【DKV】深入探究PUE

yi321yi 2019-09-27

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When developing data center energy-use estimations, energy engineers must account for all sources of energy use in the facility: computers, cooling plants, and other related equipment.

在進行數(shù)據(jù)中心能耗估算的研發(fā)工作時，能源工程師們必須考慮設施中所有的能耗來源：計算機、制冷設備和其他相關設備等。

BY WILLIAM J. KOSIK, PE, CEM, LEED AP BD C, BEMP, HP Technology Services, Chicago

作者：WILLIAM J.KOSIK，產(chǎn)品工程師，能源管理工程師，LEED認證專家，建筑能源建模專業(yè)人士資格認證，惠普芝加哥技術服務工程師。

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.

有關數(shù)據(jù)中心的文章有很多，貫穿其中的共同點是：對數(shù)據(jù)中心能源效率的思考模式仍處在轉(zhuǎn)變的過程中。這種轉(zhuǎn)變正在使我們遠離我們最了解的問題：為辦公樓建筑，實驗室，醫(yī)院和學校等設計HVAC（空調(diào)）系統(tǒng)。

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.

例如，就在五年前，大部分老式數(shù)據(jù)中心的空調(diào)送風溫度仍為55℉（典型的商業(yè)建筑做法，約13℃）。與之相比，新數(shù)據(jù)中心使用的送風溫度≥75℉（約24℃）?？照{(diào)送風溫度提高了20℉，這影響了整個制冷系統(tǒng)。正是這一變化引起了對數(shù)據(jù)中心空調(diào)系統(tǒng)的設計及運行的大規(guī)模反思。

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.

值得慶幸的是，有許多杰出的數(shù)據(jù)中心工程師和一些行業(yè)組織（如Uptime Institute，7x24 Exchange，ASHRAE等）都致力于數(shù)據(jù)中心電力和制冷系統(tǒng)的規(guī)劃和設計工作。此外，許多制造商，可以說是數(shù)據(jù)中心產(chǎn)業(yè)鏈中最重要的一環(huán)，現(xiàn)在都擁有專用于數(shù)據(jù)中心設備的完善的生產(chǎn)線。

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.

隨著計算機技術（硬件，網(wǎng)絡，存儲和軟件）以驚人的速度發(fā)展，電力和制冷系統(tǒng)的規(guī)劃和工程也在努力跟上腳步，然而這都在意料之中。我們在日常生活中看到——移動電話，個人電腦，筆記本電腦和電視這些在其最初發(fā)行后的9到12個月內(nèi)就會被淘汰。當然，消費電子市場還涉及其他不同的因素，但核心理念與企業(yè)級IT設備相同——新技術（制造工藝，材料，軟件）的進步使其性能高于之前，同時降低能耗。

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.

了解這些限制因素后，就可以理解電力和制冷設備制造商進行研發(fā)，規(guī)劃，投資和制造下一代產(chǎn)品以支持尚未開發(fā)的計算機技術的難度之大。即使最后制造商開發(fā)出能夠匹配最新一代計算機技術的產(chǎn)品，但集成功能（使設備能夠適應未來IT設備的設計）的成本實在是過于昂貴。

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.

從另一個的角度來看，當計算機制造商發(fā)布新一代服務器時，服務器熱工程師可能已經(jīng)開發(fā)出一種新穎的冷卻設計方案，使服務器在較低溫度下運行并減少風扇能耗。這是數(shù)據(jù)中心空調(diào)工程師和服務器熱工程師需要進行對話來嘗試優(yōu)化服務器和數(shù)據(jù)中心制冷系統(tǒng)的能源使用和功效的地方（當然還有其他許多方面），否則，不良后果就是擁有一臺高性能、低能耗的服務器，該服務器需要數(shù)據(jù)中心制冷系統(tǒng)，但該制冷系統(tǒng)效率低下且系統(tǒng)過于復雜或成本過高。這就是數(shù)據(jù)中心制冷系統(tǒng)能耗詳細模擬和分析的用武之地。

It’s the heat and the humidity

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.

