深入研究 | PUE的上限和下限
作者：WILLIAM J.KOSIK，产品工程师，能源管理工程师，LEED认证专家，建筑能源建模专业人士资格认证，惠普芝加哥技术服务工程师。
BY WILLIAM J. KOSIK, PE, CEM, LEED AP BD C, BEMP, HP Technology Services, Chicago
有关数据中心的文章有很多，贯穿其中的共同点是：对数据中心能源效率的思考模式仍处在转变的过程中。这种转变正在使我们远离我们最了解的问题：为办公楼建筑，实验室，医院和学校等设计HVAC（空调）系统。
A common thread running through many articles about data centers is the idea that approaches to data center energy efficiency are still in the process of a paradigm shift. This shift is moving us away from what we know the most about: designing HVAC systems for office buildings, labs, hospitals, and schools.
例如，就在五年前，大部分老式数据中心的空调送风温度仍为55℉（典型的商业建筑做法，约13℃）。与之相比，新数据中心使用的送风温度≥75℉（约24℃）。空调送风温度提高了20℉，这影响了整个制冷系统。正是这一变化引起了对数据中心空调系统的设计及运行的大规模反思。
For example, just five years ago, a large portion of legacy data centers were still running supply air temperatures at 55 F-typical of a commercial building. Contrast that to new projects where data centers will use supply air temperatures at or above 75 F. That is a 20 F increase in supply air temperature—effects cascading down into the entire cooling system. Just this one change has caused a wholesale rethinking of the design and operation of air conditioning systems that are used in data centers.
值得庆幸的是，有许多杰出的数据中心工程师和一些行业组织（如Uptime Institute，7x24 Exchange，ASHRAE等）都致力于数据中心电力和制冷系统的规划和设计工作。此外，许多制造商，可以说是数据中心产业链中最重要的一环，现在都拥有专用于数据中心设备的完善的生产线。
Thankfully, there are many smart engineers designing data centers and several industry organizations (such as Uptime Institute, 7x24 Exchange, ASHRAE, and others) dedicated to the planning and design of data center power and cooling systems. Also, many of the manufacturers, arguably the most important link in the chain, now have complete equipment lines dedicated to data centers.
随着计算机技术（硬件，网络，存储和软件）以惊人的速度发展，电力和制冷系统的规划和工程也在努力跟上脚步，然而这都在意料之中。我们在日常生活中看到——移动电话，个人电脑，笔记本电脑和电视这些在其最初发行后的9到12个月内就会被淘汰。当然，消费电子市场还涉及其他不同的因素，但核心理念与企业级IT设备相同——新技术（制造工艺，材料，软件）的进步使其性能高于之前，同时降低能耗。
As computer technology (hardware, networking, storage, and software) evolves at a blazing pace, planning and engineering of power and cooling systems are struggling to keep up. But this should come as no surprise. We see it in our daily life-mobile phones, PCs, notebook computers, and TVs that are rendered obsolete in 9 to 12 months from initial release. Certainly, there are different factors involved in the consumer electronics market, but the core idea is the same as with enterprise-level IT equipment—advances in new technology (manufacturing, materials, software) enable higher performance than the predecessors while using less energy.
了解这些限制因素后，就可以理解电力和制冷设备制造商进行研发，规划，投资和制造下一代产品以支持尚未开发的计算机技术的难度之大。即使最后制造商开发出能够匹配最新一代计算机技术的产品，但集成功能（使设备能够适应未来IT设备的设计）的成本实在是过于昂贵。
Understanding these constraints, it’s no wonder that power and cooling equipment manufacturers have a difficult time conducting R&D, planning, funding, and manufacturing their next generation of products that will support yet-to-be-developed computer technology. In the end, the power and cooling equipment manufacturers develop products that work well with the latest generation of computer technology, but integrating features that allow the equipment to adapt to future IT equipment design may simply be too cost prohibitive.
