VVT Systems

A standard packaged rooftop unit (RTU) is a single-zone system. It has one thermostat, one call for heating or cooling, and one mode at a time. You will go deep on RTU controls in Lesson 3.2; for now, the important thing is that it behaves like a single switch: heat or cool, nothing in between. That works fine for an open floor plan or a small space with a consistent load. It does not work well for a building with multiple rooms that heat and cool differently.

The textbook fix is a full VAV system: a central air handling unit with chilled and hot water coils, a duct network, and a VAV box in every zone. It gives you precise zone control and scales well. It also requires a mechanical room, a central plant, water piping throughout the building, and a significantly larger budget. For a 10,000 square foot medical office or a mid-size retail strip, it is often more system than the job warrants.

Variable Volume and Temperature, or VVT, sits in between. You keep the packaged rooftop unit on the roof, which is familiar, inexpensive to maintain, and already ubiquitous in light commercial construction. Then you add a network of zone damper boxes in the ductwork, a bypass damper to protect the unit, and a master zone controller that coordinates everything. The result is zone-by-zone temperature control from a system that looks, from the roof, exactly like any other RTU job.

VVT is a Carrier trademark, but the concept applies to similar systems from other manufacturers. You will see it most in light commercial buildings: medical offices, mid-size retail, small schools, professional buildings where multiple tenant spaces need independent control but the budget does not support a full central plant.