---
title: "Sidecar CDU Advantages for Efficient Liquid Cooling"
description: "Explore sidecar CDU advantages, including rapid deployment and no facility water requirement, optimizing cooling for high-density racks."
image: "/media/i/9dede335-9ec6-4c6e-a2d6-5c6930ba3237/sidecar-cdu-advantages-liquid-cooling-without-facility-water.webp"
---

A sidecar [**CDU**](https://www.gerchamp.com/en-US/products/liquid-to-liquid-cooling-distribution-unit-2700kW) ([Agent MD](https://www.gerchamp.com/en-US/products/liquid-to-liquid-cooling-distribution-unit-2700kW/raw.md)) earns its place through the form factor. It rejects heat into room air, and that choice drives most of the sidecar CDU advantages in a retrofit: how fast the unit goes in, which buildings accept it, and what the operator maintains afterwards.

Every item below traces to one line: sidecar CDU heat rejection without facility water, and each one is measurable.

## Sidecar CDU Definition: Form Factor and Basic Architecture

A sidecar CDU sits beside the rack row and rejects heat into room air.

### Definition: A Unit That Stands Beside the Rack

The **sidecar CDU definition** is a coolant distribution unit mounted beside a rack row. It rejects heat into room air rather than into a facility water loop.

The rejection side is what makes that **sidecar CDU definition** useful. The unit is liquid-to-air, L2A for short. Warm secondary fluid returns from the cold plates and passes through an integral coil, where fans drive room air across the fins. The fluid cools, the air warms, and nothing in the path touches a chiller, a cooling tower or a building water supply.

The unit therefore takes floor area beside the row instead of a position in it. The room's air handling also joins the cooling chain, sized for that role or not.

### Sidecar, In-Row, In-Rack: Position in the Row

| **Form factor** | **Where it sits** | **Cabinets served** | **Heat rejected to** | **Typical fit** |
| --- | --- | --- | --- | --- |
| In-rack | Inside the cabinet, usually a 4U unit | Its own cabinet | Cabinet airflow or facility water | Single cabinets, small starts |
| In-row | Takes a position in the rack row | Adjacent cabinets | Facility chilled-water loop (L2L) | New halls built for high density |
| Sidecar | Stands beside the rack row | Adjacent cabinets | Room air | Existing air-cooled and mixed halls |

In-rack units live inside the cabinet, where Gerchamp's own 4U core unit is a 150 kW-class example. A sidecar takes neither position, standing alongside with the room as its heat sink.

In-row and in-rack reach higher density per unit. A sidecar buys eligibility instead, and pays in airflow and floor area.

### What an Air-to-Liquid Retrofit Removes, and What It Keeps

An air-to-liquid retrofit takes the sidecar route, and the loop behind it is **liquid-to-air sidecar cooling**. What it removes is infrastructure, not heat.

| **Removed (water side)** | **Still required (room side)** |
| --- | --- |
| Facility chilled-water loop and its circulation pumps | **Residual sensible cooling capacity** in the hall at design conditions |
| Cooling tower or dry cooler, and the outdoor plot it occupies | Air distribution that mixes the discharge instead of letting it short-circuit |
| Primary pipework and the floor penetrations it needs | Secondary coolant temperature held above the room dew point |
| Water treatment and freeze protection for the facility loop | A dedicated three-phase feed, with its parasitic draw counted in the hall load |
| Months of construction and commissioning before first cooling | Service clearance for tool-free work, plus a structural check for the concentrated wet load |

Rejecting heat to room air does not make the heat disappear. It leaves the unit as warmer air, mixes into the hall, and is eventually collected by a CRAC or CRAH unit, so the room's air handling joins the cooling chain from the first kilowatt.

## Sidecar CDU Advantages in Air-Cooled Halls

Sidecar CDU advantages all trace back to rejecting heat into room air instead of facility water. A hall with air-handling headroom and no chilled-water infrastructure collects the full set: no water side to build, first cooling in days rather than months, and maintenance that never stops the loop. A hall that already has a chilled-water loop collects less, since that water side is paid for.

### The Advantage Set, Ranked by What It Saves

| **Advantage** | **What it means on site** | **What it saves** |
| --- | --- | --- |
| No facility water | Heat is rejected to room air, so there is no chilled-water loop | Cooling tower or dry cooler, primary pipework, floor penetrations |
| Deployment in days | Roll in, connect to the cold plates, start rejecting heat | Months of construction and commissioning |
| Density | 175 kW at ATD 10 °C inside a 900 mm-wide frame | White space and floor area |
| Serviceability without downtime | Hot-swap pumps and filters, no tools required | Planned shutdown windows |
| Air and liquid side by side | Liquid-cooled racks run alongside air-cooled servers | A hall-wide cooling rebuild |
| Modular growth | One unit runs alone, two run in parallel | Capacity bought ahead of demand |

Gerchamp's Bluearth [<u>CDU4175 L2A 175kW</u>](https://new.gerchamp.com/en-US/products/liquid-to-air-cooling-distribution-unit-175kW) is a 52U enclosure at 900 mm wide, with a 175 LPM secondary loop, a 485–501 kg assembly weight, and a noise figure below 85 dB.

