The fan blowing over surface is very effective. Evaporation takes away lots of heat, and this is what we recommended to newby reef keepers when they do not have the doughs to spend on a chiller units. The best part about evaporative cooling is ambient room temperature can be higher than the water temp, but it still works.
The only influencing factor is the ambient room humidity. If the humidity is really high, moist air blowing over water surface won't help evaporation. It is recommended to get a de-humidifier to keep room humidity down.