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With the rapid development of Internet and data service, a new round of global data center construction boom has come, then how to save energy, reduce cost and win in the competition under the premise of safe operation of the data center, is an important subject.

According to statistics, in 2008, power consumption of all data center globally has reached to 40000000000 KWH/year, accounting for 1.2% of the world's total power consumption, nearly 60% of data center’s power consumption for the air conditioning refrigeration and around electrical equipment. According to a study in Stanford University, energy consumption of the data center all over the world has doubled between 2000 and 2005, and will increase another 75% by 2020. In Gartner group’s (Gartner) recent report, it also mentioned that the power and cooling problem is the biggest problem which data center facing with, the proportion of foreign data center energy costs have surged to 48% of the operating budget. While in domestic data center, power consumption usually account for about 70% of the actual operation cost. This is because the ratio of total power consumption to IT equipment power consumption of data centers abroad is 1.8 or so, and the domestic data center PUE value generally 2.5, even as high as 3. Under such severe situation, the construction of advanced technology "green data center" is imminent.

At present, the industry's leading vendors are all in the discussion on "green data center" solutions, to elaborate how to build a high efficiency and energy saving green data center to users from different aspects. Data center energy saving scheme mainly includes four aspects: First, from refrigeration and key power source, implement energy-saving work on design and implementation of the infrastructure of the room; Second, process energy-saving work in hardware to reduce energy consumption; Third, from chip consumption saving, reduce the power consumption of the data operation. Fourthly, speed up the data center virtualization, automation and cloud computing research and development and popularize the pace of application. From the above four aspects of reducing energy consumption, energy saving in hardware equipment level and chip level have been pay more and more attention by equipment manufacturing enterprises, but energy saving and server virtualization application in infrastructure level represented by cooling and key power source still need a lot of work. In fact, due to soaring power cost, data center has become the "electricity eating tigers", so start from refrigeration and electric equipment (including power supply equipment and IT equipment), to improve the efficiency of the physical and electrical equipment, is a way to establish "green data center". Because this can resolve the problem from the source, and is the "priority" of energy saving, has twice the result with half the effort in saving energy. The followings will advise on how to choose" green data center "of the refrigeration and key power equipment from four aspects of “cooling", "back-up power equipment", "scalable, extensible, and" energy saving planning and management".

I. About data center cooling design and equipment selection scheme

According to industry electricity regulation of the People's Republic of China, when the capacity of motor is more than 200 kw, chooses high voltage motor for electric driving equipment. In most cases, the high power output of high pressure refrigerating units is more suitable for large-scale data center machine room, the refrigerating capacity of the single unit can be used for more than 5000 m2 room. In addition, the power supply voltage from the power supply bureau to high-end user is 10 kV, if use 380 V motor, it is necessary to use substation chamber to transform voltage from 10kV to 400V for use in water chiller. By this way, not only increased the electrical equipment procurement costs, also increased the operation cost.

The advantage using a high drive unit lies in:

1. Improve the electric power operation reliability of IDC computer room

After water chiller adopting step-down starting way of 10 kV high-voltage motor, starting current is only 380V, about 1/8 of the star triangle startup, can effectively reduce the impact from chiller startup to power grid, and reduce the interference to power supply system. At the same time, when 10 kV high-voltage chiller startup and run, (such as transformer, etc.), it will not induce interference to server and other low voltage 380V power supply communication equipment because of the surge is not through high and low voltage power distribution equipment in building.

2. Reduce total cooling investment

Compared with the 380V low voltage unit, when 10 kV high voltage unit can be directly used, the user does not need step-down transformer of water cooling unit, the corresponding low-voltage distribution facilities and expensive large cross-section cable. Also save the equipment installation, debugging, and a series of costs.

3. Save energy effectively and reduce operating cost

Because of the current value of high voltage transmission line is very small, line loss can be reduced effectively; At the same time, transformer loss can be avoided by using 380V low voltage transformer, for example: cold water group runs with load perennially, take a system which has a single 2800 tons of cold water chiller, total refrigerating capacity of 14000 tons for example: the running time of transformer is 8760 hours, running loss is about 150000 kWh. Calculated according to average 0.8 yuan per kilowatt-hour, active power loss of transformer of single 380V chiller is 120000 yuan per year, and reactive power loss is about 10000 yuan per year, total is 130000 yuan. If take the operation loss of low voltage cables and low voltage motor into account, the actual energy saving effect brought by the high pressure water chillers are more significant.

4. Reduce area of switching room and the room

Covering less area: When covering the same area, refrigerating capacity of high voltage is twice over low refrigerating set. When the number of refrigeration units decreases, the number of auxiliary pump, cooling tower equipment decreases. In the premise of the same total refrigerating capacity, the efficiency of the refrigerating capacity of the single big chiller is superior to many sets of small refrigerating capacity of the chiller.

