Chiller Lead-Lag Sequencing

Briefing

Three chillers serve a building cooling loop in a lead-lag arrangement. As cooling demand rises, additional units are staged on. When demand falls, lag units are shed. Runtime hours rotate the lead chiller each day to equalise wear. A chiller alarm removes that unit from the rotation and hands load to the next available unit.

Objectives

• COOLING_DEMAND >30% starts the lead chiller (CHILLER1_RUN initially)
• COOLING_DEMAND >60% stages on the first lag chiller
• COOLING_DEMAND >85% stages on the second lag chiller
• Chiller demand drops <25% sheds lag1; drops <55% sheds lag2 (hysteresis)
• CHILLER1_ALARM (or 2 or 3) removes that unit from service; next available takes over
• RESET_PB clears alarms and re-enables faulted chillers
• LAG_LOAD_BALANCE output (REAL) reports the fraction of chillers running (0, 0.33, 0.67, or 1.0)

I/O Table

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

1. #1Lead chiller starts when demand exceeds 30%

   COOLING_DEMAND=40 -> CHILLER1_RUN (initial lead)

2. #2Lag chiller stages on at >60% demand

   COOLING_DEMAND=65 -> lead + lag1 running

3. #3All 3 chillers run at >85% demand

   COOLING_DEMAND=90 -> all chillers on

4. #4Chiller alarm removes unit from service

   CHILLER1_ALARM while running -> CHILLER1_RUN stops, next unit starts

5. #5Lag chiller sheds when demand drops

   Demand drops from 65% to 20% -> only lead runs