Portfolio Manager Technical Reference: EV Charging

EV Charging and the ENERGY STAR Score in the United States and Canada

The ENERGY STAR score provides a fair assessment of the energy performance of a property relative to its peers, taking into account the climate, weather, and business activities at the property. Electric vehicle (EV) charging is becoming an increasingly common, and potentially energy-intensive service at commercial properties. The ENERGY STAR score allows for an adjustment to accommodate the presence of EV charging as the goal of the ENERGY STAR score is to rate the energy performance of the primary use of the building.

• Technical Approach. Typical values for energy use per EV charging station are used to estimate annual energy use for EV charging. The estimated energy use is subtracted from the building’s actual energy use, yielding an estimate of the energy use of the building without EV charging. This allows the building to be evaluated as though it does not have EV charging.
• Property Types. Electric Vehicle Charging Stations can be entered alongside all property types and adjustments will be incorporated into the ENERGY STAR score for eligible property types. This includes dedicated Level One Charging Stations, Level Two Charging Stations, and DC Fast Charging Stations. If an EV charging station is separately metered from the main facility with which it is associated, it does not need to be entered into Portfolio Manager.
• Adjustments. The electric vehicle charging adjustment model is based on typical values of energy use for EV charging. Users will enter the number and type of EV charging stations. Adjustments will be based on assumptions for utilization and average energy dispensed per session.
• Release Date. The ENERGY STAR adjustment for EV charging was released in July 2024.

This page details how the ENERGY STAR score accounts for EV charging. More information on the overall approach to develop ENERGY STAR scores is covered in our Technical Reference for the ENERGY STAR Score, available at www.energystar.gov/ENERGYSTARscore. 

The subsequent sections offer specific details on the development of the EV Charging model:

1. Theoretical Background
2. EV Charging Adjustment
3. Example Calculation

Theoretical Background

The energy consumption for charging electric vehicles depends on four key factors: the type and number of charging stations, utilization frequency, and the average energy dispensed per session. For each station type, general assumptions and calculations can be made based on typical energy use data and safety principles. EV charging stations come in three main types: level one, level two, and DC fast (sometimes called level three). All three types can be installed at a commercial property, although due to infrastructural barriers DC fast adoption has been slower to date. Argonne National Laboratory has conducted national research to develop the Alternative Fuel Life-cycle Environmental and Economic Transportation (AFLEET) tool¹ that estimates energy usage and emissions from various charging scenarios. AFLEET was utilized to calculate the charging scenarios described below. For each property entering EV charging stations, the following adjustment will be applied:

Estimated Total Annual Site Energy Usage (kBtu) per EV Charger 
= 
Charger type-specific Average Energy Dispensed per Session (kWh) 
× 
Charger type-specific Weekly Utilization (# sessions/week) 
× 
52 (weeks) 
× 
3.412 (kBtu/kWh)

Level One Charging

Level one charging (at 120V) is less common at commercial properties and little market data is available to estimate level one charging usage across different property types. However, AFLEET total cost of ownership (TCO) assumptions suggest that on average level one chargers dispense the same amount of energy per session as level two chargers. Therefore, the level one EV charging adjustment in Portfolio Manager conservatively estimates the same total annual site energy usage per Level One Charging Station as per Level Two Charging Station.

For the purposes of this adjustment, Level One Charging Stations can be counted as the number of vehicles which can be simultaneously charged with the property’s level one charging equipment.

Level Two Charging

Level two charging (at 240V) is most common at commercial properties and Argonne National Laboratory determined that the following property types have distinct charging and utilization patterns: Retail and Leisure, Education, Healthcare, Workplace, Multi-Unit Dwelling, and Single-Unit Dwelling. However, EPA determined that the minor differences in estimates across property types for level one and level two charging were not sufficient to warrant different EV charging adjustments for different property types. Based on AFLEET data, EPA determined that the average public energy dispensed per Level Two Charging Station across all property types is 4 kW per session for 4.63 sessions per week and 2.38 hours per session.

DC Fast Charging

Level three, or DC fast charging (at 480V) often requires significant electric infrastructure installation. However, according to the United States Department of Transportation it takes an average of 20 minutes to 1 hour to reach 80% charge in a passenger electric vehicle.² Due to these improved charge times, Argonne National Laboratory determined that the average public energy dispensed across all property types is 24 kW per session for 15 sessions per week and 0.4 hours per session. The Electric Vehicle Widescale Analysis for Tomorrow’s Transportation Solutions (EV Watts) is a project funded by the U.S. Department of Energy which brings together several Clean Cities coalitions across the U.S. as well as ChargePoint and Sawatch Labs to collect real-world use data from plug-in electric vehicles and charging stations.³ EV Watts notes that the average EV driver takes approximately fifteen trips per week of nine miles. EV drivers may also be more likely to “top off” their battery when given the chance during their daily activities rather than “filling the tank” as many drivers of petroleum fueled vehicles do, given the risks of reaching a low battery. Opportunity-based charging, therefore, lends itself to multiple charging sessions per week at shorter periods of time for high-capacity DC fast chargers.

EV Charging Adjustment

Within Portfolio Manager, the energy use assumptions described in the previous section are used to compute an EV charging adjustment within Portfolio Manager for each type of charging station. The table below shows the utilization and power supply assumptions used to create the EV charging adjustment across all scorable property types. These site energy values are then multiplied by the source-site ratio for electricity for the U.S. or Canada to determine the source energy adjustments for both countries.⁴

Table references: Average Energy Dispensed per Session(kWh)⁵, Average Utilization (Sessions per week)⁶

For example, the equation for estimated EV Charging Source Energy Usage in the United States is:

Predicted EV Charging Source Energy Usage (kBtu/yr)
= 8,663 * (Number of Level One EV Charging Stations) * 2.8
+ 8,663 * (Number of Level Two EV Charging Stations) * 2.8
+ 25,549 * (Number of DC Fast EV Charging Stations) * 2.8

A cap on the estimate of EV charging energy dispensed is applied to properties where the combined estimated EV charging source energy usage exceeds:

• 12.1296 kBtu per square foot of a U.S. property’s gross floor area, or 
• 0.090036 GJ per square meter of a Canadian property’s gross floor area. 

The cap is equivalent to one (1) Level Two Charging Station per 2,000 square feet (or per 185.8 square meters) of a property’s gross floor area. It is intended to limit the impact of the adjustment on the scores of properties with extensive unmetered EV charging infrastructure and results in a more conservative estimate for these properties. Submetering your EV charging energy is the most accurate method of accounting for EV charging.

Note that the ENERGY STAR score for the U.S. is developed using units of kBtu for energy, while the ENERGY STAR score for Canada is developed using units of gigajoules (GJ) for energy. While the calculations within Portfolio Manager occur in different units, the results for the any property (U.S. or Canadian) can be displayed in Portfolio Manager in either kBtu or GJ.

Example Calculation

As detailed in our Technical Reference for the ENERGY STAR Score, there are five steps to compute a score. The following is a specific example for an office with EV charging in the U.S.:

1. User enters building data into Portfolio Manager

• 12 months of energy use information for all energy types (annual values, entered in monthly meter entries)
• Physical building information (size, location, etc.) and use details describing building activity (hours, etc.)