to supplement emergency power, but only
if when the emergency power is up and
In the case of UW, steam is delivered
at 175 psig campus-wide and reduced to
10 psig within the buildings. Several large-scale buildings exist on campus and are
planned for the future that have year-round
steam loads – like hospital and research
facilities – and are prime candidates for
STGs. One particular candidate is a research
building currently under design that is more
than 1 million sq ft and has an estimated
peak load of more than 140,000 lb/hr. It is
estimated that the base load on the facility
would fall between 10,000 lb/hr and
This simplified analysis looked at STG
capacities within this range as well as one
size smaller and larger and the available
operating hours based on an estimated
annual load profile. Table 1 summarizes
the results of the analysis, and figure 1 is a
graphical representation of paybacks based
on electric rates and operating hours.
As seen in table 1, the paybacks are
very favorable and actually accelerate as
size increases due to the economies of
scale. Figure 1 shows even faster paybacks
when using higher electric rates. In closing,
this building and others may be candidates
for an STG if they have high-pressure
steam (>75 psig) available and a minimum
5,000 lb/hr base load of low-pressure steam
operating for more than half the available
hours per year.
Author’s Note: The author thanks Rob
Otremba of Affiliated Engineers Inc. and the
friendly folks at Turbosteam for assistance
with this article. Some recommended IDEA
resources for further reading: ( 1) “Free
Electricity From Steam Turbine-Generators:
A system level economic analysis” by Sean
Casten, Turbosteam Corp., and Thomas
O’Brien, Integrated Process Solution, District
Energy magazine, first quarter 2003, and
( 2) “Backpressure Steam Turbines Used as
Steam Pressure-Reducing Stations,” Bruce
McLay and Krishnan Ramesh, P.E., Affiliated
Engineers Inc., Proceedings from the 2003
IDEA Campus Energy Conference, Austin,
Texas. (Available free of charge to IDEA
members in IDEA’s Web archives.)
Source: Affiliated Engineers Inc., cost of STG per Turbosteam.
Table 1. Example of Induction Steam Turbine Generator Simple Payback.
STG size Output
*Estimate includes material and installation labor, design fees, permits and annual operating costs.
Electric Rate Hours of
Estimated Cost Annual Simple
Cost* per k W Savings Payback
Steve Tredinnick, P.E., is a
project engineer for Affiliated
Engineers in Madison, Wis.,
with more than 20 years’
experience related to building
HVAC systems. The past 10
years of his work have been
focused on district energy
systems. Tredinnick is a graduate of Pennsylvania
State University with a degree in architectural
engineering. He is a member of IDEA and
ASHRAE and is currently vice chair of ASHRAE
TC 6. 2 District Energy. Tredinnick may be
reached at email@example.com.
Column also available at
Two Great IDEA Workshops Together!
At the marketing workshop you will discuss strategy, messages, materials, methods
and the myriad opportunities to win the confidence of your key customers. Connect
with your colleagues. Exchange ideas. RECHARGE! We’re using ideas from the
annual conference forum meetings to determine presentations and panel topics.
At the distribution workshop, discussions will focus on the challenges of building and maintaining safe, reliable thermal piping
networks – steam, hot water, chilled water. What works… what doesn’t…what’s new?
18th Marketing Workshop and 17th Annual Distribution Workshop
Nov. 2-4, 2005
Doubletree Paradise Valley Resort
Hosted by Northwind Phoenix
Distribution and marketing professionals mark your calendars! Don’t miss your
forum workshop this fall in Scottsdale, Ariz.! IDEA is offering two separate but
simultaneous distribution and marketing workshops Nov. 2-4, 2005.
Photo courtesy Scottsdale Convention & Visitors Bureau.
A combined luncheon will bring the groups together to discuss customer service, satisfaction and communication.
Upcoming information will be posted on IDEA’s Web site www.districtenergy.org/calendar.htm – or call (508) 366-9339.