24 June 2014

Modeling of fault impacts for a multi-split ductless heat pump system

In recent years, there is an increasing interest to develop fault detection and
diagnostics (FDD) tools for vapor compression systems to avoid degradation of system performance in the field. The effects of multiple types of faults, such as liquid line restriction
and condenser fouling, on single-speed systems have been previously studied through both experimental and simulation means. However, little research has been conducted on the
fault impacts for multi-split ductless heat pump systems. These systems differ from conventional ducted systems because of the multiple indoor units and complicated control
logic associated with compressor speed and electronic expansion valve openings that are used to meet indoor unit loads. In this study, a validated model of a dual-unit multi-split
ductless heat pump was used to simulate system performance with one indoor unit subjected to liquid line restriction and electronic expansion valve faults. The simulation results are
compared to non-faulted scenarios to examine how the control of the system affects the fault impacts. To assist the development of FDD tools in the future, significant changes of system
states with fault levels, such as the superheat and subcooling, are also identified.