Hospital Study: Light and Good M/E/P Engineering a Potent Patient Rx
Natural light is a good thing: Some studies indicate it makes people feel better and even recover more quickly from surgery. Within buildings, daylighting has proven to save energy and even make workers more productive. But a recent study by the University of Oregon's Daylighting Lab, at least concerning hospitals, found that unless the whole equation is studied—HVAC, plumbing, electric lighting, lighting controls and even the structural system and shape of a room—you'll end up with uncomfortable, squinting occupants.
With funding from Portland-based Better Bricks, researchers from the lab, in conjunction with ZGF Partnership, Portland, Ore., set out to test daylighting conditions in hospital patient rooms. Seven hospitals in the Pacific Northwest were selected where the team studied room configurations and orientations to determine best practices for patient daylighting. Results of the study were presented at the USGBC's annual Greenbuild conference in Atlanta in November.
Initially, the team identified common room configurations and the typical problems that result. For example, according to ZGF's Johanna Brickman, room geometry was frequently off, as patient beds were nearer the center of rooms than windows. Toilet room configurations also affected ideal lighting conditions, as did the type of electric illumination and window glazing in place.
So what, exactly, did the team learn? According to Sarah Bernhard, another team researcher with Oregon's Daylighting Lab, natural light can, and should, be brought in via several window types. "Daylight windows and view windows have different functions and should have separate apertures," she said.
These more clearly defined apertures reduce common problems of glare, reflectivity of surfaces and solar load. Orientation, she added, is equally important, as are proper zoning and artificial lighting and shading controls. For example, with a typical view window, Bernhard said they discovered that light transmittance levels of 50% were not unusual, meaning glare was often a problem. However, by employing separate horizontal clerestory-like windows, view windows can be shaded without losing the desired daylight illumination. Additionally, the closer the patient's bed is to a view window, the smaller that window can be. Lower sill heights are another consideration for maximizing effect.
Another tip, she said, is not to orient daylighting windows at eye level, as glare results from the angle of the eye to the light source: 90 degrees is preferred.
As far as controls, Bernhard said a zone-switching scheme works well if a room is divided into zones parallel to the window, with fixtures and switching also in parallel. This should allow the area near the windows to require little, if any, artificial lighting during daytime hours.
"Automatic controls are critical," she said. "Use daylight and occupancy sensors; integrate them with lamps and fixture types that can employ continuous dimming vs. step switching, as the change is less apparent to the eye."
Uplighting, added Bernhard, is also better than downlighting schemes for continuous dimming.
As far as room geometry, David Staczek, another team member with ZGF, said proportions are more important than dimensions. Higher ceilings equal deeper daylight penetration. Wide and shallow rooms are also better than deep and narrow rooms. Ceilings tilted toward the light also make a major difference.
The team came to these conclusions in the second part of their study, which involved constructing 29 mock-ups examining multiple configurations that included placement of HVAC equipment, slope of the ceiling, the edge condition of the room (flat, pointed, notched, etc.), location of toilet rooms, and the actual structural frame of the building—conventional steel perimeter beam, upturned steel perimeter beam and post-tensioned concrete slab.
HVAC configurations included conventional design, HVAC concentrated in the hallway, HVAC partially located outside and HVAC employed as a light shelf. For the latter two categories, because equipment was located closer to or in the corridor, ceilings were pitched on an angle toward the window. Room heights were also varied from 12 ft. to 15 ft.
As far as the "edge" condition, Staczek said they found that slanted exterior walls performed best, followed by flat wall schemes with corner windows. Notched edges were a close third. Regarding toilet room configurations—inboard from the entry, outboard from the entry and shared wall—the latter proved the best option, with inbound toilets being the next-best solution.
The matter of HVAC equipment location/structural system was trickier to define, according to the researchers, as it involved more variables, including ceiling height, pitch, the structural system and equipment location. Conventional HVAC and structural design could work well, but the study found it required rooms with 15-ft.-high ceilings. HVAC concentrated toward the corridor performed better, reducing the ceiling height by as much as 6 in. with conventional steel perimeters, but by 3 ft. when employing a post-tensioned concrete slab.
Locating some HVAC outside and toward the corridor also produced positive results, but only with the upturned steel perimeter beam and a post-tensioned concrete slab system. Both schemes, however, allowed for pitched ceilings and ceiling heights of only 12.5 ft.
Of their 29 permutations, energy reduction as high as 86% was accrued in some models, with an annual savings of 675 kW in some cases. For a 200-bed hospital, these daytime electric lighting savings would translate to $30.38 per year per room or $6,000 annually.