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THERMAL STORAGE SYSTEMS System Description
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A thermal energy storage air conditioning system, or simply a thermal storage system, consists of a central plant, a chilled water or brine system incorporated with a thermal storage system, a hot water system, an air system including AHUs , terminals, return air system, smoke control systems, and mechanical exhaust systems. In addition, the electric-driven refrigeration compressors in the central plant are operated at off-peak or at off-peak and on-peak hours. Stored ice or chilled water in tanks is used to provide cooling in buildings during on-peak hours when there is a higher electric rate.34786
Hot water from the boilers in the central plant is used to provide heating in winter. Air is conditioned in the AHUs and terminals. The conditioned air is then distributed to various control zones through ducts, terminals, diffusers, and controls.论文网
A thermal storage system is
Always a central system that uses stored chilled water or brine from the central plant to cool the air
Often a multizone VAV system
Often a cooling storage system
Building Energy Consumption and Thermal Storage Systems
Lorsch (1993) analyzed the energy consumption for a 264,000 ft2 (24,536 m2) building using the Ontario Hydro electric rate structure. The chiller equipment needed 31 percent of the on-peak demand but consumed only 8 percent of the annual kWh. The annual load factor for this building is only 37 percent. Commercial buildings have poor load profiles of electric power demand. Electric utilities are a capital-intensive industry. To improve their load factor and to sell more kWh, electric utilities tend to shift daytime, more energy-inefficient diesel and gas-turbine plant operation to nighttime base-load highly efficient coal and nuclear plant operation. Electric utilities offer a higher energy rate in daytime on-peak hours and a lower energy rate in off-peak hours. A thermal storage system shifts a part of the electric power demand of the HVAC&R system from the daytime onpeak hours, usually from noon to 8 p.m., to nighttime off-peak hours.
A thermal storage system often consumes approximately the same amount of electricity as a conventional air conditioning system; i.e., a thermal storage system does not necessarily save energy.
However, a thermal storage system significantly reduces energy cost.
Electric Deregulation and the Impact on Thermal Storage Systems
Because of the electric deregulation and the use of real-time pricing (RTP) and other electricity rate
structures instead of the time-of-use (TOU) rate structure, as discussed in Sec. 25.7, open-market competition creates pressure on utilities to cut costs. According to Silvetti and MacCracken (1998) and the analyses from EIA, the following trend may dominate:
There is a conflict between the interests of the generation-owning utilities in higher-generation prices and the effects of some demand side management (DSM) programs to reduce demand and possibly to help hold down competitive prices for generation. DSM programs are causing problems.
Regarding energy-efficient equipment-related incentive plans, something is wrong when a power producer gives money to a customer to purchase less power, particularly if the financial incentive might eventually benefit a competitor.
Thermal storage systems benefit the power provider, the customer, the power user, and the industry setting the price for that energy.
Benefits and Drawbacks of Thermal Storage Systems
Silvetti and MacCracken (1998) noted why a thermal storage system is attractive:
Thermal storage systems are one of the few legitimate tools which shift the higher electric demand/ electric rate for HVAC&R fully or partially from on-peak hours to a lower electric demand/ electric rate in off-peak hours, and therefore lower operating costs.
Thermal storage systems reduce the equipment size and save initial cost.