HERS Energy Modeling and Analysis 2 — Questions and Answers
Question 1: In REM/Rate energy modeling software, what does the 'Reference Home' represent?
- The most energy-efficient home in a neighborhood
- A code-minimum baseline home built to IECC specifications used to calculate the HERS Index (Correct answer)
- The average energy consumption of homes in the same climate zone
- The builder's own home used as a comparison benchmark
Correct answer: A code-minimum baseline home built to IECC specifications used to calculate the HERS Index
The Reference Home is a code-minimum baseline constructed to IECC specifications against which the Rated Home is compared to calculate the HERS Index.
Question 2: Which input parameter has the greatest single influence on modeled heating energy consumption in a cold climate home?
- Window solar heat gain coefficient (SHGC)
- Envelope air leakage (ACH50) (Correct answer)
- Wall assembly R-value
- Heating system efficiency (AFUE)
Correct answer: Envelope air leakage (ACH50)
Envelope air leakage measured at ACH50 typically dominates heating load in cold climates because infiltration losses scale directly with the temperature difference.
Question 3: What is the purpose of the 'normalized modified end-use loads' (nMEUL) calculation in HERS rating?
- To estimate occupant utility bills
- To adjust end-use loads to account for equipment efficiency and fuel type for Index calculation (Correct answer)
- To compare homes of different square footages on a per-square-foot basis
- To normalize energy use across different climate zones
Correct answer: To adjust end-use loads to account for equipment efficiency and fuel type for Index calculation
nMEUL adjusts each end-use load by equipment efficiency and fuel-specific factors so that the HERS Index fairly represents source energy consumption.
Question 4: A rater models a home with R-38 attic insulation in a mixed-humid climate. The software shows cooling energy is higher than expected. Which input should be checked first?
- Attic insulation R-value entry
- Duct location and leakage values (Correct answer)
- Window U-factor
- Foundation wall insulation
Correct answer: Duct location and leakage values
Ducts located in an unconditioned attic with high leakage dramatically increase cooling loads in mixed-humid climates and are a common modeling oversight.
Question 5: In energy modeling, what is 'latent load' and why does it matter in humid climates?
- The structural weight load on HVAC equipment
- The energy required to remove moisture from indoor air, which drives cooling equipment sizing and runtime (Correct answer)
- The delayed response of a thermal mass wall to temperature changes
- The standby energy consumed by HVAC controls
Correct answer: The energy required to remove moisture from indoor air, which drives cooling equipment sizing and runtime
Latent load is the energy needed for dehumidification; in humid climates it can equal or exceed sensible cooling load and significantly affects equipment sizing and energy use.
Question 6: When entering window properties into energy modeling software, which combination of values most completely describes thermal and solar performance?
- R-value and visible transmittance (VT)
- U-factor and solar heat gain coefficient (SHGC) (Correct answer)
- SHGC and emissivity
- Glazing area and frame material
Correct answer: U-factor and solar heat gain coefficient (SHGC)
U-factor captures conductive/convective heat transfer while SHGC captures solar heat gain; together they fully define window energy performance in models.
Question 7: A HERS rater discovers that the modeled home's mechanical ventilation rate is set to zero in the software. What is the most likely consequence for the HERS Index?
- The Index will be artificially low because ventilation energy is not counted (Correct answer)
- The Index will be artificially high because the model assumes more infiltration to meet IAQ needs
- There is no effect because ventilation is not part of the HERS rating
- The Index will be accurate if the home's air leakage is below 3 ACH50
Correct answer: The Index will be artificially low because ventilation energy is not counted
Omitting mechanical ventilation energy undercounts the home's actual energy use, resulting in an artificially low HERS Index.
HERS Energy Modeling and Analysis 2
In REM/Rate energy modeling software, what does the 'Reference Home' represent?