GENERAL PRINCIPLES OF CONSTRUCTION OF AN ENERGY EFFICIENT DATA CENTER FOR AN ORGANIZATION

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1 GENERAL PRINCIPLES OF CONSTRUCTION OF AN ENERGY EFFICIENT DATA CENTER FOR AN ORGANIZATION AUTHOR Mr. S. N. Chavan Retd. A.G.M.(Elec.) S.B.I. & An Electrical Consultant ShreeLakshmi Electro-Tech. India has a biggest treasure of intelligent, dedicated and hard working people. It has become the hub of I.T. activities. Most of the Multinational organizations are out-sourcing their information technology related work to India. In today s fiercely competitive market immediate/speedy service to the customers has gained extreme importance. In this context availability of Information/Data at your finger tips is crucial. Hence the trend has shifted from paper-based to digital information management This involves digital storage whose demand in India has increased exponentially from about 34 Petabytes in 2007 to about 100 petabytes. This demand is growing at a compounded rate of 25-30%. Hence most of the organizations are constructing the Data Centers. Due to the above scenario the adoption of Energy Efficient measures in new and existing Data Centers has become crucial. Different Types of Data Centers Data Centers are basically divided in two categories namely Internet Data Center and Enterprise Data Center. Internet Data Centre ( I.D.C.) Internet Data Centers are also referred to as Colocation & Managed Data Center. These are built & operated by service providers. IDC s are built & maintained by the enterprises whose business is based on internet commerce. The service provider make s an agreement with customers to provide functional support to the customer s I.T equipment. The service provider s IDC infrastructure is similar to that of other type i.e. Enterprise Data Center, however the scalability need of Enterprise Data Centre is smaller because of smaller user base and services provided are comparatively less. Enterprise Data Center Enterprise Data Center s support many functions that enables different business strategies. Enterprise Data Center are evolving and this evolution is partly resulting in new trends mainly because of the criticality of the data held in Datacenters. These trends are use of n-tier, web services and grid computing etc. Due to criticality of operation and maintenance of Data Centers the Telecommunication Association( TIA) has formulated operating standards ( TIA-942) to address the requirements of Data Center Infrastructure. TIA-942 Standards Telecommunication Industry Association (TIA) has developed a TIA-942 standard for planning and building Data Center s particularly with regards to cabling systems and network design by the Data Center designer s & planners. TIA covers the following: 43

2 A. Site Selection & layout B. Cabling Infrastructure C. Reliability D. Environmental Considerations Major Factors in Selection of Site for Data Center A. Power availability B. Preferred Seismic Zone Below Zone 3. C. Adequate water Availability( for Big Data Centers where water cooled cooling systems are provided which are energy efficient) D. Free from security threat. Major advantages of Designing Datacenter s as per TIA-942 standards are as under; A. Standard nomenclature. B. Fail-safe operation. C. Robust protection against natural or human made disaster s. D. Long term reliability, flexibility and scalability. The Data center redundancy is one of the most important factor s in the designing of Data Center. Redundancy in a system design makes available alternate components to provide alternative in case of component failure. Based on the redundancy level maintained in Data Centers, the Data Center s are categorized in to four Tier Levels, namely Tier 1, Tier 2, 3,4 etc. Data Center standards define availability factor of D.C. facility. Classification of Data Center s on basis of their Tier level identifies the different Data Center site design topologies. Tier IV Data Center Infrastructure is considered to be most robust, scalable and failure-proof. Sources Contributing Towards Power Consumption in a Data Center: In a Data Center I.T. equipment s consume about 50% and Air-conditioning equipment s needed for cooling consume almost 37% of total power consumed by the Data Center (D.C.). Remaining 13% is consumed by U.P.S. P.D.U. and other accessories including the lighting. Due to the use of latest high density servers such as blade servers the power consumption has increased from earlier value of around 3-4 K.W.per rack to almost 24 K.W.per rack This has a major impact on the cooling needs of the Data Center resulting in higher demand of power for the same area of Data Center and the consequent increase in energy consumption. Ultimate result is exponential rise in monthly electricity bill of an organization. Hence selection of energy efficient components while modernization/expansion of existing D.C. Or construction of a new D.C. play a significant role. It is a very big topic and in this paper we are confining the issue to the Electrical Components involved in the power network from sub-station to the Server Room of a D.C. Most of the big and reputed organizations are adopting Tier 3 type of Data Centers in India as Tier 4 D.C. needs two different incoming power sub-stations getting incoming power supply from separate feeders coming from different switchyards which is not economically feasible at all the locations. Major electrical components of A Data Center Power Infrastructure are as under : (A) H.T. Circuit Breaker. (B) Step Down Distribution Transformer. (C) L.T. C.B. (D) Main Power Distribution Panel. (E) Diesel Generator. (F) Transient Voltage Surge suppressor/s. (G) U.P.S. with Battery Bank. (H) Automatic Transfer Switches. (I) Sub Distribution Boards (J) Power Distribution Units (P.D.U.) (K) Power Distribution Cables OR Bus-Bar Distribution system. (L) Power Strips in the Server racks. (M) Static Transfer Switches. (N) Grounding. (O) Monitoring Equipment s (B.M.S.)etc. 44

3 (A)& (C) : H.T. & L.T. Circuit Breakers. Energy saving in above breakers is comparatively negligible as compared to the scope in other components and it s major role is to safe guard the Data Center (D.C.) equipment s from any electrical faults in incoming supply or from the load side. They are designed as per the fault level of the power supply utilities and S.C. current levels of the load (for L.T. C.B.). (B) Main Distribution Transformer/ Utility Transformer for a Data Center Transformer is the heart of Power distribution network of any organization. Data Center load increases exponentially due to business needs and for business continuity of an organization adequate spare capacity of transformer needs to be ensured. Secondly, good After-Sales Service with adequate spares at a location nearer to Data Center is a necessity. All Data Centers have Non Linear loads which generate the harmonics which flow from load towards the power source. Transformers are vulnerable to overheating and premature failure due to harmonic currents generated by non linear loads. Hence K-rated transformer which is specifically designed to accommodate harmonic currents need to be selected for a Data Center. These transformers are preferred because they have additional thermal capacity to take care of overheating due to harmonics. Generally, for non-linear loads and computer rooms, the recommended K-factor is 4 to 9. (E) Diesel Generator Diesel generator is used as a backup power source during the grid failure or other failures in power system components of a D.C. Following factors need consideration during selection of a D.G. set for a D.C. 1. Reliability of a D.G. set is gravely impacted under light load conditions which lead to engine damage. Hence, operating a D.G. set below 30% of rated load is never recommended. 2. At high altitudes& high temperatures de-rating of the prime mover to deliver the torque required for full generator output needs to be done. 3. Sizing of a D.G.set depends upon load demand. Stand-by D.G. set generally have no overload capacity. It has a limited 10% overload capacity at intermittent period. In case of a D.C. the D.G. set has to be designed for prime power rating. 4. A leading power factor current can destabilize the D.G. set. The most common sources causing leading p.f. are lightly loaded UPS systems with input filters and power factor correction devices for motors. It is most desirable to ensure that load power factor is supported by the generator. 5. For an energy efficiency of a Data Center a D.G. with lower specific fuel consumption needs to be preferred. 6. Few Energy Saving Measures For D.G. Set Are As Under : A. To ensure availability of cold & dust free air at intake for engine cooling. Air filtration to be improved. B. Parallel operation of D. G. sets with load sharing capability for improving load factor and fuel economy to be given a weightage. C. Fuel injection pumps be calibrated frequently. (F.) Transient Voltage Surge Suppressor : Transient surges are caused mainly by LIGHTNING, SWITCHING & ELECTRICAL FAULTS. Secondary effect of lightning causes transient Over voltages which damage sensitive electrical and electronic equipment s installed in a D.C. The commonly used protective devices like H.R.C. fuses, M.C.B s, E.L.C.B s etc are current sensing devices and they sense & operate in few milli seconds. As the surge is a Transient Over Voltage which occurs for a few micro seconds these devices can not sense them. Hence, Indian & international standards recommend installation of Surge Protection devices at the input of the U.P.S. and the associated By-pass circuits ( including manual By- pass circuit) as well as connected branch panel. As critical loads are installed in a D.C. provision of TVSS is now mandatory. 45

4 (G) Selection of U.P.S. & Batteries Commercial power containing spikes, sags, and outages would cause Loss Of Valuable Data and severe damage to I.T. infrastructure in a Data Center. U.P.S. is one of the critical equipment in operation of a Data Center. Among the various types of U.P.S. systems ON-LINE U.P.S. model is preferred in the D.C. Apart from the reliability the Efficiency of an U.P.S. system becomes a major consideration. An U.P.S. has an incomer power transformer which should be K- rated to take care of harmonics generated by the Non linear loads in the D.C. Efficiency of an U.P.S. depends upon loading of U.P.S. Efficiency is maximum at full loads and falls sharply as the load decreases. For Reliability & Business Continuity very often N+1 combination of U.P.S. is used in a smaller and Tier 2 D.C. s. In this case the total load of a D.C.is shared equally by both the U.P.S. who get Incoming supply from a single common source. However, breakdown in the common incoming supply to both the U.P.S. will still cause shutdown of the D.C. In the case of Tier 3&4 D.C. an N+N model of U.P.S. system (where in both the U.P.S. get supply which is independent from each other) is implemented. Here also both the U.P.S. can be loaded up to Max. 45% of their rated capacity so that in the event of power failure on In- coming side of one of the U.P.S. causing its tripping the other U.P.S. will take over the full load of the D.C. with a total loading of 90%. For a design of an energy efficient U.P.S. for a D.C. it is essential to specify an efficiency of 90% at 30% load and an efficiency of minimum of 92% at 60% and above loading, which is possible and some of the manufacturers are manufacturing such U.P.S. Normally, the current harmonics in an U.P.S. at full load is designed to be 10% and at lower loads the percentage of current harmonics increase. However, as stated above in Tier 3 and 4 Data Center s the load on both the U.P.S. is shared equally and is normally below 50% and hence it is essential to specify 5% current harmonics at 50% loading which is feasible. Third major point is to specify the crest factor of around 3 as against 2.5 normally provided by all. In India the voltage fluctuation at times is very wide and hence specifying In coming voltage range of 415V 20% and 415 V + 15% for a reliable energy efficient U.P.S. is an ideal specification. Galvanic isolation by double conversion of supply initially from A.C. to D.C.( rectification) and then from D.C. to A.C.(Inversion) and use of 12 pulse I.G.B.T. is an added essential requirement in the design of a most reliable and energy efficient U.P.S. For maximum energy efficiency and reliability the latest modular U.P.S which are normally transformer less are given preference. Each module can be of as low as 1 K.V.A and as high as 50 K.V.A. These modules are hot swappable. Back up power to U.P.S. in case of failure of Utility Power supply and taking over by the Auxiliary/Standby source is provided by the batteries. Among Various types of batteries such as Lead Acid, Tubular and Sealed Maintenance Free ( S.M.F.) the S.M.F. is a preferred choice. Of late latest technology & battery less U.P.S. systems are slowly gaining importance and are being used. (H), (I ), (J) : Automatic Transfer Switches. ( A.T.S.) Sub-Distribution Boards & Power Distribution Units ( P.D.U.) : (H) : Automatic Transfer Switches : Automatic Transfer switches (A.T.S.) are recommended when no down time from power outage is tolerated. The A.T.S. enables the redundant U.P.S., back up Generators, D.C. to A.C. invertors, and other A.C. power sources etc. to be used for a single source in a D.C. The A.T.S. & accessories shall confirm to the requirements of UL1008 standards, NEPA 70 & 110,IEE 446, etc. (K )& (L) : Power Distribution Cables/ Bus-Bars & Power Strips in a Server Rack. Depending upon total floor height and clearance available between the base floor and false floor, the obstructions etc. Server Racks are connected to P.D.U. s either by the Power cables Or by an under floor Bus-Bar system having Tap-off boxes. Similarly, the P.D.U. s get the incoming power supply from the sub-distribution boards either through the power cables or the Over-head /under floor bus-bar system with tap-off boxes. Each server rack has two power strip which get incoming power supply through two different U.P.S. systems and dual power racks are plugged in to these power strips which ensures continuous power supply 46

5 to the critical servers. Modern power strips are equipped with a master Circuit Breaker and 8/12/16 sockets with a load manager which displays voltage, current consumed by the power strip which helps in effective monitoring of Data Center loads. (M) : Static Transfer Switches In a Data Centre some of the communication equipment s have only one In-built power supply source and are susceptible to failures. To prevent such an eventuality a Static Transfer Switch is provided. Function of S.T.S. is similar to A.T.S. It receives incoming power from two different U.P.S. and delivers continuous power to single supply source devices. (N) : Grounding In a D.C. all the equipment s have to be at the same potential to prevent any circulating current and the potential difference to protect sensitive electronic equipment s. Accordingly, the false floor metallic grid, server racks, U.P.S., D.B. s etc are all connected together to a common earth grid inside a D.C. On ground floor multiple earth pits are connected in a grid and two separate insulated power cables of adequate capacity depending on D.C. load run from the ground earthing grid to the D.C earthing grid and are solidly connected to each other. (O) : Monitoring/ B.M.S. system All the electrical, A.C. Fire, C.C.T.V.and Access control systems etc. are connected by the control cables to a B.M.S. system which effectively monitors satisfactory operation of all the equipment s in a Data Center. Thus planning and design of a modern Data Center is a challenging job and needs detailed and thorough study of each and every equipment to determine it s exact utility to ensure business continuity and energy efficiency. 47

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