Government building design: Electrical, lighting, and power systems
When your client is the government, engineering design can be tricky, thanks to stepped-up regulations, budgetary concerns, and other considerations. Respondents discuss electrical, lighting, and power systems in government, state, municipal, federal, and military facilities.
- Ian Bost, PE, LEED AP, Principal, Mechanical Engineer, Baird, Hampton & Brown Inc., Fort Worth, Texas
- Robert Eichelman, PE, LEED AP, Technical Director, EYP Architecture & Engineering, Albany, N.Y.
- Paul W. Johnson, PE, LEEP AP BD+C, Vice President of Mechanical Engineering, Wood Harbinger, Bellevue, Wash.
- Katie McGimpsey, PE, LEED AP, Principal Affiliated Engineers Inc., Rockville, Md.
- R. Scott Pegler, PE, LEED AP, Director of Mechanical Engineering, Setty, Fairfax, Va.
CSE: Describe some recent electrical/power system challenges you encountered when designing a new building or retro-commissioning an existing building.
Johnson: For existing buildings, inaccessible spaces usually mean unforeseen conditions that present difficulty during construction and yield change orders. It is preferable to allow additional engineering time and effort for a higher level of field investigation or existing building commissioning to mitigate unforeseen conditions. When designing new buildings, the most common power issue is availability of reliable service. More often than not, the capacity of the local utilities is overlooked during the planning/funding phase of the project.
Eichelman: Understanding arc flash incident energy levels, particularly in older existing buildings, and then taking the proper steps to minimize them, continues to be a challenge. In many existing buildings, arc flash hazard analyses have not yet been performed and any studies that may have been completed in the past are often out of date. To understand incident energy levels, most if not all of the existing system needs to be analyzed. This can be a significant effort, depending on the size of the distribution system, the number of ways the distribution system can be configured, and the availability of accurate data regarding protective devices and feeders. Small renovations or modifications to a facility can sometimes trigger a larger study, which can impact cost and schedule. This should be recognized and communicated to the client early in the process so that it can be planned accordingly. Minimizing arc flash incident energy levels on new projects can be challenging as well, and can influence decisions related to equipment selection and system topology. Incident energy levels can often exceed 40cal/cm2, such as at the secondary terminals of large transformers. At these locations,equipment should not be accessed while energized. The impact and tolerance of equipment shutdowns, and the options available to minimize these shutdowns, therefore need to be carefully considered during the design process.
CSE: What types of renewable energy systems have you recently specified in a government or military building? This may include photovoltaics, ground source heat pumps, etc.
McGimpsey: The National Institutes of Health PNRC Phase II project has both a photovoltaic (PV) array and geothermal ground source heat pump system. The PV array consists of a 300 kW dc system with 920 individual PV panels, covering approximately 24,000 sq ft of roof area. The PV supplier was Legatus 6 with a ballast mounted system. There are two invertors, one at 100 kW and one at 135 kW, which convert dc to ac. This feeds a motor control center (MCC) for mechanical loads in the penthouse.
Johnson: We most recently evaluated PV panels for a new covered wharf as well as the new SR 520 Floating Bridge for the Washington State Dept. of Transportation. Both projects had sizable power generation capacities in the range of 750 kW, but both government authorities turned them down for lack of funding. We also recently provided emergency power to serve the circulation and injection pumps for the geothermal system at a Veterans Affairs campus.
CSE: How do you keep the electrical/power system both flexible and sustainable at the same time?
Eichelman: The goals for both flexible and sustainable power distribution systems are common for most projects, and there are many strategies and opportunities to accomplish both. The degree to which a system needs to be flexible to accommodate growth, mission continuity, etc., first must be understood as a basic program requirement. The system equipment and topology can then be designed to meet those requirements while maximizing efficiency. Depending on the specific requirements,there are many opportunities that can be explored. These may include use of high-efficiency transformers and UPS equipment, harmonic mitigation transformers, and higher distribution voltages. In critical facilities, 415/240 V power can be distributed to IT equipment in lieu of conventional 208/120 V distribution to reduce losses. UPS equipment can be specified with features that allow the UPS to operate in a bypass mode under normal conditions, eliminating the losses of the pulse code modulation(PCM) rectifier/inverter assembly. Features that automatically deactivate selected assemblies under light load conditions can also be provided, to further increase efficiency. To provide for flexibility for future growth, equipment can be provided in a modular, scalable topology. This not only reduces first cost by building only what is required to support the immediate need, but also allows the equipment to operate at higher load factors, which typically results in a higher overall system efficiencies.
Johnson: Safety and reliability are first and foremost for all of our power systems designs. The next level of importance is flexibility and maintainability. The power system generally serves equipment loads from lighting to mechanical systems that are either sustainable or not. The flexibility of our designs is taken into account to assure reliability and recovery following routine maintenance or construction upgrades such that day-to-day operations are not compromised. This is especially important for secure facilities, health care facilities, and air fields. All this is done through attention to various types of networks and standby source connections and making sure the correct protection schemes are in place to mitigate nuisance outages.
CSE: What types of unique lighting requirements are government and military clients requesting?
Johnson: The government has become most interested in LED technology, specifically due to significant reduced costs of maintenance and replacement. We have moved heavily into LED lighting technology as the first choice, depending on the latest developments proven by the manufacturers. If it is being made and fits the owners' and engineering criteria, and is affordable, it gets placed into the design even if there is only one manufacturer available.
McGimpsey: LED lighting, daylight harvesting.