NABCEP Energy Efficiency & Conservation Techniques 5 — Questions and Answers
Question 1: The 'negawatt' concept in demand-side management refers to:
- Negative power factor measured in watts
- A unit of electrical power capacity saved through efficiency or conservation (Correct answer)
- Wasted electricity measured at the meter
- Power generated by microgrids during grid outages
Correct answer: A unit of electrical power capacity saved through efficiency or conservation
A negawatt represents one megawatt of power that has been saved through efficiency improvements, treated as equivalent to a megawatt of new generation capacity.
Question 2: Which climate-responsive design strategy uses high-mass exterior walls that absorb daytime solar heat and re-radiate it into living spaces at night?
- Trombe wall (Correct answer)
- Double-stud wall
- Structural insulated panel (SIP)
- Insulating concrete form (ICF)
Correct answer: Trombe wall
A Trombe wall is a south-facing masonry or concrete wall with glazing that absorbs solar heat during the day and releases it indoors in the evening.
Question 3: An energy model predicts a building's annual energy use. Which input change would most directly reduce predicted heating energy in a cold climate?
- Increasing plug load assumptions by 10%
- Improving window U-factor from 0.45 to 0.22 (Correct answer)
- Changing occupancy schedule from 8 AM–6 PM to 7 AM–7 PM
- Increasing lighting power density by 15%
Correct answer: Improving window U-factor from 0.45 to 0.22
Halving the window U-factor dramatically reduces conductive heat loss through the windows, which is a major heating load driver in cold climates.
Question 4: Which energy efficiency measure typically has the shortest simple payback in residential buildings?
- Adding attic insulation to current code levels
- Replacing single-pane windows with triple-pane units
- Air sealing accessible penetrations (attic, basement) (Correct answer)
- Installing a ground-source heat pump
Correct answer: Air sealing accessible penetrations (attic, basement)
Air sealing is low-cost and labor-light, often yielding 10–30% heating/cooling savings with paybacks of 1–3 years, outperforming capital-intensive measures.
Question 5: A peak demand charge on a commercial utility bill is based on:
- Total energy consumed over the billing month in kWh
- The highest average power demand measured during any 15- or 30-minute interval in the billing period (Correct answer)
- Power factor correction penalties assessed by the utility
- The number of hours the HVAC system operates above design temperature
Correct answer: The highest average power demand measured during any 15- or 30-minute interval in the billing period
Demand charges are assessed based on the single highest demand interval (often 15 minutes) in the month, incentivizing load leveling and peak reduction strategies.
Question 6: Which energy storage strategy is best suited for shifting residential air conditioning load from peak afternoon hours to overnight low-rate periods?
- Flywheel energy storage
- Ice storage thermal energy storage (TES) (Correct answer)
- Compressed air energy storage (CAES)
- Pumped hydro storage
Correct answer: Ice storage thermal energy storage (TES)
Ice storage systems freeze water overnight during off-peak hours and melt the ice during the day to provide cooling, reducing peak electrical demand.
Question 7: In whole-building energy performance rating systems like ENERGY STAR for commercial buildings, the score is based on:
- Absolute EUI compared to a fixed threshold
- Percentile ranking compared to similar buildings nationally using CBECS data (Correct answer)
- Compliance with prescriptive ASHRAE 90.1 requirements
- Number of green features installed divided by building square footage
Correct answer: Percentile ranking compared to similar buildings nationally using CBECS data
ENERGY STAR scores rank a building's EUI against its peer group from the Commercial Buildings Energy Consumption Survey (CBECS); a score of 75 or higher qualifies for certification.
NABCEP Energy Efficiency & Conservation Techniques 5
The 'negawatt' concept in demand-side management refers to: