Data center cooling system

Infrastructure

A data center cooling system is a set of equipment that removes heat from servers and maintains the acceptable temperature and humidity conditions in the data center. It prevents overheating, which leads to failures and a reduced service life of the equipment.

What is a data center cooling system
Types of cooling systems
How air cooling works
Liquid cooling of dense racks
Why control and redundancy matter

The data center cooling system is a set of equipment that removes heat from servers and maintains the acceptable temperature and humidity conditions in the data center. It prevents overheating, which leads to failures and a reduced service life of the equipment.

What is a data center cooling system

A data center cooling system is the engineering infrastructure that provides the removal of heat generated by server equipment and maintains the specified microclimate parameters. A rack with servers generates tens of kilowatts of heat, so without cooling the equipment overheats, loses performance and fails. The main parameters controlled by the system are the air temperature at the server intake (usually 18–27 °C) and humidity (40–60%), which prevents static electricity and condensation. Modern data centers use the layout of “cold” and “hot” aisles, separating cold supply and hot exhaust air.

Types of cooling systems

By the operating principle, air cooling, liquid (water) cooling and their combinations are distinguished. Air cooling is the most common option: precision air conditioners (CRAC/CRAH) supply cold air under a raised floor or from above, and hot air is removed to the “hot” aisle. With high rack density, air cannot cope, and liquid cooling is used: cold liquid is supplied directly to servers through pipes (rear door heat exchangers, immersion cooling). Modern data centers often use free cooling, using outside air at low temperatures, which saves electricity.

How air cooling works

The classic scheme: cold air is supplied through a raised floor into the “cold” aisle, drawn in by servers from the front, passes through the equipment, heats up and is discharged into the “hot” aisle at the back. Precision air conditioners take the hot air, cool it with heat exchangers and again supply the “cold” aisle. Air conditioners use a refrigeration circuit (compressor, evaporator, condenser) and have air- or water-based heat rejection to the outside. The process is controlled by automation that monitors the temperature with sensors at different points of the machine room. If one air conditioner fails, reserve units (N+1, 2N) continue cooling without stopping the service.

Liquid cooling of dense racks

When the rack power exceeds the capabilities of air (for example, 20–30 kW and more), they switch to liquid cooling. In a scheme with rear door heat exchangers, cold water circulates in panels behind the racks and takes heat at the outlet. Immersion cooling completely submerges servers in a dielectric liquid, removing heat as efficiently as possible, but requires special racks and reduces ease of maintenance. Liquid systems use chillers and dry coolers to remove heat outside. Distribution of cold water, redundancy of pumps and leak control are critical tasks of operating such cooling.

Why control and redundancy matter

A cooling failure quickly leads to a temperature rise and emergency shutdown of servers even with working power. Therefore, cooling systems are designed with redundancy: excess cooling capacity (N+1), independent electrical feeders and duplication of pumps and chillers. Cooling monitoring is part of the data center management system and evaluates temperature, humidity and energy consumption per rack. Energy efficiency is measured by the PUE indicator: the closer it is to 1, the less energy the infrastructure spends on cooling and other needs relative to the useful load.

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Frequently asked questions

What is a data center cooling system?

A data center cooling system is a set of equipment for removing heat from servers and maintaining an acceptable temperature and humidity in the data center. It prevents overheating and failures of equipment.

What types of data center cooling are there?

Air cooling with precision air conditioners, liquid (water) cooling with cold liquid supplied to servers, and their combinations. Free cooling with outside air is used to save money.

What is a cold and hot aisle?

Servers are installed in rows: the front sides form a “cold” aisle, where cold air is supplied, and the rear sides form a “hot” aisle, where heated air is discharged. Their separation increases cooling efficiency.

What temperature is needed in a data center?

The acceptable air temperature at the server intake is usually 18–27 °C, humidity 40–60%. The exact values are set by equipment vendors and the ASHRAE recommendations.

What is a precision air conditioner?

A precision air conditioner (CRAC/CRAH) cools the air in a machine room around the clock with high accuracy. CRAC uses a refrigeration circuit, CRAH — cold water from a chiller.

What is liquid cooling of servers?

Liquid cooling supplies cold liquid directly to servers through rear door heat exchangers or submerges the equipment in a dielectric liquid. It is more efficient than air at high rack density.

What is N+1 redundancy?

N+1 redundancy means that one reserve unit is added to the required number of air conditioners: if any unit fails, cooling continues without interruption.

What is PUE?

PUE is a data center energy efficiency indicator, the ratio of total energy consumption to IT equipment consumption. A value close to 1 means efficient infrastructure and cheap cooling.