ASHRAE Journal - June 2013 - 64

emerging technologies
temperature must be lower than in a conventional system, with
commensurate efficiency reduction.
Depending on configuration and operational parameters,
the bottom line energy consumption of a particular site may or
may not be improved with the addition of cool TES. However,
published case studies favorable to TES report that site energy
savings on the order of 10% to 20% are achievable in some
instances.4
Energy savings at the electricity source are independent
of specific energy savings at the use site. In the electrical
grid, demand must be continually matched by generation,
ideally in the least expensive way possible. Generators with
negligible fuel costs (nuclear, solar, and wind) are at the top
of the dispatch list, followed by efficient coal and gas plants.
As electricity demand rises, e.g., on a hot summer day, increasingly less-efficient plants may be dispatched to match
it, requiring increasingly more primary energy (and more
money) per kWh produced. Cool storage shifts demand out
of the peak hours, where it would likely have to be met with
an inefficient plant, into the off-peak hours, where it can be
met with an efficient plant. A 1996 study by the California
Energy Commission estimated the source primary energy
savings from cool TES (compared to conventional cooling
equipment) to be in the range of 8% to 43%, even assuming
zero energy savings at site.4
The energy mix has shifted substantially since 1996, but
the prevailing trends make cool TES even more important to
energy sustainability.5 Wind and solar generators are inherently
intermittent, and as their penetration increases, the variability
of the remaining demand that must be met with conventional
generation (“net load”) will likewise increase. Cool storage has
the potential to smooth this minute-to-minute net load variation, just as it can smooth the diurnal demand variation that has
traditionally been the driver for its use.
Electricity deregulation has in many areas meant the establishment of explicit markets for delivered and reserved energy
on a variety of timescales; essentially, cool TES is a resource
that has value in these markets, and there are models emerging
to realize that value. In one model, facilities participate directly
in the markets, buying electricity under real-time pricing. This
involves the implementation of sophisticated HVAC control
algorithms to optimize the use of the TES resource, but could
reduce electricity costs by a few percent compared to a timeof-day control scheme under time-of-use pricing.6
In another model, a third-party demand response (DR) services company acts as a middleman between the markets and the
facilities. For a fee, the DR service manages the optimization,
quantifying the TES resource’s value and controlling the HVAC
systems to reduce electrical load when it is profitable to do so,
through some combination of automated and manual channels.
In a third model, the utility owns and operates the TES resource outright. The unitary static ice TES system mentioned
previously is currently marketed under this model; the Southern
California Public Power Authority is an early adopter. By funding
the deployment of a fleet of TES units, the utility reduces its peak
64

ASHRAE Journal

DX Condensing Unit
(Integrated)
Filter

Ice Maker
Condensing Unit
(Integrated)

Evaporator
Ice Coil
Evaporator (Liquid
DX Coil Overfeed)

Conventional
Packaged Unit

Fan

Refrigeration
Management
System

Ice-On-Coil
Heat Exchanger
Ice Storage Tank

Figure 1: Diagram of unitary static ice TES system used in conjunction with packaged DX unit.1
demand and gains a directly controllable load-matching resource.
The buildings involved save money on electricity due to off-peak
pricing, with no capital investment or maintenance required.

Market Potential
Pike Research has estimated the 2011 installed cooling
capacity of commercial TES in the United States to be about
1,000 MW for ice-based systems and 355 MW for chilled water. Commercial cooling applications account for about 50%
of all installed TES in the U.S.; the remaining 50% consists of
power plant applications and electric thermal storage.7 Projected
capacity additions for all forms of TES in North America by
2020 total 768 MW of cooling capacity.7
Data from the Commercial Building Energy Consumption
Survey (CBECS)8 can be helpful in developing an estimate
of the addressable market for ice/chilled water forms of TES
in commercial buildings. Figure 2 is based on data from the
2003 CBECS and summarizes the total square footage in nonresidential, non-mall buildings that is cooled by one or more of
the indicated types of cooling. Since buildings currently using
central chillers and/or chilled water are actual or potential installation sites for TES, the addressable market for commercial
applications of TES is about 15,000 million ft2 (1.4 billion m2).
In addition, unitary systems may begin to penetrate the 40,000
million ft2 (3.8 billion m2) packaged/central direct expansion
(DX) cooling market.
TES systems have already noticeably penetrated the Florida
market for commercial building space cooling, particularly in
schools.9 Schools in Sarasota County, Hernando County, and
Orange County have installed TES systems. The 450,000 ft2
(41 805 m2) Weeki Wachee high school campus in the Herashrae.org

June 2013
ASHRAE Journal - June 2013

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