Do I understand that you will have two coils in the hot wort with a third coil in a water bath?
TAP WATER >>> COIL IN WORT >>> COIL IN WATER BATH >>> COIL IN WORT >>> WASTE
Is this what you want?
I don't think this is an appropriate use. The maximum cooling is achieved with maximum delta T between the cold fluid and the hot fluid.
A better solution is the one used by MapleCity. One way to maximize the ice is to run unchilled tap water through the system to drop the temperature of the wort to about 130 deg or so and then add the ice to the chilling water; this will maintain the largest delta T across the entire chilling process with the minimum use of ice.
TAP WATER >>> COIL IN TAP WATER BATH >>> COIL(S) IN WORT >>> WASTE
use this until the wort is about 130 or when the temperature change in the wort begins to slow down
TAP WATER >>> COIL IN ICE WATER BATH >>> COIL(S) IN WORT >>> WASTE
One of the most important actions is to continuously stir the wort. You can test this by feeling the temperature of the waste water. Check the waste water temperature without stirring, then check while stirring. The temperature difference will be dramatically hotter while stirring. BE CAREFUL THE WASTE WATER WILL BE HOT ! !
The hotter the waste water the more efficient the heat transfer.
NOTE: don't dump the waste water on the lawn; it will kill the grass or any plants. That is experience talking