Cooling solutions

In room cooling, central air conditioning or recirculating air cooling units draw in the heated air from the IT room, cool it, and return it to the server racks. Air distribution occurs, for example, via a raised floor, air ducts, or freely throughout the room. This approach is flexible and is particularly well-suited for traditional server, storage, and network infrastructures with largely evenly distributed heat loads.

Controlled airflow

For efficient operation, cold supply air and warm server exhaust air must be consistently separated from one another. Cold aisle or hot aisle containment systems reduce air mixing and ensure that the cooling capacity provided is directed specifically to the IT equipment.

The appropriate design depends, among other factors, on the rack layout, the room layout, the pressure conditions, and the building infrastructure.

In row-based cooling, the cooling units are located directly inside or at the end of a rack row. The warm exhaust air is drawn in immediately adjacent to the servers, cooled, and returned to the front of the racks via short paths. This allows cooling capacity to be targeted specifically at individual rows or areas with higher heat loads. This is particularly advantageous when power density is distributed unevenly within the data center.

In-row coolers can be supplied via a chilled water loop or a direct evaporation system. These systems do not describe the location of heat extraction, but rather the method of cooling delivery.

With rack cooling, heat is extracted directly from or inside the server cabinet. This reduces the thermal load on the IT room and allows cooling capacity to be directed specifically to individual racks.
A typical example is the rear-door heat exchanger. It cools the air expelled by the servers directly at the rear of the rack before it re-enters the room. Depending on the design, the system operates passively or with additional fans.

Another variant is closed-loop rack cooling systems, in which air circulates within a largely enclosed server cabinet between the IT equipment and the heat exchanger. Direct liquid cooling can also be installed inside the rack, but differs technically: While a rear-door heat exchanger cools the exhaust air from the servers, direct liquid cooling absorbs heat directly from the IT components.

Direct Liquid Cooling

In direct liquid cooling, a liquid coolant is directed directly to components that generate a particularly high amount of heat. So-called cold plates sit directly on processors, GPUs, or accelerators and absorb heat right where it is generated. A Coolant Distribution Unit (CDU) distributes the coolant and connects the server-side circuit to the building-side heat dissipation system. Both circuits can be hydraulically isolated from one another, allowing for different requirements regarding pressure, flow rate, water quality, and temperature levels to be accommodated.

Hybrid cooling concepts

Not all components of a server are necessarily cooled by liquid. Memory modules, power supplies, and other components often continue to dissipate heat into the air. Direct liquid cooling is therefore frequently combined with supplemental air cooling.

Single- and two-phase cooling

In single-phase cooling, the coolant remains liquid throughout the entire process. In two-phase cooling, it evaporates during heat absorption and condenses during the subsequent heat dissipation. Two-phase cooling is therefore not a standalone heat sink, but rather a thermodynamic process within a liquid cooling system.