从另一个的角度来看，当计算机制造商发布新一代服务器时，服务器热工程师可能已经开发出一种新颖的冷却设计方案，使服务器在较低温度下运行并减少风扇能耗。这是数据中心空调工程师和服务器热工程师需要进行对话来尝试优化服务器和数据中心制冷系统的能源使用和功效的地方（当然还有其他许多方面），否则，不良后果就是拥有一台高性能、低能耗的服务器，该服务器需要数据中心制冷系统，但该制冷系统效率低下且系统过于复杂或成本过高。这就是数据中心制冷系统能耗详细模拟和分析的用武之地。
Looking from a different perspective, we see that when a computer manufacturer releases a new generation of servers, the thermal engineers will have likely developed a novel cooling design to make the server run at lower temperatures and to use less fan energy. This is where the data center HVAC engineers and the server thermal engineers need to have a conversation in an attempt to optimize the energy use and efficacy of the servers and the data center cooling system, not just one or the other. An undesirable outcome is to have a high-performance, low-energy server that requires a data center cooling system that is inefficient, too complex, or too cost prohibitive to build. This is where detailed simulation and analysis of data center cooling system energy use come in.
空调送风温度是数据中心制冷系统最独特的特征。在舒适性空调中，HVAC（空调）系统的主要目标是提供足够的制冷能力以满足所有内部和外部负荷，确保建筑内的居住者感觉舒适（干球温度和空气中的含湿量）并保持适当的过滤和通风量，以保证气态和颗粒污染物保持在正常水平。数据中心通常也需要满足这些目标，但其电气设备负荷（与现代的高科技商业办公楼相比）要高出一个数量级。好消息是，相对人而言，计算机能忍受高温环境，同时亦可宽容高湿环境，这种耐高温、耐高湿的特性为能效优化提供了巨大的空间。
Supply air temperature is the most distinctive feature of a cooling system in a data center. In comfort cooling applications, the primary goal of the HVAC system is to provide enough cooling capacity to satisfy all internal and external loads, ensure that the building occupants feel comfortable (dry bulb temperature and moisture content of the air), and to maintain the appropriate filtration and ventilation rates to safeguard against higher-than-acceptable levels of gaseous and particulate contaminants. Data centers generally need to meet these goals as well, but the electrical equipment loads (when compared to a modern, high-tech commercial office building) are an order of magnitude greater. The good news is that, unlike people, computers don’t mind running very hot and are pretty tolerant to a wide range of moisture levels. With this tolerance to high heat and humidity comes tremendous opportunity for energy efficiency opportunities.
节能空间来自于蒸发温度的提高（送风温度提高）导致的压缩机功率降低以及压缩机运行频率降低这一实际情况，特别是在能够充分采用节能策略的气候条件下。仔细核算制冷系统替代方案是否可用是非常有必要的，因为虽然某个特定的选项可能会显着降低压缩机能耗，但与另外的选项相比，其他设备（风机，泵等）的能耗可能会增加。
The energy efficiency opportunities come from a combination of reduced compressor horsepower resulting from increased evaporator temperatures (supply air temperatures) and the fact that the compressors will run less often, especially in climates that enable full use of the economization strategy. This is where careful examination of the available cooling system alternatives is necessary; while a certain cooling option might offer a significant reduction in compressor energy, the other components (fans, pumps, etc.) may use more energy when compared to the other options.
制冷系统各“设定选项”之间的比较必须包括整个数据中心的每小时能耗模拟（由ASHRAE标准90.1定义）才能够分析制冷系统和子系统以确定哪些设备能耗最大。该分析的结果将为能源专业人员提供原始数据，以便就最节能的系统提出建议并提供关于每个子系统在不同运行情况下的详细数据，例如不同的送风温度和不同的室外气象参数。
The comparison of the cooling system options must include a full hourly energy simulation of the data center as a whole (as defined by ASHRAE Standard 90.1) with the ability to analyze the cooling systems and subsystems to determine which components consume the largest amounts of energy. The results of the this analysis will provide raw data for the energy professional to make recommendations on the most energy efficient system, and also offer granular data on how each of the subsystems performs under different operational scenarios, such as different supply air temperatures and in different climates.
节能装置是所有高能效制冷系统的关键组成部分，它是各种硬件设备和操作流程的简单组合，旨在通过利用室外空气有利的温湿度条件来减少HVAC系统能耗。由于不同的节能装置依赖于不同的湿度条件，因此每种装置都具有不同的性能特征。根据节能类型和控制策略，节能装置可以以三种不同的模式运行：100％关闭，部分运行和100％开启。
A critical component of any energy-efficient cooling system is the economizer. An economizer is simply a combination of operational sequences and equipment hardware that is intended to reduce energy use of an HVAC system by taking advantage of the positive psychrometric attributes of the outdoor air. Because different economizers rely on different psychrometric conditions, each one will have distinct performance characteristics. Depending on the economizer type and control strategy, the economizer will operate in three distinct modes: 100% off, partial operation, and 100% on.
