How to Select a BTMS for an Electric Truck or Bus

When selecting a battery thermal management system (BTMS) for electric trucks or buses, the decision should be based on the vehicle’s actual operating conditions, rather than solely on the battery’s kilowatt-hour (kWh) rating or nominal capacity. Before comparing different suppliers, you need to prepare a standardized set of thermal, electrical, control, and packaging parameters. This guide will explain what data to collect, how to conduct comparisons, and which aspects must be validated through prototype testing.

Start with Actual Operating Conditions (Operating Cycles), Not Just Product Catalogs

Identify the operating conditions that may determine the limits of the thermal design, such as: normal driving, heavy-load operation, charging, cold starts, and operation while parked. City buses, with their fixed stops and charging schedules, may require control strategies that are entirely different from those of trucks, which have varying loads and routes.

Be sure to have the battery team and the vehicle team jointly determine these key operating conditions; never simply assume that a certain “nominal operating condition” can cover all real-world usage scenarios.

For each operating condition, document the environmental conditions, duration, battery current, initial battery pack temperature, charging power (if applicable), and the temperature limits specified by the battery supplier. These limits must be based on the actual design of the battery pack; this document cannot provide specific values.

Translate Battery Pack Requirements into Thermal Management Requirements

Define the expected heat generation (or measured heat dissipation requirements) of the battery pack under each key operating condition, the desired coolant inlet temperature, the permissible internal temperature difference within the battery pack, and the preheating targets.

Distinguish between “short-term peak loads” and “sustained loads.” For example, a nominal “12 kW” specification does not indicate whether that capacity can actually be achieved under your specific ambient temperature, coolant temperature, and electrical conditions.

If battery pack thermal load data is missing, list it as a design input to be clarified. Never select a thermal management system based solely on battery energy (kWh). Relevant research from the National Renewable Energy Laboratory (NREL) indicates that charge/discharge rates, ambient temperature, and the geometry of the cooling system are critical to the thermal behavior of the battery.

Define the Complete Interface Between the Cooling System and the Vehicle

When evaluating suppliers, do not focus solely on cooling targets. Document in detail the coolant specifications, required flow rate range, allowable pressure drop, hose connection methods, responsibility for the water pump (who provides it), and the measurement locations for inlet and outlet temperatures. Additionally, clarify whether the battery thermal management loop is independent or shares thermal management hardware with other vehicle systems.

Next, clarify the high- and low-voltage power supplies, connector requirements, available electrical power, CAN messages, command ownership, fault reporting mechanisms, and the behavioral logic for entering a safe state.

Furthermore, consider the installation space envelope, installation orientation, no-go zones, vibration environment, and maintenance access space. Even if a component meets thermal management targets during bench testing, it may still fail validation during the vehicle integration phase.

Comparison of Candidate Systems Under Identical Conditions

Each candidate system must provide its cooling and heating performance data under identical environmental and refrigerant conditions. Compare the electrical power input, refrigerant flow rate, and pressure drop under these operating conditions. It must be confirmed whether the provided values represent “continuous operation” performance or are limited to specific operating periods.

Clearly define the scope of each test (e.g., whether components such as water pumps, fans, heat exchangers, controllers, and hoses are included); otherwise, data that is inherently incomparable may be mistakenly considered comparable.

EVLINK provides separate pages for 3 kW, 5 kW, and 12 kW Battery Thermal Management Systems (BTMS). These specifications are intended solely as a starting point for configuration discussions and do not constitute specific recommendations for any particular truck or bus.

Create a Comparison Matrix Before Requesting a Quote

A practical comparison table should be organized by “operating conditions” rather than “suppliers” as the row criteria. For each operating condition, enter the required cooling or heating capacity, the maximum duration under that load, the ambient temperature, the target coolant inlet temperature, the available electrical power, and the permissible battery pack temperature response range.

Then, ask each supplier to enter their predicted or measured performance data under the same conditions. If a value is not provided, leave the cell blank; it is far safer to handle blank entries than to rely on a default “qualified” conclusion.

List cooling, heating, and power consumption in separate columns. If a system meets the cooling target but has excessively high power consumption, it may not meet the vehicle’s energy consumption budget requirements. If a heating solution meets the steady-state target but has a response time that is too slow, it may fail to meet the specified charging time window. These are project-level decisions, not a general ranking of BTMS models.

