Have had this 8'x6' Snap n grow for about 5 years now and the only way I could cool it in summer was several fans and a mister system, they helped but I still lost plants do to heat stress. I started.looking on CL a few weeks ago and I found a very new unit for a very low price, had to buy it.
Outside temperature is 99f and RH is about 25%, inside GH with cooler, 87f and RH 68%, nice.
I have cooler on low cool and that setting works great just the right amount of air flow. If I turn it up to high It literally will blow the doors open. The nicest thing now is that I can walk in without having to move fans out of way, I can go in anytime I want, so cool.
I mounted a fan a long time ago to ceiling to act as a way to draw air up and to force some hot air out, that fan is the only one I use.
I have cooler and fan on two temperature. Controllers
Let me know what you think.
Here is a YouTube link to a short video
Swamp cooler for greenhouse - YouTube