Investigation of the Thermal Distribution of a Typical Data Centre Due to Computer Room Air Conditioning (CRAC) Failure

Tang, Sze Wei (2022) Investigation of the Thermal Distribution of a Typical Data Centre Due to Computer Room Air Conditioning (CRAC) Failure. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Cooling equipment like computer room air conditioning (CRAC) units supply cold air to feed into the servers and remove hot air from the servers. However, CRAC units may fail and as a result, the server may malfunction due to high temperature. Hence, it is crucial to evaluate the thermal distribution of air inside a server room. There will be three conditions to be evaluated which are that the cooling system is operating normally, with one and two failures of CRAC units based on the thermal distribution of an hour for each condition. Furthermore, the project objective is to verify two cooling systems designs for a Tier 3 small data centre given a specific server room. The verification is done by satisfying the average temperature range in the server room with the allowable dry-bulb temperature range of class A1 set by The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). The server room investigated in this project has a Hot Aisle/Cold Aisle (HA/CA) layout with a room-based cooling configuration. One of the cooling system designs, Scenario 1, is where the server heat flux, supply air temperature and mass flow rate is 2.89 kW/m2, 16.1°C and 12.66 kg/s, respectively, while the other design, Scenario 2, is 5.08 kW/m2, 20.9°C and 14.96 kg/s, respectively. Herewith, the thermal distribution simulation is run by Ansys Fluent simulation software that uses a finite volume method (FVM) approach. From the result generated, it is investigated that the airflow in the server room has three characteristics. The hot air flows upwards as it is less dense than cold air. Secondly, hot air turns at the edge of the server rack and flows slightly towards the cold aisle direction resulting in hot spots that will increase the temperature in the cold aisle. Lastly, the cold supply air bypass at the end of the server rack farthest from the CRAC unit. Moreover, the average temperature of the server room for Scenario 1 ranges from 16.1°C to 19.5°C for normal operating conditions and the upper-temperature limit increases to 20.1°C and 21.6°C for one and two failures of CRAC units, respectively. For Scenario 2, when at normal operating conditions, the range is 20.9°C to 24.3°C and rises to 25.7°C and 27.9°C for one and two units of CRAC failure, respectively. Next, the average cold aisle temperature when operating normally, one and two of the CRAC units breakdown is 17.43°C, 17.51°C and 18.66°C respectively for Scenario 1 and 22.25°C, 22.28°C and 25.05°C for Scenario 2. The finding from this study shows that the average CA temperature increases as a greater number of CRAC units break down. Lastly, the rate of temperature change in the server room for all conditions in both scenarios is found to be less than 10°C/hour. The two cooling system designs are safe to be built for the server room studied with all these findings.