Overview
This facility improvement measure (FIM) focused on a comprehensive upgrade of building automation and HVAC controls, transitioning from legacy pneumatic systems to a modern, integrated digital platform. The project replaced all existing controls with a SIEMENS system and incorporated a Desigo CC building management system (BMS), designed to work in tandem with Enlighted IoT lighting controls.
Project Scope
– Full replacement of pneumatic controls with direct digital controls (DDC).
– Integration of occupancy sensors from the Enlighted system into the HVAC control strategy.
– Implementation of demand control ventilation (DCV) using newly installed CO₂ sensors.
– Addition of energy-saving time-of-day schedules for air handler units (AHUs).
Occupancy-Based Control Strategy
The new control system leverages real-time data from Enlighted sensors to switch between occupied and unoccupied HVAC modes based on actual space usage. Each zone, defined by a VAV box coverage area, responds dynamically to occupancy detection:
– Occupied Mode: Triggered when any sensor within a zone detects occupancy. HVAC operates under normal conditions.
– Unoccupied Mode: Activated if no occupancy is detected for 15 minutes:
– If conditions are within a 2°F dead band and relative humidity is below 60%, the VAV damper closes fully and reheat valves are shut.
– In cooling mode, if space temperatures exceed the setpoint, dampers open as needed, but reheat remains off.
– In heating mode, both damper and reheat coil are enabled to maintain comfort.
This strategy ensures optimal energy use while maintaining occupant comfort and space conditions.
Demand Control Ventilation (DCV)
As part of the retrofit, new CO₂ sensors were installed throughout the building to support DCV:
– Outside air dampers modulate based on real-time CO₂ levels.
– A CO₂ setpoint, based on ASHRAE guidelines, governs damper movement.
– Minimum outside air damper position is set to fully closed (0%).
– Damper modulation is programmed to avoid rapid swings, ensuring stable indoor air quality without excessive energy use.
Time-of-Day Scheduling
A time-based HVAC control layer was also added:
– All AHUs are scheduled to shut down for a two-hour window between midnight and 4:00 AM.
– AHUs are staggered to avoid a full-building HVAC shutdown.
– Temperature, humidity, and CO₂ sensors remain active, and units restart automatically if space conditions exceed threshold values:
– Temperature deviates beyond a 3°F dead band
– Humidity exceeds 60%
– CO₂ levels rise above setpoint
Savings and Analysis
Energy savings were calculated using a BIN weather model comparing baseline energy use to post-retrofit projections:
– The model analyzed HVAC performance over various ambient temperature ranges.
– Control logic improvements, reduced runtime, and ventilation optimization were reflected in the proposed usage profile.
The total energy savings were analyzed in three categories based on control strategies:
- Enlighted Occupancy-Based Savings:
– Cooling Energy: 1,276 MMBTU
– Reheat Energy: 1,616 MMBTU
– Heating Energy: 281 MMBTU
– Fan Energy: 26,537 kWh
- Demand Control Ventilation (DCV) Savings:
– Cooling Energy: 632 MMBTU
– Heating Energy: 155 MMBTU
– (Reheat Energy unchanged)
- Time-of-Day (ToD) Scheduling Savings:
– Cooling Energy: 488 MMBTU
– Reheat Energy: 292 MMBTU
– Heating Energy: 347 MMBTU
– Fan Energy: 10,365 kWh
These combined strategies contributed significantly to the overall reduction in HVAC energy use, improving system efficiency and supporting the facility’s sustainability goals.
Conclusion
The HVAC controls retrofit significantly enhanced the facility’s energy efficiency and system responsiveness. By integrating occupancy-based logic and demand-controlled ventilation, the project enabled smarter, more adaptive operations. The combination of time-of-day scheduling, sensor-driven control sequences, and CO₂ monitoring provided a foundation for long-term operational savings and improved indoor air quality.
