I will be flying to the US from the new airport, and will have already cleared customs and immigration in Chiangmai, which means I will be in transit. Since I have to spend the night at the airport, I am trying to find out if the United or Thai lounges for Star Alliance Gold clients are open, and what facilities are available. Also, are there any facilities that rent day beds? What about food withing the lounges or transit area? . Is there an office to store luggage if I don't check it all through to the US?

I will be flying to the US from the new airport, and will have already cleared customs and immigration in Chiangmai, which means I will be in transit. Since I have to spend the night at the airport, I am trying to find out if the United or Thai lounges for Star Alliance Gold clients are open, and what facilities are available. Also, are there any facilities that rent day beds? What about food withing the lounges or transit area? . Is there an office to store luggage if I don't check it all through to the US?

Thai Air is the only Star Alliance member with lounges open at Suvarnabhumi, but the lounges close after the last flight, sometime around 1AM and don't reopen until about 5:30AM. So you'll be out of luck staying in a lounge. There are Louis Tavern Dayrooms, which cost 2,000 Baht per 4 hours, which you could use for the 4 hours the lounge is closed. They are located on Concourse G, and also have some rooms on Concourse A above the Louis Tavern Lounge. They are frequently fully booked, so you may not have any luck getting a room. There is a Thai economy transit lounge open 24 hours on Level 3, Concourse B. It's just an open area with comfortable seating. There are various food places inside the terminal where you can buy a meal, and also food in the Thai lounges, with reportedly hot food at times, but only pastries and cold snacks at other times. I haven't seen any places to store luggage airside. Landside there are left luggage places operated by Chubb, but you won't have access to those being you'll be clearing immigration in Chiang Mai.