Proposed Envelope Performance Factor Calculation

Space Conditioning Requirements

Conditioned Spaces

All conditioned spaces in the proposed design shall be simulated with both heating and cooling systems, regardless of the actual systems installed in the building. This requirement applies even when the design includes only heating or only cooling equipment.

Temperature control set points and operating schedules shall match those specified in the building envelope trade-off schedules for the applicable building area type. These schedules provide standardized assumptions for consistent modeling across different designs.

Semiheated Spaces

Semiheated spaces shall be simulated with heating only. No cooling system shall be modeled for these spaces.

The heating temperature set point for all semiheated spaces shall be 10°C (50°F) and shall remain constant for all hours of operation.

Model Geometry and Thermal Zones

Zone Creation Process

Step 1: Calculate Floor-to-Wall Ratio (Rc)

For each unique combination of space conditioning category and building area type, determine the ratio (Rc) of floor area to gross wall area. The index "c" refers to the specific combination of space conditioning category and building area type as defined for each surface.

Step 2: Create Perimeter Zones

Create a perimeter zone for each unique combination of building area type, above-grade wall orientation, and space conditioning category.

When multiple above-grade wall assemblies exist for a given building area type and orientation, place each assembly end-to-end in the order defined.

The area of each perimeter zone shall be calculated as the gross wall area of the zone multiplied by Rc, with a maximum value of 1.25 times the gross wall area.

Step 3: Create Interior Zones

When Rc exceeds 1.25 for any unique combination of space conditioning category and building area type, create interior zones for use in the trade-off procedure.

The area of each interior zone shall equal the total area for that combination of space conditioning category and building area type, minus the area of all associated perimeter zones.

Step 4: Create Below-Grade Zones

Create a below-grade zone for each unique combination of space conditioning category and building area type associated with below-grade walls.

When multiple below-grade wall assemblies exist for a given building area type, place each assembly end-to-end in the order defined.

The area of each below-grade zone shall be calculated as the gross wall area of the zone multiplied by Rc, with a maximum value of 1.25 times the gross wall area.

These requirements establish uniform operating conditions for energy modeling. By standardising the presence of heating and cooling systems and their operating parameters, the model evaluates building envelope performance under consistent thermal conditions, enabling fair comparison between proposed and baseline designs.

Zone Dimensions and Geometry

Zone Height

The wall height and the height of each thermal zone shall be 4.6 m (15 feet).

Roof and Floor Distribution

Roof area and floor area associated with each building area type shall be prorated among all zones of the corresponding building area type in proportion to each zone's area.

Roof area and floor area in each zone shall be centered in the horizontal plane of the zone with the same aspect ratio as the horizontal plane of the zone.

Slab-on-Grade Perimeter

Slab-on-grade floor perimeter associated with each building area type shall be prorated among perimeter zones of the corresponding building area type in proportion to each zone's area.

Fenestration Assignment

Vertical Fenestration (Windows)

Vertical fenestration area shall be assigned to the associated surface as described in Section C1.4.

Vertical fenestration shall be centered on the associated surface with the same aspect ratio as the associated surface.

Windows with equivalent U-factor, SHGC, and visible transmittance (VT) that do not include fins may be combined into a single window on the associated surface.

Skylights

Skylight area shall be assigned to the associated surface as described in Section C1.4.

Skylight area shall be prorated among interior zones containing the associated roof area, in proportion to the roof area in each zone.

If total skylight area exceeds the associated roof area in interior zones, the remaining skylight area shall be prorated among perimeter zones containing the associated roof area, in proportion to the roof area in each zone.

Zone Boundaries

Each zone shall be modeled as fully enclosed. Zone boundaries not created as described above shall be modeled as adiabatic interior surfaces (no heat transfer across zone boundaries).

Energy models by standardizing how buildings are divided into thermal zones, which is essential for code compliance calculations and building performance comparison.

