ASHRAE Journal - October 2019 - 54

ASHRAE - CELEBRATING 125 YEARS

PHOTO 7 Northwind Chicago Plant #2 under
construction with external melt ice-on-Coil units.
(courtesy Enwind Chicago)

PHOTO 6 Northwind Ice Storage Plant, Chicago.
(courtesy Enwave Chicago)

Plant 1, built in 1995, had 66,000
ton-hrs (232 MWh). Plant 2 has a
TES capacity of 125,000 ton-hrs
(440 MWh), using BAC ice-on-coil
modules, and came on-line in 1996
(Photo 7). Plant 3, built in 1997, had
97,000 ton-hrs (341 MWh). Plant
4, expanded in 1997, has 26,000
ton-hrs (91 MWh) dating from
c.1985 (when it served only the
Merchandise Mart, prior to the start
of the DC system). Plant 5 built in
2002, has no TES. All the ice TES are
BAC ice-on-coil units.
The large gray tank in the left center of Photo 8 is the ﬁrst ever application of the thermally stratiﬁed
aqueous sodium nitrite/nitrate low
temp ﬂuid (LTF) TES system.  The
TES tank was completed in 1994 by
CB&I and serves the district energy
system developed by Trigen-Peoples
(now owned and operated by the
City of Chicago).  It serves all 4 large
exhibit hall buildings comprising
McCormick Place, plus nearby hotel,
ofﬁce, and internet server facilities. 
The 8.5-million gallon (32 200 m3)
tank stores 123,000 ton-hours (433
MWh) at LTF supply/return temps
of 30/54°F (-1.1/+12.2°C), capable of
discharge rates of up to 25,000 tons
(88 MW) (up to an 18.75 MW peak
electric load shift).  The cold supply
temp was chosen for two reasons:
* to maximize Delta T, thus mini54

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PHOTO 8 Trigen-Peoples McCormick Place Stratified
Low Temp Fluid (LTF) TES, Chicago. (courtesy
Chicago Bridge & Iron Co.)

PHOTO 9 Thermal Energy Corporation (TECO),
District Energy System, Houston, using stratified
CHW TES. (courtesy TECO)

mizing tank volume in this urban
setting and
* to provide low temp airdistribution in much of the then
newly-constructed exhibit halls,
thus minimizing the size and costs
of (miles of) air-ducts and fans, and
minimizing fan power.
The low temp ﬂuid also provides
all on-going water treatment necessary for corrosion inhibition and
microbiological control.
The TECO (Thermal Energy
Corporation) district energy system provides steam and chilled
water to 18 hospitals in the Texas
Medical Center in Houston (Photo
9).  The 8.8 million gallon (33 300
m3) (100 ft D × 150 ft H [30.5 m
D × 45.7 m H]) chilled water TES
tank was provided by CB&I in 2010. 
It provides 70,000 ton-hours (246
MWh) at CHWS/R temps of 40/53°F
(4.4/11.7°C).  The TES can shift peak
loads of up to 14,000 tons (10 MW
electric).  Due to excess nighttime
wind power on the Texas grid,
TECO is sometimes paid as much
as $0.10/kWh to consume power to
recharge the TES.  And on extreme

O C T O B E R 2 0 19

peak days, the TES allows TECO to
avoid real-time power costs as high
as several dollars per kWh.

Utility Transformation Continues
At the end of the 1990s, the US
prepared for Y2K and the electric
utility industry was transforming
into a de-regulated, competitive,
non-integrated bundle of different
companies. There were GENcos,
TRANScos, DIScos, and RETAILcos,
and they were merging and divesting. Incentives and support for cool
TES made a left turn. Why would a
local distribution company pay an
incentive to avoid building another
organization's power plant? Power
plants were cheap and plentiful.
The retailers wanted to keep things
simple and sold electricity at one
price, with no on-peak, off-peak, or
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