Energy and Energy Cost Savings Analysis of the IECC for Commercial Buildings

The purpose of this analysis is to assess the relative energy and energy cost performance of commercial buildings designed to meet the requirements found in the commercial energy efficiency provisions of the International Energy Conservation Code (IECC). Section 304(b) of the Energy Conservation and Production Act (ECPA), as amended, requires the Secretary of Energy to make a determination each time a revised version of ASHRAE Standard 90.1 is published with respect to whether the revised standard would improve energy efficiency in commercial buildings. As many states have historically adopted the IECC for both residential and commercial buildings, PNNL has evaluated the impacts of the commercial provisions of the 2006, 2009, and 2012 editions of the IECC. PNNL also compared energy performance with corresponding editions of ANSI/ASHRAE/IES Standard 90.1 to help states and local jurisdictions make informed decisions regarding model code adoption.


Introduction
In support of the U.S. Department of Energy (DOE) Building Energy Codes Program (BECP), staff from Pacific Northwest National Laboratory (PNNL) performed an analysis of the relative energy performance of commercial buildings designed to meet the requirements found in the Commercial Energy Efficiency chapters of the 2006, 2009, and 2012 International Energy Conservation Code (IECC) (ICC 2006a, ICC 2009a, 2012a. The purpose of the analysis was to quantitatively evaluate the energy performance of new commercial buildings built to the minimum mandatory and prescriptive requirements of the three respective editions of the IECC. Results of this analysis will help states and local jurisdictions make informed decisions on the energy impacts of different IECC editions when considering adopting a newer edition of the code. This analysis does not consider the impact of these codes on existing building alterations.
During 2010 and 2011, researchers at PNNL conducted building energy simulations of 16 prototype buildings, 1 representing 80% of the commercial building floor area for new construction in the United States, to perform a quantitative analysis of Standards 90. 1-20041- , -20071- , and -20101- (Thornton et al. 2011. The current analysis was based on and builds upon the Standard 90.1 work. This analysis considered all mandatory and prescriptive IECC requirements applicable to the prototype buildings, and modeled them using the DOE energy simulation program EnergyPlus™. The combined impacts of each IECC edition on the suite of 16 prototype buildings in 17 climate locations were considered. This report provides background information about the modeling assumptions and methodology specific to the IECC analysis. The current report is organized as follows: Section 2.0 summarizes the overall analysis methodology; Section 3.0 describes the modeling strategies for the requirements in the IECC for the categories of building envelope, mechanical systems, service water heating (SWH), and electrical power and lighting systems; Section 4 summarizes the results of the comparison of different versions of the IECC. Appendix A summarizes the IECC analysis results relative to the corresponding Standards 90.1. Appendix B identifies a series of amendments to the 2012 IECC that would align the requirements with Standard 90.1-2010 to create equivalency on a nationally aggregated basis. Appendix C provides comparisons between Standard 90.1 editions and the corresponding IECC in energy end-use category level for each prototype. Appendix D provides energy and energy cost comparisons between Standard 90.1-2010 and the 2012 IECC by climate location and building type.

Methodology
Over the past several years, PNNL researchers expended a substantial effort into developing the prototype models for Standards 90. 1-2004, -2007, and -2010. The effort includes developing representative prototype buildings to cover a majority of new commercial constructions, implementing the applicable standard requirements to these prototypes to create compliant simulation models in representative climate locations, and analyzing the simulation results to estimate the energy savings of the standard. The results allow one to compare the national weighted average savings of one standard to its earlier editions. More importantly, PNNL has periodically implemented addenda to Standard 90.1 in the prototype models as they are approved, to measure progress towards the goal of reducing energy use of Standard 90.1-2010 by 30% compared to Standard 90.1-2004. This research effort including development of the prototypes and quantifying improvements is referred to as the Progress Indicator (PI). In 2011, PNNL published a Technical Support Document (TSD) (Thornton et al 2011) to document the development of the prototype models for Standards 90. 1-2004, -2007, and -2010, and the document is hereafter referred to as the PI TSD.
This section summarizes the general methodology developed as part of the PI, which also served as the methodology for this IECC analysis. After the PI TSD was published, PNNL has continued the PI work for the development of Standard 90.1-2013 as well as the IECC prototype development. In order to capture the requirements in the IECC and approved addenda to Standard 90.1-2010, numerous enhancements to the prototype models were made. These enhancements also are described in this section, along with changes in the Standard 90.1 analysis results since they are published in the PI TSD (Thornton et al. 2011).

Basis of Prototype Building Models
As part of the PI analysis, PNNL used a suite of 16 prototype buildings (in EnergyPlus) covering the first 7 principal building activities in the Commercial Buildings Energy Consumption Survey (CBECS; EIA 2003), representing 76% of the building energy usage of commercial buildings. Of the 16 prototypes, two multifamily prototype buildings (not included in the CBECS) were included in the analysis, because they are regulated by Standard 90.1 and the commercial provisions of IECC: Mid-Rise Apartment and High-Rise Apartment. Table 2.1 shows the 16 prototypes used in this analysis, which represent 80% of new construction floor area in the U.S. Detailed descriptions of these prototypes are provided in the PI TSD (Thornton et al. 2011).

Modeling Code Provisions
The Commercial Energy Efficiency chapter in the 2006, 2009, and 2012 IECC provides three alternative paths for a new building to show compliance: (1) comply with the mandatory and prescriptive requirements in the IECC; (2) comply with the mandatory and total building performance requirements in the IECC; or (3) comply with the requirements in the corresponding Standard 90.1. The focus of this analysis is a comparison of the mandatory and prescriptive requirements of each IECC edition.
The existing Standard 90.1 prototype models provided a foundation for the present analysis, which began with a qualitative comparison of provisions of the 2006 IECC and Standard 90.1-2004. Next, the differences were characterized as either having or not having energy impacts on the prototype buildings. For differences having prototype energy impacts, modeling strategies were developed and applied to the ASHRAE 90.1-2004 prototypes, resulting in prototypes compliant with the 2006 IECC. Following the same approach, another round of characterization was performed to identify differences between the 2009 and 2012 IECC as compared to the 2006 IECC. Those differences were applied to the 2006 IECC prototypes to create the 2009 and 2012 IECC compliant prototypes. This process ensured that all the differences between the successive editions of the IECC were captured. The comparisons were informed by prior work identifying differences between the IECC and its referenced standard. (Conover et al. 2009;Makela et al. 2011)

Construction Weights
Results of this analysis are weighted by construction volume for each building type and climate subzone in order to calculate the national weighted average Energy Use Intensity (EUI) and Energy Cost Index (ECI). Weighting factors developed by building type and climate-related geographic areas in the United States were derived from five years of recent construction data (Jarnagin and Bandyopadhyay 2010). Table 2.2 summarizes the construction floor area and percentage weighting factors by building  type. As the table shows, the selected 16 prototypes cover 80% of new construction floor area. Table 2.3 lists the weighting factors assigned to each prototype in all 15 U.S. climate subzones. The two climate subzones that occur only outside the United States-Riyadh, Saudi Arabia and Vancouver B.C., Canadawere not included in the weighted average. Simulation results for these two subzones only served as references when needing to review modeling strategies and results for individual locations.

