I am designing a cold room of size 4 m by 2.5 m by 2.5 m. The cold room will be used to store vegetables. The recommended Air change is 4 changes in a day. How do I go ahead with exhaust ducting? Do I need to have an exhaust fan? Also, I want to have control over the outflow of exhaust depending upon CO2 concentration in the room. Kindly guide through.