These requirements establish standardised zone geometry and surface distributions, ensuring consistent modeling of thermal masses, edge effects, and fenestration placement across different building designs. The fixed zone height and proportional allocation methods eliminate geometric variations that would otherwise complicate envelope performance comparisons. Adiabatic zone boundaries isolate envelope-driven loads from inter-zone heat transfer, focusing the evaluation on the thermal performance of surfaces separating conditioned spaces from exterior conditions.

Daylight Area and Photosensor Location

Residential Zones

Daylight areas and photosensors shall not be modeled in residential zones.

Nonresidential Zones

In each nonresidential zone, daylight areas and photosensor locations shall be modeled according to the requirements below.

Daylight Areas from Vertical Fenestration (Windows)

For each nonresidential zone associated with vertical fenestration, the daylight area shall be modeled as directly adjacent to the vertical fenestration.

The daylight area dimensions shall be:

• Width: Equal to the width of the vertical fenestration

• Depth: Equal to the head height of the vertical fenestration

Daylight Areas from Skylights

In each nonresidential zone associated with skylights, the daylight area under skylights shall be modeled as a bounded zone extending from the skylight edges.

The daylight area shall extend in each direction from the edge of the skylight area by:

• 3 m (10 feet), or

• The distance to the edge of the zone, whichever is less

Photosensor Location for Vertical Fenestration

For each daylight area associated with vertical fenestration, a photosensor shall be modeled at the following location:

• Horizontal position: Center of the daylight area width

• Distance from window: At the depth of the daylight area

• Height: 0.91 m (3 feet) above the floor

Photosensor Location for Skylights

For each daylight area associated with a skylight, a photosensor shall be modeled at the following location:

• Horizontal position: Center of the skylight's horizontal plane

• Height: 1.5 m (5 feet) above the floor

These requirements establish standardised locations for daylight zones and photosensors, ensuring consistent evaluation of daylighting control systems across different building designs.

Schedules

Schedule types assumed in Section C3.1.1(c) shall be required input for the energy model.

All schedules shall be consistent with those specified in the building envelope trade-off schedules and loads for the applicable building area type.

This requirement ensures that operational schedules (such as occupancy, lighting, equipment use, and thermostat setpoints) remain standardized across energy models, enabling fair comparison between proposed and baseline designs based on building area type classifications.

Building Envelope

The building envelope shall be modeled to reflect the information specified in Section C1.

Floor Area Requirements

The total floor area of the building shall be specified and broken down by:

• Space conditioning categories

• Building area type

Building Area Type Selection

Each building area type shall be selected from the classifications listed below.

Building Area Type	LPD, W/m2
Automotive facility	8.0
Convention center	6.8
Courthouse	8.4
Dining: Bar lounge/leisure	8.6
Dining: Cafeteria/fast food	8.1
Dining: Family	7.6
Dormitory	5.7
Exercise center	7.7
Fire station	6.0
Gymnasium	8.2
Health-care clinic	8.7
Hospital	10.3
Hotel/motel	6.0
Library	9.0
Manufacturing facility	8.9
Motion picture theater	4.8
Multifamily	4.9
Museum	5.9
Office	6.8
Parking garage	2.0
Penitentiary	7.4
Performing arts theater	9.0
Police station	7.1
Post office	7.0
Religious facility	7.2
Retail	9.1
School/university	7.8
Sports arena	8.1
Town hall	7.5
Transportation	5.4
Warehouse	4.9
Workshop	9.8

When three-year-aged test data for the solar reflectance and three-year-aged thermal emittance of the exterior roof surface are unavailable, the exterior roof surface shall be modeled with the following default values - Solar reflectance: 0.30 and Thermal emittance: 0.90.

This requirement ensures that the building envelope characteristics and floor area distributions are accurately represented in the energy model, with building area types standardized according to the classifications provided

Shading

Interior Shades

Manually operated interior shades shall be modeled on all vertical fenestration.

Shade Operation

Shades shall be modeled to lower when either of the following conditions occurs:

• Transmitted luminance exceeds 2000 cd/m² (candelas per square meter), or

• Direct solar transmitted energy exceeds 95 W/m²

Once lowered, shades shall remain in the lowered position for the remainder of the day.

