Air volume. According to indoor air quality standard [4], fresh air requirement should be 30m/³(hp·). There are 3.5 peoples in a room. So the total fresh air rate is 105m/³h. According to design standard for energy efficiency of residential buildings in severe cold and cold zones [5], air change rate should be 0.5h-1. So the total fresh air rate is 168m/³h. According to design code for heating ventilation and air conditioning of civil buildings [6], air change rate should be 0.5h-1, when the room area is 20 m2-50 m2. So the total fresh air rate is 168m/³h. Therefore, the total fresh air rate is 168m/³h.