CEM - Certified Energy Manager Energy Audits and Instrumentation Questions and Answers — Questions and Answers
Question 1: An energy auditor is conducting a walkthrough of a commercial building and notices that a large motor is operating continuously. To assess the electrical efficiency of this motor, which two measurements are most crucial for calculating the power factor?
- Voltage and current
- Resistance and capacitance
- Real power (kW) and apparent power (kVA) (Correct answer)
- Runtime hours and motor nameplate horsepower
Correct answer: Real power (kW) and apparent power (kVA)
Power factor is a measure of how effectively electrical power is being used and is calculated as the ratio of real power (kW) to apparent power (kVA). An energy auditor would use a power quality analyzer to measure these two values to determine the motor's efficiency. A low power factor indicates inefficient power use.
Question 2: During an ASHRAE Level 2 energy audit of a manufacturing facility, which of the following activities would be most characteristic of this audit level?
- A simple walkthrough to identify obvious low-cost energy saving opportunities.
- A detailed whole-building computer simulation to model complex capital-intensive retrofits.
- A review of utility bills and a brief site survey to establish a baseline.
- A detailed breakdown and analysis of energy consumption by end-use, with financial analysis of recommended measures. (Correct answer)
Correct answer: A detailed breakdown and analysis of energy consumption by end-use, with financial analysis of recommended measures.
An ASHRAE Level 2 audit, also known as an "Energy Survey and Analysis," builds on a Level 1 audit by providing a more detailed evaluation. It involves breaking down energy use by specific systems (end-use), quantifying potential savings, and performing a thorough financial analysis of the proposed Energy Conservation Measures (ECMs). Level 1 is a basic walkthrough, while Level 3 involves complex simulations for major investments.
Question 3: An energy manager is tasked with identifying specific locations of heat loss and insulation deficiencies in a building's envelope. Which instrument is best suited for this purpose?
- Blower Door
- Infrared Camera (Thermography) (Correct answer)
- Ultrasonic Leak Detector
- Hygrometer
Correct answer: Infrared Camera (Thermography)
An infrared camera, used for thermography, creates images that show surface temperature variations. This allows an auditor to visually identify areas where heat is escaping (indicating poor insulation) or where cold air is infiltrating. A blower door measures overall building airtightness, an ultrasonic detector finds pressurized leaks, and a hygrometer measures humidity.
Question 4: To determine the combustion efficiency of a natural gas boiler and ensure its safe operation, an energy auditor should use which of the following instruments?
- Pitot Tube
- Power Quality Analyzer
- Combustion Analyzer (Correct answer)
- Light Meter
Correct answer: Combustion Analyzer
A combustion analyzer is a portable instrument specifically designed to measure the composition of flue gases from boilers, furnaces, and other fuel-burning appliances. It measures parameters like oxygen, carbon monoxide, and flue gas temperature to calculate combustion efficiency and check for safety issues.
Question 5: An energy audit of a compressed air system is planned. The primary goal is to identify and quantify costly leaks. Which instrument would be most effective for locating these leaks while the system is operational?
- Anemometer
- Manometer
- Stroboscope
- Ultrasonic Leak Detector (Correct answer)
Correct answer: Ultrasonic Leak Detector
When gas passes through a leak in a pressurized system, it creates turbulence that generates high-frequency sound waves (ultrasound), which are beyond the range of human hearing. An ultrasonic leak detector is designed to sense these sounds, allowing an auditor to pinpoint the exact location of compressed air leaks even in a noisy industrial environment while the system is running.
Question 6: Which of the following scenarios would justify the cost and effort of an ASHRAE Level 3 audit?
- A small retail store looking for simple, no-cost ways to reduce its monthly utility bill.
- A facility manager needing to create an initial energy use baseline and identify obvious areas of waste.
- A university campus planning a multi-million dollar central plant renovation with major HVAC system replacements. (Correct answer)
- A commercial office building that has just completed a lighting retrofit and wants to verify the savings.
Correct answer: A university campus planning a multi-million dollar central plant renovation with major HVAC system replacements.
An ASHRAE Level 3 audit, often called an "investment-grade audit," is the most detailed and comprehensive type. It is reserved for situations involving large, capital-intensive projects. It uses extensive data logging and computer simulations to accurately model the expected energy savings from major retrofits, providing the high level of confidence needed for significant financial decisions.
