CEM Energy Management and Control Systems 1 — Questions and Answers
Question 1: A Building Automation System (BAS) primarily serves to:
- Replace all HVAC equipment with digital controls
- Monitor and control building mechanical, electrical, and HVAC systems from a central platform (Correct answer)
- Generate electricity for building loads
- Provide fire suppression control only
Correct answer: Monitor and control building mechanical, electrical, and HVAC systems from a central platform
A BAS integrates sensors, controllers, and actuators across HVAC, lighting, and other building systems into a centralized platform for monitoring, control, and optimization.
Question 2: An Optimal Start control strategy in a BAS saves energy by:
- Running HVAC systems at full capacity all night
- Starting HVAC just early enough to reach setpoint by occupancy time, minimizing pre-conditioning time (Correct answer)
- Maintaining constant temperature 24/7 regardless of occupancy
- Increasing ventilation rates before occupancy to flush pollutants
Correct answer: Starting HVAC just early enough to reach setpoint by occupancy time, minimizing pre-conditioning time
Optimal Start calculates the minimum pre-conditioning time needed based on outdoor conditions and thermal mass, avoiding unnecessary hours of HVAC operation before occupants arrive.
Question 3: Demand-controlled ventilation (DCV) uses CO2 sensors to:
- Monitor outdoor air pollution and close dampers when levels are high
- Modulate outdoor air supply in proportion to actual occupancy detected by CO2 concentration (Correct answer)
- Control exhaust fan speed in restrooms
- Trigger emergency evacuation when CO2 exceeds 5,000 ppm
Correct answer: Modulate outdoor air supply in proportion to actual occupancy detected by CO2 concentration
DCV modulates outdoor air dampers based on indoor CO2 levels as a proxy for occupancy, providing required ventilation only when and where needed, reducing HVAC conditioning loads.
Question 4: Setback temperature control in an unoccupied building saves energy by:
- Maintaining tighter temperature bands during unoccupied hours
- Allowing indoor temperature to drift toward outdoor conditions during unoccupied periods (Correct answer)
- Increasing supply air flow to pre-condition spaces faster
- Running chilled water loops continuously at reduced flow
Correct answer: Allowing indoor temperature to drift toward outdoor conditions during unoccupied periods
During unoccupied hours, setback allows temperatures to rise in summer or fall in winter within an acceptable range, reducing the temperature differential driving heat transfer and lowering HVAC energy use.
Question 5: Which communication protocol is commonly used in modern BAS for interoperability between different manufacturers' equipment?
- RS-232 serial protocol
- BACnet (Building Automation and Control Network) (Correct answer)
- Ethernet TCP/IP only
- Modbus ASCII only
Correct answer: BACnet (Building Automation and Control Network)
BACnet is an ASHRAE/ISO/ANSI standard protocol designed specifically for building automation, enabling interoperability between devices from different manufacturers.
Question 6: Fault Detection and Diagnostics (FDD) in a BAS is used to:
- Generate electricity demand forecasts for utility billing
- Automatically identify equipment faults and inefficiencies before they cause failures or energy waste (Correct answer)
- Schedule preventive maintenance by calendar date only
- Control lighting color temperature based on time of day
Correct answer: Automatically identify equipment faults and inefficiencies before they cause failures or energy waste
FDD uses rule-based or machine-learning algorithms to analyze sensor data and identify equipment faults, control errors, and efficiency degradation, enabling proactive maintenance.
CEM Energy Management and Control Systems 1
A Building Automation System (BAS) primarily serves to: