BAS-311 Visual Aid Library
Figure-use rule
Each figure is an orientation and reasoning aid, not a project drawing. Learners must pair it with the current sequence, point list, wiring/piping documents, manufacturer instructions, and as-found evidence.
Normal-rule anchor
The HVAC process is independent of whether the control signal is pneumatic, electric, electronic, or DDC; signal method changes the evidence path.
Case overlay
An older AHU uses pneumatic actuators with DDC EP transducers and a modern supervisor.
Calculation/evidence callout: Map percent command through 0–10 V or 4–20 mA to 3–15 psi and expected actuator direction using supplied ranges.
Normal-rule anchor
Airflow value is trustworthy only when pickup, tubing, sensor, range, K-factor, density basis, and calibration are correct.
Case overlay
A VAV box reports design airflow with the damper closed and AHU fan off.
Calculation/evidence callout: Use supplied flow=K×√ΔP relationship and min/max/dual-maximum sequence to predict state and airflow target.
Normal-rule anchor
Hybrid VVT can run on standard VAV controllers, but zone airflow measurement does not turn the central packaged source into a central VAV air handler.
Case overlay
Four zones vote for cooling while one perimeter zone needs heat and the bypass strategy is unstable.
Calculation/evidence callout: Calculate zone vote/priority, airflow target, crossflow pickup ΔP using supplied K, and central static/bypass response.
Normal-rule anchor
BAS commands are subordinate to factory safeties and OEM refrigerant/compressor controls.
Case overlay
A heat pump enters defrost while the BAS trend appears to show simultaneous cooling and auxiliary heat.
Calculation/evidence callout: Calculate stage thresholds, delays, lockouts, supply-air targets, and expected mode from supplied sequence.
Normal-rule anchor
Static and SAT resets respond to verified demand within limits; they do not excuse failed boxes, sensors, or protections.
Case overlay
Static pressure stays at maximum while many VAV dampers are nearly closed.
Calculation/evidence callout: Calculate mixed air, static/SAT reset, request response, fan speed estimates, and timing from the approved sequence.
Normal-rule anchor
VRF does not inherently provide required outdoor air; the DOAS/ventilation path and controls must be identified separately.
Case overlay
VRF zones are comfortable while CO2 rises because the DOAS is disabled by schedule.
Calculation/evidence callout: Calculate ventilation path timing, dew-point target, heat-recovery temperature effectiveness when supplied, and mode demand.
Normal-rule anchor
Ordinary HVAC optimization and operator commands never outrank approved smoke-control and fire-alarm functions.
Case overlay
A normal occupied command conflicts with an active smoke-control mode indication.
Calculation/evidence callout: Build a priority/state table from supplied approved documents; do not calculate or invent life-safety acceptance criteria.
Normal-rule anchor
Boiler availability and command do not prove flow, firing, heat transfer, or safe combustion.
Case overlay
Hot-water supply is below target while the lead boiler command is on and pump proof is questionable.
Calculation/evidence callout: Use Q=flow×ΔT×approved fluid factor, reset equations, staging thresholds, and minimum-flow criteria supplied.
Normal-rule anchor
Chiller command or run status does not prove correct water flow, capacity, efficiency, or tower operation.
Case overlay
The chiller is at high load while chilled-water ΔT is low and bypass flow is suspected.
Calculation/evidence callout: Calculate tons or heat transfer from supplied flow/ΔT factors, staging load, approach, and plant reset targets.
Normal-rule anchor
Optimized requests and resets are applied only where the approved project sequence makes them applicable and all prerequisite evidence is trustworthy.
Case overlay
A two-pipe building changes to cooling while several heating valves remain open and zone requests persist.
Calculation/evidence callout: Calculate changeover conditions, required hold/purge time, request aggregation, reset limits, and energy-balance reasonableness.