熱量和濕度

空調(diào)送風溫度是數(shù)據(jù)中心制冷系統(tǒng)最獨特的特征。在舒適性空調(diào)中，HVAC（空調(diào)）系統(tǒng)的主要目標是提供足夠的制冷能力以滿足所有內(nèi)部和外部負荷，確保建筑內(nèi)的居住者感覺舒適（干球溫度和空氣中的含濕量）并保持適當?shù)倪^濾和通風量，以保證氣態(tài)和顆粒污染物保持在正常水平。數(shù)據(jù)中心通常也需要滿足這些目標，但其電氣設備負荷（與現(xiàn)代的高科技商業(yè)辦公樓相比）要高出一個數(shù)量級。好消息是，相對人而言，計算機能忍受高溫環(huán)境，同時亦可寬容高濕環(huán)境，這種耐高溫、耐高濕的特性為能效優(yōu)化提供了巨大的空間。

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.

節(jié)能空間來自于蒸發(fā)溫度的提高（送風溫度提高）導致的壓縮機功率降低以及壓縮機運行頻率降低這一實際情況，特別是在能夠充分采用節(jié)能策略的氣候條件下。仔細核算制冷系統(tǒng)替代方案是否可用是非常有必要的，因為雖然某個特定的選項可能會顯著降低壓縮機能耗，但與另外的選項相比，其他設備（風機，泵等）的能耗可能會增加。

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.

制冷系統(tǒng)各“設定選項”之間的比較必須包括整個數(shù)據(jù)中心的每小時能耗模擬（由ASHRAE標準90.1定義）才能夠分析制冷系統(tǒng)和子系統(tǒng)以確定哪些設備能耗最大。該分析的結果將為能源專業(yè)人員提供原始數(shù)據(jù)，以便就最節(jié)能的系統(tǒng)提出建議并提供關于每個子系統(tǒng)在不同運行情況下的詳細數(shù)據(jù)，例如不同的送風溫度和不同的室外氣象參數(shù)。

Economization techniques

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.

節(jié)能技術

節(jié)能裝置是所有高能效制冷系統(tǒng)的關鍵組成部分，它是各種硬件設備和操作流程的簡單組合，旨在通過利用室外空氣有利的溫濕度條件來減少HVAC系統(tǒng)能耗。由于不同的節(jié)能裝置依賴于不同的濕度條件，因此每種裝置都具有不同的性能特征。根據(jù)節(jié)能類型和控制策略，節(jié)能裝置可以以三種不同的模式運行：100％關閉，部分運行和100％開啟。

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.

部分運行模式將在指定的溫度和濕度范圍內(nèi)運行。根據(jù)氣候的不同，部分運行模式可能在一年中占很大比例；計算部分運行模式的運行時間在確定節(jié)能解決方案的功效時是很重要的。部分節(jié)能運行的計算是通過分析全年（總共8760小時）的逐時冷負荷來完成的，以冷噸·小時為單位，這個總和成為分子，分母是冷負荷值按小時計算的總和（僅為8760 x冷負荷），以冷噸·小時為單位，相除得到的百分比基本上是節(jié)能裝置可以使用的時間。

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.

圖1根據(jù)芝加哥氣象數(shù)據(jù)的分析結果描述了不同節(jié)能裝置的月度效率。在分析赤道以南的氣象參數(shù)時（圖2），數(shù)據(jù)顯示最大的節(jié)能出現(xiàn)在北半球夏季的月份。另一種了解節(jié)能裝置功效的方法是研究其在沒有機械制冷的情況下提供的送風溫度。根據(jù)氣候類型，一些節(jié)能裝置幾乎可以在100％的時間內(nèi)使用，與此同時伴隨著極少量機械制冷甚至沒有機械制冷。這些都是數(shù)據(jù)可視化技術的案例，可用于快速了解潛在的節(jié)能。

Figure 1: The analysis using Chicago weather data depicts these efficiencies monthly by economizer type. All graphics courtesy: HP Technology Services

圖1：根據(jù)芝加哥氣象參數(shù)分析得出不同節(jié)能裝置的月度效率。所有圖表提供來自惠普技術服務

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.

