Compressed Air and Power 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 Compressed Air and Power Systems flashcards as text
When analyzing a compressed air system, a supply/demand audit measures both average flow and:
Answer: Peak flow demand and pressure profile to properly size compressors and storage
Understanding both average flow demand and peak instantaneous demand is essential for properly sizing compressors, receivers, and controls to handle actual production variations efficiently.
The specific power of a compressed air system (kW/100 CFM) is a key metric because:
Answer: It measures how efficiently the compressor package converts electricity to compressed air output
Specific power quantifies efficiency of the entire compressor system (motor, compressor, controls, dryer); lower values indicate better performance and enable comparison of different compressor technologies.
Real power (kW) and apparent power (kVA) differ in that:
Answer: Real power (kW) performs actual work while apparent power (kVA) includes reactive power that does no work but flows in the circuit
Real power (kW) is the actual work-producing component of AC power; apparent power (kVA) is the vector sum of real and reactive power, with reactive power creating current flow without useful work.
Utility interval demand data (15-minute kW) is most useful for an energy manager to:
Answer: Identify demand peaks and evaluate demand response or load-shifting opportunities
15-minute interval demand data reveals exactly when demand peaks occur, enabling targeted load shifting, demand response participation, and evaluation of storage or control strategies to reduce peak demand charges.
An energy audit of a motor-driven system should calculate energy savings from a VFD based on the:
Answer: Reduction in shaft speed raised to the third power, per the Affinity Laws
Since fan and pump power varies with the cube of speed (Affinity Laws), VFD savings calculations must use actual speed reduction ratios cubed to determine power reduction at each operating condition.
Which of the following is NOT a valid reason to right-size (downsize) an oversized electric motor?
Answer: Smaller motors have lower starting inrush current relative to full-load current
Smaller motors actually have higher starting inrush current as a percentage of their rated full-load current (locked rotor current ratio is similar or higher in smaller frames), so this is not a valid justification for right-sizing.