ASHRAE Journal - October 2019 - 43

ASHRAE - CELEBRATING 125 YEARS

subsidize one rate class at the expense of another. This
meant that the TES project would shift its peak kWh at
$0.05/kWh to off-peak at $0.025/kWh, but it had to consume twice as much energy at night. There was no customer savings, but the utility could provide an incentive
to balance its load proﬁle. These technical requirements
favored ice storage and particularly "ice harvesting"
systems (see later section, "Cool TES Technology Family
Tree.")
The equipment manufacturers, utilities, and engineering ﬁrms saw a value in design guides and technical information. Sizing tanks, estimating weekly load
proﬁles, and performance of ice slurries was neither
well understood nor documented. ASHRAE established
Technical Committee (TC) 6.9, Thermal Storage, in 1981.
TES activity had previously been part of TC 6.1, Heat
Pumps; but the research focus did not align across two
very different markets.

Electric Utility Impacts and Second Generation of TES
In 1979, the electric industry fundamentally changed
when the Three Mile Island (TMI) nuclear plant experienced an incident. Previously, nuclear power was
supposed to be so inexpensive, it would not have to be
metered. Safety concerns and public opposition rapidly
increased the cost of nuclear plants with utilities pushed
to the brink of bankruptcy. Utilities actually looked at
ways to reduce growth to avoid additional construction
costs. Demand-side management (DSM) was embraced
to address peak electric demand. As a secondary result of
the TMI accident, the Electric Power Research Institute
(EPRI)-established by the utility industry to conduct
collaborative research-began to take a closer look at
advanced technologies for using electricity. As part of its
research into DSM, EPRI invested in a portfolio of technology developments involving TES.
The new generation of TES systems had a new focus-
reduce peak demand. The systems did not have to be
revenue-neutral, which had mandated less efﬁcient
solutions such as ice harvesting. Simple ice tanks and
chilled water storage were allowable. Chilled water
storage was seen as the preferred technology by the
chiller manufacturers as their existing product lines
required no changes; but the challenge was to avoid
mixing the supply and return chilled water to maximize capacity and maintain cool supply temperature.
The TES industry experimented with various designs

PHOTO 1 Block ice farming. (courtesy of Wisconsin Historical Society)

(see later section, "Cool TES Technology Family Tree")
before settling on thermal stratiﬁcation as the simplest strategy. Extensive research was conducted at
the University of New Mexico and separately by tank
manufacturers to develop theories affecting diffuser
designs to create and maintain stratiﬁcation. EPRI
funded studies and ASHRAE TC 6.9 produced the
Design Guide for Cool Thermal Storage.
Ice storage tanks were also further developed in the
early 1980s. These included ice-on-coil internal melt,
ice-on-coil external melt, and encapsulated ice TES,
as well as ice slurries and other phase change materials (PCMs), all described in the later section, "Cool TES
Technology Family Tree."

A New Approach
The perceived energy penalty for ice-making was
an impediment, especially as global warming concerns were emerging. The TES industry developed a
novel alternative that radically departed from conventional HVAC design. Air is distributed through
ductwork in most buildings at 55°F (12.8°C) in order
to achieve ASHRAE Standard 55 comfort conditions of
76°F (24.4°C) and 50%RH. Chilled water is typically supplied to air-handling units at 44°F (6.7°C). An ice plant
can provide chilled water temperatures at nominal
32°F to 36°F (0 to 2.2°C), and its larger Delta T is wasted.
However, if the air-distribution system is designed for a
much lower supply temperature of 45°F (7.2°C), the airﬂow can be cut in half for the same cooling capacity. Fan
and duct size are reduced, offsetting the cost of the ice
O C T O B E R 2 0 19

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ASHRAE Journal - October 2019

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