Research On Optimization Design And Operation Of Water System Of Central Air-Conditioning

The chilled water and cooling water pumps contribute 30% of the whole central air-conditioning system electricity consumption in public buildings, while the refrigerating machine contributes 60%. With the sustaining improvement of technology, the energy consumption level of refrigerating machine is greatly reduced while of the water system, it contributes more and more to the whole system electricity consumption just because lack of regard on it. Based on related statistics data, the central air-conditioning equipments run at a part load of below 70% over 97% of its operation time, that's to say, the actual load is always smaller than the full load; especially when the requirement of cooling is small, the refrigerating output is low. Insuring a good operation state and efficiency, finding the optimum operation condition, and carrying out the energy-suited self-regulation through the control system will decrease the energy consumption of the whole system extraordinarily.The key of central air-conditioning water system optimization is to set up a mathematic model. To select the models, such as quadratic model,permit optimizing control model,artificial neural network model,black box model and self-suited control model, they are multifold formally, but there are only two types in sum: one gives priority to describe physical characteristic, which can describe the operation characteristic of each part and the whole system, but with a huge discriminating work of the parameters, of which some cannot even be obtained, this model misfits the optimization control of actual systems. The other type is based on statistics, system discrimination or artificial intelligence technology; it's a predictive model which has a strong applicability. Due to the physical characteristic not involved, a mass of information is required from the air-conditioning system to assure the reliability of the model. With the improvement of system integration technology, the collection of data becomes easier, which represents the future developing direction. This paper adopted the performance curve of equipments established by linear regression measure as their mathematic models, as the target of minimum total energy consumption in water system, and adopted SQP as the Algorithm made the optimization, which achieved the value of the manipulation of variables made the energy consumption to be the lowest of the air conditioning water system. This paper also applied the computer simulation technology for the study to simulate, analyzed and predicts the operation process of each equipment of the water system, and by analyzing and comparing the results, discussed and analyzed the main influential fact to the energy consumption.Besides optimization of the operation control strategy of the central air-conditioning system, this paper calculated the optimum chilled water temperature and temperature difference during the design phase. The optimization calculation based on the viewpoint of economic technology, to chilled water temperature and the temperature difference for the variable, set up the operating costs or depreciation costs model in different part of water system. And adopted the Quasi-Newton Methods, by the target of the minimum in sum of operating cost and depreciation cost; calculate the optimum water temperature and temperature difference with different energy prices. Analysis the relationship between the energy prices and optimum water temperature & temperature difference properly. This optimization calculation provided reference for deciding chilled water temperature and temperature difference in design.