CEA Energy Auditing & Assessment Techniques 4 — Questions and Answers
Question 1: When conducting an energy audit on a data center, which metric is used to assess overall infrastructure energy efficiency?
- Power Usage Effectiveness (PUE) (Correct answer)
- Energy Star score for IT equipment
- Server utilization percentage
- Cooling tower approach temperature
Correct answer: Power Usage Effectiveness (PUE)
PUE = Total Facility Power ÷ IT Equipment Power; a PUE of 1.0 is ideal, meaning all energy goes to IT loads with zero overhead.
Question 2: An energy auditor discovers that a chiller is operating at a COP of 2.8, while the manufacturer's rated COP at design conditions is 5.2. The MOST LIKELY cause is:
- Fouled condenser tubes increasing condensing temperature and reducing heat transfer (Correct answer)
- Oversized chilled water pump increasing flow rate
- Improper refrigerant type substitution in the system
- Low occupancy causing the chiller to cycle on and off frequently
Correct answer: Fouled condenser tubes increasing condensing temperature and reducing heat transfer
Fouled condenser tubes raise condensing temperature, significantly degrading chiller COP; tube cleaning is a high-ROI maintenance measure.
Question 3: In an industrial facility audit, 'pinch analysis' is used to:
- Identify the minimum heating and cooling energy required by optimizing heat exchanger network design (Correct answer)
- Determine the maximum allowable pressure drop in compressed air piping
- Calculate the thermal resistance of insulation on steam lines
- Assess the combustion efficiency of industrial process heaters
Correct answer: Identify the minimum heating and cooling energy required by optimizing heat exchanger network design
Pinch analysis identifies thermodynamic limits on heat recovery and targets opportunities to maximize heat exchanger integration, reducing external heating/cooling demand.
Question 4: A commercial building energy audit reveals a power factor of 0.72. What is the energy management implication?
- The facility may incur utility power factor penalty charges and should add capacitor banks to correct it (Correct answer)
- The building's lighting system is consuming excessive reactive power
- All motor-driven equipment must be replaced with higher-efficiency models
- The utility billing meter is malfunctioning and readings are inaccurate
Correct answer: The facility may incur utility power factor penalty charges and should add capacitor banks to correct it
Low power factor (below 0.90–0.95) causes utilities to charge penalties; capacitor banks or VFDs can correct power factor and eliminate surcharges.
Question 5: During a steam system audit, an auditor uses an ultrasonic detector and finds multiple steam traps that are 'blowing through.' This indicates:
- Failed-open traps that are wasting live steam, a major energy loss requiring immediate replacement (Correct answer)
- Properly functioning traps discharging condensate at design rate
- Traps that are stuck closed, causing condensate flooding in steam lines
- High-pressure steam flashing to low-pressure condensate return normally
Correct answer: Failed-open traps that are wasting live steam, a major energy loss requiring immediate replacement
Traps that blow through are failed-open, continuously venting live steam rather than only condensate, and represent significant direct energy waste.
Question 6: The ASHRAE Level III energy audit (investment-grade audit) is distinguished from Level II by:
- More rigorous field measurements, sub-metering, and detailed energy modeling to reduce savings uncertainty for financing (Correct answer)
- A focus on operational improvements only, with no capital expenditure recommendations
- Limiting the scope to a single building system such as HVAC or lighting
- Requiring the audit to be completed within a single 8-hour site visit
Correct answer: More rigorous field measurements, sub-metering, and detailed energy modeling to reduce savings uncertainty for financing
A Level III audit provides sufficient engineering rigor (sub-metering, calibrated simulation) to justify capital investment decisions and third-party energy project financing.
Question 7: When performing a combustion analysis on a natural gas boiler, an auditor measures 15% excess air and stack temperature of 450°F. The BEST immediate recommendation is to:
- Tune the burner to reduce excess air to 10–15% and lower stack temperature to improve combustion efficiency (Correct answer)
- Install a new condensing boiler to replace the existing unit immediately
- Increase the fuel-to-air ratio to reduce NOx emissions
- Switch fuel source from natural gas to fuel oil for higher combustion temperature
Correct answer: Tune the burner to reduce excess air to 10–15% and lower stack temperature to improve combustion efficiency
Burner tuning to optimize the fuel-air ratio and stack temperature recovery are low-cost measures that can improve boiler efficiency by 2–5 percentage points.
CEA Energy Auditing & Assessment Techniques 4
When conducting an energy audit on a data center, which metric is used to assess overall infrastructure energy efficiency?