Healthcare facilities are one of the most difficult of building types to "green" for a number of reasons. First, they are regulated more heavily that any other building type. Second, they house the most vulnerable of us. Finally, hospital administrators must allocate their resources to support their primary mission, and not to distractions like investments in solar photovoltaics.

With a guiding principal of saving energy while improving patient and staff safety and comfort, Mazzetti and Associates explored sustainable strategies on a Kaiser hospital project. One application that surface with great promise was displacement ventilation in patient rooms. However, the obvious question was how would it address infection control.

Traditional ventilation mixes room air from an overhead supply diffuser, creating a homogenous environment throughout the entire room. Displacement ventilation supplies cool air low at a low velocity, allowing it to pool across the floor. As the air picks up heat, it rises due to convection in a vertical temperature gradient, ideally in a laminar piston effect. The goal of displacement ventilation is to condition only the occupied volume and carry contaminants directly up out of the occupied zone without mixing them. Low sidewall displacement ventilation was chosen over raised floor displacement for healthcare, due to cleanliness concerns. The presumed benefit of displacement ventilation was equal or better environmental comfort and ventilation effectiveness at lower air exchange rates. There was optimism that it might also have benefits for the control of airborne infectious particles. A hypothesis was created that low sidewall displacement ventilation at lower air exchange rates would be equal to or better than overhead mixing ventilation for environmental comfort, ventilation effectiveness and airborne particle control. If the hypothesis proved to be true, the energy savings and economic benefits would be dramatic

Research

A research study was initiated to test the hypothesis; and at the same time Mazzetti & Associates became aware that Stantec, an Architectural/Engineering firm in Vancouver BC, was planning similar research. The two firms agreed to collaborate on the research and share their findings publicly.

Research included testing within laboratory mockups, field testing and computational fluid dynamics analysis. Testing focused on environmental comfort per ASHRAE Standard 55, ventilation effectiveness per ASHRAE Standard 62, and particle dispersion per a test designed by Andrew Streifel. This research indicated that displacement ventilation at 4 air changes per hour provides better particle control, ventilation effectiveness and thermal comfort than overhead ventilation at 6 air changes per hour.

Concurrent energy modeling compared overhead system versus displacement ventilation for five climatic zones and four different exposures. Savings — as expected - were dramatic. Preliminary construction cost estimating also confirmed reduced construction costs for displacement ventilation due to lower air flow rates.

Initial research demonstrated the promise of displacement ventilation, but was not rigorous enough to be accepted by organizations and agencies that govern the design of healthcare facilities. So, a more rigorous, independent Phase of research was initiated.

Displacement ventilation research - now in progress - consists of two independent blind components: numerical analysis and empirical analysis. The highly qualified researchers selected are Dr. Qianyan Chen; Purdue University for empirical testing; and Dr. Andrew Manning, Flomerics for numerical testing.

Design Application

Mazzetti and Stantec participated in the research efforts, gaining valuable insight into design considerations. Issues relating to location of supply and exhaust diffusers, and integrated versus independent heating and cooling are much better understood through the research efforts

The panel of researchers and engineers will discuss what was learned and how it is best be applied to improve the patient room environment while reducing construction cost and reducing energy consumption.