This article explains what the HERS Index is and how cove.tool can help users design an energy-efficient building that earns the lowest-possible HERS Index rating.
What is the HERS Index?
The Home Energy Rating System (HERS) Index was developed by the Residential Energy Services Network (RESNET) and is a nationally recognized system for inspecting and calculating a home’s energy performance. How it works is a certified reviewer assesses a home, then gives the property a score's on the HERS Index between 0-150. The lower the score the more energy-efficient the building is operating, and the higher the score the reviewer will recommend modifications that can be made for greater energy savings.
Home's which have received a low HERS Index Score can command a higher resale price. They are also helpful for buyers trying to anticipate the costs of energy bills and the potential cost of needed upgrades. As of 2021, over 3 MILLION HOMES in the United States have been HERS Rated.
Understanding the HERS Index Score
To calculate a home’s HERS Index Score, a certified RESNET HERS Rater does an energy rating on your home and compares the data against a ‘reference home’– a designed-model home of the same size and shape as the actual home.
For example, a standard new home is awarded a rating of 100. A home with a HERS Index Score of 70 is 30% more energy efficient than the RESNET Reference Home. A home with a HERS Index Score of 130 is 30% less energy efficient than the RESNET Reference Home.
The lower the home rates the more energy efficient it is. Since the energy rating will fall between 0 and 150, a home with a score of 150 ratings is incredibly inefficient and will require a significant financial investment to get it to somewhere efficient. A home with a score of 0 can only be a Net Zero Energy Home. This means that this home produces as much energy through renewable resources, such as solar panels, as it consumes. Two more points on the HERS index worth listing are 130, which is the typical resale home score, and 70 is considered an admirable score. More on understanding the HERS score can be seen here.
What affects a home's HERS Score?
A home energy rating includes both carrying out an energy analysis (BEM, building energy model) in the pre-construction phase and onsite inspections after construction, and typically a blower door test. Variables included in an energy rating are:
Proper Insulation and Airtightness in:
Attics, foundations, and crawlspaces
All exterior walls (both above and below grade)
Floors over unconditioned spaces (like garages or cellars)
Ceilings and roofs
Windows and doors, vents, and ductwork
Efficiency in your:
HVAC systems, water heating system, and temperature controls (thermostat)
Lighting and Appliances
How can you use cove.tool to ease the HERS rating process?
After a HERS rater evaluates your home, they provide recommendations on how you can improve your home's energy efficiency which might or might not be cheap and easily implementable. cove.tool can be used in the early stages of design and can help in the following ways:
Saving time
Creating an energy-efficient design and being aware of a home's EUI from the early/schematic design stage can prevent major design changes after the construction documents are analyzed by a HERS Rater.
Facade prototyping tool can be used to explore the best orientation and WWR of the fenestration as well as appropriate shading devices.
Saving cost
Most optimized options that fit the budget of the project can be explored using the optimization.tool after or before the HERS Rater recommendations are provided.
cove.tool can also be used proactively while the home is being designed. Each analysis tool can optimize energy performance and save cost!
Happy Modeling!!