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1、毕业外文翻译-集中供热和制冷设备的选择名师资料合集（完整版）资料(可以直接使用，可编辑 优秀版资料，欢迎下载）CENRTRAL COOLING AND HEATINGThe energy used to heat and cool many buildings often comes from a central location in the facility. The energy input may be combination of electricity , oil ,gas , coal ,solar ,geothermal ,etc. This energy is typical
2、ly converted into hot or chilled water or steam that is distributed throughout the facility for heating and air conditioning(cooling) . Centralizing this function keeps the conversion equipment in one location and distributes the heating and cooling in a more readily usable form. Also ,a central coo
3、ling and heating plant provides higher diversity and generally operates more efficiently with lower central location and a potentially large distribution system. This lesson addresses the design alternatives that should be considered when centralizing the cooling and heating sources in a facility. T
4、he economics of these systems require extensive analysis. Boilers ,gas , steam ,and electric turbine-driven centrifugal refrigeration units; and absorption chillers may be installed in combination in one plant . In large buildings with core areas that require cooling and perimeter areas require heat
5、ing , one of several heat reclaim systems may heat the perimeter to save energy .The choice of equipment for a central heating and cooling plant depends on the following :l Required capacity and type of usel Cost and types of energy availablel Location and space for the equipment rooml A stack for a
6、ny exhaust gases and its environment impactl Safety requirements for the mechanical room and surrounding areas l Type of air distribution systeml Owning and operating costs Many electric utilities impose very high charges for peak power use or ,alternatively ,offer incentives for off-peak use . This
7、 policy has renewed interest in both water and ice thermal storage .The storage capacity installed for summer load leveling may also be available for use in the winter ,making heat reclaim a more viable option. With ice storage, the low-temperature ice water can provide colder air than that availabl
8、e from a conventional system that supplies air at 10 to 13. The use of a higher water temperature rise and a lower supply air temperature, lowers the required pumping and fan energy and , in some instances, offsets the energy penalty due to the lower temperature required to make ice.Refrigeration Eq
9、uipmentThe major types of refrigeration equipment in large systems use reciprocating compressors, helical rotary compressors, centrifugal compressors, and absorption chillers.These large compressors are driven by electric motors, gas and diesel engines, and gas and steam turbines. The compressors ma
10、y be purchased as part of a refrigeration chiller that includes the compressor, drive, chiller, condenser, and necessary safety and operating controls. Reciprocating and helical rotary compressor units are frequently field assembled, and include air-cooled or evaporative condensers arranged for remo
11、te installation. Centrifugal compressors are usually included in packaged chillers.Absorption chillers are water-cooled. They use a lithium bromide/water or water/ammonia cycle and are generally available in the following four configurations(1) direct fired, (2) indirect generated by low-pressure st
12、eam of hot water, (3) indirect generated by high-pressure steam of hot water, and (4)indirect generated by hot exhaust gas. Small direct-fired chillers are single-effect machines with capacities of 12 to 90kW. Larger, direct-fired, double-effect chillers in the 350 to 7000kW range are also available
13、.Low-pressure steam at 100kPa of low temperature hot water heats the generator of single-effect absorption chillers with capacities from 180 to 5600kW. Double-effect machines use high-pressure steam up to 1000kPa or high-temperature ht water at an equivalent temperature. Absorption chillers of this
14、type are available from 1200 to 7000kW.In large installations the absorption chiller is sometimes combined with steam turbine-driven centrifugal compressors. Steam from the noncondensing turbine is piped to the generator of the absorption machine. When a centrifugal unit is driven by a gas turbine o
15、f an engine, an absorption machine generator may be fed with steam of hot water from the engine jacket. A heat exchanger that transfers the heat of the exhaust gases to a fluid medium may increase the cycle efficiency.Cooling towersWater from condensers is usually cooled by the atmosphere. Either na
16、tural draft or mechanical draft cooling towers or spray ponds are used to reject the heat to the atmosphere. Of these, the mechanical draft tower, which may be of the forced draft, induced draft, of ejector type, can be designed for most conditions because it does not depend on the wind. Air-conditioning systems use towers ranging from small package units of 20 to 1800kW to field-erected towers with multiple cells in unlimited s
