Energy Modeling and Analysis Flashcards

In REM/Rate energy modeling software, what does the 'Reference Home' represent?

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.

Which input parameter has the greatest single influence on modeled heating energy consumption in a cold climate home?

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.

What is the purpose of the 'normalized modified end-use loads' (nMEUL) calculation in HERS rating?

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.

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?

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.

In energy modeling, what is 'latent load' and why does it matter in humid climates?

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.

When entering window properties into energy modeling software, which combination of values most completely describes thermal and solar performance?

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.

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?

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.

What is the RESNET-defined default internal gains assumption used in HERS energy modeling for occupancy?

Answer: Standard occupancy is set at 0.5 + (CFA/100)^0.43 persons as defined in ANSI/RESNET/ICC 301

ANSI/RESNET/ICC 301 specifies occupancy as 0.5 + (CFA/100)^0.43, ensuring larger homes have proportionally more occupants in the reference calculation.

Which climate zone designation system is used by RESNET's ANSI/RESNET/ICC 301 standard for HERS energy modeling inputs?

Answer: IECC climate zones (1-8 with moisture designations A, B, C)

HERS ratings use IECC climate zones 1–8 with moisture designations (A=moist, B=dry, C=marine) as defined in the IECC and referenced by ANSI/RESNET/ICC 301.

A home has a cathedral ceiling with R-30 insulation between rafters. How should this be entered differently from a standard attic assembly in most energy modeling software?

Answer: Cathedral ceilings are entered as a roof/ceiling assembly without an attic air space, using the assembly R-value directly

Cathedral ceilings lack an attic buffer zone, so they are entered as a direct roof/ceiling assembly with the actual installed R-value and no attic air space node.

In HERS modeling, how is a home with a walkout basement partially below grade typically handled for foundation inputs?

Answer: Above-grade portions are modeled as walls and below-grade portions as basement walls with appropriate soil contact fractions

Software requires separate modeling of above-grade and below-grade wall fractions because heat loss rates differ significantly based on soil contact depth.

What effect does increasing the number of bedrooms have on the Reference Home's water heating energy in HERS calculations?

Answer: More bedrooms increase the assumed number of occupants, which increases hot water consumption in the Reference Home

ANSI/RESNET/ICC 301 ties hot water usage to bedroom count as a proxy for occupancy, so the Reference Home's water heating load increases with bedroom count.

A rater is modeling a home with a ground-source heat pump. Which COP value should be used in the energy model?

Answer: The site-specific COP determined by ground loop entering water temperature and manufacturer performance data

Ground-source heat pump performance varies with entering water temperature, so the model should use manufacturer performance data matched to the site's ground loop conditions.

Which metric does energy modeling software use to quantify thermal bridging through wood-framed walls?

Answer: Framing fraction combined with stud and cavity R-values to calculate an assembly U-factor

Software calculates an assembly U-factor by combining the framing fraction (typically 0.25 for 16" o.c. framing), stud R-value, and cavity insulation R-value in a parallel-path calculation.

What is the primary purpose of TMY (Typical Meteorological Year) weather data files in HERS energy modeling?

Answer: To represent a statistically typical year of hourly weather data used to simulate annual energy consumption

TMY files contain representative hourly data assembled from multiple years to reflect typical (not extreme) conditions, enabling accurate annual energy simulation.

A HERS rater is modeling a home with an ERV (Energy Recovery Ventilator). Which additional performance value beyond airflow rate must be entered to accurately model energy recovery?

Answer: The sensible recovery efficiency (SRE) and total recovery efficiency (TRE) or sensible and latent effectiveness values

Accurate ERV modeling requires sensible and total (or latent) recovery efficiencies to quantify how much heating and cooling energy is recaptured from exhaust air.

In the context of HERS ratings, what is 'source energy' and how does it differ from 'site energy'?

Answer: Site energy is measured at the home; source energy accounts for generation and transmission losses back at the power plant

Site energy is measured at the meter, while source energy traces consumption back through generation and transmission, using fuel-specific site-to-source multipliers.

How does HERS modeling handle the energy contribution of a photovoltaic (PV) system when calculating the HERS Index?

Answer: PV generation offsets the home's rated energy use, potentially resulting in a HERS Index below zero for net-zero or net-positive homes

Per ANSI/RESNET/ICC 301, PV generation is credited against the Rated Home's energy use and can produce a HERS Index of zero or below for homes that generate as much or more than they consume.

What modeling approach is used for mass walls (e.g., concrete masonry) that is different from light-frame wood walls?

Answer: Mass walls require dynamic thermal mass properties (heat capacity) in addition to R-value to accurately model time-delayed heat transfer

Thermal mass stores and releases heat with a time delay, so accurate modeling requires both R-value and heat capacity inputs to capture the mass wall's dynamic buffering effect.

A rater models two identical homes except one has east/west-facing glazing and the other has south/north-facing glazing. In a heating-dominated climate, which will likely have a lower HERS Index?

Answer: The south/north-facing home because south windows maximize passive solar gains in winter

South-facing windows capture winter solar gains more effectively than east/west windows, reducing heating energy and lowering the HERS Index in heating-dominated climates.