 2013, and Royal Jubilee Hospital’s 500-bed Patient Care Centre (PCC) in Victoria, British Columbia, Canada, that opened in 2011, offer case studies on how goals for natural ventilation were achieved and how the systems have been used since opening.


Spaulding Rehabilitation Hospital 

During the design of Spaulding, a LEED Gold-certified facility from Perkins+Will (Boston), stories from Hurricane Katrina were front-of-mind: mechanical systems failing, stifling heat, staff breaking windows with furniture to get patients some air. Recognizing the waterfront facility’s vulnerability to rising sea levels and the increasing frequency and severity of North Atlantic storms, Spaulding’s leadership decided to incorporate operable windows as part of a larger commitment to passive survivability (the ability to continue to function in an extended power-outage or other emergency).

Spaulding’s environmental control system primarily relies on mechanical HVAC, with natural ventilation used as an ancillary mode. The design team’s challenge was to integrate these methods to achieve patient comfort without wasting a lot of energy. In patient rooms, the solution is simple. Each room has an operable sash that stays locked except in cases of a mechanical HVAC fail, when the staff can use a key to open each window.

In activity spaces, such as multipurpose rooms, patient lounges, and therapy gyms, the value of operable windows as an amenity as well as a safeguard warranted a more complex solution. In these spaces, staff and patients can open banks of windows to provide access to the sounds, scents, and fresh air of the Boston Harbor. However, to avoid wasting energy, the switches that open these windows also cut off the delivery of mechanically tempered air.

Spaulding’s experience with its system has been mixed. Boston’s hot summers and cold winters mean Spaulding’s windows are open mostly on fair days during the shoulder seasons—less often than expected. When the windows do get opened in summer, heat and humidity can become uncomfortable if occupants don’t actively manage the system over the course of the day. Even after the windows close again, spaces can remain uncomfortable while the mechanical system catches up. David Burson, a senior project manager with Partners HealthCare (Boston), owner of the facility, says a refinement for the future (or for other facilities considering operable windows) could include exterior sensors to close the windows automatically, providing a faster response to outside conditions and preventing indoor temperature and humidity levels from exceeding patient comfort ranges. “We’re still learning how to adapt to a more dynamic patient care environment than most staff and clinicians are used to, at least in this country,” he says. “It’s a work-in-progress.”


Royal Jubilee’s PCC  

While emergency functionality was a significant consideration for Royal Jubilee’s PCC, a LEED Gold-certified medical, surgical, and mental health inpatient facility by CannonDesign (former Vancouver, B.C., office), the primary goal in incorporating natural ventilation was to create a more patient-centric environment. Every patient room, common area, and office window has an operable component: a cast-aluminum vent about two feet wide by four inches high. For security, the vents are set in screened and lockable aluminum housings. When a vent is open, room temperatures are permitted to range between 70-79 degrees Fahrenheit. “Depending who’s in the room, that can really improve patient comfort at different times of year,” says Michael Munro, general manager for PCC.

But getting the system in place wasn’t without controversy. During the design phase, project team members expressed some concern with how natural ventilation would impact HVAC efficiency and infection control. To address the HVAC issue, a magnetic switch in the window frame breaks a circuit when the vent opens, shutting off the supply of mechanically tempered air to the room. However, the mechanical system continues to extract air, which draws fresh air in through the window, to maintain required air changes per hour.

To address infection control, PCC project leadership invited team members to substantiate their concerns with published studies, but none were found. Instead, team members found reports suggesting that introducing outside air and its naturally occurring bacteria reduces the pooling of internally held pathogens.

Since opening six years ago, PCC’s operable windows have gotten plenty of use in Victoria’s mild year-round temperatures. But summer temperatures do spike, and staff often find it counter-intuitive to close a window when they get too hot, so Munro sends out periodic reminders to remind them to close the window if they want the air conditioning to kick in.


Looking ahead

As Spaulding Rehabilitation Hospital and Royal Jubilee Hospital’s PCC illustrate, incorporating natural ventilation into healthcare facilities requires adjustments and adaptations as facilities learn to balance operational efficiency with staff and patient comfort. The ASHRAE task group recognizes the challenges of these systems, and includes some caveats in its report. The group advises healthcare design teams considering natural ventilation to fully address some fundamental challenges—space appropriateness, climate appropriateness, acoustics, security, and outdoor air quality—and to anticipate that natural ventilation will be unfamiliar to many commissioning and air balance providers.

Going forward, the task group’s recommendations will be reviewed in September by the larger committee responsible for the standard. “Since this is a big change in Standard 170, I have no projections on the acceptability of the draft position document,” Ninomura says. Once consensus is established on a final version of the position paper, the work of developing text for incorporation into the standard will begin.


Katharine Logan is an independent writer based in Victoria, British Columbia, Canada. She can be reached through her website at