Comparison Metrics
During the PI work, researchers at PNNL developed an EnergyPlus simulation infrastructure to allow batch processing for prototype model simulations and results. The primary metrics for comparing different editions of the IECC were the national weighted average site EUI and ECI. The national weighted average EUI -energy use per square foot of conditioned building area per year (kBtu/ft 2 /year) represents the energy consumption of all prototype models weighted by construction weight, building type, and climate subzone. The national weighted average ECI -energy cost per square foot of conditioned building area per year ($/ft 2 /year) was computed using a breakdown of energy consumption by utility type (i.e., kWh of electricity and therms of natural gas); no other fuel types are used in the prototype buildings. The national weighted average EUI and ECI was compared between the IECC editions.
PNNL calculated the energy cost savings using national average energy prices from Energy Information Administration (EIA) values. The national average energy prices used in this analysis were $0.9990/therm for natural gas and $0.1032/kWh for electricity (EIA 2011). The same rates were used for all prototypes and in all climate locations.
The IECC and Standard 90.1 do not regulate many plug-and-process loads (e.g., computers, appliances) and other equipment (e.g., gas cooking equipment) in commercial buildings, but they were modeled in the prototype simulations to account for their impact on HVAC systems. The assumptions for the plug-and-process loads are documented in the PI TSD (Thornton et al. 2011). The whole-building energy simulations results are presented (1) with plug-and-process load energy usage to show the impacts on total commercial building energy usage, and (2) without plug-and-process loads to show the impacts on just the regulated energy usage. Results of the analysis are presented in Section 4.0 of this report.

Model Enhancement
PNNL has made numerous enhancements to the original prototype models since they were published in Thornton et al. (2011). The enhancements were made for several reasons, including (1) to change or improve model assumptions at the direction of the ASHRAE Standing Standard Project Committee 90.1; (2) to improve the simulation and simulation infrastructure; and (3) to add additional detail to the model to capture certain energy impacts from Standard 90.1 and the IECC. Major model enhancements included: • increased window-to-wall ratio (WWR) for Mid-Rise Apartment and High-Rise Apartment prototypes • added data center to the Large Office prototype • comprehensively modified SWH assumptions • introduced outdoor air supply via packaged terminal air conditioners (PTACs) instead of makeup air units in Small Hotel prototype • improved modeling of ventilation in multiple-zone variable air volume (VAV) systems • enhanced heat pump controls in Small Office prototype • revised the retail display lighting adder for the Strip Mall prototype based on standard requirement 2.7 • enhanced optimum start controls (controls that vary the start time of HVAC equipment based on internal loads and weather conditions so that temperature setpoint is just met as building occupancy begins) • adjusted Warehouse prototype roof reflectance and emmittance • removed occupancy sensor controls from design day schedules • accounted for vestibules when required in High-Rise Apartment prototype • accounted for unintentional heat gain from humidification and pre-heat in Large Office and Hospital prototypes • improved assumptions for fractional horsepower (hp) motor efficiency • improved modeling of fan speed and integrated economizer control in direct expansion (DX) units. Table 2.4 shows the site EUI for Standards 90.1-2004 and -2010 before and after the enhancements were made to the prototype models. The impacts of some enhancements are significant to a few prototypes. The data center added to the Large Office prototype approximately doubled the building EUI. Revised SWH assumptions also increased the EUI for most prototypes. All of the enhancements were incorporated into the Standard 90.1 prototype models, which became the starting point of the IECC model development. Therefore, the results presented in Section 4.0 of this report represent the comparison between the IECC models and the enhanced Standard 90.1 models. Note: These Standard 90.1 results differ from those published in the PI TSD report (Thornton et al. 2011), because of the enhancements. 3.1

IECC Prototype Model Development
IECC prototype model development builds on the Standard 90.1-2004 prototype models following the model enhancement summarized in Section 2.6. A methodology similar to that used for previous Standard 90.1 analysis was used extensively for this current IECC analysis. As a first step in the analysis process, a qualitative comparison was made between the prescriptive and mandatory requirements of Standard 90.1-2004 and the 2006 IECC. Next, the differences were characterized as either having or not having energy impacts on the prototype buildings. For differences having prototype energy impacts, modeling strategies were developed and applied to the ASHRAE 90.1-2004 prototypes, resulting in prototypes compliant with the 2006 IECC. Following the same approach, another round of characterization was performed to identify differences between the 2009 and 2012 IECC as compared to the 2006 IECC. Those differences were applied to the 2006 IECC prototypes to create the 2009 and 2012 IECC compliant prototypes. This process ensured that all the differences between the successive editions of the IECC were captured.
This section describes the development process and the modeling strategy pertaining to code requirements in the following categories: Section 3.1, building envelope; Section 3.2, building mechanical systems; Section 3.3, SWH; and Section 3, electrical power and lighting systems.

Building Envelope
Section 502 of the 2006 and 2009 IECC and Section C402 of the 2012 IECC specify mandatory and prescriptive requirements for building thermal envelope performance. The differences in these requirements are mainly in six design aspects: opaque assemblies, fenestration, WWR, vestibule, continuous air barrier, and cool roof. The basic construction characteristics (e.g., construction type) applied to the IECC prototype models were consistent with the Standard 90.1 prototype models.

