Consulting-Specifying Engineer - November 2007 - (Page 19) hospital was given the option to expand the system, for a fee, to be fed from two substations. Some of these decisions are based on the probability that a failure will occur in the normal system. Unfortunately, natural disasters also play a part. Tornados, hurricanes, floods, and lightning can have an impact on the operation of the normal service. Hospitals also affect the reliability of the distribution system. Neglect reduces the lifespan of equipment and increases the likelihood of problems, whereas a preventive maintenance program, with regular testing of equipment and infrared testing of service gear, will help catch some of equipment issues before an operational failure occurs. Gen #1 1,500 kW Gen #2 1,500 kW Gen #3 1,500 kW Gen #4 1,500 kW (Future) GDP ATS-CR (Priority 1) ATS-XRAY (Priority 2) ATS-MCC-CEP (Priority 3) ATS-N1 (Priority 4) What is on emergency power? The second task requires collective effort of the owner, operators, users, and sometimes the local authority having jurisdiction (AHJ). Figure 1 Normal/emergency transfer switch priority scheme. NFPA 517, 99, 101, and 110, the state and local codes, and the AIA Guidelines for Healthcare Facilities all provide some input on what must switch schemes along with distribution design enables the control of be connected to emergency power. This is the easy part. The question load priorities, including these normal loads. For example, Figure 1 is, what other items does the owner want on emergency power? Does shows a system where the radiology equipment is a priority 2, just a the facility want the complete HVAC system on emergency or just some step behind the code-required priority 1 branches. areas? What about radiology equipment? These are not required by Figure 1 is an example of a normal/emergency transfer switch priorcode, but the owner may want to use them in an extended outage. To ity scheme using multiple transfer switches. Only four transfer switches what extent will the kitchen operate? Does the facility intend to maintain are shown in the one line for clarity, but the figure includes all transfer normal operation or has the owner established a plan to maintain food switches within the system. The purpose is to break down the loads services during a power outage? Are administrative spaces required to determine what load is connected to the bus first. Priority 1 is the to be on emergency power? branch that must have power restored within 10 s, the life safety and There is a growing trend in the healthcare industry toward backing up critical branch loads as well as generator equipment loads required to the entire hospital. Often this is an owner-driven request, because there be on in 10 s. The priority 2 loads will come on second, after a pre-set are benefits the owner receives from backing up both the normal and time delay as long as the second generator is running. This will repeat essential services. Many utilities have programs where hospital owners again for the priority 3 loads and the third generator, then again with receive financial payback on their generator systems. Several of these the priority 4 loads. programs are designed to get the hospital off the grid when the utility needs the additional capacity, and the hospital gets paid based on the capacity of power they remove from the grid. Hospitals may even receive some he first question is: What is the likelihood that at some point in the life of of the capital costs for the energy plant upgrades from an emergency power system, a hospital will need to operate on generator the utility company. power for several hours, days, or even weeks? Normal service must be evaluated Providing an emergency generation system that for reliability and the following questions are helpful in determining the likelihood provides power to the entire facility in an outage proof a normal power outage: • What is the history of power problems in the area? Typically the local utility vides additional benefits for the entire system. The design still maintains a normal branch of power; in this can provide a history of what outages have occurred and the reliability of case it could be defined as the nonessential branch. the services. • Does the hospital have dual services, and if so, are they from separate This branch includes loads that typically would be connected to the normal branch and have their own substations? • What else is on the grid with the hospital and how far is the hospital from transfer switch. These loads do not require emergency power per code. Therefore, power to these branches the substation? • Is the hospital located in a high-risk area for earthquakes, tornados, or will be restored last. In Figure 1, these loads are represented as priority 400 loads, automatic transfer hurricanes? • Is the area prone to lightning strikes? switch (ATS) N1 through N4. Also in the event that • How well does this particular hospital maintain its equipment? one generator is out of service, or there is insufficient power, the non-essential branch can be shed. Transfer What are the risks? T E Consulting-Specifying Engineer • NOVEMBER 2007 19
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