部分运行模式将在指定的温度和湿度范围内运行。根据气候的不同，部分运行模式可能在一年中占很大比例；计算部分运行模式的运行时间在确定节能解决方案的功效时是很重要的。部分节能运行的计算是通过分析全年（总共8760小时）的逐时冷负荷来完成的，以冷吨·小时为单位，这个总和成为分子，分母是冷负荷值按小时计算的总和（仅为8760 x冷负荷），以冷吨·小时为单位，相除得到的百分比基本上是节能装置可以使用的时间。
The partial operation mode will operate at a specified range of temperatures and humidities. Depending on the climate, partial economization could be in effect a large percentage of the year; it is important to account for these hours in determining the efficacy of the economizer solution. Calculating partial economization is done by adding up the hourly cooling load in tons (ton-hours) in the period of hours being analyzed (8760 hours total). This sum becomes the numerator. The denominator is the sum of the hourly cooling load in tons-hours (simply 8760 x cooling load). The resulting percentage is essentially the amount of time the economizer can be used.
图1根据芝加哥气象数据的分析结果描述了不同节能装置的月度效率。在分析赤道以南的气象参数时（图2），数据显示最大的节能出现在北半球夏季的月份。另一种了解节能装置功效的方法是研究其在没有机械制冷的情况下提供的送风温度。根据气候类型，一些节能装置几乎可以在100％的时间内使用，与此同时伴随着极少量机械制冷甚至没有机械制冷。这些都是数据可视化技术的案例，可用于快速了解潜在的节能。
The analysis using Chicago weather data depicts these efficiencies monthly by economizer type (Figure 1). When analyzing a climate that is south of the equator (Figure 2), the data will show the greatest savings during the “summer” months in the northern hemisphere. Another way to look at the efficacy of the economizer is the supply air temperature it can produce with no mechanical cooling. Depending on the climate type, some economizers can be used nearly 100% of the time with little or no mechanical cooling. These are examples of data visualization techniques that are useful to gain a quick understanding of the potential energy reduction.
图1：根据芝加哥气象参数分析得出不同节能装置的月度效率。所有图表提供来自惠普技术服务
Figure 1: The analysis using Chicago weather data depicts these efficiencies monthly by economizer type. All graphics courtesy: HP Technology Services
图2：分析南半球气象数据后（如巴西圣保罗），发现最大的节能出现在北半球的夏季月份。
Figure2: When analyzing a climate that is south of the equator, such as in Sao Paolo, Brazil, the data will show the greatest savings during the “summer” months in the northern hemisphere.
由于节能装置将成为提高整个系统能效的主要驱动因素，因此通过节能技术类型对制冷系统进行分组然后再根据系统使用的组件类型进行分组是有作用的，如图3所示。（注意：本分析旨在比较各替代能源的能源利用点，并没有对系统的运行功效做出判断。）
Because the economizer will be a major driver in the energy efficiency of the overall system, it is useful to group cooling systems by economization technique and then by types of components used in the system, as shown in Figure 3. (Note: this analysis is intended to compare the energy use characteristics of the alternatives; no judgment on the operational efficacy of the systems is implied.)
图3：通过节能技术类型对制冷系统进行分组然后再根据系统使用的组件类型进行分组是有作用的。（注意：本分析旨在比较各替代能源的能源利用点，并没有对系统的运行功效做出判断。)
Figure 3: It is useful to group cooling systems by economization technique and then by types of components used in the system. (Note: this analysis is intended to compare the energy use characteristics of the alternatives; no judgment on the operational efficacy of the systems is implied.)