## Sidecar CDU Power Range: Choosing a Capacity Tier

The sidecar CDU power range sits inside a wider ladder from 150 kW to 2.7 MW, and the band follows the rack.

### The Capacity Tiers Sidecar CDUs Cover

Within the sidecar CDU power range, what separates the bands is the heat sink, not the kilowatt figure.

| **Tier** | **Typical capacity** | **Typical load served** | **Building-side prerequisite** |
| --- | --- | --- | --- |
| In-rack | 150 kW class (4U core unit, L2L) | One cabinet or a short row | Facility water side required |
| Sidecar | 175 kW class at ATD 10 °C (L2A) | One fully loaded high-density AI rack | **Not required: heat goes to room air** |
| Hall | 680 / 850 / 2700 kW class (L2L) | A whole hall, in-row or containerised | Facility water side required |

Only the sidecar tier needs nothing installed in the building. Every other tier routes heat into a facility water loop and inherits what comes with it. Selection starts from the rack's electrical limit and whether the hall has facility water.

### CDU4175 L2A 175kW Fit with NVIDIA Platforms

| **NVIDIA platform** | **Rack power (NVIDIA documentation)** | **[<u>CDU4175 L2A 175kW</u>](https://new.gerchamp.com/en-US/products/liquid-to-air-cooling-distribution-unit-175kW) at 175 kW (ATD 10 °C)** |
| --- | --- | --- |
| GB300 NVL72 | 135 kW designed, up to 142 kW | One unit |

Air cooling stops being practical above roughly 50 kW per rack.

Gerchamp's Bluearth [<u>CDU4175 L2A 175kW</u>](https://new.gerchamp.com/en-US/products/liquid-to-air-cooling-distribution-unit-175kW) carries one GB300 NVL72 with margin left over, and that margin absorbs the one specification that moves available capacity: **sidecar CDU coolant supply temperature**. The datasheet rates the unit at 175 kW at an approach of 10 °C and 125 kW at 5 °C, so a hall that demands colder coolant trades capacity for it. It still covers a 142 kW rack, but not a larger one.

A rack above that needs a second unit beside it, which is what a **sidecar CDU parallel configuration for Vera Rubin NVL72** is. Racks in the several-hundred-kilowatt class leave this tier entirely, because at that power the heat sink has to be facility water.

The datasheet also specifies 45 °C supply and up to 60 °C return on the secondary loop. That sits above the room dry-bulb and therefore above the dew point. Cold-plate surfaces never reach the condensation threshold, so the failure mode that dominates chilled-water [**liquid cooling**](https://www.gerchamp.com/en-US/solutions/liquid-cooling-solutions-for-data-centers) ([Agent MD](https://www.gerchamp.com/en-US/solutions/liquid-cooling-solutions-for-data-centers/raw.md)) is absent from the architecture.

### Why 175 kW Is the Tier That Fits

**Its usable range brackets the rack.** Approach temperature sets the capacity, as the datasheet shows, so the tier covers a band rather than a point. That band still covers a fully loaded AI rack when the hall forces a colder supply.

**It keeps sidecar CDU deployment density high.** 175 kW at an approach of 10 °C sits inside a 900 mm-wide, 52U frame at a 485–501 kg assembly weight. One rack, one unit, no added footprint. Scaling further would trade that density for more coil face, more airflow, and eventually a facility water side.

Gerchamp's Bluearth [<u>CDU4175 L2A 175kW</u>](https://new.gerchamp.com/en-US/products/liquid-to-air-cooling-distribution-unit-175kW) is that tier in product form: a 52U sidecar the datasheet specifies at 175 kW under a 10 K approach, drawing 12.5 kW of parasitic power for an mPUE of 1.10, with no chilled-water connection. At that rating, one unit carries a fully loaded NVIDIA GB300 NVL72, and a second unit is added beside it as the load grows.

## Sidecar CDU Serviceability: Redundancy and Hot Swap

Sidecar CDU serviceability decides the operational case more often than raw capacity does.

### 1+1 Pumps and Automatic Failover

Each unit carries two pumps in 1+1, running cyclically and switching over automatically on failure. A degraded pump is covered without operator action or cooling interruption, so training jobs run through the event.

### Tool-Free Maintenance on a Live Loop

Pumps and filters are hot-swappable, and maintenance is tool-free with no shutdown. The condition is clearance: enough space to withdraw a pump or filter while the loop stays live. Sidecar CDU serviceability therefore starts at the layout stage.

The controller offers two modes: constant flow for steady-state training, constant pressure for fluctuating workloads. Both log parameters remotely.

## FAQ: Sidecar CDU Advantages and Capacity Selection

**Does a liquid-to-air sidecar CDU need facility water?**

No. It rejects heat into room air through an integral radiator, so there is no chilled-water connection, cooling tower or dry cooler. The room's air handling must still carry that heat away.

**Which capacity tier does an AI rack need?**

Start from the rack's electrical limit. A full high-density AI rack lands in the sidecar tier at the 175 kW class, while hall scale means a facility-water unit.

**Why does the same unit carry two different capacity figures?**

The figure tracks the approach temperature between coolant and room air. The datasheet gives a higher capacity at a 10 K approach than at 5 K. Any comparison is meaningful only when the approach, the supply temperature and the room ambient are stated together.

---

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