2021 IECC and the R408 Path in Ekotrope

Modified on Thu, 13 Jan 2022 at 04:50 PM

Ekotrope 2021 IECC Performance Path Explained

The 2021 IECC performance path is different from other years of the IECC performance path because it requires that the rated home not only perform better than the reference home, but also satisfy one of the following two options:

1. The home performs 5% better than the reference home, i.e. the rated home energy bill is 95% of the reference home energy bill.
OR

2. The home includes at least one additional efficiency measure from section R408 and would still perform better than the reference home when modeled without that additional efficiency measure.

Luckily, rather than require the rater to check both of these options and go through the steps of modeling the home without the measures from section R408, Ekotrope will check both of these options automatically.

Here are the logical steps that Ekotrope takes to determine if a home meets the performance path:

1. First, the rated home energy bill is compared to the reference home energy bill. If the rated home bill is less than or equal to 95% of the reference home energy bill, the home passes and further steps are not necessary. Otherwise, Ekotrope performs the next step.

2. Ekotrope checks each additional efficiency option in section R408, in order. If the home satisfies a certain item from section R408, the home is then analyzed as if it did not have that particular additional efficiency feature. If the home still performs better than the reference home without the additional efficiency measure, the performance requirements are considered to be met. Otherwise, Ekotrope will continue to check the rest of the items from section R408 in the same way.

For some items in section R408, it is not immediately clear what it means to model the home without such a feature. Ekotrope worked with ICC to clarify this with an interpretation, the full text of which is copied at the bottom of this article.

The simplified version is below:

1. For section R408.2.1, the proposed home would be modeled with a total UA of 100% of the reference home UA. In order to accomplish this, all components, including fenestrations, walls, ceilings, framed floors, slabs, and foundation walls, would be modeled with R405 reference home U Factors / R Values / SHGC.

2. For section R408.2.2, the proposed home would be modeled with prevailing federal minimum efficiency levels at the time of publication of IECC 2021. Ground source heat pumps in the proposed home would be swapped for federal minimum efficiency air source heat pumps.

3. For section R408.2.3, the proposed home would be modeled with a federal minimum efficiency water heater of the same system type and fuel type as the proposed home, with a solar fraction of 0.

4. For section R408.2.4, the proposed home would be modeled with the same distribution system performance characteristics as the reference home, yielding no credit and no penalty.

5. For section R408.2.5: 1) Both the proposed and reference home will have the same infiltration as the standard reference design based on the climate zone, AND 2) If proposed home is in CZ 7 or 8, both the proposed and reference home will have an ERV with 1.2 CFM/Watts and 65% energy recovery percentage. Otherwise, both the proposed and reference home will have no mechanical ventilation system.

Full Interpretation from IECC

Ekotrope questions are in black, ICC responses are in blue.

Question:

In the context of section R401.2.5 item 2.1, shall the phrase “without including such measures in the proposed design” be interpreted in the following ways for each possible R408 option?

If option R408.2.1 is used for compliance, then the proposed home shall be modeled with a total UA of 100% of the reference home UA. In order to accomplish this, all components, including fenestrations, walls, ceilings, framed floors, slabs, and foundation walls, shall be modeled with R405 reference home U Factors / R Values / SHGC.
1. Yes, if Section R408.2.1 (Enhanced Envelope Performance Option) is utilized as the additional efficiency package, the proposed design must be modeled the same as the standard reference design per Section R401.2.5.
If option R408.2.2 is used for compliance, then the proposed home shall be modeled with prevailing federal minimum efficiency levels at the time of publication of IECC 2021. Ground source heat pumps in the proposed home shall be swapped for federal minimum efficiency air source heat pumps.
1. Yes, if Section R408.2.2 (More Efficient HVAC Equipment Performance Option) is utilized as the additional efficiency package, the proposed design must be modeled using the minimum efficiencies required by federal law for the geographic location where the equipment is installed per Section R401.2.5.
If option R408.2.3 is used for compliance, then the proposed home shall be modeled with a federal minimum efficiency water heater of the same system type and fuel type as the proposed home, with a solar fraction of 0.
1. Yes, if Section R408.2.3 (Reduced Energy Use in Service Water-heating Option) is utilized as the additional efficiency package, the proposed design must be modeled using the minimum efficiencies required by federal law for the applicable water heater per Section R401.2.5. Additionally, since Section R401.2.5 requires the exclusion of the additional package in the modeling of the proposed design, the solar fraction must be zero (0).
If option R408.2.4 is used for compliance, then the proposed home shall be modeled with a distribution system efficiency of 0.88.
1. The determination in the application of Section R408.2.4 (More Efficient Duct Thermal Distribution System Option) is subject to the opinion of the Code Official. The intent of Item 2.1 of Section R401.2.5 is to not take credit in the model for the application of the additional efficiency package utilized. It is not the intent of the provision to penalize the system when Section R408.2.4 is used.
  1. If Section R408.2.4 is not used and the duct system testing is performed, the as tested thermal distribution system effectiveness would be provided for both the standard reference design and the proposed design per Section R405.4.2 and Table R405.4.2(1). In the same way, if Section R408.2.4 is not used and the duct system testing is not performed, the default value of 0.88 would be applied to both the standard reference design and the proposed design per Section R405.4.2, Table R405.4.2(1) and Table R405.4.2(2).
  2. If Section R408.2.4 is used, Section R405.4.2 and Table R405.4.2(1) would still require the standard referenced design to apply the as tested value. Therefore, if 0.88 were applied to the proposed design, the system would be penalized for the use of Section R408.2.4. That being said, it is the opinion of staff that both the standard reference design and the proposed design will use the same as tested or not tested values.
If option R408.2.5 is used for compliance, then the proposed home shall be modeled with the same air leakage rate as the standard reference design and no mechanical ventilation system.
1. If Section R408.2.5 (Improved Air Sealing and Efficient Ventilation System Option) is utilized as the additional efficiency package, the proposed design must be modeled using the same air leakage rate as the standard reference design per Section R401.2.5. For the same reason as stated above in A6, the mechanical ventilation would be modified as required per Section 403.6. For instance, Section R403.6.1 requires an HRV or an ERV in Climate Zones 7 and 8. Therefore both the standard reference design and the proposed design would be modeled using the proposed ventilation system with a sensible heat recovery efficiency of 65 percent at 32°F. Additionally, since the standard referenced design is required to use the minimum efficiency of an ERV or HRV in accordance with Table 403.6.2, the 1.2 cfm/watt efficiency would be used for both the standard reference design and the proposed design. In climate zones other than Climate Zone 7 or 8, no mechanical ventilation will be shown in the standard referenced design and the proposed design.