直接空气——当条件允许时，直接引入室外空气，然后混合数据中心回风与室外空气。室外空气的含湿量超出要求时将限制节能装置的充分使用，可以通过加配绝热冷却以延长节能装置的使用时间。在较高的室外温度下，通过压缩制冷处理制冷需求的平衡来调节进风量以保持尽可能低的回风量。
Direct air—When conditions allow, air is taken directly from outdoors and mixing data center return air with the outdoor air. Out-of-range moisture levels of the outdoor air will limit full use of the economizers. Adiabatic cooling can be added to extend the use of the economizer. At higher outdoor temperatures, outside air volume can be modulated to maintain the lowest return air possible with compressorized cooling handling the balance of the cooling requirement.
间接空气——来自数据中心回风通过热交换器（转轮式换热器，热管等）将热量传递给室外空气。当室外空气温度足够低时，回风可以将100％的热量排放到室外。在较高的室外温度下，系统将通过压缩制冷来处理制冷需求的平衡以保持尽可能低的回风温度。通过绝热冷却以降低室外空气的温度可用于延长节能装置的使用时间。空气热交换器的固有效率损失将降低室外空气温度的可用性。
Indirect air—Heat from data center return air is transferred to the outdoor air using a heat exchanger (heat wheel, heat pipe, etc.). When the outside air is cold enough, the return air can reject 100% of the heat to the outdoors. At higher outdoor temperatures, the system will maintain the lowest return air temperature possible with compressorized cooling handling the balance of the cooling requirement. Adiabatic cooling to reduce the temperature of the outdoor air can be used to extend the use of the economizer. The inherent efficiency losses of the air-to-air heat exchangers will reduce the usefulness of the outdoor air temperature.
直接/间接水——直接使用外部空气进行水冷却通常由开放式冷却塔实现。冷却塔使热量从冷却水中散发到空气中，然后可用于冷却冷水机组内的蒸发器，独立制冷的计算机房间单元中的压缩机或直接冷却计算机设备。冷却水通常与冷冻水通过水—水热交换器以避免二次冷却设备结垢（与冷冻水构成的间接水系统）。直接/间接水系统可以提供的水温取决于室外空气的湿度水平并且在室外空气温度较低的时候可能需要额外的设备以避免冷却塔中的结冰现象发生。
Direct/indirect water—Water cooled directly using outside air is usually accomplished by open cooling towers that dissipate heat from the water into the air. This water can then be used to cool the evaporator of a packaged water chiller, cool the compressors in a self-contained computer room unit, or to cool computers directly. The water typically is run through a water-to-water heat exchanger to avoid fouling of the secondary coolingequipment. The temperature of the water that can be produced is dependent on the moisture level of the outdoor air, and at cold outdoor air temperatures, additional equipment may be required to avoid freezing in the cooling towers.
间接水——通常使用风冷冷水机组为数据中心的空气处理机组（AHU）、水冷IT机架或水冷计算机生成冷冻水。通过使用冷水机组集成的自然冷却盘管或独立的闭式冷却塔实现节能。在此系统下，室外空气和水之间的热传递是完全可行的，所以室外空气的水分含量对使用节能技术产生的水温没有影响。另外，可以通过向冷凝器盘管加水喷雾等绝热过程降低室外空气温度，在这种情况下，室外空气的湿度水平将成为影响水温的一个因素。
Indirect water—Typically an air-cooled chiller is used to generate chilled water for air handling units (AHU), water-cooled IT racks, or for water-cooled computers in the data center. Economization is achieved by using a chiller-integrated free cooling coil or by a separate closed-circuit cooling tower. Because the heat transfer between the outdoor air and the water is completely sensible, the moisture content of the outdoor air has no impact on the water temperature that is producedusing the economization technique. An adiabatic process, such as water sprays added to the condenser coils, can be added to lower the outdoor air temperature; in this case the moisture level of the outdoor air becomes a factor in the temperature of the water.
实现最高能效的关键是优化制冷系统，还要了解整个数据中心的动态。例如，ASHRAE的环境专题研究课程（图4）是为了解决数据中心在高温下的运行问题并以此作为降低能耗的手段。但是，了解高温对服务器本身的影响至关重要。
The keys in achieving the greatest energy efficiency are to optimize the cooling systems and also to understand the dynamics of the data center as a whole. For example, the ASHRAE environmental classes (Figure 4) were developed to address the operation of the data center at elevated temperatures, as a means to reduce energy consumption. However it is essential to understand the impact that higher temperatures have on the servers themselves.