圖2：分析南半球氣象數(shù)據(jù)后（如巴西圣保羅），發(fā)現(xiàn)最大的節(jié)能出現(xiàn)在北半球的夏季月份。

Economization strategies

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.)

節(jié)能策略

由于節(jié)能裝置將成為提高整個系統(tǒng)能效的主要驅(qū)動因素，因此通過節(jié)能技術類型對制冷系統(tǒng)進行分組然后再根據(jù)系統(tǒng)使用的組件類型進行分組是有作用的，如圖3所示。（注意：本分析旨在比較各替代能源的能源利用點，并沒有對系統(tǒng)的運行功效做出判斷。）

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.)

圖3：通過節(jié)能技術類型對制冷系統(tǒng)進行分組然后再根據(jù)系統(tǒng)使用的組件類型進行分組是有作用的。（注意：本分析旨在比較各替代能源的能源利用點，并沒有對系統(tǒng)的運行功效做出判斷。)

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.

直接空氣——當條件允許時，直接引入室外空氣，然后混合數(shù)據(jù)中心回風與室外空氣。室外空氣的含濕量超出要求時將限制節(jié)能裝置的充分使用，可以通過加配絕熱冷卻以延長節(jié)能裝置的使用時間。在較高的室外溫度下，通過壓縮制冷處理制冷需求的平衡來調(diào)節(jié)進風量以保持盡可能低的回風量。

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.

間接空氣——來自數(shù)據(jù)中心回風通過熱交換器（轉(zhuǎn)輪式換熱器，熱管等）將熱量傳遞給室外空氣。當室外空氣溫度足夠低時，回風可以將100％的熱量排放到室外。在較高的室外溫度下，系統(tǒng)將通過壓縮制冷來處理制冷需求的平衡以保持盡可能低的回風溫度。通過絕熱冷卻以降低室外空氣的溫度可用于延長節(jié)能裝置的使用時間?？諝鉄峤粨Q器的固有效率損失將降低室外空氣溫度的可用性。

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.

直接/間接水——直接使用外部空氣進行水冷卻通常由開放式冷卻塔實現(xiàn)。冷卻塔使熱量從冷卻水中散發(fā)到空氣中，然后可用于冷卻冷水機組內(nèi)的蒸發(fā)器，獨立制冷的計算機房間單元中的壓縮機或直接冷卻計算機設備。冷卻水通常與冷凍水通過水—水熱交換器以避免二次冷卻設備結垢（與冷凍水構成的間接水系統(tǒng)）。直接/間接水系統(tǒng)可以提供的水溫取決于室外空氣的濕度水平并且在室外空氣溫度較低的時候可能需要額外的設備以避免冷卻塔中的結冰現(xiàn)象發(fā)生。

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.

間接水——通常使用風冷冷水機組為數(shù)據(jù)中心的空氣處理機組（AHU）、水冷IT機架或水冷計算機生成冷凍水。通過使用冷水機組集成的自然冷卻盤管或獨立的閉式冷卻塔實現(xiàn)節(jié)能。在此系統(tǒng)下，室外空氣和水之間的熱傳遞是完全可行的，所以室外空氣的水分含量對使用節(jié)能技術產(chǎn)生的水溫沒有影響。另外，可以通過向冷凝器盤管加水噴霧等絕熱過程降低室外空氣溫度，在這種情況下，室外空氣的濕度水平將成為影響水溫的一個因素。

The parts are greater than the whole

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.

