A variable volume and temperature (VVT) HVAC system uses multiple airflow dampening controls to regulate the airflow from an air handling unit (AHU). This allows a single AHU to meet the heating or air conditioning needs of multiple zones without purchasing additional AHU's. Thermostat controls are linked to dampening valves that regulate the airflow being supplied to each zone by either closing or opening.

A drawback to a simple VVT system is that the AHU will fluctuate between heating and cooling modes depending on desired temperatures set for each zone. AHU's will determine its operating mode based on which one will provide the greatest benefit to the overall comfort level between zones. This can lead to zones that become colder or hotter than their set temperatures.