2.2 The Building

The building is defined through entries for zones, surfaces, and equipment. Zone types include attic, conditioned space, crawl space, basements, and garages. The roof (such as asphalt shingles or tile) is defined as either part of the attic or as part of a cathedral ceiling (also called a rafter roof). Surfaces separating conditioned space from exterior or unconditioned spaces (such as garage or storage) are modeled as interior walls adjacent to the unconditioned zone, as well as the exterior surfaces of an attached garage or storage space (modeled as an unconditioned zone). See Figure 2-1.

The input file will include entries for floor areas, wall, door, roof and ceiling areas, and fenestration areas, as well as the water heating, space conditioning, ventilation, and distribution systems.

Each area is entered along with performance characteristics, including building materials, U-factor and SHGC. The orientation and tilt (see Figure 2-2) is required for envelope elements.

Building elements are consistent with the actual building design and configuration.

To determine the standard design for newly constructed buildings, a building with the same general characteristics (number of stories, attached garage, climate zone) with wall and window areas are distributed equally between the four main compass points (north, east, south and west) is created by the software. Energy features are set to be equal to §150.1(c) and Table 150.1-A. For additions and alterations, the standard design shall have the same wall and fenestration areas and orientations as the proposed building. The details are described below.

All inputs that are used to establish compliance requirements are reported on the CF1R for verification.

2.2.1 Climate and Weather

The user specifies either the zip code or the climate zone of the proposed building. If the zip code is specified the software selects the climate zone. Compliance requirements, weather, design temperatures, and Time Dependent Valuation (TDV) of energy factors are a function of the climate zone. Compliance software assumes that the ground surrounding residential buildings has a reflectivity of 20 percent in both summer and winter.

The zip code and climate zone of the proposed design is reported on the CF1R for verification.

Figure 2-1: Floor Plan

Figure 2-2: Surface Definitions

2.2.2 Standards Version

This input determines which federal appliance efficiency requirements for cooling equipment apply to the project. It allows the user to choose compliance that will be valid only before the federal requirements change or compliance that will be valid both before and after the change in January 2015. Eligibility for solar electric system credit is only allowed with Compliance 2015.

Compliance 2014: valid only through December 2014 (with current federal air conditioning efficiency requirements)

Compliance 2015: valid any time (with 2015 federal air conditioning requirements) and solar credit.

The standard design cooling equipment efficiency is based on the specified version of the federal requirements. If Compliance 2015 is selected, a minimum SEER and (if applicable) an EER that meets the 2015 standard for the type and size of equipment modeled.

2.2.3 PV System Credit

For users with single family and town house projects in climate zone 9 through 15 who select Compliance 2015 to comply under the updated federal appliance standards, there is a credit available for photovoltaic (PV) systems that meet the eligibility requirements of Residential Appendix RA4.6.1. The PV systems must be 2 kWdc or larger. The credit is the smaller of:

Table 2-1: PV Credit Calculation Factors

		Max PV Cooling Credit
Climate	PV Generation Rate	(% of Standard Design
Zone	(kTDV/kWdc)	Cooling kTDV/ft²)
09	30269	13%
10	30342	15%
11	29791	18%
12	29556	17%
13	29676	17%
14	31969	16%
15	29536	19%

For users in the applicable climate zone with the appropriate project type and standards version, the software allows the user to input the rated power of the solar system in kilowatts DC. The software automatically calculates the solar credit.

2.2.4 Existing Condition Verified

This input is used for additions and alterations. The standard design assumption for existing conditions vary based on whether the existing conditions are verified by a HERS rater prior to construction. See Section 2.11.3 for more information.

The user inputs either yes or no. Yes indicates that the existing building conditions were verified by a HERS rater. Default assumption is no.

The standard design assumptions are based on §150.2(b), Table 150.2-B. If the user input is no, or if less than two of the listed components are being altered, the standard design for all existing components is based on the values in the second column. If the proposed design response is yes and two or more of the listed components are being altered, the standard design value for all existing components is the value in the third column.

Verification of existing conditions is a special feature and is reported in the HERS Required Verification listings on the CF1R.

2.2.5 Air Leakage and Infiltration

Air leakage is a building level characteristic. The compliance software distributes the leakage over the envelope surfaces in accordance with the building configuration and constructs a pressure flow network to simulate the air flows between the conditioned zones, unconditioned zones and outside.

The air flow through a blower door at 50 pascals (Pa) of pressure measured in cubic feet per minute is called cfm50. Cfm50 x 60 minutes divided by the volume of conditioned space is the air changes per hour at 50 Pa, called ACH50. Either cfm50 or ACH50 can be used to describe the building air leakage depending on the circumstances.

User input of an ACH50 less than the default value is a Special Feature that requires post-construction verification of building infiltration testing.

ACH50 defaults to 5 for new construction in single family buildings and townhomes and 7 for all other buildings that have heating and/or cooling system ducts outside of conditioned space and for buildings with no cooling system. In single-family buildings and townhomes with no heating and/or cooling system ducts in unconditioned space the default ACH50 is 4.4 and 6.2 for all others.

Specific data on ACH50 may be entered if the single family house or townhouse will have verified building air leakage testing. In multi-family buildings, due to the lack of an applicable measurement standard, ACH50 is fixed at the above defaults and is not a compliance variable. User input of an ACH50 less than the default value is a Special Feature that requires HERS verification.

