When utility power is interrupted, standby power system failure is not an option for mission critical facilities. Mission critical facilities, such as hospitals, data centers, and other highly critical buildings, must remain operational. Vital mission critical power system characteristics include availability, reliability, survivability, security, and efficiency. Designing reliable and efficient standby power for mission critical facilities poses unique challenges, such as determining the size of standby generators, determining level of redundancy, calculating the amount of onsite fuel, and anticipating every possible scenario that can affect system performance.
Requirements of mission critical standby power systems exceed those of standard commercial projects, which are typically designed to merely comply with applicable building codes. Many times, high expectations of systems for mission critical facilities are influenced by the desire for increased levels of reliability and efficiency.
The Feb. 16 Critical power: Backup, standby, and emergency power in mission critical facilities webcast presenters addressed questions not covered during the live event. The presenters are:
- Kenneth Kutsmeda, PE, LEED AP, engineering design principal, Jacobs, Philadelphia
- Scott Kesler, PE, LEED AP, principal, CannonDesign, Chicago.
Question: Is the mission critical rating an ISO 8528 rating?
Kenneth Kutsmeda: No. The mission critical rating is not an ISO 8528 rating. It is an industry/manufacturer rating to allow customers to obtain certification from Uptime Institute or at a minimum, comply with its requirements. The rating is more for warranty purposes. The mission critical rating allows the generator to run without limitation on hours due to the fact that data center loads generally are constant.
Question: Please discuss Type 1 essential electrical systems (EES) and the need for separated branching.
Scott Kesler: Type 1 EESs are required to be separated into three branches: life safety, critical, and equipment. Depending on the size of the system, one or more transfer switches are required. For systems 150 kVA and smaller, a single transfer switch can be used.
Question: Considering the Uptime Institute’s requirement for Tier 3/Tier 4 generator sets to be able to serve facility loads continuously at 100% of the load, how does the mission critical rating meet Uptime’s requirement for Tier 3/4 systems?
Kutsmeda: A prime rating engine that is derated per ISO can operate continuously at 100% load to meet the requirements of Uptime Institute Tier 4. A mission critical engine is a standby-rated engine that is allowed to run for more hours based on the load profile of a typical data center. Some manufacturers have indicated that this rating was created to allow a standby rating to meet the requirements of Uptime. The mission critical rating still has a limitation of 500 hours so I recommend clarifying “continuously” with Uptime Institute if you intend to get certification.
Question: For hospitals, am I to understand that NFPA 99-2015: Health Care Facilities Code changed the arrangement as shown in NFPA 70-2017: National Electrical Code (NEC), Article 517.31(b) and removed equipment branch from the essential system, and that it now refers to life safety/critical as an emergency system?
Kesler: The EES as defined by both the NEC and NFPA 99 include the three branches of life safety, critical, and equipment.
Question: In an application where you have a fire pump on a generator, have you used that capacity to also support optional standby loads (freezers), the theory being that these optional loads no longer need to be supported in the event of a fire?
Kutsmeda: Yes. The NEC allows automatic shedding of one or more optional standby loads to comply with the fire-pump capacity requirements.
Question: To what extent could onsite stationary battery installations take the place of onsite backup generators?
Kutsmeda: NEC Article 708 allows the use of batteries as the sole source of power for critical operations power systems (COPS). However, it also requires that the alternate source be capable of operating for a minimum of 72 hours at full load.
Question: On what branch do health care facility computer systems and networks fall? For nursing staff, patient information is very important. Also, many health devices these days are more connected to networks.
Kesler: The 2012 version of NFPA 99 added a new chapter titled “Information Technology and Communications Systems for Health Care Facilities” to specifically address this issue. Prior to this, there was no specific code that covered these systems that were becoming more critical to patient care. While there are some exceptions, in general, the computer systems and networks are to be served from the critical branch of the EES, and the HVAC serving the IT spaces are to be served from the equipment branch.
Question: If one is powering the entire facility from the emergency generator, say a 9-1-1 center, does there still have to be a separate transfer switch for the life safety circuits or can a single transfer switch be used for all the loads?
Kutsmeda: In my experience, a separate transfer switch and distribution system is still required for emergency life safety in a mission critical facility where the entire building is backed up by a generator. The NEC does not define COPS loads as part of the Article 700 requirements. On systems with multiple generators or generator paralleling switchgear, I recommend that this be reviewed with the authority having jurisdiction (AHJ) because an AHJ may often have different opinions on how that connection must be made.
Question: Shouldn’t staggering loads added to the alternate power source be a concern in designing an EES?
Kesler: Code stipulates that only the life safety and critical branches need to be re-energized within 10 seconds for health care facilities. The equipment branch and any optional branches can be added outside of this time frame. Adding loads in a staggered manner minimizes the in-rush current and starting kVA applied to the generator, and can result in a smaller generator needed to support the required loads.
Question: What is the requirement for ground fault protection on a mission critical generator? Is there an exception to exclude ground fault protection on standby generators?
Kutsmeda: Any 480 V generator breaker rated at 1,000 amps or more is required by the NEC to have ground fault protection if the generator is serving life-safety load and has the option of alarm only and not tripping on ground fault. Mission critical generators are considered optional standby so a ground fault would be required if more than 1,000 amps at 480 V. NEC Article 708 requires multiple levels of ground fault on feeders to prevent taking down the entire system. On medium-voltage generators, one recommendation would be to use some type of resistance grounding system.
Question: Please discuss the 3 types of EESs in health care and where each is used.
Kesler: The three type of EESs in health care facilities are aligned with the level and type of care being administered.
Category 1, or critical care, is defined where the failure of equipment of a system is likely to cause major injury or death. Category 2, general care, is defined where the failure of equipment or system is likely to cause minor injury. Category 3, basic care, is where the failure is not likely to cause injury but can cause discomfort.
Type 1 EESs are required for Categories 1 and 2 areas of hospitals and other health care facilities where patients ae sustained by electrical life-support equipment. Type 2 systems generally are applicable to nursing homes and limited-care facilities, while Type 3 systems are required for other health care facilities falling under the Category 3 classification.
Question: With 72 hours at full load of fuel storage required for COPS, what are your recommendations to cycle fuel and prevent the fuel from spoilage over time?
Kutsmeda: With any type of mission critical system where there are large amounts of fuel storage, I recommend some type of fuel polishing system. Also, having multiple tanks instead of one large tank allows you to transfer fuel between tanks through a polishing system.
Question: For a six-story building with elevators, do we need a generator?
Kesler: For health care facilities, the determination for elevators being on the EES is not determined by the height of the building, but rather the areas being served. Selected elevator service is required for patient, surgical, obstetrical, and ground floors in Type 1 facilities.
Question: Are levels of reliability for mission critical facilities governed by the AHJ or owner/user?
Kutsmeda: For public safety type mission critical facilities (NEC Article 708), the reliability is governed by the AHJ. NEC Article 708 requires the facility to have a redundant alternate source of power or at minimum a means for a roll up. For private mission critical facilities, the reliability is dictated by the owner based on his or her business case—cost of additional redundancy versus tolerance for risk and outages.