Specify BESS chiller flow rate together with external circuit pressure drop, coolant composition and operating temperature. Calculate flow from heat load and coolant temperature rise, then check the battery supplier’s branch-flow limits. Ask for the available differential pressure between the unit’s supply and return ports at that flow.
A flow rate without an accompanying pressure drop leaves the main hydraulic question open. When we review an RFQ at Cooltechx, we look for those figures together, with the coolant and operating temperature beside them. That gives you and us a clear operating point to discuss.
Start with the hydraulic schedule below and a simple loop drawing. The BESS cooling system project-input guide covers the wider selection inputs; here we focus on the numbers you need for the liquid circuit.
How to calculate BESS cooling flow rate
The numbers in the calculations below demonstrate the method; for your project, replace the inputs with data from the cell manufacturer and coolant supplier. Start with the heat carried by the coolant at steady state:
Flow (L/min) = 60 × Q ÷ (ρ × cp × ΔT)
Q = heat load in kW; ρ = coolant density in kg/L; cp = specific heat in kJ/(kg·K); ΔT = return minus supply temperature in K.
Worked example: 30 kW heat load and a 5 K rise
Using rounded water properties, ρ = 1.00 kg/L and cp = 4.18 kJ/(kg·K), the estimated flow is 60 × 30 ÷ (1.00 × 4.18 × 5) = 86.1 L/min. At a 3 K rise, the same heat load would require approximately 143.5 L/min.
Check the result against the battery supplier’s cold-plate flow limits and allowable temperature difference. Both belong in the RFQ alongside the heat load.
For glycol mixtures, give the concentration and state whether it is by mass or volume. Get density and specific heat at the design temperature from the fluid supplier, using a resource such as Dow’s heat-transfer-fluid tools.
2 MWh and 5 MWh BESS cooling calculations: from cell heat to coolant flow
Ask the battery supplier for cell heat-generation data across the intended charge/discharge duty, temperature, state of charge (SOC) and state of health (SOH). Combine that with the cell count to build the thermal budget.
Published system references
For context, Sungrow’s ST2236UX is a liquid-cooled system with 2,236 kWh capacity. CATL’s 2023 ESG report describes its 5 MWh EnerD container using 314 Ah cells. The calculations below are our own examples, not data for these products.
Step 1: establish cell count and operating current
Nominal energy (kWh) = cell count × nominal cell voltage (V) × cell capacity (Ah) ÷ 1,000
Cell current (A) = C-rate × cell capacity (Ah)
| Example | Cell basis | Cell count | Calculated nominal energy | Current at 0.5C |
|---|---|---|---|---|
| Approximately 2 MWh | 3.2 V, 280 Ah | 2,240 | 2.007 MWh | 140 A per cell |
| Approximately 5 MWh | 3.2 V, 314 Ah | 4,992 | 5.016 MWh | 157 A per cell |
At nominal voltage, these 0.5C examples correspond to about 1.004 MW and 2.508 MW respectively. With constant-power operation, current rises as battery voltage falls. 0.5P operation and constant 0.5C differ over the cycle, so use the actual current profile for the thermal calculation.
Step 2: obtain cell heat data before multiplying
Ask the battery supplier for a heat-generation map or calorimetry results. For a first estimate of irreversible losses, q ≈ I²R gives watts per cell with current in amperes and resistance in ohms. Choose an effective resistance for the operating condition and time scale. Include reversible heat and transient behaviour in the detailed model, as discussed in the research on reversible heat and temperature modelling.
An assumed effective resistance of 0.50 mΩ at 140 A gives 140² × 0.00050 = 9.8 W per cell. Check the resistance test method before using a datasheet value. The EVE LF280K one-page datasheet lists ≤0.25 mΩ at AC, 1 kHz; that AC value cannot replace the operating DC resistance in this calculation.
Case A: published 280 Ah measurements applied to a 2 MWh example
Lu and colleagues (2021) report approximately 20.2 W per 280 Ah LFP cell at 0.5C and 76.6 W at 1C, measured at SOC 10% during adiabatic charging tests starting at 15°C. The test conditions belong beside the heat value in your calculation sheet.
