coralfarmer.....you are confusing house AC and a chiller....that's our fault (we have two threads in one here). The reason that house AC has little to do a chiller as tanks grow is:
1) as the system volume grows larger, and the more lights, uv, pumps, etc. are added.....the more that you will have to rely upon a chiller.
2) also, as the water volume increases, it holds more heat....heat that is hard to remove from just a slightly lower ambient air temp.
To give you an example....my system is totally located in the garage and subject to outside air temps....house AC has no effect on the tank. I've had winter days when the outside temp is in single digits.....and my tank is still chiller driven. This is what happens when you're running 7000 watts of light. I'm even chiller driven at night....mostly from my 400watt uv unit. These numbers sound excessive....but, when compared with smaller tanks, I'm running less of everything per gallon of system water. This is another one of those areas where large tank reality is not just supersized small tank thinking......ie....cranking up the AC a bit will not necessarily cool the tank enough...if at all. Also, I'd rather run an applliance (AC unit) targeted right where I need it (the tank) and not have to cool the whole all the time.....of course, in my case, it wouldn't do any good anyway.
You should look into moonpods suggestion. I've heard good things about those units....although, I'm curious as to how well they will do with high pull down requirements that are necessary on some systems.