Balancing Extreme and Daily Operating Conditions

While maximum thermal load is certainly important, it should not be the sole basis for system design. Selecting a high-power system solely to handle brief peak loads may result in frequent start-stop cycles or low efficiency during most of the vehicle’s operation. Conversely, selecting a system based solely on typical driving conditions may fail to handle demanding scenarios such as high-load charging or hill climbing.

Confirm the duration of various operating conditions with the vehicle engineering team and verify whether the battery supplier permits temporary increases in battery temperature. For any time-limited peak rated parameters, be sure to document the underlying assumptions.

Selection in cold climates also requires rigorous evaluation. Clarify the initial temperatures of the battery and coolant, the available pre-conditioning (preheating/pre-cooling) time, and whether the vehicle can draw power from the grid while parked. Clearly define the specific criteria for the battery pack’s “chargeable” state.

When evaluating vehicle circuits, do not rely solely on the heater’s nominal power (kW value) for estimates; instead, base the analysis on actual measured temperature rise curves.

Clarify integration responsibilities as early as possible.

There are multiple interfaces between the Battery Thermal Management System (BTMS) supplier, the battery integrator, and the Original Equipment Manufacturer (OEM). All parties should clarify the following responsibilities: Who is responsible for determining the chemical composition of the coolant; who is responsible for the water pump and expansion tank; who is responsible for providing control sensors; and who is responsible for approving the CAN bus message list.

Additionally, it must be clarified which controller has the final decision-making authority when the battery issues a protection request but the vehicle system requires a different operating mode. If these responsibilities remain undefined prior to the delivery of prototype samples, project delays may occur even if the hardware itself meets technical specifications.

An interface control document must be provided, which should include connector definitions, message timing, commands under normal conditions, and fault response mechanisms.

During layout (packaging) reviews, consideration must be given not only to the physical dimensions of the components but also to the actual routing of lines and maintenance space requirements. For truck or bus fleets, the ease of operation during subsequent maintenance—such as draining, inspection, and component replacement—is just as important as the adaptability during initial installation.

How can you avoid making misleading comparisons?

Is it possible to select a battery thermal management system (BTMS) based solely on battery capacity (measured in kilowatt-hours, kWh)?

No. A battery pack’s energy rating only represents the energy it stores and does not reflect the heat generated during actual driving or charging. You should obtain thermal performance data specific to that battery pack or a validated model, and conduct a comparative evaluation of candidate systems under the corresponding operating conditions.

Does a higher cooling capacity rating necessarily mean greater safety?

Not necessarily. You need to examine the rated operating conditions, electrical load, packaging structure, performance under low load, and the vehicle’s actual operating conditions (duty cycle). If the cooling circuit design is unreasonable or the control interfaces are incompatible, simply increasing cooling capacity will not solve the problem.

What should you do if a supplier provides only a single rated capacity value?

Request that the supplier provide test boundary conditions, as well as performance data under your critical ambient temperatures, coolant conditions, and voltage ranges. Until these conditions are clarified, treat this value only as a reference for preliminary screening—not as proof of suitability for your vehicle.

How can you issue an effective Request for Quote (RFQ) to obtain useful responses?

• Vehicle type, driving routes or operating conditions, target market, and environmental design conditions.
• Battery pack configuration, permissible temperature limits, and estimated thermal load values or test data.
• Charging and cold-start conditions (including specific response time requirements).
• Coolant type, target inlet temperature, flow rate range, and pressure drop limits.
• Power supply method, CAN bus interface, control authority, and fault handling requirements.
• Enclosure drawings, installation constraints, maintenance accessibility, and prototype development schedule.
• Your testing conditions and acceptance criteria for evaluating candidate solutions.

If a parameter is not yet clear, please mark it as “to be confirmed” and designate a responsible person. This is far more meaningful than including hypothetical values in the RFQ document.

When Is the Selection Process Truly Complete?

Mere alignment between capacity specifications and estimated load does not mean the selection process is complete. The proposed solution must also be validated against mutually agreed-upon test conditions and project-specific acceptance criteria.

It is essential to validate critical driving, charging, and cold-start conditions in both bench test and vehicle integration environments, while also covering control logic and fault handling mechanisms. The U.S. Department of Energy (DOE) notes that thermal management requirements during charging are a critical factor that must be considered during system selection and cannot be inferred solely based on the battery’s energy rating.

To explore our product portfolio, please refer to the EVLINK Battery Thermal Management System. If you have vehicle specifications or preliminary circuit diagrams, please send us your operating conditions and interface information so we can conduct an engineering review.