Multiplying those points by 2,240 cells gives 45.25 kW at 0.5C and 171.58 kW at 1C. For selection, the battery supplier should provide the full duty-cycle heat profile at the intended cooling conditions.
Case B: a 314 Ah, 5 MWh sensitivity calculation
To see how cell heat affects the result, run the 314 Ah example with assumed inputs of 10, 15 and 20 W per cell. The table carries each input through to total heat and coolant flow.
| Assumed heat per cell | Total cell heat | Calculated flow at 5 K rise* |
|---|---|---|
| 10 W | 49.92 kW | 151.6 L/min |
| 15 W | 74.88 kW | 227.4 L/min |
| 20 W | 99.84 kW | 303.2 L/min |
*Assumed coolant properties: density 1.04 kg/L and specific heat 3.80 kJ/(kg·K). The return-to-supply temperature rise is 5 K.
Step 3: convert the thermal budget into flow
Using the middle 5 MWh scenario: Q = 4,992 × 15 ÷ 1,000 = 74.88 kW. Then flow = 60 × 74.88 ÷ (1.04 × 3.80 × 5) = 227.4 L/min. At a 3 K rise, the same heat load requires 378.9 L/min. The 2 MWh, 45.248 kW calculation gives 137.4 L/min with the same 5 K coolant assumptions.
Next, add the heat that busbars, connections, auxiliaries and the surroundings transfer into this loop. The integrator should also account for heat leaving through other paths and heat stored during transients. Keep the full electrical power of an air-cooled PCS out of the battery liquid-loop heat budget.
We can agree the design allowance with you and check cooling capacity at your ambient temperature and coolant setpoint.
Step 4: check pressure and branch distribution separately
For the 227.4 L/min example, 12 equal parallel hydraulic branches each need about 18.95 L/min. Ask the battery supplier for cold-plate and branch pressure-drop curves at that flow and coolant condition. The integrator then checks distribution through the manifold and common piping.
Have a 2 MWh or 5 MWh project?
Send us the cell manufacturer/model, cell count, MW/MWh duty and charge/discharge profile. Add the heat map or thermal test report, coolant specification and battery-side pressure-drop curve. Include beginning- and end-of-life requirements so we can review the same design conditions.
1. Draw the boundary of the liquid circuit
Draw the chiller supply and return ports, main pipes, manifolds and battery branches. Mark the points used for every pressure measurement. Show where the cooling-unit package ends and the integrator’s piping begins.
A marked-up drawing often clears up a quotation comparison faster than another table of numbers. When comparing quotations, ask each chiller supplier to identify its pressure reference points and the components included in its figures.
If PACK and PCS equipment share the cooling arrangement, list each load and its coolant requirements. Assign each load to its circuit so everyone works from the same scope.
2. Specify flow and pressure together
Write the required flow and external pressure drop on the same line. Add the coolant and temperature beside them. That is the hydraulic operating point we need for selection.
The integrator should calculate pressure drop through the complete external supply-and-return path. Include pipes, fittings, manifolds and valves, and get cooling-component curves from the battery supplier.
When comparing quotations, ask each chiller supplier for the available differential pressure between the external supply and return ports at your required flow. List component maximum working pressures separately as the pressure limits for the design.
List each operating case if the system varies its flow. Explain which controls set the flow and which valves change position. The flow you get depends on both the unit’s performance and the connected piping.
Pressure-drop example: compare the same operating point
For an external circuit requiring 80 kPa at 90 L/min, request at least that available pressure between the chiller ports at 90 L/min, plus the agreed design allowance. If the quotation lists an internal pump rating of 120 kPa, ask the supplier to state the corresponding flow and subtract internal unit losses to show the pressure left for your circuit.
