Electrical, power systems in mixed-use buildings
Engineering mixed-use buildings is a fine art—specifiers must combine multiple electrical and power systems for several business and residence types into one structure. Metering, submetering, and energy efficiency also must be considered.
Robbie Chung, PE, LEED AP, Senior associate, Environmental Systems Design Inc., Chicago
Raymond Holdener, PE, Senior associate, Dewberry, Fairfax, Va.
Andrew Lasse, PE, LEED AP, Associate principal/senior mechanical engineer, Interface Engineering, Portland, Ore.
Gary Pomerantz, PE, LEED AP, Executive vice president, building systems, WSP, New York City
John Sauer, PE, LEED AP, Senior director, BSA LifeStructures, Indianapolis
LeJay Slocum, Assistant director, Atlanta regional office, Aon Fire Protection Engineering Corp., Suwanee, Ga.
CSE: What’s the one issue most commonly overlooked in electrical/power systems on mixed-use projects?
Holdener: Mixed-use facilities present a number of unique challenges for the electrical/power designer. It is typical for a mixed-use facility to house multiple entities such as rental unit tenants, condominium unit owners, retail tenants, commercial office tenants, and others. These entities have very different electrical power requirements that must be considered not only individually but collectively as the electrical service entrances, generator systems, electrical distribution systems, and life safety systems are being designed.
One issue that is commonly overlooked when designing the electrical system for a mixed-use facility is coordinating with building ownership to determine the appropriate segmentation of the electrical distribution equipment and then making sure that all of that entity’s equipment is powered from its particular segment. For example, if a facility houses both rental units and condominiums, with the rental units on floors 1 through 5 and condominium units on floors 6 through 10, then it is sometimes desired by building ownership to serve the common systems of floors 1 through 5 such as lighting, general purpose receptacles, elevators, and other similar systems from electrical panels served via the rental portion of the project with the condominium floors being designed similarly. However, this arrangement is not always the case because other facilities implement extensive submetering systems to segment the power usage. Close coordination with building ownership needs to be performed as early as possible in the design process.
CSE: How have energy efficiency and sustainability requirements affected your approach to tackling electrical systems in mixed-use buildings?
Holdener: Mixed-use facilities typically present excellent opportunities for energy savings, particularly because of the constantly operating MEP systems that serve dwelling units and common areas such as lobbies, corridors, and amenity spaces. Unlike commercial office buildings where a significant portion of the building’s systems ramp down due to low occupancy as evening approaches, it is often the case that a mixed-use facility’s occupant load increases as the workday ends. Therefore, selecting energy-efficient light fixtures, implementation of lighting control systems, implementation of energy-efficient appliances, and other strategies are of paramount importance in providing the building owner with an energy-efficient and sustainable building.
CSE: Describe a recent submetering project in a mixed-use building. What were the challenges and solutions?
Holdener: A recent project included over 350 dwelling units comprising both rental and condominium types. The project also included retail tenant spaces, common areas accessible by both rental tenants and condominium owners, and a common underground parking garage. The design included electrical utility meters for the dwelling units and electrical submeters for the common area and house loads. After coordination with building ownership, it was determined that the common area loads were required to be broken down into six categories. This provided multiple challenges, including but not limited to determining the various options for segmenting the electrical distribution system, coordinating physical space for the various meters, data management, and other logistical issues. After extensive research and review, the final design implemented a submetering scheme that consisted of color-coded submeters housed within multiple meter cabinets located throughout the project. Each of the six categories of load types was assigned a color code to aid in the management of the submetering system. Data from the meters is collected via the project’s energy management and control system.