Perhaps it was wishful thinking believing that I was going to be able to cool the new cool vivarium all summer only with the help of outside air. But not really... we normally do not have much of this nice summer weather... But it has been very warm here lately so I decided to install a small portable air conditioner for cooling the cool vivarium. It is not very powerful, only 6000 BTU, but it does not have to be since it is going to be cooling such a small area. The main thing was that it had to have was a mechanical switch so I can hook it up to an external thermostat and timer. I have ordered a Lucky Reptile Thermo Control PRO II to handle the regulating part. You to set different temperatures for day and night and it has a built in minute timer for on/off functionality and you can switch between heating and cooling modes. I turned on the AC and it brought the temperature inside the viv down from 24-28 degrees to about 15-16 in about an hour. Much more info and pictures on my blog. More on the vivarium build in this thread. Video of the AC installation.