HERS Energy Modeling & Analysis 3 — Questions and Answers
Question 1: A HERS rater measures duct leakage to outside at 8% of system airflow. How should this value be entered into the energy model?
- As total duct leakage including leakage to inside
- As leakage to outside only, separate from total leakage (Correct answer)
- As a duct efficiency multiplier between 0 and 1
- As an equivalent leakage area in square inches
Correct answer: As leakage to outside only, separate from total leakage
HERS software distinguishes leakage to outside (which affects conditioned air loss) from total duct leakage, and each is entered separately.
Question 2: Which insulation metric is required when modeling attic insulation in HERS software?
- Insulation material density in lb/ft³
- Total R-value of the insulation assembly (Correct answer)
- Insulation manufacturer model number
- Thermal mass in BTU/°F
Correct answer: Total R-value of the insulation assembly
HERS software uses the total R-value of the insulation assembly to calculate heat flow through the ceiling/attic boundary.
Question 3: In HERS energy modeling, what effect does increasing window-to-floor area ratio have on cooling loads in a hot climate?
- It decreases cooling load by admitting more daylight
- It generally increases cooling load due to higher solar heat gain (Correct answer)
- It has no effect if Low-E glazing is installed
- It decreases load because windows have lower thermal mass than walls
Correct answer: It generally increases cooling load due to higher solar heat gain
More window area in a hot climate increases solar heat gain and conductive gain, raising cooling loads even with Low-E glazing.
Question 4: What does 'ACH50' represent in the context of HERS energy modeling?
- Air changes per hour at 50 Pascals of pressure differential (Correct answer)
- Annual cooling hours when outdoor temperature exceeds 50°F
- Airflow capacity of the HVAC system at 50% load
- Average ceiling height divided by 50 for ventilation calculation
Correct answer: Air changes per hour at 50 Pascals of pressure differential
ACH50 is the blower door test result expressed as air changes per hour at a 50 Pascal pressure difference, used to characterize envelope airtightness.
Question 5: A modeler is entering a heat pump with a HSPF of 9.0 and a SEER of 16.0. Which value applies to the heating season calculation?
- SEER of 16.0
- HSPF of 9.0 (Correct answer)
- The average of HSPF and SEER
- COP derived from SEER only
Correct answer: HSPF of 9.0
HSPF (Heating Seasonal Performance Factor) is the efficiency metric for heat pump heating mode, while SEER applies only to cooling.
Question 6: When a HERS rater inputs conditioned floor area into the software, what spaces should be included?
- All floors of the home including the garage and unfinished basement
- Only heated areas above grade with finished flooring
- All space within the thermal boundary that is heated or cooled (Correct answer)
- Exterior decks and porches if they are enclosed
Correct answer: All space within the thermal boundary that is heated or cooled
Conditioned floor area includes all space within the thermal and pressure boundary that is intentionally heated or cooled, regardless of finish or grade level.
Question 7: How does HERS software typically account for thermal mass in a home with concrete block walls?
- Thermal mass is ignored in all standard HERS models
- Material density and specific heat are used to calculate heat storage capacity (Correct answer)
- Thermal mass is approximated by adding R-2 to the assembly R-value
- Concrete block walls are modeled identically to wood-frame walls
Correct answer: Material density and specific heat are used to calculate heat storage capacity
HERS software uses the material's density and specific heat capacity to model how concrete block walls store and release heat, affecting peak load timing.
HERS Energy Modeling & Analysis 3
A HERS rater measures duct leakage to outside at 8% of system airflow.
How should this value be entered into the energy model?