部分優(yōu)于整體

實現(xiàn)最高能效的關鍵是優(yōu)化制冷系統(tǒng)，還要了解整個數(shù)據(jù)中心的動態(tài)。例如，ASHRAE的環(huán)境專題研究課程（圖4）是為了解決數(shù)據(jù)中心在高溫下的運行問題并以此作為降低能耗的手段。但是，了解高溫對服務器本身的影響至關重要。

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.

圖4：ASHRAE服務課程是為了解決數(shù)據(jù)中心在高溫下的運行而開發(fā)的，主要是為了了解高溫對服務器本身的影響。

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.

由于空調(diào)系統(tǒng)的節(jié)能也是ASHRAE發(fā)展的基本理念，人們可以假設送風溫度提高，壓縮機功率降低，從而獲得更長時間的經(jīng)濟運行模式。這個假設通常是正確的，但不常用。在高溫的室外環(huán)境下，提高空調(diào)送風溫度通常會顯著地減少能耗，但在低溫的情況下，節(jié)約效果不那么明顯，因為每年可以有更多的時間利用室外空氣實現(xiàn)節(jié)約策略。在這種情況下，提高送風溫度的收益不大，因為數(shù)據(jù)中心的設計溫度可能比某些氣候條件下的年度最高溫度要高。

System and subsystems

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.

系統(tǒng)和子系統(tǒng)

每個制冷系統(tǒng)由多個耗能設備組成：壓縮機、風機、泵和加濕設備等。每一項的實際運行特性的運用對形成各組件的年度能耗情況記錄至關重要。但是，基于“ASHRAE最低能耗目標”的假設可以應用于各個獨立的組件中。

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.

壓縮制冷設備——此類設備包括單一的直接膨脹式空調(diào)和水冷式冷水機組。對壓縮制冷設備進行有效的能效優(yōu)化的基礎是壓縮機與實際負載均勻同步的卸載能力（或變頻壓縮機的降頻速率）。這避免了制冷量和相應電量的過度供應或供應不足。此外，壓縮制冷設備必須能夠利用較冷的室外溫度和較低的冷凝溫度。

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.

送風風機——送風風機的功率要求取決于組成空氣處理系統(tǒng)的風量，風機/電機效率和靜壓降。當送回風溫差最大化且靜壓降盡可能小時，設備將獲得最佳能效。

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.

換氣風機——用于間接空氣系統(tǒng)，此類風機可將室外空氣引入熱交換器進行熱交換。由于間接空氣系統(tǒng)因制造商而異，因此必須了解這些風機的運行方式，包括氣體流速，電機功率和運行曲線（例如，基于室外溫度的風機轉(zhuǎn)速）。換氣風機可以根據(jù)室外空氣需要向回風有效傳遞的熱量值來改變速度。

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.

回風/排風風機——主要用于直接空氣系統(tǒng)，作為從建筑內(nèi)排出空氣的手段以避免室內(nèi)超壓。根據(jù)建筑設計，風機的最終選型可以是大功率的離心風機/軸流風機，也可以是低功率螺旋槳式風扇的排氣風機。這些風機應能根據(jù)風量改變轉(zhuǎn)速并且在一年中大部分時間的室外氣溫下內(nèi)可以利用室外空氣經(jīng)濟運行。風機系統(tǒng)應該精心設計，因為它們將在一年中大部分時間內(nèi)接近100％工況運行。

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.

水泵——僅用于水路系統(tǒng)。與風機類似的控制策略——保持壓頭盡可能低并根據(jù)流量要求改變水泵電機速度。

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.

加濕/蒸發(fā)冷卻系統(tǒng)——利用絕熱過程來加濕或冷卻空氣是實現(xiàn)節(jié)能最大化的必要條件。在很多氣候條件下，無需根據(jù)ASHRAE的溫度和濕度等級要求向空氣中添加水分，因此可能不需要設計加濕系統(tǒng)。

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IT機柜——被視作微型數(shù)據(jù)中心——空氣流動和制冷系統(tǒng)內(nèi)置在機柜中。這些機柜依靠風扇使空氣穿過安裝在機柜中的盤管并通過水泵將冷水分配到多個機柜單元中從而進行冷卻。IT機柜上的風扇和泵的能耗不能忽略且需要包含在系統(tǒng)整體的能耗計算中。

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.

