Ice Storage For Thermal Energy Storage (TES)
While there are many technologies available for thermal energy storage (TES) systems, ice storage is a
preferred choice for large-scale air conditioning environments. Ice storage systems make and store ice
during non-peak electrical use periods such as overnight or on weekends, then use the stored cold to provide air conditioning during the day when electrical loads and energy costs are at their peak.
Inhibited glycol-based heat transfer fluids — including DOWTHERM TM SR-1, DOWCAL ™ 10, DOWTHERM TM 10, DOWFROST TM HD, and DOWFROST TM 20 Fluids, in particular — are a better choice in TES applications than brine solutions such as calcium chloride because of the severe corrosiveness of salt solutions and resulting system damage.
DOWTHERM ™ SR-1, DOWTHERM ™ 10, and  Inhibited Ethylene Glycol-based Fluids and DOWFROST TM HD, and DOWFROST TM 20 Inhibited Propylene Glycol-based Fluids offer the freeze-point depression capability and low temperature capability necessary to efficiently build ice in TES service. In addition, these Dow fluids contain heavy-duty industrial inhibitor packages that help protect system piping and components against corrosion. The long fluid life and minimal maintenance requirements of these Dow fluids help ensure long-term system reliability, a critical factor in ensuring overall cost and energy savings.
Dow fluids are used in the two most common types of ice storage systems: ice-on-pipe systems and
encapsulated ice systems. Iceon-pipe systems consist of coils of plastic or metal tubing immersed in a tank of water. A chilled solution of glycol and water is circulated through the tubes to build ice on the outer
surfaces during off-peak hours. When air conditioning is needed, the same solution is circulated through the tubes, carrying heat from the building to melt the ice. This chills the glycol based solution which continues to circulate, cooling the building. Encapsulated ice systems operate similarly except the glycol solution is circulated through a tank filled with containers of water. Ice forms in the containers and is later melted by the glycol solution when cooling is needed.
 

Obtaining Excellent Heat Transfer Efficiency If you are weighing the performance of a glycol-based fluid against plain water, you may be concerned about the potential for lost system efficiency with the glycol fluid. However, the fact is, use of a glycol solution in an HVAC system can have relatively little effect on how well your system performs as long as the fluid type was taken into account during system design or the system was designed to operate with a cushion of excess capacity. In cases where there is no excess capacity, modest system modifications can often compensate for any capacity loss resulting from the introduction of the glycol fluid into the system. For example, if a glycol fluid is introduced into an air conditioning system formerly operating with plain water, any decline in capacity will probably not be noticed by building occupants as long as the system was designed with excess capacity. If the system is already nearing its design load, introduction of a glycol-based fluid may aggravate the situation. However, any problems will be noticed only on the hottest days. In cases where increased pressure drop and a resulting decline in the capacity of the system is a problem, a two-step remedy can sometimes be employed. First, flow of solution through the system should be reduced in order to return the pressure drop to its original value. This will have the beneficial side effect of reducing pump horsepower requirements and energy consumption. Next, reduce the chiller operating temperature to lower the fluid temperature into the coil. Reducing the chiller operating temperature compensates for the reduction in fluid flow and returns the coil capacity to its original level. In some cases, shifting the cooling burden from pumps to chiller can actually improve the overall efficiency of the system. Unlike pumps, chillers only use energy in proportion to system load. And, new developments in chillers have led to increased energy efficiency.