Using Load Profiles to Determine EPSS Peak Demand Load

David Stymiest, PE CHFM FASHE, DStymiest@ssr-inc.com

The author has used load profiling to determine EPSS peak demand load for more than 20 years.  The discussion below is intended to highlight some of the lessons learned.  For a full discussion, refer to the author’s 2009 ASHE Management Monograph, “Managing Hospital Emergency Power Systems – Testing, Operation, Maintenance and Power Failure Planning” available at http://www.ashe.org/.

NFPA Disclaimer: Although the author is Chair of the NFPA Technical Committee on Emergency Power Supplies, which is responsible for NFPA 110 and 111, the views and opinions expressed in this message are purely those of the author and shall not be considered the official position of NFPA or any of its Technical Committees and shall not be considered to be, nor be relied upon as, a Formal Interpretation. Readers are encouraged to refer to the entire text of all referenced documents.  NFPA members can obtain NFPA staff interpretations at www.nfpa.org.

Hospitals should document their actual EPSS peak demand load.  It is not enough to assume that the highest emergency generator kilowatt (kW) demand during an early-morning monthly test represents the true peak EPSS demand load.  This is a poor assumption due to the variability of mechanical, building, and clinical process loads during a typical hospital workday.  If an EPSS test time is chosen due to low clinical activity, then that avoided clinical load will not be reflected in the EPSS test loading.  Additionally, some equipment, such as smoke control systems and fire pumps, will not operate except during atypical situations.

Managing Hospital Emergency Power Programmes

By David L. Stymiest, P.E., CHFM, FASHE (in Business Briefing: Hospital Engineering & Facilities Management 2004 for the International Federation of Hospital Engineering (IFHE), London UK)

A hospital can have a simple or complex emergency power supply system (EPSS) but ensuring that the system continues contributing to safe and effective patient care with today’s challenges is rarely simple. Complexity is introduced because the EPSS powers other hospital systems such as the clinical, mechanical, vertical transportation and fire management systems. The hospital engineer must also respond to new requirements that affect the EPSS, including requirements for utility management, emergency management, patient safety, continuous quality improvement and staff education. All of these interrelationships cause complexity.

An EPSS includes generator sets, generator set auxiliary systems such as cooling, combustion air, fuel oil and starting systems, paralleling switchgear, automatic transfer switches, distribution panels, lighting and power panel boards, feeders and branch circuits. Some facilities that do not have EPSSs may have a stored-energy EPSS (SEPSS). Facilities can also have an uninterruptible power supply (UPS).

When the normal power fails, all normal loads are dead. All emergency loads experience a short loss of power unless they are backed up by an SEPSS or UPS. The hospital’s clinical staff must know how to deal with this condition. The monthly load testing simulates this experience as illustrated in Figure 1, although the length of time without voltage during a test is likely to be less than it would be during an actual outage. A proactive EPSS management programme will use the lessons learned from the monthly load testing, along with regular normal power shutdowns, to train the clinical staff to expect and then manage this critical element of the environment of care.

Read entire article here: Managing Hospital Emergency Power Programmes