HVCH Pressure Drop: Matching the Heater to the Vehicle Coolant Loop

Even if a high-pressure coolant heater meets the voltage and heating power requirements, it may not necessarily be compatible with the vehicle’s cooling circuit. Before approving a sample, it is essential to confirm that the water pump can deliver the required flow rate within the complete installation circuit. The heater’s pressure drop curve is only one of the reference factors for making this determination; it is not the sole basis for selecting a water pump.

For electric buses or trucks, the key question is: Under a specific heating mode, using the selected coolant and with the valves in their actual positions, what is the actual flow rate through the heater?

Clarifying the Specific Implications of Pressure Drop Data

Quotations may list only the pressure drop value at a specific flow rate. When comparing products from different suppliers, it is essential to first clarify the operating conditions underlying that data. You need to understand the heater’s specific configuration, the coolant’s formulation and concentration, the fluid temperature, the flow direction, and the measurement location. Additionally, you must confirm whether the pressure drop data applies only to the heater itself or includes test hoses, connectors, or other components.

“Pressure drop” and “allowable operating pressure” address entirely different issues. Pressure drop describes the pressure difference generated when a fluid flows through a component at a specific flow rate, whereas pressure ratings refer to the permissible pressure range. Conducting leak tests or pressure tests does not determine the actual coolant flow rate achievable in a vehicle’s cooling circuit.

Ensure consistency in units. If one supplier provides parameters in “meters” (head) while another uses “kilopascals” (pressure differential), convert the values based on the fluid’s density; never compare the numerical values directly.

The water pump should be selected based on the entire circuit (not just the heater).

For a simple series circuit, the pressure losses of each component under the same flow rate and fluid conditions can be summed as follows:

Δp_loop(Q) = Δp_heater(Q) + Δp_hoses(Q) + Δp_valves(Q) + Δp_other components(Q)

This is merely a calculation for planning purposes and cannot replace a validated hydraulic model. If parallel branches are involved, a network analysis is required: the total flow rate of the pump is not equivalent to the flow rate through the branch containing the heater.

Overlay the pump characteristic curve with the circuit demand curve; the point of intersection represents the expected operating point for that configuration. Additionally, verify the pump’s permissible operating range; simply finding the intersection point does not guarantee that the design is reasonable or feasible.

Relying solely on the “maximum flow rate” specified on the pump nameplate is insufficient as a basis for selection. Request performance curves at the intended supply voltage and control settings, and make necessary adjustments based on the selected coolant. Never simply add the maximum head to the maximum flow rate, assuming the pump can simultaneously achieve both of these maximum values.

Evaluate cold-start conditions and various valve configurations.

Hot-run conditions do not necessarily represent the most severe conditions during startup. The physical properties of the coolant vary with temperature and composition, which in turn affect circuit resistance and pump performance. Consult your pump and heater suppliers to confirm which data applies to your cold-start requirements.

Additionally, verify the various configurations created by the vehicle’s control system. Battery heating, cabin heating, and hybrid heating modes may activate different flow paths; bypass circuits may also alter flow distribution. Even if control commands increase the water pump speed, this does not necessarily mean that the required flow rate is actually being delivered to the heater.

Before ordering hardware, compile a list of operating modes. For each mode, clearly identify the activated flow paths, water pump control commands, expected flow rates in the heater branches, applicable temperature conditions, and any unresolved assumptions. Compared to repeatedly comparing heater ratings, this approach often reveals missing key information more quickly.

Ensure that thermal and hydraulic checks are correlated

The heat transfer equation for the coolant provides an effective means of consistency checking:

P_coolant = ṁ × c_p × (T_out − T_in)

where ṁ is the mass flow rate, and c_p is the specific heat capacity of the fluid under the corresponding operating conditions. The measured heat transfer rate of the coolant may not necessarily equal the electrical input power exactly, particularly during the equipment warm-up phase or when heat losses are significant.

Never derive a universal minimum flow rate based solely on this formula. Please consult the official technical documentation for the selected heater to obtain its operating limits and control requirements. Temperature rise values derived solely from calculations cannot determine local temperatures, the response of protective mechanisms, or whether the heater is suitable for low-flow conditions.

What Should Be Included in a Supplier Evaluation

Verify the installed configuration prior to commissioning.

Before testing, reach agreement on measurement boundaries, sensor suitability, initial conditions, and acceptance criteria. Record the following on a unified timeline: heater inlet and outlet temperatures, heater branch flow rates, pressure differentials, pump command and feedback signals, valve statuses, heating demand, and relevant fault information.

Please follow the approved fluid filling and venting procedures. Document any differences between the development test bench and the final production installation, including hose routing and version changes for individual components. Under no circumstances should any protective functions be bypassed to obtain “ideal” test results.

If there is a deviation between the measured flow rate and the calculated value, thoroughly inspect the circuit and measurement methods before replacing the heater or switching to a higher-power pump. Resolve this deviation in accordance with established requirements, and promptly update drawings and configuration records.

Preparing EVLINK Heater Evaluation Materials

When discussing high-pressure coolant heaters with EVLINK, please provide the following information: the proposed model, voltage range, heating requirements, coolant specifications, relevant pump parameters, and circuit diagrams, along with a description of operating modes and installation constraints.

Request relevant pressure drop data and ask for written confirmation of the operating conditions for the selected configuration. This will provide a clear basis for the engineering and procurement teams to approve samples, rather than relying solely on rated power and a single pressure drop value.