Ecmweb 8271 Centralized Power Health Care Pr
Ecmweb 8271 Centralized Power Health Care Pr
Ecmweb 8271 Centralized Power Health Care Pr
Ecmweb 8271 Centralized Power Health Care Pr
Ecmweb 8271 Centralized Power Health Care Pr

The Power-Centric Approach

June 20, 2016
Exploring centralized power distribution system design trends in health care facilities

Today’s health care facilities play a vital role in the health and welfare of modern society. No matter the size or prominence — whether nationally renowned or regionally focused — a health care facility must perform a multitude of functions in order to provide the unique care demanded by modern medicine. Accordingly, the internal infrastructure that supports these facilities must be robust, reliable, and flexible.

Pixland/Thinkstock

It is a continual struggle to keep this internal infrastructure up to date with the constant growth within existing health care facilities generated by such factors as expansions, technological advancements, evolving codes and standards, and end-user needs. Health care-essential electrical systems are no exception. New solutions are needed to support existing systems that are beginning to struggle to keep up with needs of growing facilities. One solution that is gaining traction among existing health care facilities is the movement away from older decentralized essential electrical system sources toward the consolidation of essential sources in a centralized location (to see a PDF of the Figure, click here).

Case in point

The health care campus of a major regional U.S. medical center recently took the approach to begin centralizing its essential electrical system sources. This expansive 750-bed hospital and clinic system had, until recently, relied on a distributed network of emergency generators across its campus to deliver essential power. While this method of delivery has certainly worked over the years, the drawbacks and constraints have become more apparent as the campus has grown, rendering the distributed generator infrastructure increasingly cumbersome. The need for a new way to distribute essential power became unavoidable when the medical center began its newest expansion, adding approximately 400,000 square feet of floor space to the existing campus. Adding another generator to the existing health care campus proved unacceptable due to environmental regulations.

Rather than adding generators to support the expansion alone, the medical center recognized the advantage of moving toward a centralized system that could begin to support the entire campus with room to grow. In addition to conforming to environmental regulations, the crucial advantages include reduced maintenance cost, added reliability and redundancy, and the simplification of an already sprawling essential electrical network.

Phase 1 planning quickly took place in parallel with the development of the expansion on what would eventually become the medical center’s emergency generator facility. The facility was designed to be a standalone 12,000-square-foot structure housing three 2,500kW Tier 2 diesel generators operating in an N+1 configuration connected together at a paralleling switchgear bus. From initial startup, the facility is intended to support not only the new expansion but also portions of the main hospital campus.

The paralleling switchgear bus was designed to be a main-tie-main configuration in order to meet priority 1 and 2 loads within 10 seconds; moreover, the essential power distribution system is divided equally and not dependent upon the assurance that the generators are able to be paralleled. Downstream unit substations that feed essential system automatic transfer switches offer a higher degree of resilience, redundancy, and ability to respond with contingency planning, given a number of different failure scenarios. With scalability and future growth in mind, the facility will be able to support 20MW of total installed essential power, which would support the entire medical center campus. Some key characteristics of the emergency generator facility are highlighted below:

• As a critical stand-alone facility operating in one of the most active extreme weather regions of the United States, the facility is hardened to withstand a direct hit from an EF-3 tornado and remain fully functional. Additionally, due to the unique design for cooling air intake and discharge openings, generators are not exposed to foreign object impacts associated with windblown debris. Consequently, they are less likely to receive direct physical damage. Furthermore, due to the intrinsic strength of the reinforced precast concrete, the facility is resistant to ballistic attack.

• Because available construction space in the immediate area of the hospital was limited, the facility generators and distribution system operate at 13.8kV.

• Due to the remote location, the emergency generator facility (EGF) must be monitored 24/7 against intrusion by unauthorized personnel. This is accomplished via access control systems coupled with closed circuit television (CCTV) monitoring. The CCTV does not only provide exterior coverage but also interior continuous observation of all the critical elements of the system.

• The essential power distribution system between the hospital and facility is routed entirely underground in two independent reinforced concrete duct banks. Eventually, the duct bank system will be completely looped through the medical campus and accommodate two independent essential power loops serving the hospital.

• The entire essential electrical system is monitored and controlled through a supervisory control and data acquisition (SCADA) system. Authorized hospital staff can remotely monitor, control, and adjust the system from a centralized location that is constantly manned. This system monitors each engine generator and individual campus automatic transfer switches. The SCADA communications system uses fiber-optic cabling in order to overcome the distance between the emergency generator facility and the main hospital campus.

