HERS Energy Modeling & Analysis 2 — Questions and Answers
Question 1: In REM/Rate or equivalent HERS software, what does the 'reference home' represent?
- The highest-performing home in the neighborhood
- A code-minimum home built to the same specifications as the rated home (Correct answer)
- The national average energy consumption for similar homes
- The rated home with all improvements applied
Correct answer: A code-minimum home built to the same specifications as the rated home
The reference home is a theoretical code-minimum version of the same home used as the baseline for calculating the HERS Index.
Question 2: Which parameter has the greatest impact on heating load calculations in cold climates when entering data into HERS software?
- Window SHGC value
- Wall assembly U-factor (Correct answer)
- Water heater efficiency rating
- Duct leakage to outside
Correct answer: Wall assembly U-factor
In cold climates, wall assembly U-factor directly drives conductive heat loss and dominates heating load calculations.
Question 3: When modeling a home with a sealed crawlspace in HERS software, how should the crawlspace be categorized?
- Unconditioned space with vented floor assembly
- Conditioned space with insulated walls (Correct answer)
- Exterior exposure equivalent to a slab
- Semi-conditioned with 50% heat loss factor
Correct answer: Conditioned space with insulated walls
A sealed crawlspace is modeled as conditioned space with insulation on the crawlspace walls rather than the floor above.
Question 4: A rater enters a furnace with AFUE of 0.96 into HERS software. What does the remaining 4% represent?
- Energy lost to flue gases and jacket losses (Correct answer)
- Energy used by the blower motor
- Standby pilot light consumption
- Duct distribution losses
Correct answer: Energy lost to flue gases and jacket losses
AFUE measures seasonal efficiency, and the 4% not converted to useful heat is lost through combustion exhaust and jacket radiation.
Question 5: Which of the following correctly describes how HERS software handles mechanical ventilation in the energy model?
- Ventilation energy use is excluded from the HERS Index calculation
- Ventilation fan watts and airflow are modeled as an energy load (Correct answer)
- Only exhaust-only systems are recognized by the software
- Ventilation is approximated using natural infiltration values only
Correct answer: Ventilation fan watts and airflow are modeled as an energy load
HERS software models mechanical ventilation by accounting for fan energy consumption and the conditioning load of outdoor air introduced.
Question 6: What is the purpose of entering an 'as-built' natural gas water heater's Energy Factor (EF) or Uniform Energy Factor (UEF) into HERS software?
- To determine the correct pipe insulation R-value
- To calculate annual domestic hot water energy consumption (Correct answer)
- To set the water heater's recovery time in the model
- To verify the unit meets combustion safety standards
Correct answer: To calculate annual domestic hot water energy consumption
EF/UEF is used by the model to estimate annual energy use for water heating based on efficiency, fuel type, and household demand.
Question 7: When modeling a home with photovoltaic (PV) panels in HERS software for a HERS Index calculation, what is the standard treatment of PV output?
- PV output is ignored entirely in standard HERS ratings
- PV generation offsets rated home energy use and can reduce the HERS Index below zero (Correct answer)
- PV is entered only for the reference home calculation
- PV output replaces the need to model mechanical systems
Correct answer: PV generation offsets rated home energy use and can reduce the HERS Index below zero
Under RESNET guidelines, on-site PV generation is credited against the home's energy use and can drive the HERS Index to zero or below (a 'zero energy' or 'energy positive' home).
HERS Energy Modeling & Analysis 2
In REM/Rate or equivalent HERS software, what does the 'reference home' represent?