The glycol does not affect the cooling water unless you mix the glycol in it. In this case you rename the cooling water to glycol coolant solution.
To simplify, the glycol mixture/solution has a higher boiling temperature than the water, hence you can use it in cooling processes above 100 deg C, above the water boilling temperature at atmospheric pressure. Example is the car cooling system using typically a 33% glycol solution as engine coolant.
The tracing system you mentioned sounds rather a heating process for the cooling water piping, perhaps to prevent the freezing of the line. Quite expensive and energy intensive heating process with glycol, why don't you use steam tracing instead? However, if the glycol in the tracing line is colder than the cooling water, you would expect some heat transfer to glycol (very inefficient!), hence you could provide some sub-cooling of the water. Please note that I estimate the cooling effect of glycol tracing to be some equal to the water line exposed to the environment, perhaps more benefit from the wind cooling the water line.
gr2vessels
I think you answered you own question, how does a hot heat tracing effect the cooling system. Energy goes from hot to cold. The cooling water is warmer, the water cooling (cooling tower?) will have to remove the heat gained.
I am in Northern Cananda . We use glycol tracing to keep cooling water and other process lines warm so the process fluid does not freeze in winter. 30 below 0 is a common temperature from December to March.
The only pssible way I could see a cooling water line would freeze would be in a no flow situation. During the winter months, I would assume you would cut back circulation through exchangers to keep the water out warm enough to not freeze.
