Abstract: The operational energy efficiency of multi-unit air conditioner can be effectively improved by adjusting the control strategies of suction pressure and oil return frequency combined with suction line length, so it is necessary to be able to obtain the suction line length online during the operation of multi-unit air conditioners. An online evaluation algorithm for suction line length of multi-unit air conditioners is proposed, where a generalized heat balance method for compressor based on isentropic efficiency is established to iteratively calculate the mass flow rate of refrigerant, a method of the equivalent length of suction line was theoretically derived, and the correlation between the suction length and equivalent length was developed based on experimental data. The experimental results show that the online evaluation algorithm of suction line length can effectively distinguish between long and short piping under full load and partial load conditions, and the piping length calculation error is less than 20% for over 90% working conditions.

Key words: Multi-unit air conditioner, Refrigerant pipeline, Pressure drop, Modeling, Evaluation