Page 399 - Sustainable On-Site CHP Systems Design, Construction, and Operations

372 Ca s e S t u d y 5

flexibility and reliability to meet demand. The ability to adjust generation levels and
still maintain required steam or gas pressures and temperatures is very much a function
of the district’s design.
In some cost structures, the CHP system would provide electricity to the DCOA on
a continuous basis, resulting in daily operating cost savings. In this type of configura-
tion, the CHP system is sized to meet the base thermal and electric needs of the facility.
When the macrogrid fails, the COPS generators would switch to the electric riser that
feeds COPS loads only. The absorption chiller would continue to produce cooling,
which would be directed only to data center loads and specific areas where disaster
management personnel require air-conditioning.
In other cost structures, supplemental power from the grid would serve the DCOA’s
peak power needs on a normal basis and would provide the entire facility’s power only
when the CHP system is down for planned or unplanned maintenance.
The 2008 version of Article 708 does not directly address microgrid configurations
in which CHP provides all on-site power needs. Though recent revisions of the NEC
demonstrate that its authors have adapted to the gathering pace of innovation in dis-
tributed resource technologies, the NEC is still written around the assumption of a mac-
rogrid “serving utility”, with specific requirements for service switchgear, subject to the
requirements of the state public utility commission for safety and reliability. The avail-
ability of the primary on-site source, and the backup system, must be approved by the
authority having jurisdiction as meeting the availability requirements of Article 708 and
its related annexes in the NEC. 6
In the past 10 years, major regional contingencies proved district steam systems to
be reliable to about 99.98 percent. District heating systems were the only utilities to
provide continuously uninterrupted service during:

• The natural disasters of the Loma Prieta earthquake (7.1 Richter scale) in San
Francisco in 1989
• The massive Ottawa Ice Storm in Montreal during 1998
• The destructive 6.8 Nisqually earthquake that shook Seattle in 2001

In 2006, 17 of the top 20 hospitals in America, according to U.S. News & World
Report, were served by district energy systems. Many colleges and universities, during
7
the August 2003 major regional contingency in the northeast United States and Canada,
were able to provide a limited amount of power equipment in their host communities.
If the trends described at the beginning of this chapter continue, educational facilities
will be called upon to play a larger role in homeland security.
District heating is a long-term commitment that fits poorly with a focus on short-
term returns on investment. It has to compete with the established gas grid which offers
point-of-use heating to most buildings. It requires that politicians, planners, develop-
ers, market actors, and citizens cooperate on a range of issues, but offers important
benefits as outlined in this book.

Prime Mover Possibilities
Most backup gen-sets are installed to meet the requirements of NFPA life safety codes
and are limited to about 200 hours per year before overhaul. Most of these life safety
gen-sets are rarely used; with most of the hour run-up due to mandatory testing. The