Is Your Facility Ready for a Surge in Electric Vehicle Charging?
By Rob Lahue, PE, CDT
For engineers charged with designing a solution to meet this increased electrical demand, several factors should be considered, including:
The impact of EV charging loads on a commercial building electrical system
To understand the scale of this challenge, let’s consider a (fictitious) example: Parking Inc. is developing a new 1000-space parking garage in Chicago, Illinois. The developer estimates up to approximately 5 percent of customers will drive EV’s to the garage and will require charging stations.
The developer engages an architect and engineer to design the building. Using the developer’s estimates, the engineer calculates a bulk load for 50 Level 2 AC charging circuits (assume each draw 8.3kW) for a total of 415kW. That is 1152A on a 208/120V three-phase service and could be served from a single 1600A switchboard (Note that NEC 2023, article 625.42 defines EV chargers as continuous loads). A significant load, but not insurmountable.
During the team’s due diligence review, the engineer identifies a requirement previously unknown to the developer. The Chicago Energy Transformation Code (CETC) requires that at least 20 percent of parking spaces be EV-Ready or EV-Installed. Instead of 50 parking spaces, the electrical service will need to accommodate chargers for 200 parking spaces and capacity for 1660kW of EV chargers (just over 4600A at 208/120V).
Ideally, infrastructure can be provided to accommodate the additional EV parking spaces. However, if the engineer designs for the entirety of the connected load, they are now potentially looking at multiple services and switchboards. Depending on the nature of the project, this may become cost- and space-prohibitive. It may be time to consider incorporating a load management strategy for the EV charging system – however, it’s important to first understand the capabilities and benefits that EV load management systems offer.
Capabilities of EV load management systems
To tackle a project like the one described above, our goals with EV load management are to:
Load management systems accomplish this by employing a form of either static or dynamic load management, or a combination of both.
Static load management allows constraints to be applied to a system based on a non-changing variable. This typically involves pre-defined rules and schedules, for example, setting specific hours for which vehicles are allowed to charge or manually adjusting the EV charger to a specific charging capacity. Dynamic load management allows constraints to be applied to a system based on continuously changing variables. This could include automatically adjusting vehicle charging rates based on grid conditions, quantity of vehicles charging, or their respective battery levels.
Vehicle charging systems equipped with static and dynamic load management have the potential for a huge amount of flexibility. The parking garage scenario described above lends itself well to a combination of static and dynamic load management. First, the Energy Management System (EMS) is programmed with a static (unchanging) upper limit to the main service so that it never exceeds 415kW of continuous load. The EMS is then programmed to employ a form of dynamic load management which will automatically adjust charging power to users based on the quantity of vehicles charging, and their respective battery levels. When a car is fully charged or is unplugged, the system adjusts accordingly to allow more power for other uncharged vehicles. See Figure 1 below to illustrate this example (using slightly smaller numbers).
This seems like an excellent solution for our parking garage example, but many engineers may express some hesitancy. Does this mean a system could be safely designed for installing 1660kW of EV chargers on an electrical service rated only for 415kW? Let’s see what the NEC has to say about this and review some solutions the industry is continuing to develop.
The NEC on electric vehicle supply equipment (EVSE) and load management systems
Current versions of the NEC (2020, 2023) provide some guidance on the use of load management for sizing EV infrastructure, but it is loosely defined. Articles 625 and 750 appear to offer much flexibility for sizing EV infrastructure, with two important caveats:
Keep these considerations in mind as we take a closer look at NEC articles 625 and 750, and the various solutions manufacturers are continuing to develop.
NEC 625 is unique in its approach to addressing how infrastructure should be sized for EV charging loads. There are no demand factors to calculate based on common variables like the quantity or types of chargers. Instead, it broadly addresses two systems for load management control, and permits those systems (with several exceptions) to dictate the size of the electrical infrastructure serving the EV chargers. The methods are 1) Load Control using an EMS, and 2) EVSE with adjustable settings (see Figure 2). For both methods, the NEC references article 750.30 for Energy Management Systems.
NEC 750.30 has been expanded in the 2023 edition and identifies several requirements for the EMS if one is used to limit the current on a conductor. Engineers must very thoroughly consider how these requirements will be met, and should be able to answer these questions:
The EV marketplace is developing a variety of EVSE solutions to meet both methods addressed by NEC 625. For EVSE with adjustable trip settings, many products have incorporated a manually adjustable means within the wall- or pedestal-mounted EVSE enclosure (e.g., dip switches) as a basic form of static load control. Some system configurations employ the use of “smart” circuit breakers, which have the EVSE integrated into a molded case circuit breaker and allow the EVSE output and overcurrent protection to be adjusted together.
For the energy management system approach, many providers are taking the same route. The EV chargers are equipped with communications to interface with a cloud-based energy management system. Load control is performed through software, which can apply both static and dynamic load management strategies. Both types of EV chargers described above (wall/pedestal-mounted at the parking space or integrated into a “smart breaker”) can be integrated into a cloud-based load management system.
Present and future design considerations
We advise engineers, architects, and developers to proceed with caution when designing systems that will rely on a load management system. These are exciting advancements in our industry and stand to offer great benefits, but the technology and applications of EMS and EVSE are very new. Codes and standards are racing to catch up with public demand and manufacturer solutions, leaving potential gaps in terms of safety and security. Below are several considerations we encourage industry professionals to review and discuss regarding automatic EV load management systems:
Finally, it is imperative to review the latest technologies and information available, especially before incorporating into a new project design. Identifying solutions that can adapt to evolving codes, standards, and technologies, and specifying trusted vendors who will continue to support their products in the future will be critical for facility longevity. Despite our cautionary nature as engineers, we are very excited about the future of these technologies and look forward to working with the industry to answer these questions.
Rob Lahue freely shares his experience and passion for electrical engineering and EV technology is support of ESD’s mission to improve society through the built environment.
To learn more about EV station challenges and solutions or to get more information on how our engineers can help with your project, reach out to ESD’s MEP/FP Engineering teams.
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