CEA Energy Modeling & Simulation Tools 2 — Questions and Answers
Question 1: In EnergyPlus, what does the 'DesignDay' object primarily define?
- Peak outdoor conditions used for HVAC sizing calculations (Correct answer)
- Annual average weather data for energy simulation
- Equipment schedules for occupied and unoccupied periods
- Thermostat setpoint profiles throughout the year
Correct answer: Peak outdoor conditions used for HVAC sizing calculations
DesignDay objects in EnergyPlus specify extreme weather conditions (temperature, humidity, solar) used to size HVAC equipment at peak load.
Question 2: Which simulation time step setting in EnergyPlus provides the highest temporal resolution for HVAC system interactions?
- 60 minutes
- 30 minutes
- 15 minutes
- 6 minutes (Correct answer)
Correct answer: 6 minutes
EnergyPlus supports time steps down to 6 minutes (10 steps per hour), providing the finest resolution for capturing fast-changing HVAC dynamics.
Question 3: When calibrating a building energy model to measured utility data, what statistical metric is recommended by ASHRAE Guideline 14?
- R-squared (R²) only
- CV(RMSE) and NMBE (Correct answer)
- Mean Absolute Error (MAE) only
- Standard Deviation of residuals
Correct answer: CV(RMSE) and NMBE
ASHRAE Guideline 14 requires both CV(RMSE) ≤15% monthly and NMBE ≤5% monthly for calibrated simulation acceptance.
Question 4: In eQUEST, what is the primary purpose of the 'Wizard' interface compared to the 'Detailed Interface'?
- Wizard runs faster simulations with fewer zones
- Wizard guides users through simplified inputs for quick baseline models (Correct answer)
- Wizard is used exclusively for LEED certification submittals
- Wizard generates DOE-2 input files automatically without user review
Correct answer: Wizard guides users through simplified inputs for quick baseline models
eQUEST's Wizard walks users through a streamlined question-based setup to rapidly create a baseline building model before refinement in the Detailed Interface.
Question 5: What does the term 'thermal mass' represent in building energy simulation?
- The rate of air infiltration through the building envelope
- The capacity of materials to store and release heat over time (Correct answer)
- The maximum cooling load the HVAC system must meet
- The total insulation R-value of wall assemblies
Correct answer: The capacity of materials to store and release heat over time
Thermal mass refers to a material's ability to absorb, store, and slowly release heat, which can shift peak loads and reduce temperature swings.
Question 6: In OpenStudio, which file format contains the detailed building model data used by the EnergyPlus simulation engine?
- .osm (OpenStudio Model)
- .idf (Input Data File) (Correct answer)
- .epw (EnergyPlus Weather)
- .gbXML (Green Building XML)
Correct answer: .idf (Input Data File)
OpenStudio's .osm file is translated into an EnergyPlus .idf file, which is the actual input format read by the EnergyPlus simulation engine.
Question 7: What is the significance of the 'infiltration' input in a building energy model?
- It defines occupant metabolic heat gains
- It accounts for uncontrolled air leakage through the building envelope (Correct answer)
- It sets the ventilation rates for mechanical systems
- It determines solar heat gain through windows
Correct answer: It accounts for uncontrolled air leakage through the building envelope
Infiltration inputs model unintentional air leakage through cracks and gaps in the envelope, which affects both heating/cooling loads and indoor air quality.
CEA Energy Modeling & Simulation Tools 2
In EnergyPlus, what does the 'DesignDay' object primarily define?