The use of cascade multi-functional heat pumps to provide simultaneous cooling or heating, and hot water has become essential in recent times. This study analyzed the performance of a water-to-water cascade multi-functional heat pump according to the variation of heat source and heat sink temperatures in cooling mode, hot water mode and cooling hot water mode. The cooling-hot water cycle was optimized to produce the designed capacities of the cooling and hot water cycles by maintaining the compressor speed of the low stage (LS) cycle as that in the cooling mode and increasing compressor speed of the high stage (HS) cycle above that in the hot water mode. In cooling-hot water mode, capacity of the hot water cycle and hot water temperature increased by 14.8% and 1.1 degrees C respectively, as the standard outdoor entering water temperature (OD EWT) increased by 15 degrees C. Variation of OD EWT and indoor entering water temperature had similar effects on capacity of the cooling cycle in cooling mode and cooling-hot water mode. Moreover, capacity of the hot water cycle was more stable in cooling-hot water mode than in hot water mode according to variation of hot water heat exchanger entering water temperature (HW EWT). (C) 2020 Elsevier Ltd. All rights reserved.