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A Study on the Regional Energy Conservation Effects of a Multi-stage Outdoor Air Enabled Cooling System in a Data Center
Abstract
A Data center houses a large number of server computers, storage and etc in racks. With the rapid increase of heat generation rates per rack in a data center, energy consumption rates for cooling have been increased year by year. In this study, energy conservation effects of a MOA (multi-stage outdoor air enabled) cooling system in a data center has been investigated when it is applied to 5 different locations, Korea. As results, Energy conservation effects of the MOA cooling system was achieved at about 20% to 30%. Humidifier operation time was 40 to 55 days when supply air temperature was maintained at 13, and humidity condition was kept within the allowed range even though humidifier was off. Furthermore, humidification was not needed when supply air temperature was maintained at 25^{\circ}C. In selected 5 locations in Korea, the difference of regional climatic conditions affected no more than 5% in cooling energy consumption rates.
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Energy consumption rates in a data center have increased year by year, and by this, the introduction of energy conserving cooling systems is rapidly emerging all over the world. In this study, a multi-stage outdoor air enabled (MOA) cooling system is proposed as the safer and more energy conserving system for a data center. An MOA cooling system is composed of the combination of water-side economizer, air-side economizer and mechanical cooling. Effects of an MOA cooling system are investigated by energy simulation from various viewpoints. The results show that the MOA cooling system can save cooling energy consumption rates by about 21%, and if combined with a special rack enclosure, by about 33%. Introducing outdoor air flow into the MOA cooling system decreases energy use to about half of that of the air-side economizer, and if combined with the rack enclosure, by about 9%. Thus, the concerns about particulate and gaseous contamination can be reduced. Continuous operating time of the humidifier drops to about 3 days, and if combined with the rack enclosure, to ‘0’ day. These results make it possible to remove the humidifier as part of the MOA cooling system.
Rack enclosures are a crucial link between data center airhandling units and servers. Design of rack enclosures can impact the fan performance, and therefore, cooling performance of servers. Careful consideration should be given before selecting the rack enclosures for a certain data center. Just following the best practices for the design and layout of data centers is not enough to obtain the optimum cooling performance. This article illustrates the importance of rack enclosure design and airflow management within the rack enclosures.
The main purpose of this paper is to analyze energy saving potentials of various economizers in modular data center by thermal conditions and locations in response to explosive IT demand and data centers' energy consumption increase. To investigate holistic energy saving potentials, various server thermal characteristics, economizers, and locations are analyzed on a modular data center. As a results, economizers can save cooling coil load 75-100% according to their running conditions, and indirect air-side economizer showed better performance than direct air-side economizer. Even though there is more chiller energy saving with server inlet temperature increase, total energy saving decreased more sharply due to fan energy increase. Furthermore, there should be more energy saving potentials in high latitude climates regardless of type of economizers.
Based on the climate classification of ASHRAE 90.1 and the required operating environment conditions for data centers suggested by the ASHRAE Technical Committee TC 9.9, a dynamic building energy simulation program was used to examine the potential energy savings of the air-side free cooling technology with differential enthalpy control used in data centers in 17 climate zones. The results showed that significant free cooling potential was achieved in data centers located in mixed-humid, warm-marine, and mixed-marine climate zones. Because significant humidification is required to adjust outdoor air in climate zones with a lower dew point temperature, such as very-cold, subarctic, cool-dry, and cold-dry climate zones, the power consumed is even higher. Although the cooling degree day (CDD) and heating degree day (HDD) are key factors of climate classification and air conditioning energy consumption, they are not entirely correlated to the specific operating environment conditions of data centers. The results of this study showed that for every 2 °C decline in the indoor temperature of a data center, the energy saving of free cooling technology may decrease by 2.8–8.5%. The rate of decline varies in different climate zones.
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