18 May 2017
Multi-split variable refrigerant flow (VRF) air-conditioning systems, composed of a single outdoor heat exchanger
and multiple indoor heat exchangers, are becoming increasingly popular because of the ease with which they can
be installed, their high energy savings potential, and the opportunity to realize individualized comfort control.
Because these systems exhibit strong coupling effects between different indoor units, coordinated control of
compressor speed, fan speeds, and valve openings is required. A literature review indicates there is a dearth of
comprehensive studies that explore the complex multivariable dynamic behavior of air-source VRF systems with
commercially prevalent architectures. This paper describes a first-principles model of such an air-conditioner with
four indoor units that is validated against experimental data. This validated simulation model is then used to study
the dynamic system response subject to various sets of conditions, including variations in the compressor speed,
fan speeds, and valve openings. The insights gained from such a system analysis will be beneficial to future energy
performance analysis and model-based controls design.