水冷式計算機（設備級冷卻）——理論上的最低制冷能耗者，其制冷系統(tǒng)主要是由泵和散熱設備（如冷卻塔等）組成。這些主要用于高性能計算應用，其單個服務器機柜的額定功率可以達到80 kW或更高。目標是避免使用蒸汽壓縮制冷并且只有在允許高水溫的情況下才會使用冷卻塔（水）。計算機，網(wǎng)絡和存儲系統(tǒng)中的某些部分無法進行水冷卻，因此必須通過其他方式消除此部分空調(diào)負荷并將其包含在能耗分析中。

Itemization of energy consumers

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.

能耗組成

能耗模擬是一種功能強大的工具，可用于提供數(shù)據(jù)供管理者作決策。使用能耗模擬和分析技術，工程師可以根據(jù)IT負載，送風溫度和室外氣象條件了解各個獨立組件的運行情況。以曲線圖的形式運用數(shù)據(jù)可視化技術可對各獨立組件在一年內(nèi)的能耗情況進行詳細的審查。這是必要的，因為制冷系統(tǒng)在低溫天氣下的表現(xiàn)與在高溫天氣下的表現(xiàn)差異會很大。這項技術還用于分析評估不同地域（氣候）中的制冷系統(tǒng)能耗情況。這種分析將暴露出在某些氣候條件下可能運行良好但在其他氣候條件下卻無法正常工作的制冷系統(tǒng)，因此全球范圍內(nèi)的典型解決方案應能視區(qū)域不同而進行改變。

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.

使用直接膨脹輔助進行間接冷卻——在對能源模擬結果進行詳細評估之前，對年度能源使用曲線圖進行初步的簡要觀察通常很有幫助（圖5）。該圖說明了間接空氣冷卻系統(tǒng)（系統(tǒng)1）和間接蒸發(fā)冷卻系統(tǒng)（系統(tǒng)2）之間的差異，兩者都使用直接膨脹系統(tǒng)（DX）輔助制冷。這些系統(tǒng)在無法提供設定的供氣溫度時使用直接膨脹系統(tǒng)進行冷卻，從而增強了系統(tǒng)的冷卻能力。

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.

圖5：該圖說明了間接空氣冷卻系統(tǒng)（系統(tǒng)1）和間接蒸發(fā)冷卻系統(tǒng)（系統(tǒng)2）之間的差異，兩者都具有直接膨脹系統(tǒng)（DX）輔助制冷，系統(tǒng)位于芝加哥。

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.

在這個具體案例中（摘自基于實際項目文件的分析），與其他標準數(shù)據(jù)中心制冷解決方案相比，這兩個系統(tǒng)的性能相當不錯，二者主要差異體現(xiàn)在風機功率和傳熱機制的效率上。在系統(tǒng)1中，換氣風機小時峰值功率遠小于系統(tǒng)2，但送風風機的小時峰值功率高于系統(tǒng)2。此外，系統(tǒng)2的傳熱效率優(yōu)于系統(tǒng)1。當比較代表制冷的數(shù)據(jù)點組成的曲線時能夠很明顯地看出：系統(tǒng)1具有更高的峰值功率，這一現(xiàn)象在一年中較冷的月份內(nèi)會更頻繁地發(fā)生。

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.

請注意，在這兩個系統(tǒng)中，加濕的消耗可以忽略不計。簡單來說，良好的能源性能（在溫帶氣候中）的例子是在秋季，冬季和春季月份，在這些月份中壓縮機的耗能很少或者為零。在夏季月份（北半球的6月，7月和8月），壓縮機功率曲線平滑，該曲線規(guī)律遵循室外溫度變化曲線。在數(shù)據(jù)中心中，制冷消耗的能量與室外空氣溫度具有很強的相關性并且應盡可能地遵循這些條件，以避免制冷容量過度供應，從而導致效率低下和不必要的能耗。圖6顯示了與圖5相同的參數(shù)，但使用了巴西圣保羅的天氣數(shù)據(jù)。圣保羅地區(qū)的整體能耗大于芝加哥，但其全年能耗更為均衡，另外，芝加哥夏季用電量較高。

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.

圖6：根據(jù)巴西圣保羅地區(qū)的氣象數(shù)據(jù)統(tǒng)計的間接空氣冷卻系統(tǒng)（圖1，上）和間接蒸發(fā)冷卻系統(tǒng)（圖2）之間的對比。其整體能耗高于芝加哥，但全年能耗更為均衡。

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.

帶水節(jié)能器的水冷式冷水機組——在查看水冷式冷水機組系統(tǒng)的能源使用數(shù)據(jù)圖時，首先要注意的是其使用的部件數(shù)量（圖7）。這些組件中的每一個都會耗能并且系統(tǒng)的整體效率仍然很好。這就是為什么這么多年來此類型的系統(tǒng)一直是大型數(shù)據(jù)中心和商業(yè)建筑的黃金標準。由于水節(jié)能器的運行取決于室外空氣的含濕量，因此在較潮濕的氣候條件下，節(jié)能器的每年可使用時間會更少。

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.

圖7：系統(tǒng)3（芝加哥，上）和系統(tǒng)4（圣保羅）展示了帶水節(jié)能器的水冷式冷水機組和AHU（組合式空調(diào)機組）以及使用水冷計算機代替AHU的相同制冷系統(tǒng)的年度能耗情況。

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.

在圖7中，系統(tǒng)3和4展示了帶水節(jié)能器的水冷式冷水機組和AHU（組合式空調(diào)機組）空調(diào)系統(tǒng)的年度能耗以及使用水冷式計算機代替AHU的相同制冷系統(tǒng)的年度能耗情況。系統(tǒng)3的曲線圖有一個明顯的標志表明了能效提高的空間：夏季的壓縮機功率幾乎沒有波動；也就是說，在這段時間內(nèi)幾乎沒有節(jié)約。

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.

在系統(tǒng)4中，在數(shù)據(jù)中心之外的制冷區(qū)域內(nèi)風機的能耗需求很小，這是為什么系統(tǒng)4比系統(tǒng)3更有效率的主要驅(qū)動因素，另一個重要的因素是在系統(tǒng)4中，水溫比系統(tǒng)3中的水溫度高20°F，這具有雙重影響：首先，壓縮機由于蒸發(fā)溫度升高，能耗降低；其次，由于高水溫可以接受較高的室外濕球溫度，水節(jié)能器可使用的小時數(shù)增加。

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.

為數(shù)據(jù)中心設計制冷系統(tǒng)是一個包含許多變量并需要做出許多決策的過程，包括IT設備如何與制冷系統(tǒng)相結合。工程團隊采用有條理的設計流程至關重要，其中包括詳細的能耗模擬和分析技術，這些技術將有助于在項目的整個生命周期內(nèi)做出決策。此外，考慮到IT設備能耗占數(shù)據(jù)中心年能耗的比例超過75％，我們需要仔細評估和優(yōu)化設計及運行參數(shù)以創(chuàng)造長效持久的節(jié)能協(xié)同效應。

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.

Wiliam Kosik是芝加哥惠普技術服務公司的首席數(shù)據(jù)中心能源技術專家。他曾在超過25個國家從事能源分析和戰(zhàn)略項目工作并為全球客戶提供技術咨詢。作為《Consulting-Specifying Engineer》雜志的編輯顧問委員會的成員，他撰寫了超過25篇文章并在超過45個重要會議上發(fā)言。

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