图4：ASHRAE服务课程是为了解决数据中心在高温下的运行而开发的，主要是为了了解高温对服务器本身的影响。
Figure 4: ASHRAE server classes were developed to address the operation of the data center at elevated temperatures, primarily to understand the impact that the high temperatures have on the servers themselves.
由于空调系统的节能也是ASHRAE发展的基本理念，人们可以假设送风温度提高，压缩机功率降低，从而获得更长时间的经济运行模式。这个假设通常是正确的，但不常用。在高温的室外环境下，提高空调送风温度通常会显著地减少能耗，但在低温的情况下，节约效果不那么明显，因为每年可以有更多的时间利用室外空气实现节约策略。在这种情况下，提高送风温度的收益不大，因为数据中心的设计温度可能比某些气候条件下的年度最高温度要高。
Because energy savings in the air conditioning systems is also a fundamental idea behind the development of the ASHRAE, one may assume that as the supply air gets warmer, less compressor power is needed and more hours of economization are available. This premise is generally true, but not universally. In hotter climates, increasing the supply air temperatures generally results in significant reductions in energy use. In colder climates the savings are less dramatic simply because there are more hours annually when the outdoor air can be used in an economization strategy. In these cases, increasing the supply air temperature will not accomplish much because the data center temperature may be greater than the highest annual temperature in that climate.
每个制冷系统由多个耗能设备组成：压缩机、风机、泵和加湿设备等。每一项的实际运行特性的运用对形成各组件的年度能耗情况记录至关重要。但是，基于“ASHRAE最低能耗目标”的假设可以应用于各个独立的组件中。
Each of the cooling systems consists of multiple energy-consuming devices: compressors, fans, pumps, and humidification equipment. Using the specifics of the actual project is vital in forming an itemization of the various components’ annual energy use. Nevertheless, assumptions based on ASHRAE minimum energy performance targets can be applied to the individual components.
压缩制冷设备——此类设备包括单一的直接膨胀式空调和水冷式冷水机组。对压缩制冷设备进行有效的能效优化的基础是压缩机与实际负载均匀同步的卸载能力（或变频压缩机的降频速率）。这避免了制冷量和相应电量的过度供应或供应不足。此外，压缩制冷设备必须能够利用较冷的室外温度和较低的冷凝温度。
Compressorized cooling equipment—This equipment will range from unitary direct expansion equipment to water-cooled chillers. The basis to effective energy optimization for compressorized cooling equipment is the ability to unload the compressors (or decrease speed of variable speed compressors) at an even pace that is in lockstep with the actual cooling load. This avoids over-or under-provisioning of cooling capacity and the corresponding energy use. Also, the equipment must be able to take advantage of cooler outdoor temperatures and lower condenser temperatures.
送风风机——送风风机的功率要求取决于组成空气处理系统的风量，风机/电机效率和静压降。当送回风温差最大化且静压降尽可能小时，设备将获得最佳能效。
Supply fans—The power requirement of a supply fan is determined by the air volume, fan/motor efficiency, and static pressure drop of the components that make up the air handling system. The best energy efficiency will come when the difference between the supply and return air is maximized and the static pressure drop is made as small as possible.
换气风机——用于间接空气系统，此类风机可将室外空气引入热交换器进行热交换。由于间接空气系统因制造商而异，因此必须了解这些风机的运行方式，包括气体流速，电机功率和运行曲线（例如，基于室外温度的风机转速）。换气风机可以根据室外空气需要向回风有效传递的热量值来改变速度。
Scavenger fans—Used in the indirect air systems, these fans induce outdoor air across the heat exchanger. Because the indirect air systems vary depending on the manufacturer, it is essential to understand how these fans will operate, including the airflow rate, motor power, and operational profile (e.g., fan speed based on outdoor temperature). Scavenger fans can vary speed based on the amount of outdoor air needed to effectively transfer heat from the return air.
回风/排风风机——主要用于直接空气系统，作为从建筑内排出空气的手段以避免室内超压。根据建筑设计，风机的最终选型可以是大功率的离心风机/轴流风机，也可以是低功率螺旋桨式风扇的排气风机。这些风机应能根据风量改变转速并且在一年中大部分时间的室外气温下内可以利用室外空气经济运行。风机系统应该精心设计，因为它们将在一年中大部分时间内接近100％工况运行。
Return/exhaust fans—Used primarily for direct air systems as a means of removing the outdoor air from the building to avoid overpressurization. Ultimately, depending on the building design, these fans will range from powerful centrifugal or vane-axial fans to low-powered propeller fan relief hoods. These fans should vary speed based on air volume, and in climates that can use outdoor air for economization a large percentage of the year, the fan system should be carefully designed because they will be running near 100% most of the year.
