The Energy Conservation Analysis Of Frequency-conversion VFV Central Air Conditioning Systems

Building energy consumption has been accounting for a large proportion of the totalsocial energy consumption. The energy consumption of air conditioning systems has morethan40%of the total building energy consumption,and in the energy consumption of centralair conditioning systems, the energy consumption of the water systems accounts for about60%~80%.The operation efficiency and energy consumption of the important part of the watersystem conveying equipments water pumps directly affect the whole system operationconsumption. The VFV air conditioning system can adjust flow distribution in accordancewith the load change,which can reduce the energy consumption of chillers and water pump.Inthis paper,the energy saving performance of VFV air conditioning system using frequencyconversion control was analysed and reseached.The principle of VFV air conditioning system, basic types of Variable chilled water flowsystem and the frequency conversion control methods were analysed. It is come to that, In thefrequency conversion control methods of VFV systems,the variable pressure differencecontrol method which can continuously adjust the set pressure difference according to theload has fast control response and energy-saving effect.The power consumption calculation method of the variable frequency pump wasobtained through analysis.For the calculation of variable frequency pump power consumption,if the system pipeline characteristic curve is the generalized network characteristic curve, thesimilar condition curve of the new operating point should be first obtained,then theintersection of the water pump H-Q curve of the rated condition and the similar conditioncurve is just similar to the new operating point,thus the pump efficiency after frequencyconversion can be determined,and the pump power consumption after the frequencyconversion can be calculated based on the pump shaft power formula; If the system pipeline characteristic curve is the special pipeline characteristic curve, when the tube characteristics(impedance S) is constant,and the operating points of the pump operating in different speedsare similar operating points,the water pump power consumption can be calculated accordingto the similar law,and when the pump rotation speed is changed,and at the same time, the Svalue also changes,the operating conditions in different speeds are not similar condition,andthe above relationships are not applied to it.Furthermore,the energy-saving effect of the valve regulation and the constant pressuredifference control variable frequency regulation,the constant pressure difference regulationand the end constant pressure difference regulation,and the end constant pressure differenceregulation and the variable pressure difference control frequency conversion when the centralair-conditioning chilled water system operates in variable flow control were deep analysedand compared.It is come to that the energy-saving effect of the constant pressure differencecontrol variable frequency regulation is superior to that of valve adjustment, theenergy-saving effect of the end constant pressure difference regulation is better than that ofthe constant pressure difference regulation,and the energy-saving effect of the variablepressure difference regulation is better than that of the end constant pressure differenceregulation.Thus it is drawn that,in the process of control regulation, on the one hand, theenergy loss of regulating valve should be tried to be reduced or avoided and the pipelinecharacteristic should not be changed,on the other hand, under the premise of that each end hasenough pressure difference to ensure the flow operation,the pressure difference setting valuecan be changed,so that the greatest advantages of variable frequency pump adjustment can peplayed. Therefor,it is determined that when the air conditioning system uses the variablepressure difference regulation to control variable frequency pump to change the flow,theenergy-saving effect of variable frequency pump can get the maximum embodiment.Finally,combined with the measured data, the energy-saving performance of a pumpfrequency conversion variable flow water system of Northwest Electric Power DesignInstitute in Xi’an was analysed. The energy consumption of the air conditioning chilled watersystem using the constant pressure difference regulation and variable pressure differenceregulation to control the variable frequency pump was respectively calculated andcompared.It is concluded that the energy-saving effect of this chilled water system using thevariable pressure difference regulation to control the variable frequency pump is better thanthat of the constant pressure difference regulation.It is caculated that if this system use thevariable pressure difference regulation, the average electricity-saving quantity is12.35KW/h,and the annual electricity-saving quantity is44645KW·h relative to the system operating in the control of the constant pressure difference regulation.If the price of electricityis0.65yuan/KW·h,it can save29019yuan every year,which is equivalent to16090kg/ystandard coal.