Energy Management and Control Systems Flashcards
6 cards from real CEM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Energy Management and Control Systems flashcards as text
A variable frequency drive (VFD) on a pump or fan saves energy because fan/pump power varies with:
Answer: The cube of speed
By the Affinity Laws, fan and pump power varies with the cube of rotational speed, so a 20% speed reduction yields nearly 49% power reduction.
Economizer control on an air-handling unit saves cooling energy by:
Answer: Using cool outdoor air for free cooling when outdoor conditions are favorable
When outdoor air is cool and dry enough, economizers open dampers to use outdoor air for cooling, reducing or eliminating mechanical refrigeration energy consumption.
Supply air temperature reset saves energy in an air-handling unit by:
Answer: Raising supply air temperature during mild conditions, reducing chiller and reheat energy
Supply air temperature reset raises the cooling coil leaving temperature during mild loads, allowing the chiller to operate more efficiently and reducing simultaneous heating for reheat.
A Direct Digital Control (DDC) system differs from pneumatic controls primarily because it:
Answer: Uses digital microprocessors and electronic sensors for precise, programmable control
DDC uses digital controllers with electronic sensors and software-based control logic, providing far greater precision, data logging, remote access, and programming flexibility than pneumatic systems.
Chiller sequencing control in a plant with multiple chillers saves energy by:
Answer: Staging chillers on/off to operate fewer units at higher, more efficient part-load ratios
Chillers generally operate most efficiently at 70-90% load; sequencing ensures fewer chillers run at higher efficiency rather than many running at very low, inefficient part-load conditions.
An energy information system (EIS) or energy dashboard primarily helps energy managers by:
Answer: Providing real-time and historical energy data for trend analysis and anomaly detection
An EIS aggregates meter data and presents consumption trends, benchmarks, and alerts, enabling energy managers to identify anomalies and prioritize efficiency improvements.