Healthcare & Natural Ventilation

PAYETTE Building Scientist Alejandra Menchaca speaks with the Architectural Record on natural ventilation in healthcare, citing our research on the topic led by Megan van der Linde.

At a scale unheard of in their home country, American architecture firms are using natural ventilation to achieve energy savings, resilience, and patient comfort in two major health-care projects in Asia. At Singapore’s Ng Teng Fong General Hospital (NTFGH), one of this year’s AIA COTE Top Ten Award winners, more than 80 percent of bed spaces are cooled and ventilated relying on passive strategies alone. At XiangYa Hospital, a 5.6 million-square-foot medical facility in Changsha, in south central China, slated to start construction this summer, windows will be the primary source of cooling and ventilation for all patient rooms.

As with NTFGH, the mandate for passive cooling and ventilation at XiangYa Hospital derived from established health-care design practice in the region. “We know how to open windows,” the client told Boston-based PAYETTE Architects in establishing the design parameters for the 2,500-bed facility. “We do not want air-conditioning or any mechanical systems whatsoever in the patient units.” The city’s current hospital is naturally ventilated, and the client expects the new one, which will consist of zigzagging inpatient wings atop orthogonal medical-service podiums, to improve patients’ thermal comfort through a more deliberate approach.

In many ways, Changsha is well suited to natural ventilation. Air quality is not a problem, as it is in many of China’s northern cities, and Changsha’s subtropical climate has four distinct seasons. However, increasingly frequent summer heat waves make it difficult to guarantee comfortable conditions through natural ventilation alone. “We need to design a system to protect the weakest and we couldn’t quite do it with natural ventilation year-round,” says PAYETTE Building Scientist Alejandra Menchaca.

The design solution will provide passive conditioning for what’s estimated to be 70 percent of the cooling season, based on adaptive comfort thresholds, and staff will turn on mechanical air-conditioning to moderate peak temperatures. The concept of adaptive comfort recognizes that people feel comfortable across a wider range of indoor temperatures if they have control over window operability. It’s also a function of outdoor temperature: on a hot day, people are comfortable at warmer indoor temperatures, and vice versa.

To move air, natural-ventilation systems rely on pressure differentials, which can be generated either by the wind for cross ventilation (as at NTFGH) or by temperature or humidity differences. In stack ventilation, an example of this, warmer air exits high and draws cooler air in low. This can allow a room to be selfventilating, taking air in and exhausting it through openings in the same wall. Such is the strategy planned for XiangYa.

NTFGH and XiangYa are just two among many instances of naturally ventilated healthcare facilities internationally, but North American examples are few and far between. A survey conducted by PAYETTE of health-care architects, engineers, and owners in the U.S. suggests that the industry’s main concerns pertain to a perceived lack of infection control, the logistics of controllability, patient comfort, and added construction costs. Perceived advantages include a connection to the outdoors, resilience in the event of power failure, improved working conditions and patient care, and reduced operating costs.

Infection control is highest on the list of cited concerns. But proponents of natural ventilation in health-care environments say that these worries are based on a misunderstanding of where natural ventilation will be used. Certain areas are generally considered inappropriate for it, including operating rooms, the sterile core, procedure suites, interventional radiology and cardiology areas, airborne isolation rooms (unless separately exhausted), protective environments, and intensive care units. Outside the operating room, the most common hospital-acquired infections (HAI) are pneumonia, urinary tract, bloodstream, and gastrointestinal diseases, none of which are likely to be affected by ventilation systems. In fact, HAI rates in Europe, where natural ventilation is common, are no higher than those in the U.S.

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