This simulator models a centrifugal supply fan feeding a common plenum, a filter cassette and three independently damped parallel branches, so you can see how a fan curve intersects a coupled duct network and how automatic static-pressure control responds to filter loading and sensor error.
• Equipment laboratory tab: a real-time 3D cutaway of the centrifugal supply fan, motor and drive, filter cassette, static-pressure tap, common supply plenum/trunk, branches A, B and C with their dampers, and the static-pressure controller, with Home view, Focus selected part, Show full enclosure / cutaway, Exploded view, Auto rotate and Expand camera controls plus a clickable component list with callouts. Controls include an Automatic static-pressure control checkbox, static-pressure setpoint, manual fan speed ratio, branch A/B/C damper position, filter loading, and pressure sensor bias, alongside live stats, a What is happening? sequence readout, operating-history chart, switch-state tokens and a cell-readings table. • Curves & measurements tab: a true-vs-measured static pressure and filter-loss chart, a per-branch airflow chart (branches A, B and C), the model equations, and snapshot measurement readouts. • Experiments tab: four preset investigations (fixed-speed network, close branch A, load the filter, biased pressure sensor) plus a Run model checks verification bench and a timestamped event log with trial-report export. • Learn & assess tab: lesson cards on intersecting fan and system curves, how parallel branches interact, locating the pressure sensor relative to the filter, and separating measured from true pressure, a knowledge-check quiz with reset, and a scope/references note.
The fan's pressure output falls as flow rises (Pfan = 600·N² − 90·V̇total²), while the combined resistance of the filter and the three parallel branches rises with flow squared, so the system settles wherever these two curves intersect. Because all three branches share the same plenum static pressure, adjusting one damper changes the total flow and the common pressure, which in turn redistributes flow through the other two branches — they are coupled, not independent.
The static-pressure tap sits downstream of the filter, so it sees true plenum pressure plus whatever pressure-sensor bias you've dialed in. In automatic mode, the model-based controller adjusts fan speed (within a finite rate limit and a 120% speed ceiling) to try to hold the measured pressure at setpoint — but because the sensor's bias is baked into what it measures, a biased sensor drives the true physical pressure away from the intended setpoint even while the measured value matches it.
The pressure chart plots true duct static, measured static and filter pressure loss together, letting you see how a dirty filter consumes fan pressure upstream of the tap and how a sensor bias creates a persistent gap between true and measured pressure. The branch-flow chart shows how airflow splits across branches A, B and C — throttling one branch's damper redistributes flow to the other two rather than isolating the change.
The Run model checks button in the Experiments tab exercises independent fresh models — leaving your current trial untouched — to confirm relationships such as branch flows summing to total flow and a fixed-speed network's fan/system curves reaching a consistent operating point. This is a quasi-steady incompressible air-network model with representative fan and resistance curves and 65% combined fan/drive efficiency — it excludes fan stall, acoustic prediction, flexible-duct deformation, duct leakage and equipment-rating certification.
A quasi-steady incompressible air network: a centrifugal fan curve (Pfan = 600·N² − 90·V̇total²) intersecting the combined resistance of a loadable filter and three parallel damper-controlled branches, with a 65% combined fan/drive efficiency and a 0.015 damper-leakage conductance floor. It is not a certified fan-selection or duct-leakage model.
All three branches draw from the same common plenum, so they share the same static pressure. Closing branch A raises the common plenum pressure (at a given fan speed), which pushes more flow through branches B and C — the branches are hydraulically coupled through that shared pressure, not independent.
The pressure tap reports true plenum pressure plus a pressure sensor bias you can set. In automatic mode the controller drives the measured value to setpoint, so a nonzero bias means the true physical duct pressure settles above or below the setpoint by roughly the bias amount, even though the measured reading looks correct.
The Run model checks button runs independent, freshly-initialized models to confirm invariants such as branch airflows summing to total airflow and the fan/system curve intersection producing a consistent, physically sensible operating point.