Shade Properties

Shades shall be modeled with the following optical properties:

• Visible light transmittance: 0.10

• Visible light reflectance: 0.40

• Solar transmittance: 0.21

• Solar reflectance: 0.23

Permanent Shading Devices

Permanent shading devices such as fins and overhangs shall be modeled as part of the building geometry.

Dynamic Glazing

Automatically controlled dynamic glazing is allowed to be modeled with its full control capabilities.

Manually controlled dynamic glazing shall be modeled using the average of the minimum and maximum values for both:

• Solar Heat Gain Coefficient (SHGC)

• Visible Transmittance (VT)

Air Leakage

Building Envelope Air Leakage Rate

The air leakage rate of the building envelope (I₇₅Pa) at a pressure differential of 75 Pa shall be 2.03 L/s·m² of building envelope area.

Air Leakage Conversion

The air leakage of the building envelope shall be converted to describe air leakage as a function of the area of above-grade walls that separate conditioned spaces and semiheated spaces from the exterior.

The conversion formula is:

$$I_{AGW} = 0.112 \times I_{75Pa} \times S/A_{AGW}$$

Where:

• I₇₅Pa = air leakage rate of the building envelope (L/s·m²) at a fixed building pressure differential of 75 Pa

• S = total area of the building envelope (m²), including the lowest floor, any below-grade walls or above-grade walls, and roof (including vertical fenestration and skylights)

• IAGW = adjusted air leakage rate of the building envelope (L/s·m²) at a reference wind speed of 4.47 m/s, relative to the area of above-grade walls

• AAGW = total area of above-grade walls that comprise the building envelope (m²)

If the simulation program cannot simulate air leakage as a function of the area of walls that separate conditioned spaces and semiheated spaces from the exterior, the air leakage of the building envelope shall be converted to the appropriate units to describe the air leakage as a function of gross floor area as follows:

IFLR = 0.112 × I75Pa × S/AFLR

• IFLR​ = adjusted air leakage rate of the building envelope (L/s·m²) at a reference wind speed of 4.47 m/s, relative to the gross floor area

• AFLRA_{FLR} AFLR​ = gross floor area (m²)

These requirements establish standardized assumptions for shading device operation, dynamic glazing control, and air leakage characteristics, ensuring consistent evaluation of envelope performance across different building designs.

Infiltration Schedule

Infiltration shall be adjusted in accordance with the infiltration schedule specified in the building envelope trade-off schedules and loads for the applicable building area type.

This requirement ensures that infiltration rates vary according to standardized schedules that reflect typical building operation patterns, such as reduced infiltration during occupied hours when HVAC systems pressurize the building, and increased infiltration during unoccupied hours.

Interior Surfaces

Interior surfaces shall be modeled with the following visible light reflectances:

• Ceilings: 0.80

• Walls: 0.50

• Floors: 0.20

Interior surfaces shall be modeled with a thermal emittance of 0.90.

These standardised reflectance and emittance values ensure consistent modeling of interior surface properties across different building designs.

Lighting

Lighting Power Density

The modeled lighting power shall be determined using the lighting power density allowances for the applicable building area type.

Lighting Schedule

The modeled lighting power shall be adjusted in accordance with the lighting schedule specified in the building envelope trade-off schedules and loads for the applicable building area type.

Daylight Dimming Controls

50% of lighting in daylight areas shall be modeled with continuous daylight dimming controls.

Dimming Operation

When sufficient daylight is available at the corresponding photosensor, lighting power shall be reduced to maintain the following illuminance levels:

• Conditioned spaces: Minimum 50 fc (footcandles)

• Semiheated spaces: Minimum 30 fc (footcandles)

Dimming Performance Characteristics

The continuous daylight dimming system shall be modeled with the following characteristics:

Minimum light output: 6% of peak light output

Power input relationship:

• At minimum light output (6%): Power input = 20% of lighting power

• At peak light output (100%): Power input = 100% of lighting power

• Between minimum and peak: Power input scales linearly

These requirements establish standardised lighting power densities, operating schedules, and daylight dimming performance characteristics to ensure consistent evaluation of daylighting benefits across different building designs.

