ASHRAE Journal - January 2014 - 40

2013 ASHRAE TECHNOLOGY AWARD CASE STUDIES
allows improved wire-to-water
transfer of energy, reducing overall
energy consumption considerably.
Innovation
The use of a natural gas turbinedriven
CHP/heat recovery steam
generator/duct burner to provide
for the base steam demand, and that
required to run the steam-driven
chiller, has resulted in a substantial
shift in demand from the existing
utility power grid to the natural gas
utility and allowed us to produce up
to 2,800 tons (9847 kW) of chilled
water from free steam for only the
cost associated with running the
condenser-chilled water pumps and
cooling tower fans.
HMH can produce up to 6,800 tons
(23 915 kW) of emergency cooling
in the cogeneration (CHP) island
mode if all power is lost due to rolling
brownouts or storm damage.
This upgrades the ability to operate
a significant portion of the campus
while maintaining patient care and
2010 - 2011 Energy Mix
2011 - 2012 Energy Mix
Electricity MMBtu
Gas MMBtu
FIGURE 1 Cogeneration decreased the dependency on electricity, reducing electric consumption and avoiding $1.85 million
in net expense over 12 months. This cogeneration project is expected to return investment in fewer than two years.
12
10
8
6
4
2
0
2010 - 11 Blended $/MMBtu
2011 - 12 Blended $/MMBtu
Feb.
Mar.
Apr.
May
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Jan.
FIGURE 2 Year-over-year change. Due to the reduction in electricity use (a higher expense energy source) the overall
$MMBtu was reduced significantly and savings are higher than modeled.
research demands while reducing dependence on the
local power grid.
The hospital's steam demand profile requires producing
approximately 20,700 lb/h (2608 g/s) of steam
to meet heating, sterilizing, humidification, domestic
hot water steam loads, along with the steam demand
of a 2,800 ton (9847 kW) steam-driven centrifugal
chiller (requiring 25,300 lb/h [3188 g/s] of high-pressure
steam). This allows us to base load the CHP for
electrical power generation and recovered thermal
energy while rarely having to fire the high NOX steam
boilers.
Operation & Maintenance
Existing reliability, redundancy and other O&M issues
addressed during the project design and construction
phase included adding cooling tower capacity, along with
system piping and electrical system modifications that
provided a higher degree of overall functionality and reliability.
We have achieved cold weather operation of the
CUP using one 2,800 ton (9847 kW) steam-driven chiller
40
A SHR A E J O U RNA L
ashrae.org JAN UARY 2014
where previously it took a minimum of two 2,000 ton
(7034 kW) chillers.
This was achieved by improving AHU coil designDT to
match the original design of 12°F (22°C)DT and adding
UVC lights to keep cooling coils clean when replacing old
lowDT air-handling units, by adding UVC lamps to existing
cleaned and refurbished AHU coils, and by better
secondary and primary chilled water systems differential
pressure and VFD control. The addition of the CHP and
associated protective switchgear has made the overall
system much more complex, but the added BAS automation
and increased O&M training required by the system
have resulted in a more reliable and easier to troubleshoot
overall central utility plant, and one that certainly can
operate during extended power grid outages.
Cost Effectiveness
The natural gas-fired CHP cogeneration/heat recov-
ery steam generator/duct burner units were installed
to address both power capacity and emergency cooling
capability concerns. This gives HMH the ability to
Blended $/MMBtu

ASHRAE Journal - January 2014

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