HERS Energy Modeling Software 3 — Questions and Answers
Question 1: In HERS rating software, how is the Solar Heat Gain Coefficient (SHGC) of windows used in the energy model?
- It determines window condensation risk only
- It quantifies solar energy transmitted through the glass, affecting cooling and heating loads (Correct answer)
- It is used only for passive solar home designs
- It replaces the U-factor for climate zones 1–3
Correct answer: It quantifies solar energy transmitted through the glass, affecting cooling and heating loads
SHGC determines what fraction of solar radiation passes through the window, directly affecting the model's solar gain calculations for heating and cooling.
Question 2: A rater is modeling a home with two HVAC systems serving different zones. How should this be entered in REM/Rate?
- Average the efficiencies of both systems into a single entry
- Enter each system separately and assign the conditioned area each system serves (Correct answer)
- Model only the primary system and note the secondary in comments
- Enter the combined tonnage as one system with blended SEER
Correct answer: Enter each system separately and assign the conditioned area each system serves
REM/Rate supports multiple HVAC systems, and each should be entered separately with its served area to accurately model zoned performance.
Question 3: Which of the following correctly describes how HERS software handles a heat pump water heater?
- It is modeled identically to a standard electric resistance water heater
- It is entered with an Energy Factor or Uniform Energy Factor reflecting its COP-based efficiency (Correct answer)
- It is excluded from HERS calculations as a plug load
- It uses the same efficiency multiplier as an air-source heat pump for space heating
Correct answer: It is entered with an Energy Factor or Uniform Energy Factor reflecting its COP-based efficiency
Heat pump water heaters are entered with their EF or UEF rating, which captures their higher efficiency compared to electric resistance units.
Question 4: When modeling mechanical ventilation in REM/Rate, what information is required to correctly characterize an HRV?
- Only the CFM capacity of the unit
- CFM capacity, sensible heat recovery efficiency, and fan watt draw (Correct answer)
- Brand name and model number only
- Duct length and filter type
Correct answer: CFM capacity, sensible heat recovery efficiency, and fan watt draw
HRV modeling requires airflow rate, sensible recovery efficiency, and fan power consumption to accurately calculate ventilation energy impact.
Question 5: What is the effect of entering a lower heating system AFUE in HERS software?
- The HERS Index decreases because the system runs less
- The HERS Index increases because more fuel is consumed per unit of heat delivered (Correct answer)
- AFUE only affects cooling season calculations
- The software flags it as an error if below code minimum
Correct answer: The HERS Index increases because more fuel is consumed per unit of heat delivered
Lower AFUE means the furnace wastes more energy as exhaust heat, increasing annual fuel consumption and raising the HERS Index.
Question 6: In energy modeling software, what is the primary function of the 'orientation' input for a home?
- To determine prevailing wind direction for infiltration modeling
- To calculate solar gains on each window and wall surface based on compass direction (Correct answer)
- To assign local utility rates by geographic zone
- To set daylight saving time adjustments in the simulation
Correct answer: To calculate solar gains on each window and wall surface based on compass direction
Home orientation determines the angle of incidence of solar radiation on each surface, affecting solar heat gain and daylighting calculations.
Question 7: Which output metric in REM/Rate directly tells a rater how much of the HERS Index penalty comes from excess air leakage?
- Total source energy use
- Component contribution report showing infiltration's share of energy load (Correct answer)
- Duct leakage to outside (CFM25out)
- Annual heating degree days
Correct answer: Component contribution report showing infiltration's share of energy load
REM/Rate's component contribution breakdown isolates each building element's contribution to the HERS Index, including the infiltration penalty.
HERS Energy Modeling Software 3
In HERS rating software, how is the Solar Heat Gain Coefficient (SHGC) of windows used in the energy model?