SZVAV — single-zone variable air volume. A machine serving one room that holds a supply-air setpoint, resets it upward as the load falls and slows its fan, so the room gets less air rather than warmer air. How a machine is run → Constant volume and SZVAV.
A constant-volume unit meets a smaller load by making its supply air warmer: the fan runs flat out and the coil unloads. A single-zone VAV unit does the opposite first — it holds a cold supply-air setpoint and slows its fan, so the room gets less of the same cold air. Fan power falls with roughly the cube of the airflow, which is why ASHRAE 90.1 §6.4.3.10 requires it on larger single-zone units: the same room, the same comfort, a fraction of the fan energy.
The setpoint itself is reset as the load falls — up toward the room temperature — so at light loads the machine runs both slower and warmer, inside a band the designer sets. HVAC Builder's SZVAV strategy carries the setpoint, the reset ceiling and a fan floor; the controller lands the fan speed and the coil together every hour, and a fan declared with a static-pressure setpoint reads its part-load power off its own curve rather than the cube law.
Open the builder — the examples in the Design tab's sources list include a machine of this kind, and the Simulate tab runs it against a year of weather.
DOAS — dedicated outside-air system · VAV terminal box · Economiser · Waterside economiser · Demand-controlled ventilation · Face-and-bypass · Head-pressure control · Humidity ceiling and floor · Cycling and modulation · Coupling · Priority · Category · Nested system · Design point and TMY year