Keeping the chiller performance at an optimum level is desirable because chiller is one of the energy-consuming equipment in buildings. Chiller is responsible for 40% to 70% of building energy consumption. Therefore, monitoring chiller performance is essential to keep its performance at a desirable level. Knowing chiller performance needs information about the water flow rate. Unfortunately, not every chiller is equipped with the water flow meter. Fortunately, in the last decade, some researchers have been developing virtual flow meters (VFM) to eliminate the need for flow meter equipment. One of the well-known methods of VFM is the energy balance method. There are two types of energy balance methods. Firstly, using theoretical work input to a compressor in calculating energy balance to estimate the flow rate. However, this method needs free-fault data from manufacturer or field measurement to obtain the theoretical compressor work input from a regression analysis. The second method uses actual compressor work input in energy balance analysis. This method needs trend data generated from the building automation system (BAS) for the energy balance analysis. Our research proposes the use of isentropic compressor work input to estimate the water flow rate. The proposed method may eliminate the need for manufacturer or field measurement data or trend data from BAS. The result shows that the comparison with the measurement values indicates that the use of isentropic work to estimate the water flow rate has good accuracy. However, it is sensitive to a low?temperature difference in evaporator and condenser and refrigerant overcharged fault.