5. Less dosage of refrigerant, more environmentally friendly

At present, the maximum power of high pressure refrigerating set is 2800 ton of refrigeration, when the maximum power of low-pressure refrigerating set is1250 ton of refrigeration, under the condition of same refrigerating capacity, refrigerant consumption of single unit is far less than that of multiple units. When using high pressure refrigerating units, we must pay attention to the conditions and requirements in terms of high voltage power supply. On the one hand, we must communication with local power supply department early, to get corresponding technical support; On the other hand, the enterprise needs electrician with high-voltage operation qualification on duty.

II. Large IDC data center backup power equipment design and selection schemes
(I) Use of the AC generator set

In the MW level data center which require high reliability, it is recommended to use multiple 10kV voltage level high pressure oil machine used in parallel, its characteristic is:

1. Due to the use of high pressure oil machine, so in the case of the same power, the sectional area of unit output cable reduces significantly in the case of the same power, about 1/25 of the low-pressure oil machine, thus reduce the material consumption. The metal materials procurement costs rise significantly today, for example, from 2004 to 2007, the price of power cable rises above 100%. Therefore by using high voltage motor directly, cable procurement costs will drop by more than 75% year-on-year. At the same time, with limited resources, reducing the material consumption is also the goal of infrastructure.

2. As a result of adopting high-voltage transmission, the line loss of power transmission reduces, and it is suitable for long distance transmission of electricity.

3. Compared with the 380V low voltage unit, in the area where 10kV high pressure oil machine can be use directly, it can be used with the vast majority of high and low voltage power distribution facilities in public, therefore saves the relevant equipment and some large cross-section cable investment, and installation, debugging and a series of engineering construction costs of these facilities.

4 When generator units are in parallel, its cabinets wire reduces relevantly, and has a greater output capability.

5. When used with high pressure water chillers, compared with low pressure oil machine, avoid using step-up transformer.

When using high voltage generator set, pay attention to the conditions and requirements in terms of high voltage power supply, On the one hand, we must communicate with local power supply department early, to get corresponding technical support; On the other hand, the enterprise needs electrician with high-voltage operation qualification on duty.

MW level data center which have shortage in electric power can consider to use 10 kV voltage level industry high pressure gas turbine engine unit which can continue to run more than 8400 hours, its characteristic is:

1. Small noise Gas turbine generator set has all-day sound insulation, fire protection cover. From the unit 1 meter above the ground 1.5 meters, noise is less than 85 dBA in the place where 1 meter above the set and 1 meter above the ground. Waste heat flue gas machine is also equipped with sound insulation devices, noise is less than 72 dBA in the place where 1 meter above the set and 1 meter above the ground.from unit 1 meter, 1.5 meters of above ground.

2. High integration of unit design is very high, covers a small area, fuel system, startup system, control system, excitation system and device are installed on the lever, greatly save installation time and effort. It takes about a month or so to complete the installation of the unit. Generator does not need cooling water, air cooling fan is provided with the unit, it is very simple.

3. High reliability, high availability Unit has high reliability, start-up success rate is 99.97%, and the availability is 98% or more. Overhaul period of unit is 30000 hours, there is almost no maintenance before the overhaul except for replacing some consumable accessories. Overhaul use exchange unit, with only 1 day. The consumable parts cost is about $10000 a year.

4. The principle which initial investment of larger units conform to in design, is to let the user has stable control of the total cost of the equipment in their life cycle (fuel, initial investment and maintenance), to get balance among efficiency, maintenance cost and price. Enabling users to utilize equipments for more than 20 years at relatively a much smaller cost.

5. Certain energy-saving property

(II) The construction layout of UPS system

In the premise of the same self-reliability of UPS, reliability of UPS power supply system is often ensured by raising the redundancy. The higher the redundancy of the UPS operation is, the less actual load rate is. Therefore, at present, a new generation of network UPS has improved the following indicators:

1. Practical adjustment of output power factor Indicators: Because the power input factor of new server is greater than 0.9 (The worst of earlier server input power factor is around 0.6 to 0.7), for the index improvement of the new server type load, the output of the new type UPS power factor is changed from 0.7 to 0.8 to 0.9 (Capacitive load), results in 10% active power increase of the same capacity of UPS equipment, which means that the same capacity of UPS can increase 10% load for new server.

2. The input power factor and harmonic have been improved: At present, due to the mature and perfection of 12 pulse rectifier technology, active filter technology and IGBT rectifier technology, the input power factor index of rectifier rose from earlier 0.88-0.93 to existing 0.94-0.99, and harmonic current (THDi) reaches to less than 5% index, to reduce UPS equipment’s interference to the power, then improve the efficiency and reliability of power supply.

