Views: 0 Author: Site Editor Publish Time: 2026-09-30 Origin: Site
A liquid-to-air (L2A) CDU lets an AI GPU rack run direct-to-chip liquid cooling in a room that only has air cooling. The CDU pumps coolant through the GPU cold plates, then rejects that heat to room air through a fin-and-tube coil and EC fans — no chilled-water or facility-water connection is needed. CSTHEATEXCHANGER manufactures the heat-rejection coil, the fan section and the associated dry-cooler or rear-door modules that L2A CDU builders and integrators use, and we build them to the customer's drawing or performance datasheet.
At CSTHEATEXCHANGER we have supplied rack-level air-to-liquid coils, EC fan wall units, dry coolers and liquid-cooling heat exchangers for high-density computing for several years. This article explains where an L2A CDU fits, what the heat-exchanger side has to do, and how we specify it.
Modern AI accelerator racks concentrate far more heat than the server rooms they are installed in were designed for. Operators who want to deploy a small number of GPU racks face a dilemma: the GPUs need direct liquid cooling, but the building has no facility-water loop at the rack row, and adding one is a long project.
The L2A CDU resolves this. The technology cooling loop (TCS) stays closed and clean; the CDU's internal coil acts as the "radiator", and the room's existing air-conditioning carries the heat away as it always has. In practice an L2A CDU turns a liquid-cooled rack back into an air-cooled heat load from the room's point of view.
CDU function | Component | What CSTHEATEXCHANGER provides |
|---|---|---|
Heat rejection to room air | Fin-and-tube air-to-liquid coil | Copper tube / aluminium fin coil sized to the coolant flow, inlet temperature and target air-side ΔT; hydrophilic or anti-corrosion fin coating on request |
Air movement | EC fan array | Parallel EC fan modules (the same architecture as our Fan Wall Unit) with N+1 redundancy |
Alternative rack-level rejection | Rear Door Cooling Coil | Rack-mounted air-to-liquid heat exchanger, active or passive, for standard 19-inch racks |
Facility-side option for later upgrade | Dry cooler / plate heat exchanger | Outdoor dry cooler or stainless-steel plate heat exchanger when the site adds a water loop and migrates to L2L |
We do not sell a sealed "black-box" CDU chassis; we build the thermal hardware that determines whether the CDU actually meets its capacity, and we build it to drawing.
A liquid-to-air coil in a CDU is sized backwards from the GPU side:
Coolant return temperature from the cold plates — this sets the hot-side inlet to the coil.
Room supply-air temperature at the CDU intake — this sets the cold-side inlet. The approach between these two numbers is the whole design problem.
Allowable air-side pressure drop and noise — decides fin pitch, rows and fan selection.
Coolant type — water/glycol or a dielectric fluid; affects tube material, header material and velocity limits.
Footprint — in-rack, side-car or end-of-row CDU; dictates coil face area and whether a single deep coil or multiple shallow coils are used.
The output is a coil drawing with face dimensions, rows, fins per inch, tube OD and wall, circuiting, header material and connections, which the customer approves before we build. Our standard tube programme covers 7 mm, 9.52 mm, 12.70 mm and 15.87 mm OD; fins are 8006 H22 aluminium as standard with copper or coated options.
Situation | L2A CDU | Better alternative |
|---|---|---|
1–6 GPU racks in an existing air-cooled room | ✅ Fast deployment, no plumbing | — |
Room air-conditioning already near capacity | ⚠️ The CDU adds no capacity; the room must still remove the heat | Rear door heat exchanger on chilled water, or L2L CDU |
Full hall of GPU racks | ❌ Air-side rejection at this scale is inefficient | L2L CDU with facility water and dry coolers |
Site with no chilled water and no plan for it | ✅ | Add an outdoor dry cooler loop later |
We say this plainly because an L2A CDU specified for the wrong case fails at commissioning, and the coil usually gets blamed.
An L2A CDU rejects heat from the coolant into room air through a coil and fans. An L2L CDU rejects it into a facility water loop through a plate heat exchanger. CSTHEATEXCHANGER supplies the heat exchanger for both types.
Yes. Send the enclosure drawing, coolant data and target air conditions; we return a coil drawing and performance sheet for approval before manufacturing.
Water, water/glycol mixtures and common dielectric coolants. Tube and header material are selected to match the fluid.
Yes. Our EC fan modules are built in parallel arrays, the same approach we use for Fan Wall Units, so a single fan failure does not stop cooling.
Yes. Many customers start with an L2A CDU and later add a dry cooler loop or chilled water, switching to an L2L arrangement. We supply the dry coolers and plate heat exchangers for that step.
If you are building or integrating a liquid-to-air CDU for AI GPU racks, send CSTHEATEXCHANGER your coolant flow, return temperature, room air conditions and enclosure dimensions. We will return a coil and fan selection, a drawing for approval and a quotation.
Email: info@cstheatexchanger.com
International business: +86 15618652003
Website: https://www.cstheatexchanger.com/
CSTHEATEXCHANGER — the heat-exchanger side of liquid cooling, built to your drawing.