Opaque Assemblies
Tables 502.2(1) and 502.2(2) in the 2006 IECC specify opaque envelope component requirements expressed in terms of minimum R-value for roofs, above-grade walls, below-grade walls, floors over outdoor air or unconditioned space, and slab-on-grade floors; and maximum U-factor for opaque doors. These requirements are applicable for all conditioned space categories; there are no distinctions for nonresidential, residential, and semi-heated spaces.
Tables 502.1.2, 502.2(1), and 502.2(2) in the 2009 IECC modify the 2006 IECC requirements by adding a parallel maximum U-factor compliance options for above-ground opaque envelope components, including roofs, above-grade walls, and floors over outdoor air or unconditioned space; C-factor for below-grade walls; and F-factors for slab-on-grade floors. These factors are defined for two distinct space type categories: "Group-R" (residential space types) and "All-Other" (all commercial and semi-heated spaces). The 2012 IECC has similar classifications for opaque assembly components, but increases the stringency for many of them.
For modeling in EnergyPlus, the U-, C-, and F-factors corresponding to construction types and components defined in the prototype buildings (e.g., metal frame wall) were modified to reflect the

Fenestration
Section 502.3 in the 2006 and 2009 IECC and Section C402.3 in the 2012 IECC have requirements for maximum fenestration U-factor and SHGC, including requirements for glass doors. These requirements are the same for all space categories (nonresidential, residential, and semi-heated spaces). The 2006 and 2009 IECC provide prescriptive requirements for windows based on the fenestration frame construction type for up to a maximum of 40% WWR for vertical fenestration. The 2006 and 2009 IECC define two types of vertical fenestration frame construction: nonmetal framing and metal framing.
In contrast to the 2006 and 2009 IECC, the 2012 IECC limits WWR to a maximum of 30% and classifies vertical fenestration as fixed windows, operable windows, or entrance doors, regardless of the frame construction type. Different U-factor requirements are specified for the three classifications, and SHGC requirements are the same for all classifications.
The 2006, 2009, and 2012 IECC provide maximum U-factor and maximum SHGC requirements for skylights, and they limit skylight area to a maximum of 3% of roof area that is glazed.

Window-to-Wall Ratio
The IECC differs from Standard 90.1 in its definition of "window-to-wall ratio." The IECC considers only above-grade walls in the calculation of WWR, unlike Standard 90.1, which considers both belowgrade (basement) and above-grade walls in determining WWR. Maximum permitted WWR is 40% for the 2006 and 2009 IECC, and 30% for the 2012 IECC. Most prototypes had WWRs of less than 30% based on definitions from both IECC and Standard 90.1, and therefore were not impacted by the more stringent requirements of the 2012 IECC. However, four prototypes (Primary School, Secondary School, Medium Office, and Large Office) had WWRs between 30% and 40% in their 2006 and 2009 IECC models, and their WWRs were reduced to 30% for the 2012 IECC models.

Vestibules
(a) Exemption for buildings in climate zones 1 and 2. (b) Required, but not simulated because there is no relative difference between the ASHRAE and IECC prototypes. (c) Required by the 2012 IECC as door opens to spaces more than 3,000 ft 2 . (d) Exemption for doors opening to spaces 3,000 ft 2 or less.
When the air infiltration rate through a door (with or without a vestibule) is modeled, the rate was calculated for each building using a simplified method. That method considered design wind speed, door area, and building height to a neutral pressure plane (used to estimate the stack effect driven air pressure on the door) of one-half the building height and a multiplication coefficient that is a function of door opening frequency (Cho et al. 2010). The PI TSD (Thornton et al. 2011) summarizes the strategy used to simulate vestibules in the Standard 90.1 prototypes. The same strategy was used to develop the IECC prototype models.

Continuous Air Barrier
Section 502.4 of the 2006 and 2009 IECC, mandates air leakage requirements for window and door assemblies, curtain wall, storefront glazing, commercial entrance doors, loading dock weather seals, and 3.4 sealing of the building envelope. Although the requirements (for example fenestration air leakage rate) are slightly different from Standard 90.1-2004, it was decided to use the same air leakage input as the Standard 90.1-2004 prototypes. A whole building infiltration rate of 1.8 cfm/ft 2 at 0.3 in. w.c. of exterior above-grade envelope surface area was used, based on the average air tightness levels summarized in a National Institute of Science and Technology report (Emmerich et al. 2005).
Section C402.4 of the 2012 IECC addresses the air leakage requirements as a continuous air barrier is needed throughout the building envelope in other than climate zones 1-3; and three compliance options are provided including (1) materials, (2) assemblies, (3) whole building air leakage test. The first two options are very similar to the two options in Section 5.4.3.1.3 of Standard 90.1-2010. It was decided to use the same air leakage model assumption developed for the Standard 90.1-2010 prototypes for the 2012 IECC prototypes.
Both the IECC and Standard 90.1 have requirements for sealing recessed lighting fixtures that open into unconditioned spaces. These requirements were not modeled for either Standard 90.1 or the IECC because there is no relative energy saving impact to be captured. Table 3.2 shows the infiltration values for all the prototypes for the three editions of the IECC. The PI TSD (Thornton et al. 2011) summarizes the process for calculating these infiltration rates for both buildings with and without continuous air barriers. The infiltration rates shown in Table 3.2 were used to calculate the infiltration for the different IECC edition models.

Cool Roof
The IECC and Standard 90.1 are similar in their definition of minimum reflectance or emmittance requirements for roofs. Similar to the corresponding Standard 90.1-2004, the 2006 and 2009 IECC do not specify minimum reflectance or emmittance requirements for roofs. Section C402.2.1.1 of the 2012 IECC requires a minimum three-year-aged solar reflectance of 0.55 and a minimum three-year-aged thermal emmittance of 0.75 for roofs in climate zones 1 through 3, which is similar to Standard 90.1-2010. However, the exceptions in Standard 90.1-2010 and the 2012 IECC are slightly different. Standard 90.1-2010 exempts steep-sloped roofs, roofs over semi-heated spaces, and metal roofs from cool roof requirements. This exempts the Small Office, Quick-Service Restaurant, and Full-Service Restaurant prototypes, which have steep slopes, and the Warehouse prototype because the roof is over a semi-heated space. The 2012 IECC does not have exceptions for roofs over semi-heated spaces or metal building roofs, but it does have an exception for steep-sloped roofs. Therefore, the 2012 IECC requires cool roofs for the Warehouse, but exempts cool roofs for the Small Office, Quick-Service Restaurant, and Full-Service Restaurant prototypes.

3.5
The PI TSD (Thornton et al. 2011) specifies in detail the modeling strategy used to simulate the cool roof requirement for Standard 90.1 prototype models. The same strategy was followed for modeling the cool roof requirement for the IECC prototype models.