HVAC Systems

One HVAC system shall be provided for each thermal zone and shall have the following characteristics:

Fan Control

Constant-volume fan control.

Cooling System

Electrically provided cooling with Coefficient of Performance (COP) from the tables below, based on requirements for split-system air conditioners with heating section type "all other" between 19 kW and 40 kW.

Air Conditioners, Air Cooled

Less than 19 kW

Size Category	Heating Section Type	Subcategory or Rating Condition	Minimum Efficiency
<19 kW	All	Split system, three phase and applications outside U.S. single phase	3.81 SCOP_C (before 1/1/2023)<br>3.93 SCOP2_C (after 1/1/2023)
<19 kW	All	Single-package, three phase and applications outside U.S. single phase	4.10 SCOP_C (before 1/1/2023)<br>3.93 SCOP2_C (after 1/1/2023)

19 kW to <40 kW

Size Category	Heating Section Type	Subcategory or Rating Condition	Minimum Efficiency
≥19 kW and <40 kW	Electric resistance (or none)	Split system and single package	3.28 COP_C<br>3.78 ICOP_C (before 1/1/2023)<br>4.34 ICOP_C (after 1/1/2023)
≥19 kW and <40 kW	All other	Split system and single package	3.22 COP_C<br>3.76 ICOP_C (before 1/1/2023)<br>4.28 ICOP_C (after 1/1/2023)

40 kW to <70 kW

Size Category	Heating Section Type	Subcategory or Rating Condition	Minimum Efficiency
≥40 kW and <70 kW	Electric resistance (or none)	Split system and single package	3.22 COP_C<br>3.63 ICOP_C (before 1/1/2023)<br>4.16 ICOP_C (after 1/1/2023)
≥40 kW and <70 kW	All other	Split system and single package	3.17 COP_C<br>3.58 ICOP_C (before 1/1/2023)<br>4.10 ICOP_C (after 1/1/2023)

70 kW to <223 kW

Size Category	Heating Section Type	Subcategory or Rating Condition	Minimum Efficiency
≥70 kW and <223 kW	Electric resistance (or none)	Split system and single package	2.93 COP_C<br>3.40 ICOP_C (before 1/1/2023)<br>3.87 ICOP_C (after 1/1/2023)
≥70 kW and <223 kW	All other	Split system and single package	2.87 COP_C<br>3.34 ICOP_C (before 1/1/2023)<br>3.81 ICOP_C (after 1/1/2023)

223 kW and Greater

Size Category	Heating Section Type	Subcategory or Rating Condition	Minimum Efficiency
≥223 kW	Electric resistance (or none)	Split system and single package	2.84 COP_C<br>3.28 ICOP_C (before 1/1/2023)<br>3.66 ICOP_C (after 1/1/2023)
≥223 kW	All other	Split system and single package	2.78 COP_C<br>3.22 ICOP_C (before 1/1/2023)<br>3.60 ICOP_C (after 1/1/2023)

Space Constrained, Air Cooled

Size Category	Heating Section Type	Subcategory or Rating Condition	Minimum Efficiency
≤9 kW	All	Split system, three phase and applications outside U.S. single phase	3.52 SCOP_C (before 1/1/2023)<br>3.43 SCOP2_C (after 1/1/2023)
≤9 kW	All	Single package, three phase and applications outside U.S. single phase	3.52 SCOP_C (before 1/1/2023)<br>3.43 SCOP2_C (after 1/1/2023)

Small Duct, High Velocity, Air Cooled

Size Category	Heating Section Type	Subcategory or Rating Condition	Minimum Efficiency
<19 kW	All	Split system, three phase and applications outside U.S. single phase	3.52 SCOP_C (before 1/1/2023)<br>3.52 SCOP2_C (after 1/1/2023)

