Energy Modeling & Analysis Flashcards

In REM/Rate or equivalent HERS software, what does the 'reference home' represent?

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.

Which parameter has the greatest impact on heating load calculations in cold climates when entering data into HERS software?

Answer: Wall assembly U-factor

In cold climates, wall assembly U-factor directly drives conductive heat loss and dominates heating load calculations.

When modeling a home with a sealed crawlspace in HERS software, how should the crawlspace be categorized?

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.

A rater enters a furnace with AFUE of 0.96 into HERS software. What does the remaining 4% represent?

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.

Which of the following correctly describes how HERS software handles mechanical ventilation in the energy model?

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.

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?

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.

When modeling a home with photovoltaic (PV) panels in HERS software for a HERS Index calculation, what is the standard treatment of PV output?

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).

A HERS rater measures duct leakage to outside at 8% of system airflow. How should this value be entered into the energy model?

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.

Which insulation metric is required when modeling attic insulation in HERS software?

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.

In HERS energy modeling, what effect does increasing window-to-floor area ratio have on cooling loads in a hot climate?

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.

What does 'ACH50' represent in the context of HERS energy modeling?

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.

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?

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.

When a HERS rater inputs conditioned floor area into the software, what spaces should be included?

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.

How does HERS software typically account for thermal mass in a home with concrete block walls?

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.

A rater is modeling a two-story home where the second floor overhangs the first floor by 2 feet. How does this overhang affect the energy model?

Answer: It creates an exposed floor assembly that must be modeled with appropriate R-value and area

A cantilevered floor exposed to outside air must be modeled as a separate exposed floor assembly with its own insulation R-value and square footage.

Which HERS software input directly affects the calculated internal gains used in the energy model?

Answer: Number of bedrooms

RESNET protocols use the number of bedrooms as a proxy for occupant count and appliance loads, which determines internal heat gain inputs.

When modeling a gas fireplace in HERS software, what efficiency value is typically entered?

Answer: The Annual Fuel Utilization Efficiency (AFUE) for the fireplace insert

Gas fireplace inserts with documented AFUE values are modeled using that efficiency; otherwise RESNET default values are applied.

A HERS rater is analyzing a home with both a gas furnace and an electric air conditioner sharing the same duct system. How should this be modeled?

Answer: Enter both systems separately, sharing the same duct leakage inputs

Split HVAC systems are modeled by entering the heating and cooling equipment separately while linking them to the same duct system distribution inputs.

What is the significance of the 'heating degree days' (HDD) value used in HERS energy modeling?

Answer: It quantifies the cumulative heating demand of the local climate over a heating season

HDD reflects how cold and how long winters are at the site, directly influencing the magnitude of annual heating energy calculations in the model.

In HERS modeling software, what is meant by 'distribution system efficiency' for a forced-air system?

Answer: The fraction of heating or cooling energy delivered to conditioned space after duct losses

Distribution efficiency accounts for duct conduction and leakage losses, representing what fraction of the system's output actually reaches the conditioned living space.