Research And Realization Of Optimal Working Strategy Of Air Handling Units In Air Conditioning System

Central air-conditioning systems tend to retain a considerable margin in the type selection of design to meet the largest demand of building cooling load under the condition of extreme weather and declining of equipment efficiency after a long running. It could lead to huge waste of energy when lacking of refinement management measures in its subsequent operation. Therefore, it is of great significance to carry out the research of optimization strategies for central air-conditioning system’s energy-saving operation.In this paper, an optimal control method is demonstrated for air handling unit(AHU) of comfortable air conditioning systems which are commonly used in buildings. Aiming at the problem that AHU’s operating parameters lack basis of dynamic adjusting, an optimal calculation method based on BP neural network and Genetic algorithm is presented, which can be useful to calculate AHU’s energy efficient operating parameters under different operating conditions.The main researching work in this paper is summarized as follows:(1) A detailed analysis of the structure and energy saving principle of the central air-conditioning experimental platform which was established by the research team is presented. Then the energy consumption models of the main equipment in air-handling system are developed based on the experimental data, whose unknown parameters are identified through method of least squares. The verification results show that the maximum relative error of the model is within 6%, which can meet the engineering application requirements;(2) Due to its excessive inputs and complex thermal calculation, the existing model of cooling coil is not suit for applying in practice. In this paper, a dynamic model of the cooling coil based on improved BP neural network is established, which is vital importance to the control and optimization of air-handling system. Simulation results show that the model’s maximum relative error is within 5%, it shows a high precision. Based on the model, a study on the thermal characteristics of cooling coil under variable-volume condition is achieved, which can provide a reference for the optimization of AHU in the following.(3) Aiming at the problem that AHU’s operating parameters lack basis of dynamic adjusting, an optimal calculation method based on Genetic algorithm is presented, which can be useful to calculate AHU’s energy efficient operating parameters under different operating conditions. This method takes the minimum energy consumption of air-conditioning unit as its target. And using the penalty function method transforms parameters optimization question constrained by cooling load into an unconstrained problem, which simplifying the optimization process. Finally, simulation and experimental results show that, comparing with constant air volume operation strategy, the optimization operation strategy can reduce 17.72% and 15.2% in the aspect of energy consumption. Meanwhile, the energy saving rate can be 4.9% when compared with “conventional VAV” operation strategy.The study shows that the optimal operation strategy proposed in this paper has good energy saving effect, which can provide a theoretical basis and reference for the optimal control of central air conditioning after VAV transformation.