Add parallel branch flows to get total flow; use the controlling branch path plus common supply/return losses for pressure drop, rather than adding parallel branch pressure drops. Check balancing at that operating point. Grundfos’ explanation of pump curves shows how pump and system characteristics work together.
3. State the actual coolant and its temperatures
Give the fluid name, additive specification and concentration approved by the battery supplier. State whether the concentration is by mass or volume. This lets us assess the same fluid that will run through the equipment.
Supply and return temperatures should cover the full operating range. When we check hydraulics, the fluid temperature matters just as much as its concentration: both affect the properties used in the calculation.
List the battery-loop coolant and the chiller refrigerant in separate fields. Have the battery supplier and integrator confirm coolant compatibility with all wetted materials.
4. Describe the parallel branches
Branches that look alike on a schematic can have different resistance once pipe lengths and fittings are included. A useful branch schedule gives the connection arrangement, required flow and pressure drop for each path. Highlight differences in cold plates, pipe lengths and fittings.
Have the integrator define the balancing method and branch measurement points. During commissioning, check individual branch flows alongside the total flow at the chiller.
Describe what happens when a valve closes or a branch is isolated. The integrator defines these operating cases; we check the unit’s flow range and controls against them. Agree the commissioning checks before ordering.
5. Build a hydraulic RFQ schedule
The battery supplier provides cell heat data and battery-side flow requirements; the integrator supplies the loop drawing, piping losses and installation conditions. We use the shared hydraulic RFQ schedule to review the cooling unit and its interfaces, with units and operating conditions beside each value.
| RFQ field | Information to provide or request |
|---|---|
| Liquid-circuit boundary | Annotated schematic and the exact supply and return reference points. |
| Coolant | Approved fluid specification, concentration basis and relevant temperatures. |
| Required flow | Total and branch requirements, operating cases and permitted limits. |
| External pressure drop | Complete circuit resistance at the specified flow and fluid condition. |
| Available external pressure | Supplier confirmation at the unit connections for the same operating point. |
| Pressure limits | Applicable equipment limits, kept separate from circulation pressure requirements. |
| Connections | Port location, size, connection standard and approved interface drawing. |
| Controls and verification | Flow-control approach, required signals, measurement points and acceptance responsibilities. |
If the piping is still being designed, mark unknowns as “to be confirmed”. We can discuss a preliminary selection using the available inputs. Agree who will close each open item before releasing the equipment specification.
6. Use product data as a starting point for the interface review
Use the capacities, rating conditions and model-specific flows in the Cooltechx containerized BESS chiller range to shortlist candidates. Then compare the external operating point and connection arrangement with your RFQ.
For cabinet projects, review the C&I BESS liquid cooling range alongside your cabinet layout. Choose the mounting format with port access, piping and service space in mind.
Review thermal duty and hydraulics together. A useful selection sheet shows cooling capacity, flow and available external pressure at the project conditions.
BESS chiller flow rate and pressure drop: FAQ
What flow rate does a BESS chiller need?
Start with heat load, coolant properties and the allowed supply-to-return temperature rise. Check the calculated result against the battery supplier’s branch requirements.
Is pump head the same as available external pressure?
No. The pump also has to overcome losses inside the cooling unit; available external pressure is what remains between the unit’s supply and return ports at the required flow. Pump shutoff head describes zero flow, so request the external pressure at your operating point.
Can I compare pressure drop in kPa with pump head in metres?
Convert using Δp = ρgH with consistent SI units. For water near 1,000 kg/m³, 1 m of head is approximately 9.81 kPa. Use your coolant’s density in the conversion.
What if my pressure-drop data are not ready?
The integrator can start with the loop drawing and component curves. Agree the remaining pipe sizes, valve settings and branch arrangement before finalising the external pressure requirement.
Discuss your BESS chiller selection
Send your hydraulic RFQ with the loop drawing and supporting battery data. Include project location, quantity and timeline. We can then discuss a cooling-unit configuration against a clear set of inputs.
Email your project specifications
The email button opens a project checklist. Attach your loop drawing and supporting data sheets before sending.
