Designing, enhancing office buildings: Electrical, power, and lighting
Office buildings might seem like relatively simple structures, but engineers with experience in the field know differently. Electrical, power, and lighting systems are discussed.
Christopher Arnold, PE, Vice President, Wick Fisher White, Philadelphia
Saied Nazeri, PE, CPD, LEED BD+C, Senior Vice President, WSP | Parsons Brinckerhoff, San Francisco
Reardon D. Sullivan, PE, LEED AP, Principal, WFT Engineering Inc., Rockville, Md.
Jill Walsh, PE, LEED AP, Principal in Charge of Mechanical Engineering, OLA Consulting Engineers, Hawthorne, N.Y.
Michael Walsh, Project Manager, PEDCO E&A Services Inc., Cincinnati
CSE: Describe a recent electrical/power system challenge you encountered when working on an office building.
Arnold: A general challenge when working in office buildings is to locate the main electrical room on each floor to house the power-distribution panelboards, transformers, and branch panelboards. Depending on the footprint of the building and the layout of the floors, the main electrical room per floor is normally insufficient; it requires additional small closet(s) if flushed-mount panelboard(s) in wall are not desired. It is mainly for 208/120 V branch panelboards to take care of voltage drops on the conductors between the power source and the loads.
Michael Walsh: A client in the Cincinnati area recently purchased two office buildings due to their need for additional space. The client desired to provide generator-backed power for the two buildings. The challenge was to provide a design that allowed the construction team to retrofit the power distribution system in occupied buildings as quick as possible. We accomplished this by providing a new service entrance to the buildings that paralleled with the generator. A new electrical-equipment room was created to house the new service entrance switchgear, which in turn re-fed the old service equipment to reuse the existing power distribution system as much as possible. The changeover to the new service happened during a weekend outage to minimize downtime to the occupants.
Sullivan: The requirement to control 50% of office "plug" loads with occupancy sensors that turn the power off when the space is not in use can significantly impact the cost of the project by adding circuits, circuit breakers, panelboards, and occupancy control devices to the power distribution system. Determining which circuits to control while not causing user nuisances also makes this a design challenge.
CSE: How do you work with the engineer, owner, and other project team members to make the electrical/power system both flexible and sustainable at the same time?
Michael Walsh: Flexibility is the key. You need to have discussion early on with a client to understand their culture and help them develop their vision for handling future changes to their office environment. A couple of examples are from data center power designs. Typically, in a data center you either run flexible conduit under a raised floor or overhead-mounted to cable tray. When we designed a 376,000-sq-ft office building with an open-floor plan for a local client, one of the reasons we decided on raised flooring throughout was the flexibility it provided to relocate the power to office furniture as the business units changed. Also, in an adjacent building of theirs where they have an in-house printing operation, we installed cable tray overhead with power distribution that allowed them to easily relocate equipment and reconnect power through the tray. By making the power system flexible, it is at the same time sustainable because there is a greatly reduced need to remove existing materials and run new conduit and wire to furniture and equipment.
Arnold: It requires knowing what the goal is, what can be achieved, feasible space, budget, payback, etc.
Sullivan: WFT Engineering has found that it is not only important to understand the present and near-future space program, but also the long-term space program to assist in the design of power systems that can evolve with the changes in the space usage. Additionally, each building owner has particular preferences such as type and complexity of lighting control systems and panelboard/circuit metering to meet code mandates.
CSE: What unique lighting or lighting control systems have you completed?
Arnold: A digital-network-integrated lighting control system was specified and installed for an office enclosed with glazed walls at all sides. The installed system was to incorporate a daylight-harvesting system at all perimeter zones of the office spaces and occupancy sensors throughout the spaces. The system was to take advantage of available ambient daylight and contribute to energy savings by dimming electric lights during periods when there is sufficient daylight, thus reducing electricity use associated with artificial light. The system also interfaces with an automatic-operating shading system at all exterior windows, using an astronomical time clock and cloud sensor of the lighting control system to activate shades based on a given time of day and month, for each orientation of the building, to control glare.
Sullivan: The new lighting standard in the office market is LED. The LED lighting systems are significantly more flexible, allowing better quality of lighting, improved dimming control, and lower energy usage. The market is still in flux regarding the control systems for LED lighting.
Michael Walsh: We have finally turned the corner on LED light fixtures from a cost perspective and have several projects where all of the fixtures are LED. One recent retrofit project in the middle of an office building included a controller with individual control to more than 1,200 LED fixtures over four floors. The system gave the capability to individually switch fixtures on and off, as well as dimming. Scenes were programmed for spaces depending on the use and were controllable from the central system or from an AV interface.