Feature
THERMAL STORAGE:
ENERGY SAVING COOLING
By Ntsako Khosa
As costs increase and uncertainty regarding sustainable power provision
remains, thermal ice storage is considered one of the viable solutions to
generating cooling power.
T
hermal ice storage provides many environment-friendly
opportunities that are a result of reduced peak electrical
demand. Andre van der Merwe, managing director at Evapco
says, “Anyone who has a desire to be environmentally
responsible and save energy would find using a thermal storage
system beneficial.”
WHAT IS THERMAL STORAGE?
“Thermal storage as it pertains to HVAC is a way to store energy
in various forms to be used later,” says Wayne Muller, national
sales manager at Airco. Garid Glenn, head of marketing and
refrigeration sales at Baltimore Aircoil Company (BAC) adds
that a thermal storage system creates ice to build up and store
cooling when cooling demand and/or energy rates are low and
the system then uses the ice for air conditioning or process
cooling purposes when energy rates are high, for instance, during
the day. According to Evapco, this then reduces overall kilowatt
demand and energy usage.
“Thermal ice storage has been around since the 1930s,” says
Andre van der Merwe. “Ice thermal storage has been used for air-
conditioning and process cooling for over 60 years. In the early
years of air-conditioning thermal energy storage was used for
high diversity loads such as churches and theatres to reduce the
cost of equipment,” says Bill Bartley, Evapco president and CEO.
Christo van der Merwe from Marine & Refrigeration
Engineering (MRE) notes that thermal storage has been used as:
• a means to shift a cooling requirement away from peak
electrical tariff periods to times of lower demand, and
• a means of reducing the peak cooling load on a process
plant that has peak loads caused by pasteurisation (hot
processes) or cooling demand from receiving heated
products.
THE SYSTEM
Ice coils found within a thermal ice storage system.
DIFFERENT FORMS OF ICE STORAGE
Step 1: During night-time and off-peak hours, water that
contains 25% ethylene or propylene glycol is cooled by a
chiller. That solution circulates inside the heat exchanger
within the Ice Bank tank, freezing 95% of the water that
surrounds the heat exchanger inside the tank. The water
surrounding the heat exchanger never leaves the tank.
Step 2: Ice is created uniformly inside the Ice Bank tank
via counter-flow-heat exchanger tubes. As ice forms,
water still moves freely which prevents damage to the
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RACA Journal I May 2020
Equipment that makes up a thermal storage system “is basically
a chilled water system with chillers, air handling units (AHUs)
or fan coil units, circulation pumps, piping, valves and controls.
tank. To fully charge an Ice Bank tank usually takes
from six to 12 hours.
Step 3: During the daytime, in peak hours, the glycol
solution circulates through the ice storage tanks and then
through cooling coils in air handling units.
Step 4: Fans blow air over the coils to deliver cooling to
the occupant spaces. People feel cool and comfortable
and never know ice storage is being used to save money
on cooling costs.
Source: Calmac Manufacturing Corporation
www.hvacronline.co.za