VRF制冷系统变吸气状态下频率与阀开度的同步调节

Synchronous Adjustment of Frequency and Valve Opening of VRF Refrigeration System under Variable Suction Condition

针对变流量制冷(Variable Refrigerant Flow,VRF)系统变吸气状态下带液量的精确控制以及控制元件所引起的滞后或超调现象,以变频滚动转子式制冷系统为研究对象,分别通过恒定频率不同阀开度与恒定阀开度不同频率两个实验,建立其单独控制下的拟合模型,得到其在不同工况下的同步控制方法。结果表明:过热度随阀开度的增大而减小,在过热度为6 K以下,即阀开度为27.8%~30%时,过热度控制难度上升,提高冷冻水温度可改善这一状况;过热度随频率的降低而减小,在过热度为5 K以下,即频率为44.5~46.5 Hz时,控制难度上升;吸气干度随阀开度增大而下降,随频率降低而减小;在某一工况下,以系统质量流量为控制目标,可以拟合得到频率与阀开度的关系式,实现同步控制,在变吸气状态可以精确控制吸气干度,不损坏压缩机,并使系统迅速达到稳定状态。

Aiming at the precise control of liquid quantity in variable suction state of VRF(Variable Refrigerant Flow)system,and solving the hysteresis or overshoot phenomenon caused by control elements,.The refrigeration system with variable frequency rolling rotor is used as the research object.The curve fitting model for the separate controls of constant frequency with variable valve opening and of fixed valve opening while varying frequency was established through two experiments,and the synchronization control method under different working conditions was obtained.The results show that the degree of superheat decreases with the increase of valve opening.When the degree of superheat is below 6 K and the valve opening is 27.8%-30%,the degree of superheat control is difficult to increase.Increasing the temperature of chilled water can improve this condition.The degree of superheat decreases with the decrease of frequency.When the degree of superheat is below 5 K and the frequency is 44.5-46.5 Hz,the control difficulty increases.The dry degree of suction decreases with the increase of valve opening and decreases with the decrease of frequency.Under a certain working condition,the relation between frequency and valve opening can be obtained by fitting the mass flow rate of the system as the control objective,to realize synchronous control.After changing the suction state,it can precisely control the suction dryness without damaging the compressor,and make the system reach the stable state quickly.