水泵——仅用于水路系统。与风机类似的控制策略——保持压头尽可能低并根据流量要求改变水泵电机速度。
Pumps—Used in water-based systems only. Similar strategies to fans—keep head pressure as low as possible and vary pump motor speed based on flow requirement.
加湿/蒸发冷却系统——利用绝热过程来加湿或冷却空气是实现节能最大化的必要条件。在很多气候条件下，无需根据ASHRAE的温度和湿度等级要求向空气中添加水分，因此可能不需要设计加湿系统。
Humidification/evaporative cooling systems—Using an adiabatic process to humidify or cool the air is necessary to achieve maximum energy savings. In some climates it is not necessary to add moisture to the air based on the ASHRAE temperature and humidity classes, so designing a humidification system may not be necessary.
水冷式IT机柜——被视作微型数据中心——空气流动和制冷系统内置在机柜中。这些机柜依靠风扇使空气穿过安装在机柜中的盘管并通过水泵将冷水分配到多个机柜单元中从而进行冷却。IT机柜上的风扇和泵的能耗不能忽略且需要包含在系统整体的能耗计算中。
Water-cooled IT cabinets—Think of these as miniature data centers—the cooling and air movement are built-in. These cabinets rely on fans to move air across a coil mounted in the cabinet and pumps that distribute water to multiple cabinets. The energy used from the fans in the IT cabinet and pumps are not trivial and need to be included in the overall energy use calculation.
水冷式计算机（设备级冷却）——理论上的最低制冷能耗者，其制冷系统主要是由泵和散热设备（如冷却塔等）组成。这些主要用于高性能计算应用，其单个服务器机柜的额定功率可以达到80 kW或更高。目标是避免使用蒸汽压缩制冷并且只有在允许高水温的情况下才会使用冷却塔（水）。计算机，网络和存储系统中的某些部分无法进行水冷却，因此必须通过其他方式消除此部分空调负荷并将其包含在能耗分析中。
Water-cooled computers (component level cooling)—Theoretically the lowest cooling energy consumer, the primary components are pumps and heat rejection (cooling towers, etc.). These are primarily used in high-performance computing applications where individual server cabinets are rated at 80 kW (or more). The goal is to avoid using vapor compression cooling and rely on cooling tower water only given the allowable high cooling water temperature. Parts of the computer, network, and storage systems are not able to be water cooled, so this air conditioning load must be accounted for and cooled by some other means and included in the energy analysis.
能耗模拟是一种功能强大的工具，可用于提供数据供管理者作决策。使用能耗模拟和分析技术，工程师可以根据IT负载，送风温度和室外气象条件了解各个独立组件的运行情况。以曲线图的形式运用数据可视化技术可对各独立组件在一年内的能耗情况进行详细的审查。这是必要的，因为制冷系统在低温天气下的表现与在高温天气下的表现差异会很大。这项技术还用于分析评估不同地域（气候）中的制冷系统能耗情况。这种分析将暴露出在某些气候条件下可能运行良好但在其他气候条件下却无法正常工作的制冷系统，因此全球范围内的典型解决方案应能视区域不同而进行改变。
Energy use simulation is a powerful tool that can be used to provide data to make decisions. Using energy simulation and analysis techniques gives the engineer insight into how the individual components behave based on IT load, supply air temperatures, and outdoor conditions. Applying data visualization techniques using line graphs allows for a detailed scrutiny of the energy usage of the components over the course of a year. This is necessary because the cooling systems perform very differently in cold weather than they do in hot weather. This approach also is used for evaluation of cooling system energy when analyzing different locations (climates). This type of analysis will expose cooling systems that might work well in certain climates and not in others, so worldwide prototypical solutions can be varied by location.