The standard design shall have 5 ACH50 for single family buildings and 7 for other buildings (ducted space conditioning).

When the user chooses verified building air leakage testing (any value less than the standard design), diagnostic testing for reduced infiltration, with the details and target values modeled in the proposed design, is reported in the HERS Required Verification listing on the CF1R.

The compliance software creates an air leakage network for the proposed and standard design using the building description. Air leakage is distributed across the envelope surfaces according to the factors in Table 2-2. The air network is insensitive to wind direction. For buildings modeled with multiple conditioned zones, either a 20 square foot open door or 30 square foot open stairwell (in a multi-story building) is assumed between any two conditioned zones.

The only difference between the air network for the proposed and standard designs is the ACH50 if the user specifies a value lower than the default.

Multi-family buildings that have floors between dwelling units, must define each floor as a separate zone or each dwelling unit as a separate zone.

Table 2-2: Air Leakage Distribution

	% of Total Leakage by Surface
Configuration	Ceilings	Floors	Exterior Walls	House to Garage Surfaces
Slab on grade	50	0
Raised Floor	40	10
No Garage			50	0
Attached Garage			40	10

2.2.6 Insulation Construction Quality

The compliance software user may specify either standard (unverified) or improved (verified high quality insulation installation, also called Quality Insulation Installation or QII)) for the proposed design. Buildings with standard insulation installation are modeled in the program with lower performing cavity insulation in framed walls, ceilings and floors and with added winter heat flow between the conditioned zone and attic to represent construction cavities open to the attic (see Table 2-3). Standard insulation does not affect the performance of continuous sheathing in any construction.

The compliance software user may specify improved quality insulation installation at the building level. The default is unverified/standard insulation installation. See Section 2.3.3for information on modeling spray foam insulation.

The presence of improved/verified high quality insulation installation is reported in the HERS Required Verification listings on the CF1R. Improved quality insulation installation is certified by the installer and field verified to comply with RA3.5. Credit for verified quality insulation installation is applicable to ceilings/attics, knee walls, exterior walls and exterior floors.

Table 2-3: Modeling Rules for Standard Insulation Installation Quality

Component	Modification
Walls	Multiply the cavity insulation R-value/inch by 0.7
Ceilings/Roofs	Multiply the blown and batt insulation R-value/inch by 0.96-0.00347*R
Ceiling below attic	Add a heat flow from the conditioned zone to the attic of 0.015 times the area of the ceiling below attic times (the conditioned zone temperature - attic temperature) whenever the attic is colder than the conditioned space

For alterations to existing pre-1978 construction, if existing wall construction is assumed to have no insulation, no wall degradation is assumed for the existing wall.

2.2.7 Number of Bedrooms

The number of bedrooms in a building is used to establish mechanical ventilation requirements and to determine if a building qualifies as a compact building for purposes of incentive programs.

The standard design shall have the same number of bedrooms as the proposed design.

2.2.8 Dwelling Unit Types

Internal gains and indoor air quality (IAQ) ventilation calculations depend on the conditioned floor area and number of bedrooms. For multi-family buildings with individual IAQ ventilation systems each different combination of bedrooms and conditioned floor area has a different minimum ventilation cfm that must be verified. A dwelling unit type is one or more dwelling units in the building, each of which has the same floor area, number of bedrooms and appliances.

The standard design shall have the same number and type of dwelling units as the proposed design.

The number of units of each type and minimum IAQ ventilation for each unit is reported on the CF1R for use in field verification.

2.2.9 Front Orientation

The input for the building front orientation is the actual azimuth of the front of the building. This will generally be the side of the building where the front door is located. The orientation of the other sides of a building viewed from the outside looking at the front door are called front, left, right, back, or a value relative to the front, and the compliance software calculates the actual azimuth from this input. Multiple orientation compliance can be selected for newly constructed buildings only.

The user chooses whether compliance is for all orientations or for a site-specific orientation. For the specific orientation case, input the actual azimuth of the front in degrees.

The compliance software constructs a standard design building that has 25 percent of the wall and window area facing each cardinal orientation.

A typical reported value would be "290 degrees (west)". This would indicate that the front of the building faces north 70° west in surveyors terms. The closest orientation on 45° compass points should be reported in parenthesis, e.g., north, northeast, east, southeast, south, southwest, west or northwest. When compliance is shown for multiple orientations, "all orientations" or “cardinal” is reported as a Special Feature on the CF1R.

2.2.10 Natural Gas Availability

The user specifies whether natural gas is available at the site. This is used to establish the TDV values from Reference Appendices JA3 used by the compliance software in determining standard and proposed design energy use.

The standard design has natural gas space and water heating if natural gas is available at the site; otherwise it is propane.

2.2.11 Attached Garage

The user specifies whether there is an attached garage. The garage zone is modeled as an unconditioned zone (see Section 2.9).

The standard design has the same attached garage assumption as the proposed design.

2.2.12 Lighting

The user specifies interior lighting and exterior lighting which are accounted for in internal gain assumptions. There are no tradeoffs between lighting and other building features.

Fraction of portable lighting, power adjustment multiplier and the exterior lighting power adjustment multiplier (Watts/ft2).

2.2.13 Appliances

Appliance data is available for projects other than Title 24, Part 6 compliance. The information impacts internal gains with no effect on the Title 24 energy compliance margin.

The user specifies whether the following appliances are in the building, their fuel consumption or fuel type, and the zone that contains the appliance: