暖通3000字英文翻译.doc

附录A 英语原文 Air-Conditioning Design for Data Centers Accommodating Current Loads and Planning for the FutureAbstractTodays modern enterprise data center must be capable of efficiently operating at current average power densities of 30 to 50 W/ft2 (320 to 540 W/m2) and, based upon industry trends, support growth in the foreseeable future toward 150 W/ft2 (1,610 W/m2) and also incorporate provision to possibly support significantly higher power densities in local areas. This paper summarizes the industry trends toward greater power consumption and higher processing speed servers and gives an overview of current and expected techniques for cooling high power consuming cabinets and mainframes. The potential impact of these trends and new techniques on the design of the raised floor cooling system will also be discussed. Additionally, during the installation of new equipment and the migration of equipment from other data centers to the new center, the new data center at start-up is often required to operate with almost no computing equipment load. The start-up conditions can be an operational problem for equipment sized to operate at maximum load. In response to the potentially large range of power density operation and the high costs of data center construction, the majority of owner operators plan to accommodate this expected power density growth in phases. This paper summarizes the planning to accommodate the various load conditions of the mechanical systems for one recently designed data center, including raised floor cooling, central plants, and pipe distribution.1 INTRODUCTION The air-conditioning system in todays modern enterprise data center must be capable of continuously supporting on a 7cays/week, 24 hours/day, 365 days/year basis with current power densities averaging 30 to 50 W/ft2 (320 to 540 W/m2)and, based on the industry trends of faster processing speed requirements and higher power consuming servers, incorporate provision for growth in the foreseeable future toward 150W/ft2 (1,610 W/m2). In addition, currently available computing equipment can be configured to require significantly higher power densities in local areas. The modern data center must also be capable of supporting these local higher densities as well. For the purposes of this paper, power density capacity of a data center in W/ft2 is defined to be the total electric power capacity available to the computing equipment in watts divided by the total raised floor area in square feet of the data centers computer room Power density capacity (W/ft2) = total UPS power (W)/total raised floor area (ft2) The computer room floor of the data center would incorporate all of the computing equipment, required access for that equipment, egress paths, air-conditioning equipment, and power distribution units (PDUs). The actual power density is defined as the actual power used by the computing equipment divided by the floor area occupied by the equipment plus any supporting space as described above.Actual power density (W/ft2) = computer power consumption (W)/required computer area (ft2) Empty or “white” space should not be included in the calculation of the actual power density.Computing equipment in the data center is generally composed of legacy rack servers, modern rack servers, blade servers, mainframes, network devices, and storage devices. Within each of these different categories of equipment there are numerous types of computing devices, many having different sizes and different power and cooling requirements. Ultimately, the total power consumption on the raised floor (and therefore the majority of the raised floor cooling load) is the sum of the actual power consumption of the individual computers themselves. Ideally, the air-conditioning system designer would have access to a complete list identifying the make and model of all equipment used, the power and cooling requirements of the equipment, and the clients preferred equipment arrangement. In many cases, this list and plan are unavailable during the design phase of a project as the information technology (IT) planning for the center is generally on a design path parallel to the design of the data center itself. Often during the design phase, the project designers are asked to plan for any of the computing equipment placed anywhere on the raised floor. Within defined guidelines, the design criterion is often that the supporting mechanical and electrical systems must be able to support dense groups of IT cabinets containing blade and rack servers consuming significantly more power and requiring significantly more cooling than the average specified cooling requirement. In the end, air-conditioning design success is often judged on the ability to cool these dense groups of high power consuming computers and the mainframe equipment.Complicating things further, storage equipment and mainframe computers have very specific requirements from a cooling standpoint (locations of intake and exhaust as well as airflow and temperature) that generally require a different cooling approach to the cooling of servers. Additionally, from the IT planners standpoint, future generations of computers could require substantial reprogramming of the raised floor and substantially different cooling distribution systems. The infrastructure system should accommodate at least five changes in technology, with technology changes occurring approximately every three years.2 DATA CENTER POWER REQUIREMENTSAs indicated previously, data center power consumption and cooling requirements are a function of the types and quantities of computing equipment to be installed. In general, the new blade and rack servers consume the most power on a unit area footprint basis followed, respectively, by the tape storage devices and mainframes/large partitioned servers and tape storage devices. Data centers primarily supporting older legacy servers and tape storage/retrieval