Building Mechanical Systems
Section 503.2 of the 2006 and 2009 IECC and Section C403.2 of the 2012 IECC specify mandatory requirements for building mechanical systems; those requirements that potentially have energy impacts on the prototype models are heating, ventilating, and air-conditioning (HVAC) equipment performance; HVAC system control; ventilation; energy recovery; and air system design and control. The IECC prescriptive requirements for building mechanical systems are separately specified for simple HVAC systems (Section 503.3 of the 2006 and 2009 IECC and Section C403.3 of the 2012 IECC) and complex HVAC systems (Section 503.4 of the 2006 and 2009 IECC and Section C403.4 of the 2012 IECC). The differences captured in the IECC prototype models are described in this report based on the energy-saving technology. Table 3.3 summarizes the equipment included in the IECC prototypes that have mandatory efficiency requirements in the IECC. Unit heaters are not included in this table because the efficiency requirements do not change between the three editions of IECC. 3.6

Heating, Ventilating, and Air-Conditioning Equipment Performance Requirements
Section 503.2.3 of the 2006 and 2009 IECC and Section C403.2.3 of the 2012 IECC specify minimum HVAC equipment efficiency as mandatory requirements. HVAC system efficiency requirements depend on the system size, which varies with external climate conditions, internal loads, and outdoor air ventilation rate. Design day simulation is used for HVAC system sizing, and the procedure for defining the system capacity is described in Sections 3.3 and 4.5.2 of the PI TSD (Thornton et al. 2011). Once the equipment types and capacities were determined, proper equipment efficiency inputs were assigned to the EnergyPlus simulation model based on the IECC requirements. Only the efficiency requirements of those HVAC equipment represented in the prototypes has been accounted for in the simulation process, which include: • unitary air-conditioner efficiency in Table C503

Optimum Start Control
Section C403.4.3.3 in the 2012 IECC requires optimum start control to be provided for each HVAC system regardless of system size; the 2006 and 2009 IECC do not have similar requirements. As described in Section 4.1 and Appendix C of the PI TSD (Thornton et al. 2011), most of the prototype buildings had thermostat setback at night, except for some spaces in Mid-Rise Apartment, High-Rise Apartment, Hospital, Small Hotel, and Large Hotel, which are intended to be occupied at night. For those spaces with thermostat setback at night, when optimum start control is not required (the 2006 and 2009 IECC), the occupied thermostat setpoint began two hours before the building is occupied. When optimum start control is required, the occupied thermostat setpoint began when the building is occupied; in addition, a thermostat setpoint two degrees Fahrenheit (°F) higher (for heating) or lower (for cooling) than the night temperature setpoint was applied to the thermostat schedule one hour before the building is occupied. 3.7

Shutoff Damper Controls
The 2006, 2009, and 2012 IECC have the same mandatory requirements for motorized damper for both outdoor air supply and exhaust ducts, but the exceptions to the requirements are different from the corresponding ASHRAE standards. All the IECC exempt motorized damper requirements if the building is less than three stories in height or is located in climate zones 1, 2, and 3. Section 5.2.2.20 of the PI TSD (Thornton et al. 2011) specifies in detail the modeling strategy used to simulate the motorized damper for Standard 90.1 prototype models. The same strategy was followed for modeling the shutoff damper controls for the IECC prototype models.

Ventilation Requirements
System outdoor air ventilation rates can have a significant impact on commercial building energy use.  (ICC 2006b, ICC 2009b, 2012b. The system ventilation rate requirements affect the prototype models through both the zone ventilation rate requirement and the calculation methods used to determine system ventilation requirements. Section 4.5.5 of the PI TSD (Thornton et al. 2011) describes the implementation of system ventilation rates in the Standard 90.1 prototype models. In order to use the zone ventilation rates specified in ASHRAE Standard 62.1, a consistent mapping of the modeled thermal zones to the space types categorized in the ventilation standards was established.  . The purpose of the comparison was to determine if the zone ventilation rate requirement (cfm/person and/or cfm/ft2) established for the Standard 90.1 prototype models could be directly used for the IECC prototype models. The comparison indicated that there were no essential differences in the zone ventilation rate requirements between the IMC and their Standard 62.1 counterparts. Therefore, the zone ventilation rate requirement established for the Standard 90.1 prototype models was used for the IECC prototype models. Design system ventilation airflow for a single-zone system is based on the sum of ventilation rate of each space served by that system. The calculation for design system ventilation rates for multiple-zone VAV systems is described in Section 3.2.12 of this report.

Demand Controlled Ventilation
The 2006 IECC does not have a requirement for demand controlled ventilation (DCV). Section 503.2.5.1 of the 2009 IECC specifies a DCV requirement for spaces larger than 500 ft 2 and with an average occupancy load of 40 people per 1,000 ft 2 of floor area. Section C403.2.5.1 of the 2012 IECC reduces the thresholds to spaces larger than 500 ft 2 and with an average occupant load of 25 people per 1000 ft 2 . If a system, under which the zone is required to have DCV, has energy recovery ventilation (ERV), the DCV requirement is exempted according to the 2009 and 2012 IECC.
The methodology for implementing the DCV in the IECC models was the same as that for the Standard 90.1 models. Based on the occupancy load (25 people per 1000 ft 2 ) in the 2012 IECC, the classroom zones of the Primary School are required to have DCV. However, due to EnergyPlus program limitations in modeling DCV zones under multiple-zone VAV systems, this 2012 IECC DCV requirement for the Primary School classrooms was not simulated.

Energy Recovery Ventilation
ERV requirements in the 2006, 2009, and 2012 IECC are very similar to those in corresponding Standard 90.1 editions. According to Section 503.2.6 of the 2006 and 2009 IECC, ERV is required for systems with a fan size larger than 5,000 cfm and the design outdoor airflow fraction greater than 70% of the system fan size. Section C403.2.6 of the 2012 IECC specifies the energy recovery requirements by climate zones for different outdoor air fractions and design supply fan size thresholds.
The methodology for implementing ERV in the IECC models was the same as that for the Standard 90.1 models. Section 5.2.2.9 of the PI TSD (Thornton et al. 2011) describes the calculation methodology in detail and as such, this description is not included here.

