【作者】 郭安；

【导师】 端木琳；

【作者基本信息】 大连理工大学 ， 供热、供燃气、通风及空调工程， 2009， 硕士

【摘要】 建筑能耗在社会总能耗中占有很大的比重,而空调能耗又是建筑能耗中的大户。目前大多数一次泵系统为定流量系统,运行时流经制冷机组的水流量不能跟随负荷的变化而改变,水泵始终按照设计流量全速运行。而空调系统在实际运行中,95%的时间内是处于部分负荷工况下的,因此水泵容量往往大于实际需要,空调系统的运行费用高居不下。因此降低空调水系统的输配电耗,对于降低空调系统的全年运行能耗具有重要意义。针对定流量系统设计及运行中常出现的问题,本文以一次泵变流量系统作为研究对象,将冷冻水系统和冷却水系统作为一个整体来研究。首先,对空调水系统采用一次泵变流量的可行性及节能性进行了分析,当冷冻水和冷却水流量在一定范围内变化时,机组的性能不会下降很多,是完全可行的,但冷却水变流量相对于冷冻水变流量对机组性能影响要更大一些。对比分析了制冷机组与水泵的能耗关系可知,水泵节能率随着负荷的降低而增加,水泵相对机组功率越大,节能性越好。同时阐述了一次泵变流量系统的设计要点、存在的问题及其解决措施,深入分析了用户侧和冷源侧的流量及温差变化不一致的原因,这是由表冷器和制冷机组的换热特性所决定的。本文提出采用干管压差旁通法来平衡用户侧和冷源侧的流量及温差不一致问题。其次,根据系统优化理论及优化步骤,结合一次泵变流量系统的工作原理,在满足舒适性和节能性的基础上建立了一次泵变流量水系统优化运行的数学模型,给出了模型的具体表达式、模型中各参数的辨识方法并进行了模型验证。选取冷冻水流量和冷却水流量作为优化控制变量,结合安全性等因素列出了约束条件。根据优化模型的特点,应用MATLAB软件通过编制基于GA的优化程序进行求解。利用本文所提出的优化方法可以确定一次泵变流量水系统优化运行的参数设定值,从而为空调系统在部分负荷下节能运行及提高空调系统的运行效率提供科学依据。最后,以某工程为例,利用本文所提出的优化运行控制策略的设计方法,将原有的空调水系统改造成一次泵变流量系统并进行优化计算,将改造前后的运行结果进行了对比分析,结果表明一次泵变流量系统虽使机组能耗有所增加,但是相对于水泵节约的能耗来说增加并不大,从而使系统性能COP_s比传统控制时增加,而且负荷率越低,增加越大。采用优化控制后,部分负荷下的大部分时间内冷冻水侧和冷却水侧的温差均能维持在5～6℃之间,最小温差也有3.5℃,空调系统保持在较大的温差状态下运行。在空调系统的实际运行中,对于每一个负荷率均存在着与之相应的最佳流量,只有让冷冻水和冷却水的流量处于最佳值,才能使系统性能COP_s达到最大。经变流量改造后,仅3个月水泵的节电率达到63.1%,水系统总能耗的节电率达到12.8%。当空调系统采用一次泵变流量设计方案时,应综合考虑水泵相对主机功率、主机变水量性能以及空调负荷特点等因素。本文以优化理论为基础,以空调水系统节能运行为目标,将GA引入到一次泵变流量系统的优化设计中,提出了一套适用于一次泵变流量系统优化运行的控制策略设计方法,对新建建筑和旧有建筑中空调系统的设计、节能改造及优化运行具有一定的参考和推广价值。更多还原

【Abstract】 In the overall social energy structure,a large proportion of energy will be attributed to buildings,in which air conditioning facilities consume considerable energy.Up to now,most primary systems are designed with constant flowrate,which fails to adjust in accordance with the actual load,thus pumps always run with full power.Since systems are often run under part-load condition for approximate 95%of their operation time,the capacity of pumps always exceeds the actual requirements.High operation expenses have made air conditioning systems a heavy burden in building management.Therefore,enhancing the efficiency of water transport systems possesses great significance in reducing the energy consumption of air conditioning system.Seeing the problems of constant flow system during the design and operation stage,this research aims to offer pertinent insight into optimal operation of variable primary flow(VPF) systems,by incorporating the chilled and chilling water systems into a single model.Firstly,feasibility and efficiency of VPF are analyzed.It is shown that only minor decrease of the chiller’s performance takes place if the chilled and chilling water change is restricted within certain limits.Comparably,the chilling water change induces greater fluctuation of COP than chilled water.The analysis of correlation of chillers and pumps shows an increasing energy saving rate along with the decreasing load.The larger ratio of pump power against chiller power,the more energy will be saved.At the meantime,design key points, problems and solutions of VPF are analyzed.In addition,the non-uniform change of water flow and temperature differences between the consumer side and cooling source side are analyzed, which is determined by the heat transfer characteristics of surface coolers and chillers. Therefore,the main pipe bypass approach is introduced to balance the foregoing non-uniformity.Then,based on optimization theory and operation principles of VPF,this research establishes the mathematical model of VPF optimal operation,aiming to ensure both comfort and energy saving requirements.Identification method of model expressions and related parameters is given and then validated.By selecting chilled and chilling water flow rate as control parameters,and listing constraints with security concerns,this research applies genetic algorithm to compile and solve optimization program,with MATLAB tool box.With the proposed optimization method,parameters in VPF can be properly ascertained,which contributes to improve the efficiency of air conditioning systems,especially under part-time load.Finally,a real case is investigated by employing the optimization approach into the transformation of VPF.Comparison of energy consumption of a project before and after optimization shows great amount of energy consumed by pumps can be saved in spite of minor energy increase by chillers.Therefore the system COP_s is greatly enhanced.The lower cooling load brings much less energy consumption and more efficiency.For most of the time,the water temperature difference both in the chilled and chilling side of optimized system is maintained at 5～6℃,with the lowest exceeding 3.5℃.A single load ratio will respond to a optimum flow rate, which ensures the maximum COP_s.After transformation,63.1%of total electricity consumption by pumps,or 12.8%by the whole water system are saved.In the design of VPF systems,special attention should be paid to power ratio between chiller and pump,chiller performance under variable water flow,as well as cooling load,et al.Targeted at efficient operation of air conditioning networks,based on optimization theory, this research incorporates the genetic algorithm into the design of VPF systems,and proposes a set of optimal control strategies,which are applicable to energy saving design,reconstruction, as well as operation management of air conditioning systems.更多还原