Here's What You Need to Know About Ekotrope RATER Version 4.0.0
We are so excited to share that Version 4.0 is finally here! Our team has been working tirelessly to make this update as swift and efficient of a transition as possible. Version 4.0 includes quite a few new updates including HVAC grading, appliances, and support for dehumidifiers. The new version provides full support for RESNET/ANSI/ICC Standard 301-2019 including Addenda A and B and MINHERS interim Addenda 53i and 55i.
While we are eager to unveil this new version, we understand that with change often comes stress around the unknown. There are quite a few updates to how homes are modeled and how scores are generated. However, all things considered, we believe this change is positive, as it will enable virtually any multifamily unit to be HERS rated and it provides a way to accurately assess (and earn credit for) the quality of HVAC installation.
Let’s go over some of the updates as well as some key points to keep in mind for potential score changes. We will also offer a few integral troubleshooting tips along the way to ensure a smooth transition as we release our latest updates.
Score Statistics:
With these new updates come some score changes. Across a broad sample of recently registered homes (after appliances are switched to RESNET defaults and undersized heat pumps are upsized) the scores changed as follows:
HERS:
Average goes up 1.35 in Version 4.0
83% of homes are within 3 points of their pre-update HERS Score
Average IECC delta: 1.4% tougher in Version 4.0
Average 45L delta: 3.5% easier in Version 4.0
Appliances:
Addendum A has completely changed how appliance consumption works, especially washers and dryers. Due to these changes, homes using anything other than “HERS Reference” or “ENERGY STAR” defaults cannot be compared across versions. To compare, you must update appliances to one of these defaults.
Water Heater Internal Gains:
Standard 301-2019 specifically requires water heaters to be modeled as heat sources/sinks for whatever space they are in. Since the HERS Reference home typically has a less efficient water heater, it has more internal gains. You will see cold-climate homes with water heaters inside conditioned space see HERS Index scores go up because of this. This is especially significant for multifamily homes.
Infiltration Changes:
Standard 301-2019 requires that multi-family homes with a ratio of exterior envelope surface area to Compartmentalization Boundary (Aext) below 0.5 and exhaust-only ventilation be set to have 0.30 ACHnat infiltration in the rated home. This usually forces HERS Index scores to go up.
Ventilation Changes:
Standard 301-2019 updates the minimum ventilation calculation to use ASHRAE Standard 62.2-2016 (including Addendum S) which does two things:
It usually increases the required ventilation for the rated home because infiltration rates are low in new homes, ventilation is usually not balanced, and in that situation 62.2 2016 requires more ventilation than 2013.
It decreases the amount of ventilation required by the reference home because there is no longer the ⅔ limit for the contribution of infiltration to total air flow.
Addendum 55i also specifies that if ventilation for the rated home needs to be increased, hours and/or wattage should be increased proportionally as CFM is increased. It is important to note that this can increase the HERS Index, especially for homes that have high wattage ventilation.
Heat Pumps:
Undersized heat pumps do not perform as well in Ekotrope Version 4.0 because our new heat pump algorithm takes capacity into consideration when determining if backup heat is enabled for each hour.
In order to mitigate this issue, matching the heat pump capacity to the design load will ensure that the heat pump is not over-penalized for backup heat.
Furnace Auxiliary Energy:
With Standard 301-2019 Addendum B, furnace auxiliary energy (i.e. fan energy) is calculated using fan wattage and runtimes rather than EAE. In previous versions, the EAE modeling allowed for some IECC performance compliance benefits because a furnace would get re-sized (most often down-sized), but the EAE would remain the same, resulting in a higher runtime at the same wattage. This behavior no longer exists in version 4.0, so some projects will see a decline in IECC performance metrics.
To help mitigate the impacts of this, we are introducing the Source BTU performance path exception in version 4.0 as an alternate way to meet the IECC performance path. This may help some projects achieve compliance, and will automatically be considered as part of Ekotrope’s analysis.
Reference Home Basement Walls:
Standard 301-2019 modified the basement walls of the reference home to specify an R value instead of a U Factor and to specify that the soil and concrete of the basement wall in the reference home are not included in that R value. This may impact the HERS Index of homes that have basements or crawl spaces. In some cases, especially if there is a significant portion of foundation wall above grade, this can lower the HERS Index. In other cases, it could increase the HERS Index.
Latent Loads:
Included in version 4.0 is a more accurate calculation associated with latent loads. For the most part this enhancement does not have a significant impact on the HERS Index. In some cases, it does have a tendency to slightly increase the HERS Index, especially in homes with significant cooling savings, because the rated and reference home latent loads typically do not vary by as much as the rated and reference home sensible loads. Thus, the ratio of rated / reference consumption is increased.
Non-HERS Calculations:
For calculations other than the basic energy consumption, the HERS Index, ENERGY STAR, and the 45L Tax Credit, HVAC Grading is not included. This means that for calculations like IECC Performance Path, Utility Program savings, etc, systems are not penalized for being grade III, and are not credited for being grade I. It is possible this could change in the future as additional programs, codes, and standards adopt ACCA 310 methodologies.
We hope that this outline of updates, troubleshooting tips, and explanations for such is helpful for you. As always, please contact us with any questions at support@ekotrope.com. We are always happy to help with any issues you may have.
