Data Center Liquid Cooling instrumentation
Liquid-cooled data centers need four measurements at each CDU: coolant flow, supply/return temperature (ΔT), differential pressure across pumps and filters, and coolant quality (conductivity and pH). Supmea supplies turbine, ultrasonic and magnetic flow meters, compact pressure transmitters, RTD temperature transmitters, radar level meters and water-quality analyzers for these points.
The measurement challenge
AI and HPC racks now exceed what air can remove, so heat is carried by liquid through cold plates or immersion tanks to a coolant distribution unit (CDU) and on to facility water. Every kilowatt removed is calculated from flow × ΔT, so the instruments in that loop decide whether the cooling system can prove its capacity and catch a failing pump before a GPU throttles.
Supmea's data center range was recognised in 2026 with a Best Thermal Management Sensor Supplier award for liquid cooling, and includes products built for this duty such as the SUP-PE100 pressure transmitter and FLC420 turbine flow meter.
- Coolant in the secondary loop (TCS) is often low-conductivity treated water or PG25 propylene glycol. Check conductivity before choosing a magnetic flow meter.
- Tight CDU and manifold spaces need compact sensors with OEM-friendly outputs: 0.5–4.5 V, 4–20 mA and Modbus.
- Heat-removal reporting depends on accurate ΔT, so matched RTDs on supply and return matter more than absolute accuracy.
- Leaks and coolant degradation are slow failures, and continuous level, conductivity and pH trends are the early warning.
Measurement points and recommended instruments
| Point | Variable | Instrument | Why |
|---|---|---|---|
| CDU secondary loop flow | Flow | SUP-LWGY Liquid Turbine Flow Meter | Works on low-conductivity coolant; compact; pulse or Modbus output |
| Facility water (FWS) flow | Flow | LDG-SUP-A100 Electromagnetic Flow Meter | Large conductive chilled-water lines, no pressure loss |
| Supply / return temperature | Temperature | SUP-ST500 Programmable Temperature Transmitter | Pt100 inputs to 4–20 mA for ΔT and kW calculation |
| Pump ΔP, filter ΔP, manifold pressure | Pressure | SUP-PE100 Compact Pressure Transmitter | Compact, 10 ms response, EPDM seals for glycol |
| Reservoir / expansion tank | Level | WSR201 60 GHz Radar Level Meter | Non-contact, narrow beam for small tanks |
| Coolant quality | Analysis | SUP-PH6.5 Online pH/ORP Meter | pH trend detects inhibitor depletion and contamination |
How to calculate heat removal from flow and ΔT
Heat removed Q (kW) = ṁ × cp × ΔT, where ṁ is mass flow (kg/s), cp the specific heat of the coolant and ΔT the return minus supply temperature. A 5% flow error becomes a 5% capacity error, and a 0.2 K error on a 10 K ΔT adds another 2%. For capacity verification, use a Coriolis meter (FCC-300) on the test bench as the mass-flow reference, and matched Pt100s for ΔT.
Choosing the flow technology by loop
The facility water side usually carries conductive chilled water in DN80–DN300 pipe, which suits a magnetic flow meter. The technology cooling system (TCS) side runs smaller pipe and may use deionised water or glycol below the magmeter's conductivity limit. There, a turbine or ultrasonic meter is the safer choice. Our Q&A on choosing a flow meter for liquid cooling walks through the decision.
Reference guidance
Design temperatures and water quality for liquid cooling are covered by ASHRAE TC 9.9 publications and by the Open Compute Project cooling work. Use them to set alarm limits for supply temperature, ΔT and coolant chemistry.
Frequently asked questions
Can a magnetic flow meter measure PG25 coolant?
Only if the coolant's conductivity is above the meter's minimum (≥50 µS/cm for the LDG-SUP-A100, about 2 µS/cm for low-conductivity models). Measure the actual coolant; inhibited glycol and deionised water vary widely.
Which output is best for CDU controllers?
4–20 mA is the most robust over cable; Modbus RTU reduces wiring when many sensors share a controller; 0.5–4.5 V suits OEM boards.
What should a leak detection strategy include?
Reservoir level trend, loop pressure decay and flow imbalance between supply and return together catch leaks earlier than any single sensor.
Instruments for data center liquid cooling
Liquid Turbine Flow Meter
Clean water, glycol, fuel and oils in small lines, 0.5%R accuracy.
Electromagnetic Flow Meter
Conductive liquids from DN10 to DN1000 with no moving parts and no pressure loss.
Programmable Temperature Transmitter
Turns RTD or thermocouple signals into a clean two-wire 4–20 mA loop.
Compact Pressure Transmitter
Small-format pressure for CDUs, pumps and chilled-water loops.
60 GHz Radar Level Meter
Non-contact level for tanks and open water, ±5 mm with a 6° beam.
Online pH/ORP Meter
Panel-mount pH/ORP control with isolated 4–20 mA and dosing relays.
Plan the instrumentation for your data center liquid cooling project
Send the medium, pipe size, flow or level range, temperature, pressure and required output. You'll get a recommended model, the datasheet and a quotation.
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