CEA Building Systems & Energy Efficiency 4 — Questions and Answers
Question 1: Which type of lighting control provides the greatest energy savings in private offices?
- Dimming ballasts without sensors
- Occupancy/vacancy sensors with auto-off
- Daylight harvesting with continuous dimming (Correct answer)
- Scheduled time-of-day switching
Correct answer: Daylight harvesting with continuous dimming
Daylight harvesting with continuous dimming reduces electric light output in proportion to available daylight, providing savings throughout occupied hours rather than only when spaces are unoccupied.
Question 2: A chilled water system is being converted from a constant-flow to a variable primary flow system. The primary benefit is:
- Higher chiller COP at full load
- Reduced pump energy through variable speed operation (Correct answer)
- Elimination of cooling towers
- Lower chilled water supply temperature
Correct answer: Reduced pump energy through variable speed operation
Variable primary flow eliminates the need for a primary/secondary decoupler and allows pump speeds to vary with load, drastically reducing pump energy via the affinity cube law.
Question 3: What is the Solar Heat Gain Coefficient (SHGC) of a window?
- The fraction of incident solar radiation transmitted through the window as heat (Correct answer)
- The U-factor adjusted for solar exposure
- The ratio of visible light to total solar transmittance
- A measure of frame thermal conductance
Correct answer: The fraction of incident solar radiation transmitted through the window as heat
SHGC represents the fraction of incident solar energy (both direct transmission and absorbed/re-emitted) that enters the building as heat; lower SHGC reduces cooling loads.
Question 4: An energy audit reveals that a compressed air system has a leak rate of 25%. What is the best first step to reduce this waste?
- Install a larger compressor
- Conduct a leak detection survey and repair leaks (Correct answer)
- Reduce system pressure by 20 psi
- Replace reciprocating with centrifugal compressors
Correct answer: Conduct a leak detection survey and repair leaks
Leak detection (using ultrasonic detectors or soap solution) and prompt repair is the highest-priority, lowest-cost measure for compressed air systems, typically with paybacks under one year.
Question 5: In energy modeling, what is the purpose of a 'baseline' building model under ASHRAE 90.1 Appendix G?
- To simulate worst-case weather conditions
- To establish a code-compliant reference against which proposed design savings are measured (Correct answer)
- To predict peak demand for utility sizing
- To calculate embodied carbon of materials
Correct answer: To establish a code-compliant reference against which proposed design savings are measured
The Appendix G baseline model represents a code-minimum building and is used to calculate the percentage energy cost savings of the proposed design for programs like LEED.
Question 6: Which heat pump type is generally most efficient in climates with ground temperatures between 45–75°F year-round?
- Air-source heat pump
- Ground-source (geothermal) heat pump (Correct answer)
- Water-to-water heat pump using cooling tower
- Absorption heat pump
Correct answer: Ground-source (geothermal) heat pump
Ground-source heat pumps exchange heat with stable ground temperatures, avoiding the efficiency penalties of air-source systems during extreme outdoor temperatures.
Question 7: A roof membrane with a solar reflectance of 0.75 and thermal emittance of 0.90 is classified as a 'cool roof.' This primarily reduces:
- Roof conductive U-factor
- Cooling loads by reducing solar heat absorbed by the roof surface (Correct answer)
- Roof membrane longevity
- Precipitation runoff
Correct answer: Cooling loads by reducing solar heat absorbed by the roof surface
High solar reflectance rejects most incident solar radiation before it converts to heat, reducing roof surface temperatures and the conductive heat flux into the building below.
CEA Building Systems & Energy Efficiency 4
Which type of lighting control provides the greatest energy savings in private offices?