使用直接膨胀辅助进行间接冷却——在对能源模拟结果进行详细评估之前，对年度能源使用曲线图进行初步的简要观察通常很有帮助（图5）。该图说明了间接空气冷却系统（系统1）和间接蒸发冷却系统（系统2）之间的差异，两者都使用直接膨胀系统（DX）辅助制冷。这些系统在无法提供设定的供气温度时使用直接膨胀系统进行冷却，从而增强了系统的冷却能力。
Indirect cooling with direct expansion assist—Before a detailed evaluation of the energy simulation results is performed, it is often helpful to do a visual investigation of the annual energy use line graphs to make initial observations (Figure 5). This figure illustrates the difference between an indirect air cooling system (system 1) and an indirect evaporative cooling system (system 2), both with direct expansion (DX) cooling assist. These systems are designed to use DX cooling when the supply air temperature setpoints can no longer be maintained, augmenting the cooling capability of the system.
图5：该图说明了间接空气冷却系统（系统1）和间接蒸发冷却系统（系统2）之间的差异，两者都具有直接膨胀系统（DX）辅助制冷，系统位于芝加哥。
Figure 5: This figure illustrates the difference between an indirect air coolingsystem(system 1, top), and an indirect evaporative cooling system (system 2), both with direct expansion (DX )cooling assist. This system is based in Chicago.
在这个具体案例中（摘自基于实际项目文件的分析），与其他标准数据中心制冷解决方案相比，这两个系统的性能相当不错，二者主要差异体现在风机功率和传热机制的效率上。在系统1中，换气风机小时峰值功率远小于系统2，但送风风机的小时峰值功率高于系统2。此外，系统2的传热效率优于系统1。当比较代表制冷的数据点组成的曲线时能够很明显地看出：系统1具有更高的峰值功率，这一现象在一年中较冷的月份内会更频繁地发生。
In this specific example (excerpted from analyses based on actual project documentation), the two systems perform quite well when compared to other standard data center cooling solutions. The primary differences show up in the fan power and the effectiveness of the heat transfer mechanisms. In system 1, the scavenger fan energy is much less than for system 2, but the supply fan energy is higher than in system 2. Also, the heat transfer effectiveness of system 2 outperforms system 1. This is evident when inspecting the line representing the data points for the cooling energy; system 1 has higher peak power occurring more often during the colder months of the year.
请注意，在这两个系统中，加湿的消耗可以忽略不计。简单来说，良好的能源性能（在温带气候中）的例子是在秋季，冬季和春季月份，在这些月份中压缩机的耗能很少或者为零。在夏季月份（北半球的6月，7月和8月），压缩机功率曲线平滑，该曲线规律遵循室外温度变化曲线。在数据中心中，制冷消耗的能量与室外空气温度具有很强的相关性并且应尽可能地遵循这些条件，以避免制冷容量过度供应，从而导致效率低下和不必要的能耗。图6显示了与图5相同的参数，但使用了巴西圣保罗的天气数据。圣保罗地区的整体能耗大于芝加哥，但其全年能耗更为均衡，另外，芝加哥夏季用电量较高。
Notice that in both systems, the humidification energy is negligible. In simple terms, good energy performance (in a temperate climate) is exemplified by little or no compressor energy expended during the fall, winter, and spring months. During the summer months (June, July, and August in the northern hemisphere), compressor energy is depicted by a smooth curve that follows the curve represented by outdoor temperatures. The cooling energy expended in a data center has a strong correlation to outdoor air temperatures and should follow these conditions as closely as possible to avoid over provisioning of cooling capability causing inefficiencies and unneeded consumption of energy. Figure 6 shows the same parameters as Figure 5, but Sao Paulo, Brazil, weather data is used. The overall energy usage is greater than Chicago, but there is a more uniform energy use across the year, where Chicago has higher spikes of power use in the summer months.
图6：根据巴西圣保罗地区的气象数据统计的间接空气冷却系统（图1，上）和间接蒸发冷却系统（图2）之间的对比。其整体能耗高于芝加哥，但全年能耗更为均衡。
Figure 6: Sao Paulo, Brazil, weather data is used to show an indirect aircoolingsystem(system1,top), and an indirect evaporative cooling system(system2). The overall energy usage is greater than in Chicago, but there is a more uniform energy use across the year.
