Optimization Control Of Chilled Water System Of HVAC

From Middle East oil crisis of1970s on, energy conservation and sustainable development is paid more and more attention to in the world. HVAC accounts for the largest proportion of building energy consumption. Saving of HVAC energy consumption is the important way of energy conservation study, and HVAC energy conservation is imperative under such a circumstance.Air-conditioning system with variable chilled water volume is system in contrast with constant water volume. Its main characteristic is that:according to the change of indoor cooling or heating load, the volume of chilled water can be adjusted by adjusting the revolving speed of chilled water pumps automatically to satisfy the indoor thermal comfortable requirements. Under conditions of partial load, the indoor load requirements can be satisfied through reducing the revolving speed of pumps and energy consumption of pumps are also reduced. Air-conditioning system with variable chilled water volume has large potential of energy conservation.In this paper, optimization control of air-conditioning system with variable chilled water volume includes two parts:optimal combination of frequency and amount and optimization control of the pressure difference value of variable frequency pumps.In a large HVAC, the load of it changes largely with time and combination forms of variable frequency pumps changes with change of load through controls of pump frequency and amount. This paper presents the study and analysis of variable pumps of different types and it is found that the optimization control of these pumps is a complicated optimization problem of combined action of continuous variable and discrete variable. Optimization combination of frequency and amount of pumps is controlled by the two constraint conditions of chilled water volume and lift. Performance curve of the pump is obtained by linear regression method as the mathematical model of the pump. The mathematical model with the objective function of total energy consumption is established under conditions of parallel running of different types of variable frequency pumps. Optimal combination problem meeting constraint conditions of large group of pumps is solved by combining exhaustive enumeration method and generalized reduced gradient method.Optimization control of the pressure difference value is studied simulation experiments before. In this paper it is studied in a HVAC system of an office building in Hong Kong. Based on the valve opening of the end equipment AHU, the frequency of the pump is controlled over the change of the pressure difference value of index circuit. Optimization control software of static pressure of chilled water in HVAC system based on VB language is tested online and the test result is analyzed and studied. The test result indicates that the optimization control strategy is stable and has larger energy conservation than conventional control strategy of constant pressure difference value with satisfying the load requirements.