Fan Power Limitation
The

Fan Motor Efficiency
The IECC does not specify the efficiencies for some equipment covered by federal rules, including electric motors. Applicable requirements of the Energy Policy Act of 1992 (EPAct 1992) are used for the 2006 and 2009 IECC models. Section 313 of the Energy Independence and Security Act of 2007 (EISA 2007) mandates that the efficiency of general-purpose motors that are rated at 1.0 horsepower and larger be increased for motors manufactured on or after December 19, 2010. The efficiency requirements specified by EISA (2007) are used for the 2012 IECC prototype models.

Economizers
Economizers are required in all three IECC editions if the cooling capacity exceeds a specified threshold. Table 3.4 characterizes the economizer requirements by cooling capacity thresholds and climate subzones for the IECC. Where allowed by the applicable IECC, differential dry bulb economizer control type is modeled. When this control is not allowed, differential enthalpy control is used. Whenever an economizer is required, motorized outdoor air dampers are used as they are necessary for economizer operation. Motorized damper operation is described in Section 3.2.4 of this report.
According to guidance provided in the 2009 International Energy Conservation Code and Commentary (ICC 2009c), all economizers are required to be integrated in the IECC (i.e., they should be able to operate simultaneously with mechanical cooling).
The PI TSD (Thornton et al. 2011) describes the economizer modeling in EnergyPlus. Modifications to that strategy were implemented to more accurately model economizers for DX units as part of the model enhancements discussed in Section 2.6 of this report. The EnergyPlus Energy Management System feature was used in the modeling to correctly simulate integrated economizers with DX systems. The built-in EnergyPlus algorithm for economizers assumes perfect integration between the economizer and cooling coil. In practice, however, it is difficult to integrate economizer operation with mechanical cooling without lowering the delta T provided by the cooling coil. This requires the compressor to have more than one stage. The improved strategy calculated the integration of the economizer at every time step based on the outdoor conditions, the space load, and the compressor stage. Thus, the difference between an economizer with two stages of cooling versus one stage can be correctly captured. 3.10

Variable Air Volume Fan Threshold and Control
The VAV fan control requirement provided in Section 503.4.2 of the 2006 and 2009 IECC requires that individual VAV fan systems with motors 10 hp or larger will either: • be driven by a mechanical or electrical variable-speed drive, or • have other controls or devices so the fan motor demand be no more than 30% of design wattage at 50% of design airflow rate when the static pressure setpoint equals one-third of total design static pressure based on manufacturer-certified fan data.
The requirement of the 2012 IECC (Section C403.4.2) reduces the fan motor size thresholds from 10 hp to 7.5 hp and adds one more prescribed option-a vane axial fan with variable pitch blades. This requirement was implemented by applying different fan curves in EnergyPlus inputs based on the fan size. A VAV fan with power higher than the threshold was assumed to be controlled by a variable frequency drive and otherwise via discharge dampers. One of the two VAV fan system part-load curves, representing either a forward curved fan with "good" static pressure reset or a forward curved fan with discharge damper control, was used in the EnergyPlus simulation. The coefficients of fan performance curves can be found in Table 5.14 of PI TSD (Thornton et al. 2011).

Multiple-Zone Variable Air Volume System Ventilation
Section 503.2.5 of the 2006 and 2009 IECC and Section C403.2.5 of the 2012 IECC require buildings to meet system outdoor ventilation requirements specified in the corresponding 2006, 2009, and 2012 IMC. Section 3.2.5 in this report describes how zone ventilation rate in cfm/person and/or cfm/ft 2 were identified.
Six prototype buildings have multiple-zone VAV systems, including Large Office, Medium Office, Primary School, Secondary School, Hospital, and Large Hotel. Section 403.3 of the 2009 and 2012 IMC (referred to by the 2009 and 2012 IECC, respectively) both require multiple-zone ventilation calculations for design system outdoor air rate, and the calculation method is specified essentially the same as in the Section 6.2.5, Appendix A, and Section 6.2.7 of Standard 62. Unlike the three IECC, Standards 90.1 (Section 6.5.2.1) allows VAV zone minimum damper position (MDP) higher than prescriptive maximums if an overall system annual energy usage reduction can be demonstrated. Optimizing these MDPs resulted in significant outdoor airflow reduction in the Standard 90.1 models. The IECC do not have such a provision, therefore the calculation procedure in Sections 6.2.5, Section 6.2.7, and Appendix A of Standard 62.1-2004 was followed for the six IECC prototype buildings; and the MDPs were set to 30% of the zone design peak supply rate or the peak outdoor air requirement, whichever is greater. This can lead to extremely high system outdoor airflow rates in some systems in the IECC models. 3.11

Supply Air Temperature Reset
The 2006 IECC does not require multiple-zone HVAC systems to reset supply air temperature in response to zone loads; therefore, the 2006 IECC prototype models with multiple-zone systems maintained a constant cooling supply air temperature selected to satisfy the peak cooling load. Section 503.4.5.4 of the 2009 IECC and Section C403.4.5.4 of the 2012 IECC added supply air temperature reset requirements for multiple-zone HVAC systems. Similar to the provisions in Standard 90.1-2010, the 2009 and 2012 IECC allow the supply air temperature reset based on either of two alternative strategies: (1) reset based on the representative building loads, or (2) reset based on outdoor air temperature. Standard 90.1-2010 exempt climate subzones 1A, 2A, and 3A from this requirement, but this exemption is not present in the 2009 and 2012 IECC. The implementation method described in Section 5.2.2.18 of the PI TSD (Thornton et al. 2011) was used to simulate the supply air temperature reset in the 2009 and 2012 IECC prototype models.

Service Water Heating
SWH for general hot water usage was included in all prototype models, but some prototypes also included SWH for specific loads (e.g., commercial kitchens and laundry facilities). The simulations combined loads and storage into a single water heater for most prototype models, although loads on an hourly basis may have used separate hourly schedules with the combined hourly load applied to the single water heater. Some prototypes modeled more than one water heater: the Small Hotel prototype separated the laundry and guestroom loads into two separate water heaters; the Strip Mall prototype included one water heater per store; and the Mid-Rise Apartment prototype included one water heater per apartment. Details of the SWH equipment and schedules are presented in Table 4.15 and Appendix C of the PI TSD (Thornton et al. 2011), but some modifications have been made since including: • using a central gas-fired water heater to replace the small electrical water heater in each guestroom of the Large Hotel • changing the fuel type from natural gas to electricity in Small Office and Strip Mall • adding electrical booster water heater in the kitchen for Hospital, Large Hotel, Full-Service Restaurant, and the two schools • adding/splitting natural gas-fired laundry water heaters for Hospital and the two hotels • modifying the volumes and capacity of the water heaters  The equipment efficiencies of the categories are provided either in energy factor (EF) or thermal efficiency (Et) and standby energy loss (SL). In the building energy simulation using EnergyPlus, the equipment efficiencies were modeled through two input parameters: burner efficiency and tank heat loss coefficient. These two parameters are derived from the efficiency quantities (EF or Et and SL) provided in the performance requirement tables of these four categories in the standards.

