CEA Building Systems & Energy Efficiency 3 — Questions and Answers
Question 1: A boiler operates at 78% thermal efficiency. If the boiler input is 1,000 MBH, what is the useful heat output?
- 780 MBH (Correct answer)
- 1,280 MBH
- 220 MBH
- 1,000 MBH
Correct answer: 780 MBH
Useful output = input × efficiency = 1,000 MBH × 0.78 = 780 MBH; the remaining 220 MBH is lost through flue gases and jacket losses.
Question 2: What does ASHRAE 90.1 primarily regulate for commercial buildings?
- Indoor air quality minimum ventilation rates
- Energy efficiency design requirements for building envelope, HVAC, lighting, and service water heating (Correct answer)
- Fire and life safety egress requirements
- Occupant comfort temperature setpoints
Correct answer: Energy efficiency design requirements for building envelope, HVAC, lighting, and service water heating
ASHRAE 90.1 is the Energy Standard for Buildings Except Low-Rise Residential Buildings, setting minimum efficiency requirements for envelope, HVAC, lighting, and SWH systems.
Question 3: Which control strategy directly reduces plug load energy consumption in an office?
- Occupancy-based power strip switching (Correct answer)
- Demand-controlled ventilation
- Variable speed drives on fans
- Window shading controls
Correct answer: Occupancy-based power strip switching
Occupancy-based smart power strips cut power to workstation peripherals when a workstation is unoccupied, directly targeting plug and process loads.
Question 4: In a heat recovery ventilation (HRV) system, what is the function of the heat exchanger core?
- Filter particulates from outdoor air
- Transfer heat between exhaust and supply air streams without mixing them (Correct answer)
- Boost supply air humidity in summer
- Preheat domestic hot water
Correct answer: Transfer heat between exhaust and supply air streams without mixing them
The HRV core transfers sensible heat (and in ERV systems, moisture) from the warmer exhaust stream to the cooler supply stream, recovering energy that would otherwise be wasted.
Question 5: What is the 'stack effect' in tall buildings and how does it affect energy use?
- Warm air rises creating pressure differentials that drive infiltration and increase heating/cooling loads (Correct answer)
- Cool air sinking increases basement cooling loads
- Stack effect only occurs in industrial chimneys
- It reduces elevator energy by using air pressure assistance
Correct answer: Warm air rises creating pressure differentials that drive infiltration and increase heating/cooling loads
Stack effect creates a buoyancy-driven pressure difference that forces warm air out at upper floors and draws cold outdoor air in at lower floors, significantly increasing heating energy in winter.
Question 6: A facility manager wants to benchmark energy performance against similar buildings. Which tool should they use?
- ASHRAE 90.1 compliance calculator
- ENERGY STAR Portfolio Manager (Correct answer)
- DOE EnergyPlus simulation software
- LEED credit calculator
Correct answer: ENERGY STAR Portfolio Manager
ENERGY STAR Portfolio Manager is the EPA's free online tool for tracking and benchmarking energy and water consumption relative to similar buildings nationwide.
Question 7: In demand-controlled ventilation (DCV), CO₂ sensors are used to:
- Detect fire and activate smoke control
- Modulate outdoor air intake based on actual occupancy levels (Correct answer)
- Monitor boiler combustion efficiency
- Control chiller staging
Correct answer: Modulate outdoor air intake based on actual occupancy levels
DCV uses CO₂ as a surrogate for occupancy; when CO₂ rises above setpoint, outdoor airflow increases, saving fan and conditioning energy during low-occupancy periods.
CEA Building Systems & Energy Efficiency 3
A boiler operates at 78% thermal efficiency.
If the boiler input is 1,000 MBH, what is the useful heat output?