What Has Changed in Version 4.1?
We released Version 4.1 of the Ekotrope energy simulation in Beta on December 7th, 2022. We have submitted our accreditation application to RESNET and will fully release Version 4.1 once it is approved.
With this new Version, there will be changes to HERS scores and other results for some homes. In this article, we will share how we are seeing results change and describe the improvements we made that are causing those changes. For a full list of changes in 4.1 and other versions, refer to our Version Release Notes.
Impact on Results:
We compared a sample of randomly selected HERS rated homes to see how results change in Version 4.1 compared to the latest Version, 4.0.2. Those results are as follows:
HERS:
Average goes up by 0.4 in Version 4.1
90% of homes are within 1 point of their Score in 4.0.2
A small fraction of homes had a large increase. There are two major reasons (explained later in this article) behind this increase:
We improved our duct load calculation and because of this, homes with high duct leakage rates using default values for design airflow would result in an increase in HERS score.
We fixed the HERS reference home to have fully insulated basement walls. In earlier versions, it was modeled to have an insulation area similar to the rated home. This will result in an increase of HERS score when a home has partially insulated basement walls.
IECC:
IECC 2018 ERI: Number of homes passing the code increased by 11%. This was caused by an update to the ERI reference home based on an important interpretation from the ICC. In earlier versions, IECC 2018 and 2021 ERI reference homes are modeled to have a sum of balanced mechanical ventilation rate and infiltration rate equal to the minimum ventilation rate specified in the respective IECC codes. In Version 4.1 we have updated both ERI reference homes to have infiltration rates as per ANSI/RESNET Std 301.
IECC 2015 Performance Compliance: 0.95% easier in Version 4.1
DOE Zero Energy Ready Home:
Target HERS score increased by an average of 1 point, making DOE ZER slightly easier to meet.
ENERGY STAR 3.1:
Target HERS score increased by an average of 0.26 points
Federal Minimum Efficiencies 2023:
On January 1, 2023, higher minimum efficiency requirements for heat pumps and air conditioners are going into effect across the country. (1) Various reference homes and utility programs that use the federal minimum standards for updating heating and cooling equipment efficiencies will use these new efficiency values in Version 4.1. In general, with this change, we expect to see a decrease in the savings earned by a home when compared to a reference home with updated federal minimum efficiencies.
Corrections in IECC Codes:
The IECC 2021 reference home is corrected to use updated efficacy values for mechanical ventilation systems. ERI reference homes for IECC 2018 and 2021 are updated to use infiltration rates as specified in ANSI/RESNET 301. This may result in more homes passing the ERI code in Version 4.1.
Revision 8 of DOE Zero Energy Ready Home (ZERH) Program:
DOE ZERH Rev 8 requires the target home to apply HVAC Grade III along with some other minor changes to lighting and appliances and Version 4.1 will include these changes. In Versions earlier than 4.1, we did not apply HVAC Grading to DOE ZERH analysis to avoid providing any credit/penalty to homes with HVAC Grading. In Version 4.1, we expect homes to get credit if they achieve HVAC Grades better than III.
Improvements in Algorithm:
Version 4.1 includes some key improvements to our duct load calculations. We were seeing homes getting penalized for using specified design airflow value compared to a default airflow configuration. We have updated our duct load calculations to use separate design airflow values to provide more accurate analysis. Version 4.1 will also utilize MINHERS Section 303.1 Exception 4 (2) to estimate default airflow value (i.e., 400 CFM per ton) for duct load calculations. Due to this change, homes with high duct leakage rates in unconditioned space may see an increase in duct loads and hence, the HERS score. When they are known, we recommend specifying design airflow values rather than using the defaults to improve accuracy.
Bug-fixes:
In Version 4.1, we have fixed a handful of issues in our calculations. Some of these were reported by our users to our support team. Thanks to those of you who reported issues! Please continue to do so. These fixes are:
1. Foundation walls
Reference homes with a specified R-value for insulation to foundation walls are now considered to be fully insulated in Version 4.1. This may result in reduced performance when compared to such reference homes (e.g., HERS, IECC, EnergyStar, etc.). We have also fixed a bug related to the UA value calculation for foundation walls without continuous insulation.
2. Gross COP (Coefficient of Performance) calculation:
In Version 4.0, we were using measured watt draw to estimate the gross COP for a heating/cooling system. This resulted in some odd behavior where a lower measured watt draw could result in worse overall performance. With Version 4.1, we have updated our algorithm to calculate gross COP using fan efficiency estimated based on the motor type and the equipment’s rated efficiency.
3. Water recirculation pump energy calculation:
Version 4.1 includes a fix to our energy consumption calculation to incorporate the energy used by a recirculation pump for the water system. This may result in an increase in HERS score as the HERS reference home is specified to not have any recirculation pump according to the ANSI/RESNET Standard 301-2019.
4. Miscellaneous:
Apart from the improvements listed above, we have fixed a few minor issues with the analysis related to energy consumption calculations for equipment with more than one attached distribution systems, latent cooling consumption, dehumidifier consumption, etc. These changes will have little or no impact on the HERS score as they will also apply to the HERS reference home.
We appreciate continuous efforts provided by our users and other stakeholders in this industry to help us in improving the energy modeling and overall experience with Ekotrope RATER. We hope you find the information provided on updates and improvements in Version 4.1 are useful for you to troubleshoot any unexpected change in results. Please feel free to contact us at support@ekotrope.com for any further questions. We look forward to helping you with any issues you may have.
(1) For more information on this, please checkout our blog on the impact of SEER2 and HSPF2.
(2) Reference: https://www.resnet.us/wp-content/uploads/MINHERS-Updated-1-1-2021.pdf