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10. Start the brine circulating pumps in sequence. During on-peak hours, the brine circulating pump needs a greater head to overcome the pressure drop of the coil in the AHU as well as the pressure drop of the coil in the ice storage tanks.
System Characteristics
An ice-on-coil, internal-melt ice storage system is a modular system consisting of many closely packed storage tanks connected in parallel. Such an ice storage system is more flexible during the installation of storage tanks, especially for retrofit projects.
In ice-on-coil, internal-melt ice storage systems, off-peak cooling of the building can be provided by direct cooling from the chillers. During ice burning, melted water separates the tube and ice. Water has a much lower thermal conductivity (0.35 Btu /h ft °F, or 0.61 W/m °C) than that of ice (1.3 Btu /h ft °F, or 2.25 W/m °C), so the capacity of the ice-on-coil, internal-melt ice storage system is dominated by the rate of ice burning or melting. Other system characteristics of ice-on-coil, internal-melt ice storage systems are listed in Table 31.1.
31.3 ICE-ON-COIL, EXTERNAL-MELT ICE STORAGE SYSTEMS
System Description
In an ice-on-coil, external-melt ice storage system, ice builds up on the outer surface of coils or tube banks, which are submerged in water in a storage tank. The refrigerant flows and evaporates inside the tubes. When the ice melts, it cools the water at a temperature between 34 and 38°F (1.1 and 3.3°C) for cooling in the AHUs. The central plant (cooling) and chilled water incorporated ice storage system of an ice-on-coil, external-melt system consists of chillers, evaporating coils, storage tanks, condenser, heat exchanger, refrigerant pumps, chilled water pumps, air system controls, piping, and fittings. A typical ice-on-coil, external-melt ice storage system is shown in Fig. 31.4.
Screw and centrifugal compressors are often used because of their higher efficiency. For an iceon-coil, external-melt ice storage system with a capacity less than 2400 ton h (8438 kWh), a reciprocating compressor may also be used. Evaporatively cooled condensers have a higher system energy efficiency ratio (EER) and are often used in many new projects.
Ice Builders
Ice builders are large, well-insulated steel tanks containing many serpentine coils, usually made of steel pipes of 1- to -in. (25- to 31-mm) diameter. HCFC-22 is often used as the refrigerant. The refrigerant-filled serpentine coils are submerged in water in the ice builder and function as evaporators. The ice build up on the coil is between 1 and 2.5 in. (25 and 64 mm) thick. When ice builds up on the coil, the suction temperature of the compressor falls to 22 to 24°F ( 5.6 to 4.5°C).
Ice is melted by the water circulating over it. The steel tubes of the serpentine coil should be spaced so that the built-up ice cylinders do not bridge each other. If the cylinders are bridged, the paths of water circulation are blocked. Baffle plates are sometimes added to guide the water flow and provide a secondary heat-transfer surface between the refrigerant and water. The storage tanks containing refrigerant coils are usually located at a lower level or on a grade because of their weight. Because the chilled water system in a multistory building is always under a static head at lower levels, a heat exchanger, usually plate-and-frame type, is used to isolate the storage tank brine system from the chilled water system connected to the AHUs. An alternative is to supply chilled water directly to the storage tanks and pressurize the tanks. This arrangement obviates the use of a heat exchanger and a corresponding increase in brine temperature of about 3°F (1.7°C).
蓄冷系统
★系统概况
蓄冷空调系统，或一个简单的蓄冷系统，由以下部分组成：中央总动力厂、与蓄冷系统相组合的冷却水或盐水系统、热水系统、包括空气处理单元的空气系统、终端设备、回风系统、控烟系统、机械排烟系统。此外，总动力厂中的电力驱动制冷压缩机是在高峰及非高峰时间运转的。在电力高峰期时，由储存的冷冻水及冷却水来为建筑进行制冷。中央锅炉中的热水是用于提供冬天所需的热量的。空气在空气处理单元以及终端中进行处理。经处理完的空气将通过管道输送到不同的控制区域中，如终端，扩散器，及控制器。