Air Conditioners, Water Cooled

Size Category	Heating Section Type	Subcategory or Rating Condition	Minimum Efficiency
<19 kW	All	Split system and single package	3.55 COP_C<br>3.60 ICOP_C
≥19 kW and <40 kW	Electric resistance (or none)	Split system and single package	3.55 COP_C<br>4.07 ICOP_C
≥19 kW and <40 kW	All other	Split system and single package	3.49 COP_C<br>4.02 ICOP_C
≥40 kW and <70 kW	Electric resistance (or none)	Split system and single package	3.66 COP_C<br>4.07 ICOP_C
≥40 kW and <70 kW	All other	Split system and single package	3.60 COP_C<br>4.02 ICOP_C
≥70 kW and <223 kW	Electric resistance (or none)	Split system and single package	3.63 COP_C<br>3.99 ICOP_C
≥70 kW and <223 kW	All other	Split system and single package	3.58 COP_C<br>3.93 ICOP_C
≥223 kW	Electric resistance (or none)	Split system and single package	3.58 COP_C<br>3.96 ICOP_C
≥223 kW	All other	Split system and single package	3.52 COP_C<br>3.90 ICOP_C

Air Conditioners, Evaporatively Cooled

Size Category	Heating Section Type	Subcategory or Rating Condition	Minimum Efficiency
<19 kW	All	Split system and single package	3.55 COP_C<br>3.60 ICOP_C
≥19 kW and <40 kW	Electric resistance (or none)	Split system and single package	3.55 COP_C<br>3.60 ICOP_C
≥19 kW and <40 kW	All other	Split system and single package	3.49 COP_C<br>3.55 ICOP_C
≥40 kW and <70 kW	Electric resistance (or none)	Split system and single package	3.52 COP_C<br>3.58 ICOP_C
≥40 kW and <70 kW	All other	Split system and single package	3.46 COP_C<br>3.52 ICOP_C
≥70 kW and <223 kW	Electric resistance (or none)	Split system and single package	3.49 COP_C<br>3.55 ICOP_C
≥70 kW and <223 kW	All other	Split system and single package	3.43 COP_C<br>3.49 ICOP_C
≥223 kW	Electric resistance (or none)	Split system and single package	3.43 COP_C<br>3.49 ICOP_C
≥223 kW	All other	Split system and single package	3.37 COP_C<br>3.43 ICOP_C

Condensing Units

Size Category	Minimum Efficiency
≥40 kW	3.08 COP_C<br>3.46 ICOP_C
≥40 kW	3.96 COP_C<br>4.10 ICOP_C
≥40 kW	3.96 COP_C<br>4.10 ICOP_C

The COP shall be adjusted to remove the fan power in accordance with:

$$\text{COP}_{\text{nf,cooling}} = 9.13 \times 10^{-4} \times \text{COP}_C \times Q + 1.15 \times \text{COP}_C$$

$$\text{COP}_{\text{nf,cooling}} = -0.0885 \times \text{SCOP}_C^2 + 1.295 \times \text{SCOP}_C$$

Heating System

Gas furnace with constant thermal efficiency equal to the minimum Annual Fuel Utilization Efficiency (AFUE) allowed for gas-fired warm-air furnaces with maximum capacity less than 66 kW, in accordance with the following:

Equipment Type	Size Category (Input)	Subcategory or Rating Condition	Minimum Efficiency
Warm-air furnace, gas fired for application outside the U.S.	<66 kW	Maximum capacity	80% AFUE (nonweatherized) or<br>81% AFUE (weatherized) or<br>80% E_t
Warm-air furnace, gas fired	≥66 kW	Maximum capacity	80% E_t (before 1/1/2023)<br>81% E_t (after 1/1/2023)
Warm-air furnace, oil fired for application outside the U.S.	<66 kW	Maximum capacity	83% AFUE (nonweatherized) or<br>78% AFUE (weatherized) or<br>80% E_t
Warm-air furnace, oil fired	≥66 kW	Maximum capacity	81% E_t (before 1/1/2023)<br>82% E_t (after 1/1/2023)
Electric furnaces for applications outside the U.S.	<66 kW	All	96% AFUE
Warm-air duct furnaces, gas fired	All capacities	Maximum capacity	80% E_c
Warm-air unit heaters, gas fired	All capacities	Maximum capacity	80% E_c
Warm-air unit heaters, oil fired	All capacities	Maximum capacity	80% E_c

