A fan will give a cooling effect to your dog for sure, however, it won't cool the dog in the same way as it does to humans. Dogs usually sweat and eliminate heat via the paws or via panting instead of the body. So wetting their paws and putting them in front of the fan will definitely lower the temperature of your dog. But relying on a fan to cool your dog down won't be an entirely reliable solution by itself, consider combining it with summer dog grooming.