Page 350 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Princeton University District Ener gy System 323

steam-driven induced-draft (ID) and forced-draft (FD) fans to allow for short exhaust
stacks that met campus architectural requirements.
In 1950, three new vibro-grate boilers replaced the originals and a 750-kVA, 26-kV
substation was built on the far side of the campus.
The existing chilled water plant was built in 1960 and began with a 700- and 1100-
ton chiller. The plant was entirely steam-driven until the need for off-peak cooling dic-
tating the use of a small electric-driven pump. In 1965, the original 500-kVA Curtiss
generator was replaced with a 3750-kVA three-phase generator. In 1964 and 1965, 2200-
and 3400-ton chillers were added. In 1967, the boilers were converted from coal and oil
to natural gas, rail lines that had been used for coal deliveries were removed and air
pollution standards were imposed. The boilers were retubed to add efficiency and 10 to
15 percent capacity.
In 1970, the campus substation was expanded to 15,000 kVA and the first dormitory
bedrooms were added to the district heating system. In 1978, a campus energy manage-
ment system was installed in response to the energy crisis. In 1985, a 1500-ton electric
chiller was added. In 1986, an additional 20-kVA substation was constructed. In 1988, a
second 1500-ton electric chiller was installed.
By the late 1980s, the main boilers were in need of extensive (and expensive) repairs.
Air emission laws would also require significant control upgrades. After many design
studies, plans for a cogeneration system were developed that allowed more economical
and less polluting simultaneous generation of heat and power.

The Modern Cogeneration Era
In 1996, the cogeneration plant replaced the boilers and added 15 MW of generating
capability. Over the 1990s, all CFCs in the chilled water plant were replaced with HCFCs
and chiller speeds were increased to recover their original capacities. In year 2000, by
replacing an original 700-ton steam-driven chiller with a 2500-ton electric chiller, the
plant cooling capacity was brought to 15,500 tons.
In 2001, Princeton added an economic dispatch model of the plant that was to pro-
vide expert guidance for the plant operators. Prior to this, plant equipment had been
operated for reliability based on a general understanding of seasonal fuel and electric-
ity prices. Over the next few years, a complete energy and economic dispatch system
was developed to most cost-effectively meet the campus energy needs. On August 1,
2003, this system became far more valuable due to the increased electric price volatility
caused by deregulation of New Jersey electric markets.
In 2005, the stone boiler house was renovated and now houses the offices of public
safety and campus planning. 40,000 ton-h of chilled water thermal storage and two
additional chillers were installed adding capacity, reliability, and economic responsive-
ness to the energy plant.
In 2006, the Elm Drive and Charlton Street Substations were upgraded and circuit
breakers were added to provide two independent feeds to each side of the campus from
the PSEG 26-kV system.
In 2007, Princeton pioneered the use of biodiesel. The energy plant was the first to
obtain an Environmental Improvement Pilot Test permit to burn biodiesel in stationary
boilers in New Jersey. The plant also was the first in the world to operate a General
Electric LM-1600 gas turbine on biodiesel.
In 2008, another form of combined heat and power was added to the district energy
system. Two Carrier “Microsteam” backpressure turbine-generators were installed in