Electrical Power and Lighting Systems
Section 505 of the 2006 and 2009 IECC and Section C405 of the 2012 IECC specify mandatory and prescriptive requirements for building interior and exterior lighting systems, including lighting power limits and control requirements. Section C406 of the 2012 IECC specifies three additional efficiency package options. One of the options (Section C406.3, "Efficiency Lighting System") was selected to develop the 2012 IECC prototype models.

Interior Lighting Power
Interior lighting power requirements in the IECC are generally based on lighting power density, although the requirements for dwelling units are based lamp efficacy.

Lighting Power Density
Section 505.5 of the 2006 IECC provides prescriptive interior lighting power requirements for all building types though the building area table (Table 505.5.2). Section 505.5 of the 2009 IECC maintains the same interior lighting power allowances as the 2006 IECC but adds more exceptions in Section 505.5.1. While these exceptions have an energy impact associated with them, the current prototype building models do not have specific provisions for capturing this impact. For this reason, the interior lighting power allowances for the 2009 IECC were considered equivalent to the 2006 IECC for the scope of this study. Section C406 of the 2012 IECC requires choosing one of three high efficiency options: either (1) a high-efficiency HVAC system, (2) an efficient lighting system, or (3) on-site renewable energy for compliance. For this analysis, option (2) high-efficiency lighting (Section C406.3) was chosen because this option is more likely chosen for most building designs than the option (3) on-site renewable (Section C406.4). Option (1) high-efficiency HVAC system (Section C406.2) was not chosen because this option doesn't allow a comparison of the 2012 IECC with its counterpart ASHRAE 90.1-2010 with their HVAC equipment at the same minimum efficiencies addressed in the National Appliance Energy Conservation Act (NAECA), Energy Policy Act (EPAct), and the Energy Independence and Security Act (EISA). Section C406.3 of the 2012 IECC provides lighting power allowances under the high-efficiency lighting option in Table C406.3. 3.14 Standard 90.1 provides two alternate compliance paths for determining allowed lighting power density: the space-by-space method and the building area method. In the Standard 90.1 models developed by PNNL, the lighting power density (LPD) values were implemented using the Standard 90.1 space-byspace method for all prototypes except the Small, Medium, and Large Office prototypes. For the three office prototype models, the Standard 90.1 general office LPD value from the building area method was used. The following methodology was used to incorporate the information from the Standard 90.1 models as much as possible and still create models that represent the IECC requirements adequately.
• Whole-building average LPDs were calculated for all ASHRAE 90.1 prototypes by area-weighting the space-by-space LPDs. This calculation was not necessary for the three office prototypes, as the general office area LPD was used directly.
• Adjustment factors were calculated for each prototype by dividing the IECC allowed LPD by the Standard 90.1-2004 whole-building average LPD.
• Each Standard 90.1-2004 space-type LPD was multiplied by the adjustment factor to yield a wholebuilding LPD that matched the IECC requirements.  The methodology for implementing the additional display lighting allowance in the 2006 and 2009 IECC models was the same as that for the Standard 90.1 models. Section 5.2.4.6 of the PI TSD (Thornton et al. 2011) describes the calculation methodology in detail. Therefore, this description is not included here.

Dwelling Unit Lighting Power Density
The 2009 IECC requires at least 50% of all permanently installed luminaires in dwelling units to be high efficacy. The 2012 IECC increases this requirement to 75% high efficacy. High efficacy is defined by the IECC as compact fluorescent lamps, T-8 or smaller diameter linear fluorescent lamps, or other lamps with a minimum efficacy of: 60 lumens per watt for lamps over 40 watts, 50 lumens per watt for lamps over 15 watts to 40 watts, 40 lumens per watt for lamps 15 watts or less.
Since Standard 90.1 does not regulate lighting in dwelling units, the LPD for dwelling units in the two apartment prototypes for the Standard 90.1 models was calculated from the Building America Research Benchmark Definition (Hendron 2008) at 0.36 W/ft 2 . This baseline is treated the same in the 2006 IECC and assumes that 86% of all lamps are incandescent (low efficacy) and the remaining 14% are fluorescent (high efficacy). Dwelling unit LPDs for the 2009 and 2012 IECC cases were determined by recalculating annual hard-wired lighting energy using 50% and 75% fluorescent fractions respectively using Equations 3.1 and 3.2 from Hendron (2008). The ratio of the prototype hard-wired lighting (kWh/year) from each subsequent version of the standard to the prior version is multiplied by the LPD of the prior version to come up with the new LPD.