processes can operate at power densities as low as 30 W/ft2 (320 W/m2). Data centers primarily performing processing operations using new servers typically operate in the 60 to 100 W/ft2 (645 to 1,075 W/m2) range. Standard 2.2 meter (86 inch) IT cabinets are subdivided into 42Us of available computing equipment installation, with the “U” being the incremental unit height of computing equipment.3 DATA CENTER PLANNING GENERALThe majority of new corporate data center projects begin with both the migration of existing equipment and the installation of new equipment. This generally puts the initial design loads in the 40 to 60 W/ft2 range (430 - 645 w/m2), although the power requirements at start-up are often much less, due to the fact that installation of equipment can be relatively slow but the data center must become operational upon installation of the first piece of hardware. Multi-year IT plans are developed identifying phased-in equipment and projected loads. These IT loads can then be translated to a phased-in plan for growth of the power and cooling systems.The most significant factors affecting construction cost of the data center are the design power density and the level of reliability. At a 75 W/ft2 (810 W/m2) design power density, the construction cost can range from $1000 to $1500/ft2 ($10,750 to $16,130/m2) of raised floor, depending upon the required level of reliability. Given the high costs of data center construction, there is little reason to construct mechanical and electrical infrastructure that might see little use for a number of years. Developing phased plans for the installation of mechanical and electrical equipment, matching cooling and electrical infrastructure to IT requirements, makes cost-effective sense, requiring infrastructure costs only to be expended when required.In large data centers the mechanical and electrical infra-structure space requirements to support the power and cooling needs are significant relative to the size of the raised floor. At 75 W/ft2 (810 W/m2) over 100,000 ft2 (9,300 m2), the infra-structure space requirement can equal the size of the raised floor. Ultimately though, the maximum power requirement will set the physical size of the infrastructure and the ultimate delivery capability of the cooling systems and incoming electrical systems. Once the maximum capabilities of the infra-structure and the required growth stages have been set, the sizes and numbers of chillers, pumps, air handlers, and other support equipment can be determined and then the corresponding sizes of the mechanical and electrical rooms set.Due to the nature of the constant electric load that occurs in the data center, the use of “green” or energy-saving mechanical systems has been limited. Research into the use of more energy-efficient air-conditioning solutions is ongoing 2. However, when outdoor air temperatures permit, “free cooling” can be utilized as long as relative humidity control can be maintained.Decisions to increase power and cooling capabilities beyond the initial design levels will likely require invasive infrastructure expansion or even building additions. We there-fore believe it is critical to project power and square footage requirements as far forward as possible and also to consider a contingency for unexpected growth.Generally, the schematic design of a data center includes general arrangements and one-line drawings showing the initial and phased growth of all supporting infrastructure. Mechanical and electrical infrastructure should be in alignment from a power and cooling capability standpoint. Excess capability of either plant generally cannot be taken advantage of and is usually a poor investment. Once the specific infra-structure systems and the initial build density have been deter-mined, future increments of growth should be planned for using modules of the initially selected equipment and installed without interruption of any of the operating infrastructure.4 HUMIDIFICATION AND PRESSURIZATION Control of humidity within the data center is essential to ensuring proper operation of the IT equipment. Humidity levels that are too low can cause a static electric discharge. Humidity levels that are too high can cause media failures in tape devices and other types of equipment failures. CRAH units, which perform relative humidity control using built-in reheat and humidification equipment, can work against each other (some units in heating and others in cooling) when control set points are not identical and control tolerances are too small. This scenario can also occur even with all units operating with similar set points and dead-bands when control sensors are out of calibration or different areas of the data center operate under significantly different electrical power demands.To eliminate the possibility of this potentially energy-wasting scenario, the subject data center eliminated the electric reheat coils and humidification from the CRAH units and incorporated central station air handlers (AHUs) that served to provide humidification to the data center and a minimum reheat capability. The AHUs also served to introduce outdoor air as necessary to ventilate and pressurize the data center. Positive pressurization of the data center minimizes air infiltration along with potential pollutants that could negatively affect the computing equipment. To further minimize effects of the outdoor environment, the subject data center was constructed completely internal to the building (no common exterior wall), with vapor barriers provided on the data center walls as well as the entire building perimeter. Air locks were also provided at all entrances to the corridors that surrounded the data center.At 319.8 MBH (93.7 kW) of capacity, the cooling coils of the CRAH units operate with virtually no latent cooling. Based on this, the data center will operate with minimal requirement for humidification until a high-density