how to control the temperature

[novice]

Ron, you've been a great help and we are getting ready to build a permanent greenhouse is northern Texas. I have read your sight and now have a question about how to control the temperature here when it reaches 100+ - do I understand that since I have a low dewpoint (less than 60) that I cannot use a swamp cooler and must use and air conditioner? if so, what size to you recommend of a 12 x 14 greenhouse that will get a lot of shade, but the temps are high - thx novice