Certified Energy Auditor Motors, Drives, and Compressed Air Questions and Answers

Question 1

A centrifugal fan's speed is reduced from 100% to 70% using a Variable Frequency Drive (VFD). According to the Affinity Laws, what is the approximate reduction in power consumption?

Accepted Answer

66%

Answer

30%

Answer

51%

Answer

91%

Question 2

An energy auditor identifies a compressed air system with a significant number of audible leaks. The plant operates 24/7. Which of the following actions will likely provide the most rapid and cost-effective reduction in energy consumption?

Accepted Answer

Implementing a comprehensive ultrasonic leak detection and repair program.

Answer

Replacing the primary air compressor with a new VSD model.

Answer

Increasing the size of the primary air receiver tank.

Answer

Lowering the system pressure by 5 psig.

Question 3

The NEMA Premium® efficiency designation on an electric motor indicates that the motor:

Accepted Answer

meets or exceeds a set of minimum full-load efficiency levels established by NEMA.

Answer

is specifically designed to be operated with a Variable Frequency Drive (VFD).

Answer

has a service factor of 1.25 or higher for handling overloads.

Answer

is interchangeable with any other motor of the same horsepower rating.

Question 4

An energy audit of a factory reveals that 100 psig compressed air is being used through open-ended hoses to blow dust and debris off workbenches. A more energy-efficient alternative would be to use a low-pressure blower. This situation is a classic example of:

Accepted Answer

inappropriate use of compressed air.

Answer

artificial demand.

Answer

a lack of system storage.

Answer

compressor short-cycling.

Question 5

An energy auditor observes a 100 hp motor operating at a consistent 40% of its rated load. The motor's nameplate efficiency is 95.0% at full load. The auditor should conclude that the motor's actual operating efficiency is:

Accepted Answer

Likely significantly lower than 95.0%.

Answer

Higher than 95.0% because the motor is not stressed.

Answer

Exactly 95.0% as per the nameplate rating.

Answer

Impossible to determine without power factor measurements.

Question 6

Which of the following is the primary energy-saving mechanism when a throttling valve on a centrifugal pump is replaced with a Variable Frequency Drive (VFD) to control flow?

Accepted Answer

The VFD allows the motor to run at a slower, more efficient speed, eliminating the energy wasted across the valve.

Answer

The VFD corrects the motor's power factor, reducing reactive power charges.

Answer

The VFD reduces the motor's inrush current during startup, saving demand charges.

Answer

The VFD's internal electronics operate more efficiently than the motor itself.

A centrifugal fan's speed is reduced from 100% to 70% using a Variable Frequency Drive (VFD).According to the Affinity Laws, what is the approximate reduction in power consumption?

A centrifugal fan's speed is reduced from 100% to 70% using a Variable Frequency Drive (VFD).
According to the Affinity Laws, what is the approximate reduction in power consumption?