What is the Ice storage system?

Water as one of thermo storage media for latent heat storage which we call it Ice storage. In HVAC applications such as air conditioning, space heating, and water heating, water is often the chosen thermal storage medium; it provides virtually all of the desirable characteristics when kept between its freezing and boiling points. In lower temperature applications, aqueous secondary coolants (typically glycol solutions) are often used as the heat transfer medium, enabling certain storage media to be used below their freezing or phase-change points.

Thermal Energy Storage is a technology that stores “cooling” energy in a thermal storage mass. As Figure 1 shows, the storage mass can be a third major component of an air conditioning or cooling system in a building. In most conventional cooling systems, there are two major components:

  i) Chiller—to make water or some other fluid cool

  ii) Distribution system—to take the cool water (or fluid) from the chiller to a place

where it cools air for the building occupants. In conventional systems, the chiller must be run only when the building occupants want cool air. In a storage cooling system, the chiller can be run at times other than only when the occupants want cooling.

 

There are some advantages to being flexible as to when the chiller can run, since the chiller is typically the most energy intensive part of a cooling system. For example, Figure 2 shows the amount of cooling desired at various hours of the day in a typical commercial office building. Not surprisingly, the cooling demands are highest when the building is occupied and when the outside temperature is hottest during the afternoon. In a conventional cooling system the electricity use follows the demand for cooling—since the chiller must run to cool the building.

On-peak  Period

Air conditioning (and industrial process cooling) makes up almost a third of the aggregate electricity demand on power utility systems during the summer. Therefore, the aggregate utility demand tends to have the same pattern as a building’s cooling demand.

Moreover, to keep over-all electricity costs down, electric utilities run their most economic (and typically most efficient) “base load” power plants as much as possible. Other power plants are somewhat less efficient. These “intermediate” power plants see limited use during the day. Finally, plants with the highest operating costs (and typically lowest efficiency) are mainly used during the few “on-peak” hours. Hence, they are called “peak” load power plants or sometimes just “peakers.”

The cost to produce a kWh of electricity is highest during these on-peak hours. Two factors contribute to these high costs. First, Our utilities must build enough capacity to meet the highest or peak demand. Therefore, much of the utility’s capacity related costs are charged during these on-peak hours (often as peak “demand”

charges). Second, because the least efficient power plants run during the on-peak hours, the costs of generating the electrical “energy” are higher during those hours. This leads to a situation in which electricity users can reduce their electricity costs under Time-of-Use rates if they can reduce their peak electricity use. TES provides electricity users that opportunity.

There are typically two basic strategies for using TES to reduce on-peak electricity use, as Figure 4 shows. The first strategy, “full storage,” sizes the chiller and storage tank so that the chiller does not run at all during the peak hours even on the hottest days. In contrast, the “partial storage” strategy sizes the chiller and storage tank so that a smaller chiller runs continuously on hot days. The main advantage of the “full storage” system is that it minimizes electricity costs. The main advantage of the “partial storage” system is that a smaller chiller and smaller storage tank reduce the capital costs of the TES system.

                     No Ice-Storage                                     Partial Ice-Storage

                                                Full Ice-Storage

 

How does it work?

The system consist of chiller and ice storage tanks utilizes a standard packaged chiller to produce ice during the night, which is built and stored in modular tanks. This stored ice provides cooling the following day to meet the building’s air conditioning load requirement.

            

Comparing with traditional design, HVAC system design engineers must take lot of work on chiller selection and ice tank balance. EnPlus offer package type ice storage system which is consisted of chiller and ice tank together. Each unit is tested before delivery. Also these products are modular design leading to assemble freely in the field.

The essential element of Ice tank is a modular, insulated, polyethylene tank containing a spiral wound plastic tube heat exchanger surrounded with water. At night, water containing 25% ethylene glycol, is cooled by a chiller and is circulated through the heat exchanger, extracting heat until eventually about 95% of the water in the tank is frozen solid. The ice is built uniformly throughout the tank by the patented temperature averaging effect of closely spaced counter-flow heat exchanger tubes. The following day, the stored ice cools the solution from 52 F to 34 F. A temperature modulating valve set at 44 F in a bypass loop around the tank permits a sufficient quantity of 52 F fluid to bypass the tank, mix with 34 F fluid, and achieve the desired 44 F temperature.

Our chiller (air cooled or water cooled) is well designed for ice making condition. Hermetic scroll compressor is used in the package system to get the high performance and reliability.

 

What’s the benefit of TES?

Off-peak operation

Running the chiller at night substantially reduces electrical costs since energy is used off-peak when electric generating facilities are typically under-utilized by 50 percent or more. Many suppliers offer time-of use rates that include a 20 to 90 percent reduction in electrical energy prices at night specifically to encourage load shifting. This, with the reduction of all or part of the demand charges, results in a substantial saving in operating costs. In general, Cool Storage increases a building's load factor, which significantly reduces operating costs and increases a user's ability to negotiate favorable rates. In essence the customer becomes a Preferred Power User.

Constant full-load operation

On-off cycling and capacity modulation occurs throughout the day in most air conditioning systems in response to the cooling load of the building. Therefore, most air conditioning systems operate within their most efficient range less than 25 percent of the time. With the Ice storage system, the chiller runs at or near full load (peak efficiency) continuously, eliminating the inefficient cycling that accompanies part-load operation.

Cold air distribution

The use of 44 F air in the duct system rather than the usual 55 F air permits further huge savings in initial and operating costs. This colder air is achieved by piping low temperature (36-38 F) water-glycol solution from the ice tanks to the air handler coil. The 44 F air is used as primary air and is distributed to a high induction rate diffuser or a fan-powered mixing box where it is fully mixed with room air to obtain the desired room temperature. The 44 F primary air requires much lower airflow than 55 F air. Consequently the size and cost of the air handlers, motors, ducts and pumps may be cut 20 to 40 percent. Colder air also lowers relative humidity, therefore occupants feel comfortable at higher, energy-saving thermostat settings.

Products

Ice storage systems

 

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