What Has Changed in Version 4.2?
We first released Ekotrope Version 4.2 in Beta on June 7th, 2023, and after receiving accreditation from RESNET, we released it out of Beta on October 13th, 2023.
This new Ekotrope Version includes significant algorithm changes that will impact HERS and other building energy code results for some homes. Through this article, we would like to share how results may change along with a summary of important improvements and fixes. You may find the list of all changes included in 4.2 in our Version Release Notes.
Impact on Results:
We compared a sample of 2,000 randomly selected HERS rated homes to see how results changed in Version 4.2.0 compared to our latest Version 4.1.2. These results are as follows:
HERS:
Average HERS score decreases by 2 points in Version 4.2. The chart below shows the distribution of HERS Index changes on the sample homes:
Following are the major improvements in our algorithm that results in the HERS difference
Updated ground heat transfer calculations to accurately predict slab and foundation loads
Updated duct supply and return fractions in the calculation of distribution system efficiency
Updated calculation of effective duct insulation R-value
Energy modeling results with V4.2 will likely reduce HERS scores, especially in warmer climates, but in the medium term (6-8 months) we will need to make more changes to our algorithm to comply with new RESNET energy modeling requirements. These changes may increase HERS scores, probably in cold and moderate climates (CZ 4 and up). We will be performing due diligence to minimize the negative impact, but we recommend building buffers for builders’ HERS targets to the extent you are able to do so.
IECC:
IECC ERI:
As mentioned above, changes to our ground heat transfer calculation and duct load calculations results in differences in ERI target score.
IECC Performance Compliance:
IECC 2021: 0.76% increased compliance margins compared to V4.1.2.
IECC 2015: 0.7% increased compliance margins compared to V4.1.2.
DOE ZERH and Energy STAR:
Target HERS score decreases by an average of 1.42 points for Energy STAR V3.2, 1.49 points for V3.1, and 1.76 points for DOE ZERH V1. Although, it is worth noting that, as the algorithm improvements apply similarly to the proposed and target home, the overall differences in the Pass/Fail status is negligible:
Improvements in Algorithm:
1. Improvements in our foundation load calculations:
Version 4.2 includes a major improvement to our foundation load calculations. While performing analysis on Ekotrope Algorithm for benchmarking with EnergyPlus and DOE-2.0, we observed an overestimation in ground heat transfer. The impact of this improvement may result in increased or reduced building heating/cooling loads for homes with slabs and/or foundation walls. On average, we noticed that homes with a slab and/or foundation wall result in 20.14% and 2.48% of reduction in heating and cooling load respectively.
The new algorithm relies not only on the heat transfer properties of slabs and foundation walls, but also on the type of construction. We strongly encourage our raters to use our Assembly Calculator to model foundation walls to get accurate results in Ekotrope Version 4.2 onwards. We have also updated our modeling guidelines for slabs and foundation walls in the Building Envelope Modeling Help articles on Freshdesk.
2. Improvements as per ANSI and MINHERS standard update:
There are several important updates to the ANSI/RESNET 301-2022 standard affecting the overall calculations. Major improvements in this area include updating the duct load calculations (ANSI/RESNET 301-2022 Addendum C), correction in conversion factors used for SEER2/HSPF2 (MINHERS Addendum 71f), using updated rates for emission calculations as proposed by Carbon Index calculation (MINHERS Addendum 66f), and using 100% adjacent shading factor for glazings in all proposed and reference homes irrespective of the input (to improve consistency across software tools).
3. Corrections in National Energy Codes and Bug-fixes:
In Version 4.2, we fixed a handful of issues in the modeling of reference homes for several national Energy Codes and other calculations. It is worth mentioning that a portion of these were brought to our attention by our users through our support team. We greatly appreciate those of you who found issues in Ekotrope RATER and reported them to help us improve! Please continue to do so. These corrections are as follows:
Removed skylights in all IECC based reference homes, following Table R405.4.2(1).
Updated the backup fuel type of Air Source Heat Pumps to be electric with efficiency 1 in ENERGY STAR V3 and V3.1 reference home builders in certain climate zones, according to the ERI target documents.
Updated ENERGY STAR MFNC 2019 reference homes to set window operability the same as in the rated home and fixed a bug related to the infiltration calculation.
Fixed a bug in the following reference homes related to the application of capacity fault factors and sizing of HVAC equipment:
HERS Rated and Reference homes
Tax Credit Reference home
ENERGY STAR V3.2 and DOE ZERH SF V2 Target home
IECC 2018 and 2021 ERI Rated and Reference homes
New York and Georgia 2020 ERI Rated and Reference homes
Fixed the calculation of conditioned space gains from shared water heaters.
Fixed a bug in updating shared water heaters to federal minimum efficiency.
Changed the equipment type of a Ground Source Heat Pump to a Residential Water Heater if reference homes specify different equipment specifications (this only corrects reports and does not have any impact on energy modeling).
Fixed a bug in R&A reference homes related to updating duct locations such that the supply and return duct area does not exceed 100%.
We hope that this information helps you as you transition to new versions of Ekotrope. As always, we are grateful for the contributions made by our users and other industry stakeholders as we grow and continue to enhance energy modeling experience with Ekotrope RATER. Please feel free to contact us at support@ekotrope.com if you have any further questions. We look forward to helping you with any issues you may have.