带水节能器的水冷式冷水机组——在查看水冷式冷水机组系统的能源使用数据图时，首先要注意的是其使用的部件数量（图7）。这些组件中的每一个都会耗能并且系统的整体效率仍然很好。这就是为什么这么多年来此类型的系统一直是大型数据中心和商业建筑的黄金标准。由于水节能器的运行取决于室外空气的含湿量，因此在较潮湿的气候条件下，节能器的每年可使用时间会更少。
Water-cooled chillers with water economizer—The first thing that becomes evident when reviewing the line graph of the energy use data for water-cooled chiller systems is the number of components used (Figure 7). Each of these uses energy, and the overall efficiency of the system is still good. This is why this type of system has been the gold standard for many years in large data centers and commercial buildings. Because the water economizer is based on the moisture contained in the outdoor air, in more humid climates less time is available annually to use the economizer.
图7：系统3（芝加哥，上）和系统4（圣保罗）展示了带水节能器的水冷式冷水机组和AHU（组合式空调机组）以及使用水冷计算机代替AHU的相同制冷系统的年度能耗情况。
Figure 7: Systems 3 (Chicago, top) and 4 (Sao Paolo) show the annual energy use of a water-cooled chiller with water economization and AHU,and the same cooling system using water-cooled computers in place of AHUs.
在图7中，系统3和4展示了带水节能器的水冷式冷水机组和AHU（组合式空调机组）空调系统的年度能耗以及使用水冷式计算机代替AHU的相同制冷系统的年度能耗情况。系统3的曲线图有一个明显的标志表明了能效提高的空间：夏季的压缩机功率几乎没有波动；也就是说，在这段时间内几乎没有节约。
In Figure 7, systems 3 and 4 show the annual energy use of a water-cooled chiller with water economization and AHU, and the same cooling system using water-cooled computers in place of AHUs. The line graphs for system 3 have a telltale sign indicating room for energy efficiency improvement: the compressor power in the summer months shows little fluctuation; that is, there is little economization taking place during this time period.
在系统4中，在数据中心之外的制冷区域内风机的能耗需求很小，这是为什么系统4比系统3更有效率的主要驱动因素，另一个重要的因素是在系统4中，水温比系统3中的水温度高20°F，这具有双重影响：首先，压缩机由于蒸发温度升高，能耗降低；其次，由于高水温可以接受较高的室外湿球温度，水节能器可使用的小时数增加。
In system 4, very little fan energy is needed except for cooling areas outside of the data center area. This becomes a primary driver of why system 4 is more efficient than system 3. Another important contributing factor is that in system 4, the water temperature is 20 F warmer than the water in system 3. This has a twofold effect: first, the compressor energy is lower because of the increased evaporator temperature, and second, there is an increase in the number of hours in which the water economizer can be used based on a higher acceptable wet-bulb temperature.
为数据中心设计制冷系统是一个包含许多变量并需要做出许多决策的过程，包括IT设备如何与制冷系统相结合。工程团队采用有条理的设计流程至关重要，其中包括详细的能耗模拟和分析技术，这些技术将有助于在项目的整个生命周期内做出决策。此外，考虑到IT设备能耗占数据中心年能耗的比例超过75％，我们需要仔细评估和优化设计及运行参数以创造长效持久的节能协同效应。
Designing cooling systems for data centers is a process that has many variables and requires many decisions, including how the IT equipment will interface with the cooling. It is vital that the engineering team use a methodical design process that includes detailed energy simulation and analysis techniques which will help make decisions throughout the life the project. Also, taking into consideration that the IT equipment will consume more than 75% of the data center annual energy, there needs to be a careful assessment and optimization of the design and operational parameters to create long-lasting energy-savings synergies.
Wiliam Kosik是芝加哥惠普技术服务公司的首席数据中心能源技术专家。他曾在超过25个国家从事能源分析和战略项目工作并为全球客户提供技术咨询。作为《Consulting-Specifying Engineer》杂志的编辑顾问委员会的成员，他撰写了超过25篇文章并在超过45个重要会议上发言。
Wiliam Kosik is principal data center energy technologist with HP Technology Services, Chicago. He has worked on energy analysis and strategy projects in more than 25 countries, and consults on client assignments worldwide. A member of the Consulting-Specifying Engineer editorial advisory board, he has written more than 25 articles and spoken at more than 45 conferences.
翻译：陈亮宇 校对：李建利