Abstract:

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.