Other drivers, other responses

The system employed by this medical center is only one example of a growing trend for essential power generation within existing health care facilities. Each campus presents unique circumstances, creating the driving factors prompting them to change their strategies.

A centralized generation design minimizes the multiple points of failure exhibited by distributed and independent generators located throughout a facility. These multiple points of failure introduce the possibility of any single generator failure potentially placing a major function of a hospital in jeopardy. Decentralized networks often provide a workaround for this concern by providing a cross-tie system that back feeds multiple loads from other generators not originally designed to serve them directly. Implementing a cross-tie system can become a safety concern in existing facilities if proper (kirk-keyed) lockout controls are not implemented; additionally, back feeding loads via a cross-tie introduces the potential of overloading a single generator, which could cause additional system failure. Centralized generators that are redundant to each other are inherently resilient to any single point of failure. Where any one generator (or more) is considered operationally offline in a centralized design, load is able to be distributed to other paralleled generators. This becomes extremely useful in terms of general maintenance and care as it provides an efficient means for servicing generators while still providing adequate protection against all generator sets being inoperable simultaneously.

As mentioned earlier, many health care facilities are in a state of constant flux. Rarely does the space programming within an existing hospital remain the same as it was originally conceived to be. What used to be a wing of offices has now become a row of surgical suites 20 years later. This creates a burden on an older distributed network of emergency generators because most likely the generator for that region of the hospital is of inadequate size (assuming there is emergency power in that region of the hospital at all). Although a quick solution could be to just replace the local generator, this is often difficult due to physical constraints and associated downtime. With a centralized system, the aforementioned issues related to changing hospital programming are largely avoided with proper system size planning. Moreover, a centralized design can be made modular so that system expansions are as simple as “plug-and-play” with new generator sources, if the distribution system has been sized for the future additional generation.

Much like the electrical distribution systems discussed, when a facility expands over time, other behind-the-scenes utility services must expand to meet the needs of the end-user. These other utilities can come to represent some of the largest loads for a hospital and a significant driver for generator placement and sizing. Where generators are organized in a decentralized network, it can become difficult to support such large loads as they quickly either outsize or monopolize a single generator’s capacity. Centralized sources are able to absorb these larger loads with lower concerns for available capacity.

In some cases, a health care facility needs or wishes to parallel its essential electrical system with the local electric utility system. The reasons why a facility may wish to do so are many, including base loading and peak shaving. But this paralleling requires specialized sequencing from a generator perspective to be successfully accomplished. This function becomes exceedingly difficult (if not impossible) to accomplish with decentralized generators. A centralized emergency source can tie with the electric utility much easier with the proper use of paralleling controls and synchronization; moreover, centralized systems can often be designed to match the native electric utility voltage for simplification of paralleling systems.

Any structure in the built environment is subject to forces of nature, and best planning revolves around thinking in “inevitabilities” and not “possibilities.” Even with a hardened structure in place, consideration must be given to such forces as a 100-year flood plain when siting the centralized generation facility — particularly considering the disastrous outcomes of hurricanes Katrina and Sandy in recent years. The evaluation must include critical consideration of the essential power distribution system within the hospital itself — double-ended substations located in the subbasement of the hospital are exposed to possible flooding conditions. Furthermore, these facilities must also be secured against internal destruction due to fire. Alternative methods for fire suppression should be considered, such as aqueous foam systems. These fire suppression systems extinguish the fire without exposing adjacent equipment to water damage as conventional sprinkler systems would do, thus preserving the electrical integrity of a centralized source.

Takeaways and conclusion

The decision for any health care facility to transition its essential electrical system from distributed sources to a centralized system is not one that should be done without careful planning and consideration. Long-term goals and expectations for the hospital should all be considered in order to design a system that captures all the advantages that a centralized system has to offer.       

Flickinger and Hood are electrical engineers at Affiliated Engineers, Inc., Madison, Wis. They can be reached at [email protected] and [email protected].

SIDEBAR: Benefits of a Centralized Power Distribution System

Some of the key features that centralized essential electrical systems offer include:
•     Inherent system redundancy through paralleled generation sources.
•     Ease of maintenance and serviceability.
•     Increased system capacity.
•     Improved system resiliency.
•     Improved system hardening and security.
With these advantages in mind — and careful consideration directed toward facility planning — many health care facilities can reap the rewards of an essential electrical system that is both effective for today and preparing for the future.

About the Author

Thomas Flickinger, P.E. | Electrical Engineer

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