I really think it is an exhaust issue. That is usually the biggest problem with closet growing. I would suggest a stronger exhaust system, but if that is not possible then try rotating frozen water bottles in and out of your closet as needed to help keep temps down. I did that one summer and found that I could control grow room temps by adding and subtracting frozen water bottles. It may not be a highly scientific process, but it works and is inexpensive. Just make sure the humidity doesn't get too high or the chances of mold increase.