Demonstrates the cooling of a room by a nonlinear valve which regulates ambient air flow. Varying heat flow is prescribed to the room to model heat loss due to door opening and closing as well as the fluctuating heat capacity (people, computers etc.). Because the supply air temperature in this system is assumed constant, the air flow rate must vary to meet the rising and falling heat gains or losses within the room. A temperature sensor is used and fed into a PID controller. A digital pulse is then generated to drive the variable air volume box which is basically the nonlinear VAV damper.