Operating room is a sterile zone in the hospital that controls 17-27 °C temperature and 45-55% RH humidity.  The main feature  of  the operating  room  is to reduce contaminated microorganism, diseases,  bacteria,  virus,  spore-forming to fungi,  mold,  mites,  and   dust.   Bacteria    and   other biological   contaminants   control   and   keeping   relative   humidity  between  40 %  to  60 %. The Air   Handling   Unit  shall   supply   by  an  uncontaminated  clean  air   by   replacement  air flow in the operating room. That air  flows  pass  through  HEPA  filtration system with 99.9999% efficiency to remove airborne contamination. HEPA filter  located  on  the ceiling above the surgical table and other surgical instruments. Absolutely, those clean fresh air must supply by  efficiency  air handling unit with special design and produced to suit for operating room function.
Air handling is the equipment to collect air from operating room return duct, mixing with new fresh air in the mixing box or mixing chamber. Delivery those air to pre-filter, filtering again by the medium filter. Cooled it by cooling coil system in order to reduce the temperature.Pass through the humidity control equipment which connect to cooling system. Distribute by air duct to the operating room through HEPA filter to sterile zone.
There are several questions in the different AHU function of normal indoor airsuch as office, rooms in a house, department store or buildings and operating rooms. The major difference is normal indoor air condition doesn’t precision control humidity. Humidity which over 60% RH will be a cause of the proliferation of bacteria and other biological contaminants. Situative humidity control of operating room settles at  45-55% RH. It needs additional equipment in AHU for humidifying and dehumidifying of air. Hot gas reheat system or heat pipe system is adding design by specialist in order to work properly with the cooling system for this humidity control solution.