International Energy Conservation Code
The International Code Council’s International Energy Conservation Code (IECC) is a model document intended to be adopted by state and local governments. The document consists of provisions for both residential and commercial buildings. For most modeling of new commercial buildings, the requirements are presented in Chapter 4 and include:
- C401 General
- C402 Building Thermal Envelope Requirements
- C403 Building Mechanical Systems
- C404 Service Water Heating
- C405 Electrical Power and Lighting Systems
- C406 Additional Efficiency, Renewable, and Load Management Requirements
- C407 Simulated Building Performance
- C408 Maintenance Information and System Commissioning
- C409 Calculation of the HVAC Total System Performance Ratio
Plus, several appendices.
Section C407 Simulated Building Performance describes the rules for simulating building performance, which is an annual energy cost comparison of the design of a building with a reference building. Jurisdictions can optionally decide to use site or source energy as the comparison metric. Factors are provided in the code when using source energy. Table C407.4.1(1) is the primary description of how to model the standard reference design and the proposed design. This table includes:
- Space use classification
- Roofs
- Walls, above-grade
- Walls, below-grade
- Floors, above-grade
- Floors, slab-on-grade
- Opaque doors
- Vertical fenestration
- Skylights
- Lighting, interior
- Lighting, exterior
- Internal gains
- Schedules
- Outdoor airflow
- Heating systems
- Cooling systems
- Service water heating
- Energy recovery
- Fan power
- On-site renewable energy
HVAC system selection for the standard reference design follows Table C407.4.1(2) and requires one of 11 different systems depending on the condenser cooling source being water or ground versus air or none and a heating classification based on fossil fuel, heat pump, or electric resistance. This overall approach is very similar to the ASHRAE Standard 90.1 Energy Cost Budget Method, and many of the details are exactly the same. The 11 different systems include:
- Variable air volume with parallel fan-powered boxes
- Variable air volume with reheat
- Packaged variable air volume with parallel fan-powered boxes
- Packaged variable air volume with reheat
- Two-pipe fan coil
- Water-source heat pump
- Four-pipe fan coil
- Packaged terminal heat pump
- Packaged rooftop heat pump
- Packaged terminal air conditioner
- Packaged rooftop air conditioner
C407.4.2 describes how thermal blocks need to be defined and, in general, they need to be consistent between the standard reference and proposed designs.
Documentation requirements in C407.3 include a compliance report and an inspection checklist for the proposed design. Additional documentation includes the component characteristics of the reference design, thermal zoning diagrams, input and output reports from the simulation program, an explanation of messages from the simulation program, a signed certification, and documentation of on-site renewable energy.
C407.5 describes the requirements for the BEM software being used for the modeling, including how the software is approved, the software’s minimum capabilities, and testing requirements based on Standard 140. This section also describes the process of using an exceptional calculation method.
For residential buildings, Section R405 is the Simulated Building Performance Option, which uses a cost-based tradeoff between the proposed and standard reference design models. Site or source metrics can optionally be used if adopted. It includes Table R405.4.2(1), which is also broken out into different building components, as well as sections on compliance documentation and BEM software requirements. As an alternative to R405, section R406 is on Energy Rating Index Compliance, which is based on RESNET .
Additional Resources
ICC Overview of Energy Efficiency
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