Common BAS Programming Mistakes to Avoid

Problem

New programmers create control logic that works in testing but fails in real-world scenarios: schedules don't run right, overrides get stuck, dampers flutter, or setpoints don't track.

Most Common Mistakes

1. Not Handling Manual Overrides Properly

• Mistake: Schedule always overwrites manual override
• Fix: Check for active override before applying schedule logic

2. Polling Too Frequently

• Mistake: Pulling data from a device every 1 second
• Result: Crushes network, device firmware crashes
• Fix: Use reasonable polling intervals (5–30 seconds for setpoints, 1 minute for diagnostics)

3. Missed Sensor Validation

• Mistake: Using any sensor value without checking for validity
• Result: Control logic acts on bad data (sensor fails at 127°F = max value)
• Fix: Always validate range: IF (temp >= -50) AND (temp <= 150) THEN use_value ELSE alert_fault()

4. PI Loop Tuning Never Done

• Mistake: Using default PID parameters from manual
• Result: Overshoot, hunting, slow response, or oscillations
• Fix: Tune on-site after startup; don't use defaults (every building is different)

5. Deadband Too Small

• Mistake: Setpoint = 72°F, no deadband → if temp 71.95°F, don't heat; if 72.05°F, start heating
• Result: Heating/cooling cycles every few seconds (hunting)
• Fix: Set deadband of at least ±1°F: heat if <71°F, cool if >73°F

6. No State Transitions

• Mistake: Fan turns on/off based only on current temp (no hysteresis)
• Result: Fan cycles constantly at setpoint, chatter in solenoids
• Fix: Implement clear state machine: "If COOL_MODE and temp > 73, turn on fan. Don't turn off until temp < 71."

7. Forgetting Occupied/Unoccupied Schedule

• Mistake: Setpoints hardcoded; don't change based on occupancy
• Result: HVAC running at full load nights/weekends when unoccupied
• Fix: Use occupancy schedule; setpoints drop 5°F when unoccupied

8. Not Documenting Setpoints and Logic

• Mistake: Program works but no one knows what the values mean or how to change them
• Fix: Add comments in code; create a parameter sheet