3. Half load input efficiency improved greatly: Half load efficiency of UPS increases from early 75-80% to 93-95%, about 15-18% improvement. The improvement is that UPS system improves the usability of reliability has greatly increased by using increased redundancy, and provides guarantee to maintain the high efficiency of the power supply system. Based on performance improvement of the new generation network UPS, create system improvement plan which reduce the number of UPS parallel under the condition that guarantee the same power supply capacity of parallel operation system: namely when creating UPS parallel operation power supply system, use 3 units of 500KVA UPS parallel operation system with output power factor of 0.9 instead of 4 units of 400KVA UPS parallel operation system with original output power factor of 0.8, to obtain system with higher reliability, and higher cost performance.

The new dynamic UPS using trend introduction

This kind of dynamic UPS consists of diesel generating set, flywheel energy storage device, electric clutch, reactor, static electronic regulator (see below). With commercial power supply, driven synchronous motor and the flywheel energy storage device are in a coaxial state, maintain electric synchronization with the grid operation and supply power to the load, electric clutch keep diesel engine in stationary state; When commercial power supply interrupted, first driving synchronous motor to supply power to load uninterruptedly in stable frequency and voltage power supply state by the flywheel energy storage device, when the diesel engine starts up without load quickly to reach to the rated speed, power system supply power to the load uninterruptedly in the control of clutch; After commercial power supply recovers, UPS system returns to electric synchronous running state. The device can also comprise multiple redundant parallel operation system.

Due to the fact that this kind of dynamic UPS does not have power semiconductor devices in the main circuit, its reliability is much higher than static UPS, it is a kind of mature product with high reliability and availability. This kind of dynamic UPS combines modern flywheel energy storage technology, filtering technology, electronic technology, power factor compensation technology, circuit breaker uninterrupted conversion technology and fuel generator set redundant start-up technology organically, adopts power reactor with high heat capacity, synchronous machine to construct "T" type filter network, both has very high resistance capability of the surge over voltage and overload, and load from the power source input completely on the function of "isolation" : "T" type filter network can absorb more than 95% of the harmonic currents generated by nonlinear loads, minimizes the harmonic impact to power grid; By adjusting the excitation of synchronous machine, it can also have the effect of adjusting the input power factor, so from the concept of green IDC, compared with normal static UPS, dynamic UPS is the real green power supply.

In the United States, Great Britain, France, Netherlands, Japan, South Korea and other foreign IDC data center, this kind of UPS with more than 1700 kVA capacity has operating experience of nearly 10 years. In domestic, dynamic UPS with output capacity of 2000 kVA has been applied in the semiconductor chip manufacturing industry situation which needs continuous backup power supply now, but there is still no IDC data center using case in domestic, it needs further argumentation and experimentation before practical implementation. The characteristics of dynamic UPS are as followings:

---Main power supply circuit without power electronic components, with high reliability and availability

---Input harmonic distortion and capacity of nonlinear load can reach the level of static UPS

---Effective surge and harmonic filtering functions make the input harmonic distortion 3% or less

---With power factor correction function, the input power factor can reach to 0.98

---Efficiency can reach above 96%

---Strong ability to resist current shock (Typical value 10-15 In.)

---Can be used without installation of air-conditioning, reduce energy consumption

---Flywheel storage energy can substitute classic back-up battery system, more environmental friendly

---More than 25-year service life

---Flexible system construction, can be updated gradually

---Compared with static UPS system, maintenance quantity reduced by 50%

---40-50% covering area reduction than conventional UPS systems

III. The construction and use of IDC room should follow the concept of "scalable, extensible"

In fact, excessive planning is also a reason which leads to high energy consumption and low efficiency of data center. Traditional data centers tend to use "Once" engineering design, this not only leads to high investment in purchasing UPS and air conditioning equipment, but also increases the cost of later energy consumption and service. Therefore, it should be divided into several stages according to the requirements of the future demand, purchase the required room facilities in different phase. "Upgradeable refrigeration equipment and power equipment solution" is processed for the concept of "use and upgrade", at the beginning of room using, it can save more than half of the power and cooling loss of data center.

IV. Energy saving planning and management of new IDC room

At present, the energy saving management of data center room is to develop precision, therefore, an effective power and refrigeration capacity planning and management has become a prerequisite for energy saving. For example, there could be a real-time environment detection of cabinet in order to avoid unnecessary power and cooling consumption. Adopting intelligent cabinet with blow rate control function, can provide cooling capacity according to the actual demand of IT equipment in machine cabinet; Implement closed-loop speed control in chilled water, cooling water and large air supply equipment motor to reduce energy consumption; It can also formulate corresponding automation management procedure using natural cold source equipment room, minimize usage of air conditioner; Users can also know real-time parameters such as power, temperature, humidity of the room, thus to make the operation plan of the air conditioning system and of the power equipment accordingly, to make the best operation of the equipment loaded to achieve the goal of promoting efficiency and saving energy.