Integrating and optimizing power and mechanical systems
Enhancing emergency power
Per NFPA 70: National Electrical Code, Article 700, Emergency Systems are designed and installed to maintain illumination and provide power for essential equipment if normal power supply fails. These systems are essential for life safety (Category 1). Per NFPA 70 Article 701, Legally Required Systems are intended to provide electric power to aid in firefighting, rescue operations, control of health hazards, and similar operations (Category 2). Per NFPA 70 Article 702, Optional Standby Systems are typically installed to provide an alternate source of electric power to prevent physical discomfort or serious disruption to business (Category 3).
Building code may require a typical commercial building to have generator backup power for fire protection pumps, firefighter elevators, emergency lighting, stair pressurization fans, and smoke management systems subject to national and local building codes. However, a variety of building types have their own independent requirements as well.
After examining the applicable code and taking into account any additional requirements based on the building’s function, it becomes clear that additional standby power may be required to support the operation of the code-required systems. For instance, the firefighter elevator requires backup power per building code in most cases. To ensure proper elevator operation, the elevator machine room cooling system may also require generator backup power. Ventilation serving the machine room is required to be on emergency power if available, per IBC 3003.1.4.
Power management system
The power management system (PMS) provides integrated control of the mechanical and electrical systems to optimize the generator use. Critical systems requiring generator backup power are organized into prioritized tiers based on code and operational requirements as indicated above. The categories are then divided into load blocks that can be added or removed from generator support in a sequential manner depending on available generator capacity. The PMS controls generator load by controlling which systems are physically connected to the generator plant and then controlling the mechanical systems once connected. It optimizes generator use by controlling how many generators are running and matching the generator capacity to the load.
The PMS provides a dynamic balance between load and running generator capacity. It also acts as a safeguard to ensure that code-mandated life safety loads have the highest priority. For example, if a generator fails causing the generator plant to become overloaded, the PMS will shed lower priority loads and start generators until the overload condition is eliminated.
The first category of the emergency power system is the emergency loads as defined by Article 700 of NFPA 70. This branch is intended to automatically supply egress illumination and power to life safety equipment in the event normal power is lost.
The second category of emergency power systems includes legally required standby systems as defined under NFPA 70. This branch is typically installed to serve loads such as heating and refrigeration, communications systems, ventilation and smoke removal systems, elevators used as a path of egress, sewage disposal equipment, lighting systems, and industrial processes that, when stopped during any interruption of normal electrical supply, could create hazards or hamper rescue and firefighting operation.
In addition to the above-required loads, the third category of optional standby systems are typically installed to provide an alternative source of electric power to serve certain loads in event of any power outage could cause discomfort and serious interruption to process. For instance, firefighter elevator cooling or underground garage exhaust systems can be created to reflect the owner’s requirements and the building’s function, thus using more power capacity offered from the generator than the required systems. Furthermore, a hospital in a cold climate may want to put a patient room heating system onto a third category of generator power, and an office building in a hot climate may want to consider an additional cooling system.
Engineers should identify which systems should go into this third category of PMS, which requires mechanical and electrical systems integration as well as collaboration between the owner and the engineers through consideration of the building budget and the intended design.
The dynamic nature of power control systems offers a wide range of features that make building emergency power systems more effective and efficient. It also offers high visibility into power movement within the emergency systems. It calculates the real-time power consumption versus total power capacity based on hierarchy architecture. Within the same category, upon receiving signal, a block of power can be control and access as required.
Additional systems with dual power connection can increase the scope of the emergency distribution system as well as the size of the generator, resulting in higher initial capital costs. Sophisticated emergency power management requires a high-speed data transfer system to ensure emergency system activation and accurate time delay between systems, which will increase the cost of the building’s network systems.
Emergency power systems can be among the most critical investments for any large, complex facility. While creating tiers of MEP systems to use emergency power as it becomes available may increase a building’s first costs and will require additional HVAC, electrical, and BAS integration, these power systems will also champion safety and use the building’s existing MEP systems to their fullest potential, optimizing operations even during a critical outage.
Suzan X. Sun-Yuan is a senior associate and lead mechanical engineer with Environmental Systems Design. She has experience with super-tall buildings, food labs, and central plant designs and upgrades. Mohsen Aghai is a senior associate and lead electrical engineer with Environmental Systems Design. He has experience with super-tall, mixed-used, commercial, and governmental buildings as well as hospitals and central plant designs and upgrades.
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Read more: 2015 Salary Survey