Interior Lighting Control
There are various types of interior lighting control requirements in the IECC. The 2006 and 2009 IECC require lighting reduction controls that allow occupants to manually reduce the lighting load by at least 50%, automatic lighting shutoff in buildings larger than 5,000 ft 2 , occupant override devices where automatic switching devices are provided, and holiday scheduling and master switches in sleeping units in hotels and motels that control all permanently wired receptacles. Most of these requirements are similar to Standard 90.1-2004. Some differences (e.g., the bi-level controls required by the 2006 IECC) exist, but it is difficult to model the human behavior aspect of these provisions and hence, the energy impacts from these provisions were not captured in this study.
The 2012 IECC requires occupancy sensors in classrooms, conference/meeting rooms, employee lunch and break rooms, private offices, restrooms, storage rooms, janitorial closets, and other areas less than 300 ft 2 enclosed by floor-to-ceiling partitions. The control devices need to turn the lights off within 30 minutes of the occupants leaving the space and can be either manually turned on or automatically controlled to turn the lighting on to no more than 50% power. Full automatic on controls are allowed in some specified areas. This requirement is very similar to the Standard 90.1-2010 requirement with some exceptions. The 2012 IECC requires occupancy sensors in all enclosed areas less than 300 ft 2 , while Standard 90.1-2010 does not include this provision explicitly, but adds requirements for occupancy sensors in copy rooms, printing rooms, dressing rooms, and fitting rooms. PNNL assumed that most enclosed space types less than 300 ft 2 are included in the Standard 90.1 requirements and these minor differences result in little or no functional difference and therefore were not modeled. On the other hand, Standard 90.1-2010 requires bathroom lighting control in hotel/motel guestrooms and stairwell lighting control. This difference was captured in the analysis.
The savings from occupancy sensors was calculated using a methodology similar to the one described in Section 5.2.4 of the PI TSD (Thornton et al. 2011). However, the savings was applied to the occupied hours of the zone lighting schedule instead of the zone LPD. An outline of the procedure for determining savings from occupancy sensors is as follows.
• Appropriate building areas that fall into the 2012 IECC occupancy sensor requirements were identified.
• In prototypes like the Small, Medium, and Large Offices and Stand-Alone Retail, where detailed zoning is unavailable, appropriate building areas were determined using the National Commercial 3.17 Construction Characteristics (NC 3 ) database (Richman 2008). 2 The NC 3 database provides a compilation of the Standard 90.1 prototype buildings and the proportion of common building areas.
• Percent lighting energy reduction due to occupancy sensors were determined for all qualifying areas using the same methodology as used in Standard 90.1-2010 as explained in Section 5.2.4.3 of the PI TSD.
• This percentage reduction was applied to the occupied hour values of the lighting schedule used by the specific zone.
• Where a separate zone does not exist in the model for a particular space, the reduction factor was calculated as a product of (1) space area as a fraction of whole-building area from the NC 3 database, and (2) target lighting energy savings percentage. This reduction was similarly applied to the occupied hours of the whole-building lighting schedule.
The starting point of the commercial IECC models was the Standard 90.1 models. Standard 90.1-2004 requires occupancy sensors in conference rooms, classrooms, and employee lunchrooms. The lighting schedules for these spaces are assumed to already contain savings from occupancy sensors. The 2006 and 2009 IECC do not have any requirements for occupancy sensors. To account for this, the Standard 90.1-2004 lighting schedule values are increased by a value equal to the calculated savings from occupancy sensors in the conference rooms, classrooms, and employee lunchrooms.

Exterior Lighting Control
Section 505.2.4 of the 2006 IECC requires lighting for all exterior applications to have automatic controls capable of turning off exterior lighting when sufficient daylight is present or when lighting is not required during nighttime hours. It also requires lighting not designated for dusk-to-dawn operation to be controlled by an astronomical time switch, and lighting designated for dusk-to-dawn operation to be controlled by an astronomical time switch or a photosensor. These requirements are identical to Standard 90.1-2004 as specified in Section 9.4.1.3.

3.18
The 2009 IECC modified this Section 505.2.4 requirement to require all exterior lighting to be controlled by either a combination of a photosensor and a time switch or an astronomical time switch. This change does not make any functional change to the requirements and for the purpose of this study; the 2009 IECC requirements for this section are considered the same as the 2006

Daylighting (Envelope and Lighting Control)
Daylighting requirements for the 2006 IECC are similar to Standard 90.1-2004 for the most part. The 2006 and 2009 IECC require general lighting in daylight zones to be controlled separately, but they do not require automatic daylighting controls. As a result, no savings are taken from these two standards for daylighting. Section C402.3.2 of the 2012 IECC requires a minimum skylight area in spaces larger than 10,000 ft 2 and requires multilevel automatic controls in daylight zones from skylights; however, the section does not require multilevel automatic controls for spaces with sidelighting. Only manual controls are required to control general lighting in spaces with sidelit daylight zones. The Primary School and Secondary School prototypes have skylights in the gymnasium zones; however, the Primary School gymnasium zone is smaller than 10,000 ft 2 and does not need to comply with this requirement. The Secondary School prototype required multilevel daylighting controls. No sidelighting control requirements were triggered.
The high-efficiency lighting path in the 2012 IECC contains interior lighting power allowances in Section C406.4. The section allows a higher LPD to be used in offices and retail spaces if daylight zones comprise more than 30% of the total conditioned floor area in the building. It also requires that the daylight zone be controlled by automatic controls. The Stand-Alone Retail, Small Office, and Medium Office prototypes have daylight zones comprising 30% or more of the total conditioned floor area in the building as shown in Table 3.8. Automatic daylight controls were modeled for these areas. Section C406.4 also specifies that warehouses are required to have more than 70% of the floor area in the daylight zone with automatic controls. This requirement necessitated adding more skylights to the Warehouse prototype model. Table 3.9 provides details of skylight area and number of skylights required in the Warehouse model to meet this requirement. In summary, the Small Office, Medium Office, Stand-Alone Retail and Warehouse prototypes required automatic controls for general lighting in daylight zones, similar to those implemented in ASHRAE 90.1-2010, as described in Section 5.2.4.1 of the PI TSD. The Secondary School prototype has multi-level controls, which require only one step of control below 35% of full output.

IECC Energy Savings and Energy Cost Savings Results
This section provides the results of the quantitative savings analysis-the estimated site energy and energy cost savings for the 2009 and 2012 IECC compared to the 2006 IECC. Table 4.1 shows the national aggregated results using the construction weighting factors (see Table 2.3 in this report). Site energy is utility electricity and natural gas delivered and used at the building site. Energy cost savings were based on the site energy usage results and national average costs of electricity and natural gas (see Section 2.5 in this report). Table 4.1, the Energy Use Intensity (EUI) and Energy Cost Index (ECI) are reduced with each subsequent edition of the IECC. For example, the 2009 IECC results in savings as high as 11.4% when compared to the 2006 IECC. Results are shown both with and without including loads not regulated by the IECC (i.e., plug-and-process loads).     The 2012 IECC results in the highest energy savings for the Warehouse prototype, primarily due to the large increase in envelope insulation requirements. Negative energy savings were observed for the Hospital prototype, due to higher outside air ventilation rates in the 2009 and 2012 IECC models than in the 2006 IECC models. As discussed in Section 3.2.5 of this report, zone ventilation rates in some healthcare spaces in the Outpatient Healthcare and Hospital prototypes were based on outside air requirements in To eliminate the impact of plug-and-process loads end use on the energy savings analysis,   Section 304(b) of the Energy Conservation and Production Act (ECPA), as amended, requires the Secretary of Energy to make a determination each time a revised version of ASHRAE Standard 90.1 is published with respect to whether the revised standard would improve energy efficiency in commercial buildings. When the U.S. Department of Energy (DOE) issues an affirmative determination on Standard 90.1, states are statutorily required to certify within two years that they have reviewed and updated the commercial provisions of their building energy code, with respect to energy efficiency, to meet or exceed the revised standard. (EPAct 1992 Section 42 USC 6833) As many states have historically adopted the IECC for both residential and commercial buildings, PNNL has also compared energy performance of ANSI/ASHRAE/IES Standard 90.1 with corresponding editions of the IECC to help states and local jurisdictions make informed decisions regarding model code adoption. Of the 41 States with commercial building energy codes currently, 29 use a version of the IECC (BECP 2012a).       Table A.8 includes descriptions of the key differences between Standard 90.1-2010 and the 2012 IECC. The table is organized by end-use category. For each requirement area where there is a modeled difference between the standard and code, a description of the difference is provided.

