CEM Compressed Air and Power Systems 1 — Questions and Answers
Question 1: Compressed air systems are considered energy-intensive because:
- Compressors run at 100% mechanical efficiency
- Only 10-15% of electrical input is converted to useful work at the point of use; the rest is wasted as heat (Correct answer)
- Compressed air is always produced at higher pressure than needed
- Compressor motors always operate at unity power factor
Correct answer: Only 10-15% of electrical input is converted to useful work at the point of use; the rest is wasted as heat
The compression process generates large amounts of heat and has multiple energy conversion losses; only about 10-15% of electrical input reaches the end-use tool or process as useful work.
Question 2: Reducing compressed air system header pressure by 2 psig typically reduces compressor energy consumption by approximately:
- 0.1%
- 0.5-1% (Correct answer)
- 5-10%
- 20-30%
Correct answer: 0.5-1%
As a rule of thumb, each 2 psig reduction in discharge pressure reduces compressor energy consumption by approximately 0.5-1%, providing an easy, no-cost savings opportunity through pressure optimization.
Question 3: In a compressed air system, air leaks are significant because:
- They cause pressure surges that damage pneumatic tools
- Leaks waste compressed air continuously, forcing compressors to run longer and consume more electricity (Correct answer)
- Leaks introduce moisture into the compressed air system
- Leaks cause excessive pressure buildup in headers
Correct answer: Leaks waste compressed air continuously, forcing compressors to run longer and consume more electricity
Leaks in typical industrial compressed air systems waste 20-30% of total compressor output, requiring compressors to run additional hours to compensate for the constant air loss.
Question 4: A compressor with a modulating control will save more energy than one with a load/unload control because:
- Modulating control maintains full-load current regardless of demand
- Modulating control continuously matches compressor output to actual demand, reducing unloaded running losses (Correct answer)
- Load/unload control requires a larger receiver tank than modulating control
- Modulating control operates the compressor at higher pressure
Correct answer: Modulating control continuously matches compressor output to actual demand, reducing unloaded running losses
Modulating controls throttle compressor inlet valves to precisely match output to demand, while load/unload controls cycle between full load and unloaded (wasteful) operation.
Question 5: Heat recovery from compressed air systems is feasible because:
- Compressed air cools significantly during compression
- About 80-93% of electrical energy input to compressors is converted to heat, which can be recovered for space or water heating (Correct answer)
- Compressed air heat is at temperatures suitable for steam generation
- Compressor heat recovery reduces the need for cooling towers
Correct answer: About 80-93% of electrical energy input to compressors is converted to heat, which can be recovered for space or water heating
Since 80-93% of compression energy becomes heat in the compressed air and compressor components, this heat can be recovered using heat exchangers to provide useful building heat or hot water.
Question 6: Pressure/flow controllers installed in compressed air systems save energy by:
- Increasing system pressure to reduce compressor run time
- Decoupling supply and demand sides, allowing lower supply pressure while maintaining stable header pressure for end uses (Correct answer)
- Eliminating the need for air dryers
- Increasing receiver tank volume automatically
Correct answer: Decoupling supply and demand sides, allowing lower supply pressure while maintaining stable header pressure for end uses
Pressure/flow controllers allow the supply side to operate at minimum safe pressure while providing a stable, slightly higher pressure to the demand side, reducing compressor energy without affecting end-use tools.
CEM Compressed Air and Power Systems 1
Compressed air systems are considered energy-intensive because: