I cool them by the lights turning off and during the summer I use cold water in the trays. Plus I live in Oregon and most nights are below 60 so its usually not bad. It is only 90 plus around here maybe 3 weeks out of the year so that is not a problem either. But i keep the plants at around 80 degrees with 70 percent humidity during the day to 60 degrees in the night with 90 percent humidity. If you need to cool your plants I would suggest a fogger or an a/c unit that does not kill humidity.