Hi guys, I new to this group & glad to join the group to discuss Refrigeration.I need some help for conditioning of the air. If anyone have come across the following problems, please advise.Previously, I have a fresh air system for food process. Air is conditioned through 3 AHUs to +2C & is filtered by HEPA from AAF of AAF AstoCel 1. Recently I done a upgrade of the system & brought the air temp down to -15C. However I noticed that HEPA freezed after 30 min of operation & system pressure went from 1.6KPa to 4KPa. When we revert back to the old parameters, system pressure went back to 1.6KPa.Therefore I am asking if anyone have done a project like this & have come across this problem. Also, do anyone know if there are HEPA filtration for temp as low as -10/-15C?Thanks in advance, Hui