We finally switched over to MH's and now run a 240 watt MH bulb and two 20 watt actinics and the temp stays pretty steady during the day at 80-81 degrees. It gets a little warmer at night; about 82.5 degrees.
We run two fans across the top of the water that are installed in our canopy, and they do really well at keeping the temp down.
I don't think you really need a chiller for anything; you just have to find out what kind of system works for you.
Some peope have switches that control the different equipment. For example, in the morning, when the Halides come on, your heater turns off and the fans turn on. If the temp gets too low, past a set point, the heater turns back on and the fans turn off. If the temp gets too high, past a set point, the opposite happens.
There are many ways you can work it.