Data center cooling optimization

For a renowned data center operator, several aspects of the cooling of their data centers have been researched and improved where necessary. This concerned both the distribution of the cooled air in the data rooms themselves and the short circuiting of hot air between the installations on the roof.

A datacentre provides space for a large amount of computer equipment. This equipment produces a significant amount of heat which must be cooled by means of Computer Room Air Conditioning (CRAC) units. It is imperative that the intake temperature of the IT equipment remains between 18 °C to 27 °C as recommended by the ASHRAE. Outside this temperature range, the risk of hardware failure increases significantly.

Different cooling designs are used in datacentres. A commonly used design is the use of cold paths. In this design, cold air is supplied from the CRAC units to a closed cold room (path) that is used to cool the equipment.

Various modifications of the basic design can be investigated quickly and at an early stage with CFD simulations. In the case below, the influence of various modifications to the system design on the server intake temperature has been investigated.

Explanation

In this project, the data room is cooled by 18 Computer Room Air Handler (CRAH) units which blow cool air into a floor plenum through 4 centrifugal fans per unit. The cool air then flows through perforated floor tiles to a number of cold aisles. Here the air is supplied to a large number of servers. According to ASHRAE, the supply air of a server for this type of data center should be between 18 and 27 ° C.

Base scenario
  • Three large eddies in the floor plenum
  • Low pressure in the middle of the eddy
  • Low pressure has an effect on the cold paths
  • Warm air leaks into the cold aisles
  • 4.28% of the servers have a higher intake temperature than 27 ° C
Increase flow rate CRAH units
  • Flow rate of the CRAH units has been increased by 14%
  • Air distribution in the floor plenum is unchanged
  • Higher pressure in the floor plenum and in the cold paths
  • Due to overpressure of the cold pad, less leakage of warm air
  • 0.26% of the servers have a higher intake temperature than 27 ° C
Placing air conductors
    • Two air guides are placed in the floor plenum
    • Three large eddies in the floor plenum
    • Two of the three eddies are not directly below the floor plenum
    • The low pressure in the floor plenum has less effect on the cold paths
    • Less leakage of warm air to the cold paths
    • 2.42% of the servers have a higher intake temperature than 27 ° C
Reducing the number of air-permeable floor tiles
  • Middle row floor tiles are closed for every cold aisle
  • Air distribution in the floor plenum is unchanged
  • Greater pressure loss between the floor plenum and the cold paths
  • Slightly higher pressure in the cold aisles
  • Slightly less leakage of warm air due to overpressure in the cold aisles
  • 2.02% of the servers have a higher intake temperature than 27 ° C
Adjusting direction of rotation of fans CRAH units
    • Direction of rotation of centrifugal fans is reversed for half of the CRAH units
    • Large number of smaller eddies in the floor plenum
    • Slightly better pressure distribution in the floor plenum
    • Better pressure distribution results in less leakage from warm air to the cold aisles
    • 2.58% of the servers have a higher intake temperature than 27 ° C