데이터센터의 외기도입 냉방시스템 적용에 따른 에너지 저감효과 및 경제성 분석

Abstract

With the rapid advancement in domestic IT industry, geometrical development of performance and processing capabilities of related equipments and rapid increase in the demand for data centers, the market size of the domestic data center is increasingly expanding. However, the expansion of the market size of the data center has led to the vast increase in power consumption of server equipments in the data center where is operated for 365 days, and cooling power consumption for removal of heat load of server apparatuses. For such reason, at the moment, domestic and foreign studies on the improvement in air-conditioning efficiency and cooling system are in progress to cut cooling energy spent in data centers. Air-side economizer system is effective in reducing energy consumption by introducing the outside air to the server room directly during intermediate season and winter season that outside air's temperature is low. But, in spite of the need for reflection of the changes of energy consumption which considers temperature and dust of the outside air, for the application of the air-side economizer system, there is a shortage of research on this. Accordingly, this study analysed the effect of the improvement in energy consumption and air-conditioning efficiency of the central chilled water system in the existing data center on the reduction of energy consumption, according to the changes of chiller's chilled water setting temperature, through a TRNSYS dynamic energy simulation. Moreover, case study was performed to analyse the effect of the air-side economizer system on the reduction of energy consumption depending on types of applied filters and control conditions and furthermore, its economic efficiency was examined. The major research findings are as below.

1) When analysing central chilled water system's annual power consumption, chiller, amongst system devices, showed the highest power consumption(47%), and raising chiller's chilled water setting temperature to 7 degrees was helpful in cutting energy consumption by 8% each year without additional device, due to the improvement of chiller's COP. m widely, optimal design method for it is needed. However, there should be consideration of the decrease in the number of server racks to the unit area which is caused by the improvement of air-conditioning efficiency.

2) This research performed a case study on control methods of the introduced outside air and applied filters of the air-side economizer system's without separate mixing chamber, for mixing of exhaust. As a result, it was revealed that energy consumption was cut by 49%, compared to the existing central chilled water system. But this is the most ideal case, and thus may cause malfunction of server equipments and inequal air currents in the server room coming from the introduced outside air. Though the case study for enthalpy and temperature control was able to remedy these shortcomings, the energy reduction effect declined. Plus, the energy reduction effect showed a slight fall, because of the increase of outside air pan's power, as the applied filter's grade was higher, and ASHRAE recommended filter, Medium Filter was applied to 34% of the cases. Therefore, it is thought that there would be need for the application of filters in consideration of dust in the outside air in each region.

3) LCC(Life Cycle Cost) was estimated, based on the market research and the result of dynamic energy simulation, and air-side economizer system's economic efficiency was evaluated. After the application of the air-side economizer system, the initial investment cost increased by 17%, but it was possible to reach the break-even point in nearly 2 years, regardless of filters, since power costs that occupied the biggest proportion of LCC, decreased, and it had the lowest LCC, too when the sensitivity was analysed, according to the real rate of interest. Consequently, it was more efficient economically than the existing central chilled water system.

In conclusion, further research needs to examine total energy consumption in data centers, since this study was limited to the analysis of cooling power consumption of the data center for evaluation of energy reduction effect and economic feasibility. There is also research on water-side and air-side energy economizer systems for reduction of data center's energy consumption, currently, however, it would be required in the future to develop a system to cut down on data center's energy consumption using geothermal heat and stream water, as in domestic environment, they are not used a lot during summer season that wet-bulb temperature of the outside air is high, and to cut energy consumption in cooperation with other industries like hot spring industry which needs hot water throughout the year.