This study examined the overall system performance of a water chiller that is subject to the influence ofnanofluids. The system performance of a 10 RT water chiller (air conditioner) located in a well-controlled chamber was observed. Multiwalled carbon nanotubes (MWCNTs) were used as the heat transfer medium in the evaporator. The system performance was tested at the standard water chiller rating condition in the range of the flow rate (60 L/min to 140 L/min). The static measurement of the thermal conductivity of the nanofluids showed only a 1,3% marginal increase relative to the base fluid, so it was surprising to find that a 4.2% increase in cooling capacity and a slight decrease of about 0.8% in power consumption occurred in the nanofluids system at a flow rate of 100 L/min. In summary, with the introduction ofnanofluids, the coefficient of performance (COP) of the water chiller is increased by 5.15% relative to that without nanofluids.