BAS-102 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
HVAC manages heat, moisture, air quality, pressure, and time-dependent loads; a temperature complaint is not yet an equipment diagnosis.
Case overlay
A sunny west zone is hot at 3 PM while shaded zones are comfortable and the supply temperature is normal.
Calculation/evidence callout: Calculate temperature difference, simple heat-load comparisons from supplied data, percent time outside band, and reasonableness.
Normal-rule anchor
Heat flows because of temperature difference, but rate depends on material, area, fluid flow, phase, and equipment; one sensor is limited evidence.
Case overlay
A coil has a large air temperature drop but low airflow, so space capacity remains poor.
Calculation/evidence callout: Calculate delta T, Q=mCpDeltaT from supplied values, Btu/h-to-watt/ton conversions, measurement error, and plausibility.
Normal-rule anchor
Relative humidity depends on temperature; safe conclusions require temperature, moisture, airflow, mode, and location together.
Case overlay
A space is cool but clammy after a cooling coil cycles at low airflow and poor condensate removal.
Calculation/evidence callout: Calculate mixed-air temperature from supplied flows, moisture/temperature comparisons, ventilation percentage, and dew-point margin from supplied data.
Normal-rule anchor
Command, fan proof, airflow, pressure, temperature, and space response are separate evidence layers.
Case overlay
A supply fan is commanded on and proven, but airflow is low because filters load and dampers are closed.
Calculation/evidence callout: Calculate CFM relationships from supplied data, airside heat Q=1.08 x CFM x DeltaT where applicable, outdoor-air fraction, and pressure/flow comparisons.
Normal-rule anchor
The learner does not diagnose refrigerant charge from BAS data alone; only qualified technicians perform refrigerant and energized service procedures.
Case overlay
A heat pump heats normally, then produces cool air during a defrost cycle while auxiliary heat fails.
Calculation/evidence callout: Calculate entering/leaving air delta T, runtime, capacity comparisons from supplied manufacturer data, and coefficient-of-performance awareness.
Normal-rule anchor
A pump command or valve position does not prove water flow or heat transfer; temperature and pressure must be interpreted with mode and load.
Case overlay
A hot-water valve is open and pump proof is on, but supply/return temperatures show no heat transfer.
Calculation/evidence callout: Calculate water heat Q=500 x GPM x DeltaT for supplied assumptions, differential pressure, temperature drop, and flow/position plausibility.
Normal-rule anchor
Plant equipment has manufacturer and safety limits; BAS supervisory logic cannot replace listed safeties or qualified operation.
Case overlay
A second chiller stages while isolation is closed and flow proof is unreliable, causing a trip.
Calculation/evidence callout: Calculate plant delta T, approximate load from supplied flow, stage thresholds, runtime balance, efficiency metrics from supplied data, and recovery margin.
Normal-rule anchor
Hybrid VVT can use standard VAV-capable controllers and crossflow pickup evidence, but remains a single central source whose mode and pressure strategy constrain zones.
Case overlay
A perimeter zone calls for heat while the rooftop unit cools; its hybrid box controls airflow but cannot create local heating.
Calculation/evidence callout: Calculate airflow from supplied differential-pressure relationship, zone vote percentage, minimum/maximum airflow, diversity, and changed-mode behavior.
Normal-rule anchor
VRF moves refrigerant to zones and may recover heat, but ventilation, exact operating limits, proprietary control, refrigerant safety, and gateway semantics require separate evidence.
Case overlay
A VRF zone is comfortable but CO2 rises because the associated DOAS is off; the gateway still reports indoor-unit fan operation.
Calculation/evidence callout: Calculate connected/diversified capacity from supplied data, ventilation deficit, runtime, gateway update age, and heat-recovery energy comparison.
Normal-rule anchor
BAS evidence is strongest when physical condition, signal, object, logic, command, proof, process response, time, and mode agree. A professional foundation avoids parts guessing: define normal, verify evidence, test one useful distinction, respect boundaries, and close every temporary state.
Case overlay
A cooling valve command rises with no position feedback, discharge temperature change, or trend-quality warning. Changed case: A cold-zone complaint includes a wrong schedule, stale space sensor, and partially closed damper; only one is the root cause in the current mode.
Calculation/evidence callout: Calculate command/proof error, response delay, trend sampling adequacy, percent outside limits, and point-evidence completeness. Rank hypotheses, calculate evidence coverage and timing, compare expected/actual values, and reconcile all observations and temporary states.