requirement causes a number of the units to operate at full load. An analysis of the IT plan showed that a significant portion of the load (1875 kW) could be high-density cabinets, ultimately requiring a minimum of 17 units operating at full load (397 MBH (116.5 kW) sensible cooling and 24 MBH (7.0 kW) latent cooling. This corresponds to a total latent load of 408 MBH (119.6 kW) (17 units 24 MBH 7.0 kW each), whichrequired a maximum of 384 #/h (2.9 kg/s) of steam. To meet this maximum requirement, each of the AHUs was furnished with ultrasonic humidifiers, each capable of meeting this load. To control humidity within the data center, the return air relative humidity and temperature in the return air to the AHUs was measured and converted to an absolute humidity, in grains of moisture per pound of dry air. Humidification is then enabled as necessary to ensure that the data center remains within an acceptable range of absolute humidity.5 SUPPORTING MECHANICAL INFRASTRUCTUREThe subject data center was initially planned for three phases of overall growth: phase 1 50,000 ft2 (4,650 m2) at 50 W/ft2 (540 W/m2), phase 2 100,000 ft2 (9,300 m2) at 50 W/ft2 (540 W/m2), and phase 3 100,000 ft2 (9,300 m2) at 75 W/ft2 (810 W/m2). Although the largest component of the air-conditioning load is the electrical power that powers the IT equipment, there are numerous other components to the load that significantly increase the load over that required to directly support the IT equipment. An accurate summary of all components of the load through all phases of growth is necessary to ensure that all air-conditioning requirements can be met both at start-up and throughout all phases of the growth. Additionally, the infrastructure is normally planned such that mechanical and electrical equipment is added as the load grows. As well as design loads, the air-conditioning system needs to be able to operate at start-up with minimal IT equipment in the data center. This requires an accurate analysis of the loads at start-up to ensure that the equipment selected can also operate properly at the minimum load.Many of the individual loads that compose the total air- conditioning load of a data center are typical of those found in office or institutional buildings, but there are also a number of other loads that are either unique to the data center or significantly larger. Typical to the conventional building are skin, lighting, and personal ventilation loads. These loads are generally less than those found in other buildings, as data center functions require no windows, overall lower lighting, and minimal personal ventilation due to the minimum staffing requirements to operate a center. Loads unique or significantly larger than those found in a commercial building include uninterruptible power supplies (UPS), battery room ventilation, and transformers. The modern data center contains numerousseparate electrical transformers that serve to step down voltage from the utility to the emergency power generation level, the UPS equipment, the mechanical, and the computing equipment itself. Load bank transformers are normally data center requirements as well to permit testing of the UPS equipment.To provide a Tier 4 (system plus system, dual path) mechanical and electrical infrastructure system that can provide 75 W/ft2 (810 W/m2) of power over 100,000 ft2 (9,300 m2), the subject data center required about 100,000 ft2 (9,300 m2) of supporting infrastructure space. This space included UPS and battery rooms, numerous electrical rooms, and indoor centrifugal chiller and emergency generator power plants. Typically, the total square footage of the facility is built at day one and the building lit and air-conditioned. The combined lighting and skin loads in the subject data center vary from 4 to 6 W/ft2 (43 to 65 W/m2) over the 200,000 ft2 (18,600 m2) facility (depending upon location in the facility) and are minimal when compared to the full growth load of 75 W/ft2 (810 W/m2) over the 100,000 ft2 (9,300 m2). These loads are only slightly more significant when compared to the stage 1 load of 50 W/ft2 (540 W/m2) over 50,000 ft2 (4,650 m2). If minimal IT load is available at start-up, the skin and lighting loads will compose the majority of the air-conditioning load. Air-conditioning equipment sized for operation at the maximum design loads is significantly oversized for cool-ing without an IT load and possibly not capable of operation at all without some IT load. Generally, data centers are constructed with an office component that adds to the initial required air-conditioning load. A thorough analysis of both the maximum and minimum loads is therefore required during design to ensure that the selected equipment is suitable for operation over its total expected operating range.When the operating loads meet the design loads, the majority of the air-conditioning requirement is to support the electrical loads. In addition to providing the design air-conditioning requirement on the raised floor, the air-conditioning system must also cool a number of electrical devices, the most significant of these being the UPS. The UPS converts the incoming AC power to DC and back to AC for the purposes of power cleaning and in the process rejects up to 8% of the incoming electrical power as a heat load. Additionally, numerous transformers step down power from the incoming voltage to the 208 or 120 volts used by the IT equipment. Transformers stepping down the voltage to the voltage used by the UPS (normally 480 volt) are often located in the UPS rooms them-selves. The transformers stepping down from the UPS voltage to the voltage used by the IT equipment (208 or 120 volts) are often located on the raised floor itself. Transformers generally reject up to 2% of the stepped down energy as heat. Additional electrical transformers also step down the voltage to that used by the mechanical equipment and other non-IT loads. For the subje