A.2 Key Differences between Standard 90.1-2010 and the 2012 IECC Prototype Models
Each difference is coded to indicate which standard or code will use more energy, based on a qualitative assessment of the relative provisions within the IECC and Standard 90.1. Where the 2012 IECC is expected to use less energy than Standard 90.1-2010, a less than sign (<) is used. Where the 2012 IECC is expected to use more energy, a "greater than" sign (>) is used. While the individual energy impact for each item was not determined, an estimate is made of the magnitude of difference overall and multiple symbols are used when the magnitude is expected to be greater. For example, the lack of a dynamic ventilation efficiency reset requirement in 2012 IECC is expected to have a large impact on energy use, so a triple symbol is used (>>>). PNNL identified a series of amendments to the 2012 IECC that would better align the requirements with Standard 90.1-2010 to create parity on a nationally aggregated basis. Those amendments are located in Appendix B. A.8 A.9

.2 Outdoor air intakes and exhausts.
Outdoor air supply and exhaust openings in the building thermal envelope, ducts, or equipment shall be provided with Class I IA motorized dampers with a maximum leakage rate of 4 cfm/ft 2 (20.3 L/s · m 2 ) at 1.0 inch water gauge (w.g.) (249 Pa) when tested in accordance with AMCA 500D. Outdoor air supply and exhaust motorized dampers shall be configured to automatically close when the systems or spaces served are not in use.

Exceptions:
1. Gravity (nonmotorized) dampers having a maximum leakage rate of 20 cfm/ft 2 (101.6 L/s · m 2 ) at 1.0 inch water gauge (w.g.) (249 Pa) when tested in accordance with AMCA 500D are permitted to be used as follows: 1.1. In buildings less than three stories in height above grade for exhaust and relief dampers. 1.2. In buildings less than three stories in height above grade. 1.3. For ventilation air intakes and exhaust and relief dampers in buildings of any height located in climate zones 1, 2 and 3. 1.34. Where the design outdoor air intake or exhaust capacity does not exceed 300 cfm (141 L/s). Gravity (nonmotorized) dampers for ventilation air intakes shall be protected from direct exposure to wind.

B.1.3 Economizer and Fan Speed Controls
Purpose: • Fan Speed Controls. Reduce the system capacity threshold at which variable-speed drives are required for variable-flow systems saves significant fan energy • Single Zone VAV. Require single zone systems with cooling capacities greater than 110,000 Btuh to use either variable-speed drives or multi-speed fan motors to reduce air flow, saving both fan and cooling energy. • Economizer Improvements. Current economizer language in IECC is ambiguous regarding economizer requirements for complex systems. The changes make it clear that complex systems require air-side economizers. Energy is saved by reducing the amount of mechanical cooling required to maintain comfort conditions. 2. Driven by a vane-axial fan with variable-pitch blades; or 3. The fan shall have controls or devices that will result in fan motor demand of no more than 30 percent of their design wattage at 50 percent of design airflow when static pressure set point equals one-third of the total design static pressure, based on manufacturer's certified fan data.

B.1.4 Multiple-Zone VAV Reheat System Improvement
Purpose: Variable-air-volume (VAV) systems with reheat can benefit from multiple system improvements: • Multiple-Zone Minimum Airflow Adjustment. This additional exception allows the designer to increase zone minimum airflow above code requirements when it will result in a reduction in overall ventilation air. Energy is saved by reducing excess outside air, resulting in reduced heating and cooling. • Ventilation Efficiency Optimization. Ventilation optimization is an automated control procedure that allows reduction in VAV fan main ventilation airflow when critical zones are receiving higher than minimum zone airflow to maintain thermal conditions. Energy is saved by significantly reducing excess outside air, resulting in reduced heating and cooling. • VAV for Zones with Special Pressurization Requirements. This amendment removes a blanket exception for VAV in zones where special pressure relationships are maintained and replaces it with a minimum airflow allowance to meet other codes or accreditation standards. Energy is saved by significantly reducing total airflow and reducing reheat required to maintain comfort conditions; this reduces heating, cooling, and fan energy.

Specific Amendment to 2012 IECC:
Revise C403.4.5 and add C403.4.5.5 as follows: C403.4.5 Requirements for complex mechanical systems serving multiple zones. Sections C403.4.5.1 through C403.4.5.3 shall apply to complex mechanical systems serving multiple zones. Supply air systems serving multiple zones shall be VAV systems which, during periods of occupancy, are designed and capable of being controlled to reduce primary air supply to each zone to one of the following before reheating, recooling or mixing takes place: 1. Thirty percent of the maximum supply air to each zone. 2. Three hundred cfm (142 L/s) or less where the maximum flow rate is less than 10 percent of the total fan system supply airflow rate.

The minimum ventilation requirements of Chapter 4 of the International Mechanical
Code. 4. Any rate that can be demonstrated to reduce overall system annual energy use by offsetting reheat/recool energy losses through a reduction in outdoor air intake for the system, as approved by the code official. 5. The airflow rate required to comply with applicable codes or accreditation standards, such as pressure relationships or minimum air change rates. Exception: The following define where individual zones or where entire air distribution systems are exempted from the requirement for VAV control: 1. Zones where special pressurization relationships or cross-contamination requirements are such that VAV systems are impractical. (Renumber remaining exceptions from 2-6 to 1-5) C403.4.5.5 Multiple-zone VAV system ventilation optimization control. Multiple-zone VAV systems with direct digital control (DDC) of individual zone boxes reporting to a central control panel shall have automatic controls configured to reduce outdoor air intake flow below design rates in response to changes in system ventilation efficiency (E v ) as defined by the International Mechanical Code.