Having just arrived in Bangkok for the 6th time this year, all through Don Mueang, I was asked by someone on your site to provide an update after my arrival re the risk of refused entry. On asking the Immigration officer he told me there is no limit by air, until you reach 180 days duration in Thailand. And then it starts a clean slate on 1st January for the calendar year. All of my trips have been for less than the 30 days. I gather from that I could have 10 or 20 trips as long as the time here doesn’t exceed the 180 day total. It may be his interpretation, I don’t know, but he seemed very explicit and certain. Cheers, hope it helps someone.