Specifying electrical and power systems for new, existing office buildings
Office buildings might seem like simple structures from the outside, but engineers engaged in such projects know they can be highly complex, with specialized fire/life safety requirements, laboratory spaces, and other unique needs. This looks at the building electrical and power systems.
J. Patrick Banse, PE, LEED AP, Senior mechanical engineer, Smith Seckman Reid, Houston
Robert Ioanna, PE, LEED AP, Vice president, Syska Hennessy Group, New York City
Douglas Lacy, PE, LEED AP BD+C, Senior associate, ccrd partners, Dallas
CSE: What’s the one factor most commonly overlooked in electrical systems in such buildings?
Lacy: The most overlooked item tends not to be technical in nature. Identifying what the requirements for tenant power will be in the final leasing agreements continues to be a challenge. Core and shell design often starts and progresses before the developer, leasing agents, and tenant brokers have finalized the lease language. While engineers can design to codes and standards and can anticipate some abnormalities based on previous engineering experience, there inevitably will be unique requirements requested by tenants in their leasing negotiations. Promoting these discussions to happen early in the design process as to avoid costly change orders is imperative to a successful project and satisfied clients.
Ioanna: A major issue with existing building electrical distribution systems is identifying non-compliant systems. There are a lot of installations grandfathered in place that if evaluated on current codes are noncompliant. When grandfathered equipment is modified, this equipment often needs to be replaced. There could be clearance issues and parts might not be readily available as well. Often increasing construction costs are unanticipated by the owner.
CSE: Describe a recent project in which you had complex metering and submetering in a building.
Lacy: We recently completed a corporate headquarters and food development complex for a national restaurant conglomerate. The building housed test kitchens and a data center as well as typical office space. The design had to allow for the owner to accomplish asset allocation and tracking for each brand housed within the complex. The system needed to be able to separate costs for similar function of different brands co-located within the same building or even the same room. A series of distributed networkable meters were employed to track power usage. The system selected also had the capabilities to add future meters to the network as they moved, changed, or expanded each department.
CSE: Describe a power quality issue you encountered, and provide details about how you overcame it.
Ioanna: On a commissioning effort we had a power quality issue with generator-UPS system compatibility. The generators were sized without considering harmonics and leading power factor caused by the UPS filters’ contents and the performance of the UPS. This caused the generator to hunt (up-and-down voltage and frequency). The solution was to lower the UPS recharge current to reduce harmonics when generators are feeding the UPS system and the filters were engaged at relatively higher UPS loading. We have had power quality issues with chiller motor controllers such as variable frequency drives (VFDs). This may cause a zero sequence current activating the upstream breaker with ground fault protection (GFP). The solution is to increase the GFP setpoint (current and time delay) to mitigate this starting/transient condition.
CSE: What type of backup or standby power systems have you specified into an office building?
Lacy: The backup power systems tend to be divided by building class. Low-rise value office buildings tend to use only battery backup for life safety lighting and fire alarm systems, and hydraulic or battery return for elevators. Class B mid-rise and high-rise as well as Class A buildings tend to employ diesel standby generators. In the developer market there tends to be a separation between generators used for “base building” purposes such as life safety functions and those generators used to back up tenant purposes such as IT and call center operations. Also, a portion of most facilities, regardless of class, requires a UPS for the IT equipment rooms.
Ioanna: Traditionally we have supplied standby power with diesel or natural gas-powered generator sets. We also typically provide 90-minute battery backup power for fire alarm system and lighting. The critical building loads are typically run through UPS to mitigate momentary power interruption caused by power transients/abnormality. We have seen an increased request for the use of co-generation, micro-turbine, and fuel cell systems in metropolitan areas. This is due to the availability and low cost of natural gas. These systems sized for partial load or peak shaving load show very attractive levels of return on investment (ROI).
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