Hello everybody, Currently, I am working on the project where I must simulate how mechanical ventilation affects the inside air temperature of my building located in hot and humid climate. I am using the "SIMPLE" HVAC system in "Model Options" and "Room ventilation" for the "Mechanical ventilation method" (also in Model Options). I have an airflow rate to 4 ACH, deltaT is 2 degree C, and minimum inside temperature is 22.7 degree C (to avoid overcooling, but because it is hot climate the temperature almost never falls below 22.7). The schedule is 16.00-8.00 every day. The problem that I face that when I simulate my model the airflow rate alway never reaches 4 ACH, it fluctuates from 0 to 2 ACH (I am looking for "Mech vent + Nat vent + infiltration" in the outputs). I have set deltaT to 2 degree C, so to avoid hot air coming inside. But then shouldn't it be 0 ACH (when it is off or when outside is hot) or 4 ACH (when it is ON and outside is cold). Why it is never reaching 4 ACH?