From: Fire and Ice
How Ice Storage Works
The working principle of an ice
storage system calls for chillers to make ice inside storage tanks during
off-peak, nighttime hours when the energy is produced more efficiently,
economically, and environmentally. Ice Storage uses the stored “thermal” energy
of the ice to cool the buildings during the daytime peak-usage periods. This
effectively shifts the electrical load off-peak, while avoiding higher-price
energy and demand charges that are imposed by many utilities.
The operation of an Ice Storage
System is comprised of two normal modes: the ice charging mode and ice melt/burn
mode.
During the ice charging mode, a
designated ice-making chiller produces low temperature, 25% glycol solution that
freezes the water inside an ice storage tank. This closed glycol loop consists
of the ice storage cooling tanks, heat exchangers, and glycol pumps. The
ice-charging mode continues until full ice capacity has been reached (usually
about eight to 10 hours).
Initiated via an automated
process, the ice melt mode begins when the temperature differential increases
between the chilled water supply and the chilled water return. During the Ice
Melt Mode, the chillers are either turned off or used to supplement the cooling
requirements of the system.
The Benefits of Ice Storage
Cooling
In many cases, ice storage allows
for reducing the size of installed refrigeration capacity. For example, if the
installed cost of the chiller is $600 per ton, every avoided ton of
refrigeration capacity related to the installed ice storage system capacity
saves $600. This assumes that the installation already has supporting chiller
equipment in place, such as cooling towers and pumps. For a new installation,
this amount can exceed $1,500 per ton, in which case the chiller plant size
reduction can often completely offset the cost of storage.
March-April 2009
From: Fire and Ice
How Ice Storage Works
The working principle of an ice
storage system calls for chillers to make ice inside storage tanks during
off-peak, nighttime hours when the energy is produced more efficiently,
economically, and environmentally. Ice Storage uses the stored “thermal” energy
of the ice to cool the buildings during the daytime peak-usage periods. This
effectively shifts the electrical load off-peak, while avoiding higher-price
energy and demand charges that are imposed by many utilities.
The operation of an Ice Storage
System is comprised of two normal modes: the ice charging mode and ice melt/burn
mode.
During the ice charging mode, a
designated ice-making chiller produces low temperature, 25% glycol solution that
freezes the water inside an ice storage tank. This closed glycol loop consists
of the ice storage cooling tanks, heat exchangers, and glycol pumps. The
ice-charging mode continues until full ice capacity has been reached (usually
about eight to 10 hours).
Initiated via an automated
process, the ice melt mode begins when the temperature differential increases
between the chilled water supply and the chilled water return. During the Ice
Melt Mode, the chillers are either turned off or used to supplement the cooling
requirements of the system.
The Benefits of Ice Storage
Cooling
In many cases, ice storage allows
for reducing the size of installed refrigeration capacity. For example, if the
installed cost of the chiller is $600 per ton, every avoided ton of
refrigeration capacity related to the installed ice storage system capacity
saves $600. This assumes that the installation already has supporting chiller
equipment in place, such as cooling towers and pumps. For a new installation,
this amount can exceed $1,500 per ton, in which case the chiller plant size
reduction can often completely offset the cost of storage.