For a thermal power system

cold source temperature fluctuates throughout a year in many areas due to the change of ambient temperature. Therefore

off-design operation of an organic Rankine cycle (ORC) system is often unavoidable. The effect of cooling water temperature on ORC performance was studied by using R123 working fluid to generate power from low-grade waste heat. When the inlet temperature of cooling water in the condenser was increased but the hot source temperature was kept constantly

the condensation pressure was increased and the evaporation pressure was increased slightly

whereas the heat load of evaporator and condenser as well as the pressure difference and ratio between the inlet and outlet of scroll expander was decreased. Hence

the electric power output and thermal efficiency of the system were decreased. In the range of study that the cooling water temperature increased from 21.82℃ to 42.10℃

the electric power output declined from 2.357 kW to 1.535 kW

thermal efficiency declined from 7.25% to 5.76%

and the electric power output and thermal efficiency linearly decreased by 34.87% and 23.86%

respectively. Under these operating conditions

the electric power output decreased by 0.0411 kW and 1.74% at every 1℃ increase of cooling water temperature. Therefore

cold source temperature significantly affected the performance of an ORC system with low-grade waste heat

which could serve as important reference for designing cold source system and optimizing ORC system performance with consideration of local weather conditions.