Ventilation Rate

The ventilation rate for each building area type shall be consistent with the ventilation rate specified in the building envelope trade-off schedules and loads for the applicable building area type.

Air Economizers

Air economizers shall be modeled for all climate zones except Climate Zones 0 and 1.

The high-limit shutoff shall be "Fixed Dry Bulb" type as described in the following table.

Required High-Limit Set Points (Economizer Off when)

Control Type	Allowed Only in Climate Zone at Listed Set Point	Equation	Description (Required High-Limit Set Points (Economizer Off when))
Fixed dry-bulb temperature	0B, 1B, 2B, 3B, 3C, 4B, 4C, 5B, 5C, 6B, 7, 8	T_OA > 24°C	Outdoor air temperature exceeds 24°C
Fixed dry-bulb temperature	5A, 6A	T_OA > 21°C	Outdoor air temperature exceeds 21°C
Fixed dry-bulb temperature	0A, 1A, 2A, 3A, 4A	T_OA > 18°C	Outdoor air temperature exceeds 18°C
Differential dry-bulb temperature	0B, 1B, 2B, 3B, 3C, 4B, 4C, 5A, 5B, 5C, 6A, 6B, 7, 8	T_OA > T_RA	Outdoor air temperature exceeds return air temperature
Fixed enthalpy with fixed dry-bulb temperature	All	h_OA > 47 kJ/kg or<br>T_OA > 24°C	Outdoor air enthalpy exceeds 47 kJ/kg of dry air or outdoor air temperature exceeds 24°C
Differential enthalpy with fixed dry-bulb temperature	All	h_OA > h_RA or<br>T_OA > 24°C	Outdoor air enthalpy exceeds return air enthalpy or outdoor air temperature exceeds 24°C

• T_OA = Outdoor air temperature

• T_RA = Return air temperature

• h_OA = Outdoor air enthalpy

• h_RA = Return air enthalpy

System Design Supply Air Rates

System design supply air rates shall be based on a supply-air-to-room-air temperature difference of 11.0°C in cooling mode.

System Capacities

System capacities used in the annual simulation shall be 1.5 times the capacities determined by the sizing simulations.

Fan Operation and Power

Fans shall cycle ON whenever the space calls for heating or cooling.

The fan power shall be 0.64 W·s/L (watts per liter per second).

Fan energy shall be modeled explicitly.

These requirements establish a standardized baseline HVAC system for each thermal zone, ensuring consistent evaluation of building envelope performance with typical system characteristics and operating parameters.

Miscellaneous Loads

Miscellaneous loads shall be modeled as included in the building envelope trade-off schedules and loads for the applicable building area type.

This requirement establishes standardized miscellaneous equipment loads (such as plug loads, process equipment, and other internal gains) based on building area type, ensuring consistent internal heat gain assumptions across different building designs for fair envelope performance comparison.

Occupant Density

The occupant density shall be modeled according to the peak occupant density and the occupancy rate schedule in the building envelope trade-off schedules and loads for the applicable building area type.

This requirement establishes standardized occupant densities and schedules based on building area type, ensuring consistent internal heat gains and ventilation loads from occupants across different building designs for fair envelope performance comparison.

Heat Gain from Occupants

The sensible and latent heat gain due to occupants shall be modeled as included in the building envelope trade-off schedules and loads for the applicable building area type.

This requirement establishes standardized sensible and latent heat gain values from occupants based on building area type, ensuring consistent internal heat gain assumptions from human metabolism across different building designs for fair envelope performance comparison.