A data center is a facility used to keep computer related equipments. It is estimated that heat production rate of the data center is doubled in every two years and hence the inevitability of the cooling system gets increased. In due course power consumption of a data center is augmented and more cost is spent on the power usage of the cooling system rather than the equipment purchase. As a result power savings for the cooling system is strongly desired. In this paper we conferred two primary free cooling systems namely air economizer and water economizer. A free cooling economizer system uses the outside air which is forced to the data center when outside climate is suitable to meet the ASHRE’s cooling requirements. We have also conducted a survey and simulation based estimation using TRACE[TM] Chiller Plant Analyzer Tool. In this study, the energy consumption in a data center using conventional cooling system is compared with Air Economizer and Water Economizer for three different Zones namely Chicago, Atlanta and Phoenix in view of the fact that the outside air is relatively cool most of the year. From the projected result it is observed that both economizers reduce energy and cost when compared with conventional system and the usage of Economizer permits the chiller to shut down or reduce chiller energy load under suitable weather conditions. The results show that Water economizers are shown to consistently outperform air economizer which provides significant improvement in cooling system efficiency and cost at data center. The performance ratio of the conventional, air economizer and the water economizers are 50%, 76% and 79% respectively that shows economizers provide more savings relative to the conventional system.
A data center is a facility used to keep computer associated equipments like server, storage devices, networking devices, backup power supplies, and environmental controls such as air conditioning, fire suppression and security tools. Day - by - day the power consumption of a data center is increased and more cost is spent on its electricity usage rather than the equipment purchase. Lawrence Berkeley National Laboratory has studied the trends of power consumption for a number of data centers . It is estimated that only 30% of the energy is consumed by IT equipments 40% of the energy is by the cooling system and the remaining 30% is used for UPS and lighting. The primary goal of Energy management in the data center is minimizing the energy consumption and maximizing the performance of the active equipment. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends  a Data Center room temperature should be in the range of (16°C – 24° C) or (61° F – 75° F) and Humidity range of (40% – 60% RH). This environment can be achieved only by conveying cold air to every piece of equipment. Hence the temperature of all the equipments in the data center never raise beyond its maximum allowable temperature and the room temperature and Humidity level can be maintained in the ASHRE’s level.
In the traditional cooling system  the servers are mounted on the raised floor with perforated tiles. The racks are lined up as sequential rows forming corridor between the two rows called aisle. The cold air passageway is called cold aisle and the hot air passage way is called hot aisle. Figure 1 depicts the cross section of such hot / cold aisles. In this system air enters at the top of the CRAC(Computer Room Air Conditioning) unit, passes over the cooling coils which is cooled by the chiller plant and the cold air is ejected to the under floor plenum. Fans inside the server draw the cold air upward through the perforated tiles and then absorbs the cold air in front row of server and pushes the equipment generated hot air behind these rows. The departed hot air rises and moves to the intake of a CRAC unit. This approach works well only in low to medium level data center application and does not offer good performance in high level applications. Moreover the mixing of hot and cold air over and around the top of the rack also wastes energy due to overrun of the cooling system.
In this paper we propose free cooling economizer systems that are used in associated with traditional cooling system to reduce energy consumption. A free cooling economizer system uses the outside air which is forced in to the data center when the outside climate is suitable to meet the ASHRE’s cooling requirements. When the economizer system starts functioning, reduces or eliminates the working of chiller which consumes the greater part of energy in the air conditioning system.
We have also carried out estimation and simulation based assessment using TRACE[TM] Chiller Plant Analyzer Tool. The purpose of this study is to compare the energy saving in a data center using conventional cooling system with Air Economizer and Water Economizer system for three different Zones namely Chicago, Atlanta and Phoenix in view of the fact that the outside air is relatively cool most of the years and the economizers can be effectively used for maximum possible hours. In these geographical locations, economizers can satisfy a large portion of data center’s cooling requirements during winter season. The savings from the economizer depends on the local climate and at the same time as the cold weather increases the number of hours that the economizer is operating is increased.
The results show that Economizer system provides greatest savings in Phoenix and the least savings in Chicago. Water Economizer consumes lowest total Annual power at Atlanta and Phoenix.
The rest of this paper is organized as follows: Section II denotes the related work focusing on energy efficient free cooling system. Section III explores the two primary methods of cooling systems and evaluation principle. Section IV presents the experimental setup, system requirements and experimented result analysis. Section V gives conclusion.
II. RELATED WORK
Studies have revealed that the thermal management practices like increasing air flow rate, attaching extra fans will be incapable for handling the high thermal load and would also become soundly  expensive and alternative methods such as row-based cooling systems have to be implemented.
Liquid cooling was mostly used to reduce power consumption in the data center. Systems with air-to- liquid heat exchangers mounted on the rack to cool the hot air to form a self-contained cooling loop reduces the distance the hot exhaust air must travel before reaching the CRAC units, which minimizes the adverse effects of hot air recirculation. Moving the heat exchanger to the rack relies on air as the heat transfer medium for heat removal from the servers and performance of such systems are limited by airside heat transfer coefficient.
Thermal performance metrics for systems level electronics cooling based on the concept of thermal resistance were formulated and applied to data centers . The metrics considered the spatial uniformity of thermal performance to characterize poor designs causing local hot spots. In another system , the wet side economizer was decoupled from the condenser water used to reject chiller heat to cooling towers.