| The nation has pinned its basic policy that aims to encourage energy saving andimprove energy efficiency. With the rapid development of domestic economy andurbanization, recent years has witnessed a considerable growth in energy consumption inthe field of construction, and thus energy saving is in the meantime greatly motivated.Among all the sources, air-conditioning devices are listed on top of the list in terms of theamount of energy consumption. Therefore, it is critically important to impose an effectivecontrol over air conditioning systems.Due to the recent fast emergence of large-scale commercial buildings, CBD core areas,and University Mega Town, the District Cooling Systems (DCS) have been launched invarious applications. Compared to the traditional central air-conditioning systems, the DCSis the future direction for district buildings, largely thanks to its advantages such as highenergy efficiency, being capable of improving the thermal environment of the districtbuildings, environmental friendliness, and being economically maintainable. However, theDCS, with the characteristics of heavy cooling load, large scale, multiple devices, and highcomplexity, has to meet the high standards of operational optimization and adapt to the highlevel of control technology in order to maximize its performance and well combine theoperation with energy-efficient results.The operational efficiency of the system will considerably influence the maximumelectricity load within the region and has major impact to the environment; besides, theoperational cost of the system is subject to the level of the detected efficiency. Taking intoconsideration three factors, namely the overall energy consumption of the DCS, theoperational energy efficiency and the thermal comfort, this thesis has explored thecomprehensive assessment method and index system for the energy efficiency of the DCS,and designed the online monitoring system that aims to trace in detail the accurate values ofoperational efficiency of the system, and elaborated the parameters that have to bemonitored, the monitoring equipment and its accuracy, and the spots to be allocated for monitoring.In order to addressed the issues of long delay and lack of a reasonable model foraccurate cold supply controlling, the author has introduced the initial quantity prioritizedadjustment and the secondary quality prioritized adjustment made by the plate heatexchanger of the secondary cold supply exchange station as a typical example forillustration. On the basis of such an empirical exemplification, the author further studied thefluctuations of the air-supplying temperature from the end equipment of the air conditionerand the average temperature of the air-conditioned room, both influenced by the quantity ofcold water flow through the secondary cold supply exchange station. Then, the author hasalso set up the controlling model of the indoor average temperature in the air-conditionedrooms of the construction, and proposed a method to design the fuzzy PID controller. As aresult, it is able to overcome the deficiency of utilizing the conventional PID controller andeven achieve an anticipated control over the inertial systems with significant time delay anduncertain parameters.DCS involves long-distance and delayed transport, and a complicated process of coldsupply. This thesis analysed the time-delay characteristic of the system and the dynamicprocess of cold supply that starts from the regional cold supply station, then to theconstructions and eventually to the air-conditioned rooms. To serve the practical goal ofmaintaining the comfort in the air-conditioned rooms, also investigated is the principles onhow the cooling load in air-conditioned rooms varies with respect to the outdoormeteorological parameters. Based on this, the thesis established the equation oftransportation and variation of cool supply, the dynamic equation of the variation of indoortemperature and relative humidity in air-conditioned rooms, as well as the incrementalmodel of the cooling load in air-conditioned rooms, providing a crucial basis for anenergy-efficient system with optimized operations.The nominal capacity of the equipment is determined based on the design condition ofthe project. However, the partial load condition and the disparities of cold supply amongdifferent constructions will definitely result in redundancy in the system capacity. Moreover, the imperfect technologies for operation regulation and control will definitely lead to lowsystem efficiency, excessive energy consumption and the waste of cold supply under certainloads of the system. With the consideration of the above mentioned issues and on the basisof the energy consumption models of various types of equipment that serves the system, theauthor established the optimal operation model on energy consumption, and proposedcorresponding solutions and the overall procedure for optimal operation and control, inorder to maximize the energy efficiency of the system. This approach saves over20%expenses on cold energy.In the end, the author proposed the general framework of District Cooling System forEnergy Efficiency, as well as the software platform and hardware structure for eachcomponent. Moreover, the author also developed the corresponding platform for bothsoftware and hardware. Several sub-systems were already applied to a University MegaTown, such as South China University of Technology, Guangdong PharmaceuticalUniversity, Guangdong University of Foreign Studies, South China Normal University andGuangzhou Univeristy of Chinese Medicine, with promising energy-saving performanceachieved. After the Third-Party Testing on energy-saving, it demonstrates our system is ableto save20%-40%expenses on cold energy. |
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