Case study: Integrating medical building lighting

This freestanding 30,000-square-foot medical office building — designed to be the first of many on a campus — was a pilot-style prototype for future branches of a prominent Massachusetts health care organization working to change its care delivery strategy. Before meeting with the client, the CannonDesign team was aware of the lofty net zero energy goals, and also understood that there was a strong push to keep the cost low so that it could be easily repeated on other sites.

The project followed the 2015 edition of the International Energy Conservation Code and the client was forward-thinking, but had enough experience with different lighting systems to know its level of comfort. Having used a similar product on another site, the team looked to implement fixtures outfitted with onboard presence and daylight-sensing controls.

This type of system, while a higher material cost, had a lower installation cost and eliminated the need for a separately installed control system of maintainable parts. It created deep, granular, energy savings out of the box. The integrated control system CannonDesign specified — a new feature for the client — also allows fixtures to be controlled individually or grouped by zone or space, providing design flexibility to suit other sites as well as reconfiguration future-proofing for changes down the road. A condition of this type of system is that it can feel unnatural to a user if each individual light in a larger space is acting independently, so grouping the fixtures made for a welcoming environment.

The program of the space was repeatable from exam rooms, team stations, corridors, lobby/waiting and back of house support spaces. To maintain visibility from the building approach, the lobby ended up facing northwest. With the site located in the Northern Hemisphere, this meant for most of the day there was ample useable daylight in the lobby, with a small time period in the afternoon/evening where direct sun would penetrate the lobby, late enough to avoid unwanted glare. This offered great opportunities for daylight harvesting.

Because a system like this had such granularity in how it was configured, it was important for the programmers and commissioning team to have a strong and clear set of drawings to guide them during installation. A sequence of operations accompanied each space type, traditional switch legs helped to denote which fixtured required grouping or zoning.

To meet sustainability goals, the project relied primarily on direct lighting approaches to minimize required lighting energy, and attention was paid to lensing, optics and cutoff to ensure visual comfort was upheld. Undercabinet lighting was used in all exam rooms to achieve higher light levels where the task required, without over lighting the entire space.

The calculated lighting power density was a low 0.6 watts/square foot. Extensive energy modeling was performed to gauge how well the building envelope and all of the systems would work together. An occupancy schedule was used based not only on the hours of operation, but with existing data from other buildings. The lobby façade was evaluated for the special daylight autonomy to show which areas of the space would achieve greater than 30 footcandles for more than 50% of business hours annually.

The project has been operational now for more than a year. When data were compared, overall energy usage was higher in the cooler months and lower in the warmer months. Annually, the building is operating just about where the energy model indicated. This can be contributed to accurate assumptions in the design phase, but more importantly, commissioning and ongoing commissioning to ensure the design intent was met.

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