From: Essential Information <ei@igc.apc.org>
Newsgroups: sci.energy
Date: 31 Dec 92 13:54 PST
Subject: Re: Energy Ideas - HVAC-2
Nf-ID: #R:cdp:1466300134:cdp:1466300141:000:3323
Nf-From: cdp.UUCP!ei    Dec 31 13:54:00 1992



PUTTING YOUR COOLING SYSTEM ON ICE

Thermal Energy Storage (TES) systems make ice during off-peak
utility hours and then use that ice for cooling during peak
hours. While it is possible to design a TES system that is more
energy efficient than a conventional system, the main appeal of
these systems is economic. TES systems operate chillers at night
rather than during the day, lowering a facility~s (and therefore
the utility~s) daytime electric demand, generally allowing the
facity to pay a lower rate for electricity. By lowering peak
demand, these systems minimize a utility~s use of inefficient and
polluting boilers.

How TES Works

TES systems make ice at night when electricity rates are lower
and then pass chiller water through the ice during the day to
provide cooling. Instead of using pure water, the TES chiller
water is mixed with ethylene glycol (an antifreeze) at about a
three-to-one ratio. At night, the chiller (either
vapor-compression or absorption) chills the water to about 25o F,
rather than the usual 45o F. This supercooled solution is
circulated through a pipe (a mile or longer in length) which has
been tightly coiled and submersed in water within a storage tank.
The water in the tank loses heat to the solution and freezes (as
the water freezes it expands upwards). During the day, a control
system combines both the chiller and the ice as the cooling
system. The installation of this system allows a smaller chiller
(about 40 percent smaller) than the building would require, since
the chiller has all night to make ice which will supplement the
cooling load during the day.

Antifreeze Poses Danger to Animals

Because of its toxicity, care should be exercised in the handling
of ethylene glycol and other antifreeze agents. The danger does
not arise from the use of the antifreeze, but rather accidental
spills during transporting and handling the substance. According
to the U.S. Fish and Wildlife Service, ethylene glycol is a
colorless syrup alcohol which has a sweet flavor that attracts
animals. The antifreeze crystallizes in the kidneys, leading to
kidney failure. 

Energy Efficiency of TES

Typically, TES is less energy efficient than a conventional
system. The freezing and melting of ice has its own built-in
inefficiencies which do not exist in conventional systems.
However, the introduction of adjustable speed drives can reduce
the total energy used by the system. In addition, the ice can
provide colder chiller water than conventional systems, which
means that less water is necessary to cool the air in the air
handlers. This translates into less water which must be
circulated and a corresponding energy savings.

CASE STUDY:

TES System at Police Station
The City of Phoenix, Arizona replaced an inefficient 120-ton
chiller system with a 60-ton high efficiency chiller system and
ice storage at the Police Training Academy. The chiller will
operate at night, making ice to be used for cooling during the
day. In addition to the $38,250 equipment rebate for shifting 153
kilowatts to off-peak time, $6,130 and 94,300 kWh will be saved
annually. The city coordinated with the utility to determine the
best load and rate schedule for the project. (Contact: Dimitrios
Laloudakis, Energy Conservation Manager, 2631 South 22nd Ave.,
Phoenix, AZ 85009, (602) 261-8813.)


Newsgroups: sci.energy