The cooling capacity of the heat exchangers is based on the outlet water temperature being 10°C above the ambient temperature. The rated cooling capacity will apply when there is a temperature differential between the inlet and the outlet of 10°C, e.g., in those conditions water would return to the cooling unit at 20°C above ambient. The heat extraction rate will vary according to the differential between the inlet and ambient temperatures. The greater this differential, the great the heat extraction rate at the cooler.