Nowadays many existing CASs lack an updated overall design. The implementation of additional compressors and various applications in several stages along the installation lifetime without a parallel redesign from the original system have frequently resulted in a suboptimal performance of a CAS.
One fundamental parameter in a CAS is the pressure value. A number of pressure demands, depending on the application, usually sets up a trade-off between low pressures giving a higher energy efficiency and high pressures where smaller and cheaper devices can be used. The majority of consumers use a pressure of about 6 bar(g), but there are requirements for pressures of up to 13 bar(g). Often the pressure is chosen to meet the maximum pressure needed for all devices.
It is important to consider that too low a pressure will cause malfunctioning of some machines, while a pressure higher than necessary will not, but will result in reduced efficiency. In many cases, there is an 8 or 10 bar(g) system pressure, but most of the air is throttled to 6 bar(g) by pressure reducing valves.
It is state-of-the-art to choose a pressure which satisfies 95 % of all needs and uses a small pressure-increasing device for the rest. Operators try to eliminate the devices needing more than 6 bar(g), or having two systems with different pressures, one with a higher pressure and one for 6.5 bar(g).
Another basic parameter is the choice of the storage volume. As compressed air demand typically comes from many different devices, mostly working intermittently, there are fluctuations in air demand. A storage volume helps to reduce the pressure demand fluctuations and to fill short-timing peak demands (see Section 3.7.10).
Smoothed demand allows a steadier running of smaller compressors, with less idling time and thus less electric energy is needed. Systems may have more than one air receiver. Strategically locating air receivers near sources of high short-timing demands can also be effective, meeting peak demand of devices and making it possible to lower system pressures.
A third fundamental design issue for a compressed air system is dimensioning the pipework and positioning the compressors. Any type of obstruction, restriction or roughness in the system will cause resistance to the airflow and will cause the pressure to drop, as will long pipe runs. In the distribution system, the highest pressure drops are usually found at the points of use, including undersized hoses, tubes, push-fit connectors, filters, re gulators and lubricators. Also, the use of welded pipework may reduce frictional losses.
Sometimes the air demand has grown 'organically' over the years and a former side branch of the pipework – with a small diameter – has to transfer a higher volume flow, resulting in pressure loss. In some cases, plant equipment is no longer used. The airflow to this unused equipment should be stopped as far back in the distribution system as possible without affecting operating equipment.
A properly designed system should have a pressure loss of less than 10 % of the compressor’s discharge pressure to the point of use. This can be reached by: regular pressure loss monitoring, selecting dryers, filters, hoses and push-fit connectors having a low pressure drop for the rated conditions, reducing the distance the air travels through the distribution system and recalculating the pipe diameters if there are new air demands.
What is often summed up under the point 'overall system design' is actually the design function of the use of compressed air. This can lead to inappropriate use, for example, over- pressurisation followed by expansion to reach the proper pressure, but these situations are rare. In industry nowadays, most people are aware of compressed air as a significant cost factor.
現今有些壓縮空氣系統欠缺整體設計的更新。在壓縮空氣系統的使用年限中，增加更多空壓機及使用用途時，原來系統未隨之更新設計，往往導致此壓縮空氣系統並非在最佳情況下運作。
壓縮空氣系統最基本的參數是壓力值。壓力值的需求會隨應用面的需求而定。通常是低壓力會有較高的能源效率；高壓力則可以用較小型且較廉價的設備，此二者間互為長短。
大多數使用者使用大約6個大氣壓力的表壓，但也有需求壓力高到13個大氣壓力的表壓。通常壓力的選用必須要能滿足所有設備的最大操作壓力。
需要特別注意的是，操作壓力太低會使某些機械工作不良；同樣地，壓力太高也會使機械失效，還會降低效率。部分壓縮空氣系統的供應壓力是8~10大氣壓力的表壓，但大部分在使用時以減壓閥調節至6大氣壓力表壓。
巧妙的作法是選擇一個壓力值可滿足95%的設備所需，而用一套小型增壓設備滿足其他設備的需求。操作人員可嘗試去減少需要大於6大氣壓力表壓的設備；或採取兩套壓力的方式，一套給高壓，另一套給低壓使用。
壓縮空氣系統第二個基本參數是儲存容量。壓縮空氣會因設備而有不同用量需求。大多數間歇性作業的壓縮空氣需求是波動的。壓縮空氣儲氣筒用來協助減少壓力需求的波動及滿足短期高峰需求。
平穩地用氣需求可用較小型的壓縮機作穩定的運轉，減少其空轉的時間，這樣可以降低電力需求。策略上把儲氣筒設置在靠近高度、短時需求的工作源附近，可有效地適合設備的尖峰需求，以降低系統壓力。
壓縮空氣系統第三個基本設計議題是系統的管路尺寸大小和壓縮機的位置。系統中任何形式的阻礙、限制或粗糙面都會造成其中空氣流動的阻力，而在管路中產生壓降。
有些時候空氣的需求會逐年增加，於是一些原有的管路支管(通常都是較小口徑)，必須輸送較多量的空氣而造成壓力損失。有些時候工廠的設備不再使用了，這時候應將這不使用設備的空氣從配氣系統之最靠近前端關閉，方不致影響運轉中的設備。
一個正確設計的系統自壓縮機出口壓力到使用端應會有小於10%的壓力損失。這減少壓力損失的設計來自：正常壓降監測、乾燥器的選用、過濾器，皮管及接頭等要有低壓降的特性；減短空氣在配氣系統中流動的距離、於有新空氣需求時要重新計算管線尺寸。
往往在「整體系統設計」才是使用壓縮空氣真正的設計方法。這可能導致不正確的用法，例如以過壓空氣以膨脹方式降壓以達到所需壓力，這情況並不多見。工業界大家都知道壓縮空氣是一顯著的成本因素。
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There are many compressed air systems, with estimates as high as 50 % of all systems, that could be improved by a revision of their overall design, with a gain of 9 % by lowering the pressure and with better tank dimensioning (in 50 % of systems) and 3 % by lowering pipework pressure losses (in 50 % of systems) resulting in 6 % = 0.5 x (0.09 + 0.03) energy savings.
System design may also include the optimisation of certain end use devices, typically in 5 % of all systems it is possible to lower the demand by some 40 %, resulting in 2 % (i.e. 0.05 x 0.4) energy savings.
估計大約有50%的壓縮空氣系統可以經修改其整體設計而得到改善，其中9%來自將低壓力即將加的儲氣筒的大小，3%來自減少管路壓損，而得到6%的節能[ 50% x( 9% +3%)=6%]
系統設計也包括優化一些終端使用設備，在所有系統的5%可以減少40%的需用量，這可以有2%的節能[ 5% x 40% =2%]。
The costs of revising a compressed air system with consequent readjustment of pressure and renewing pipework is not easy to calculate and depends very much on the circumstances of the particular plant. The savings in a medium size system of 50 kW can be estimated to be:
50 kW x 3000 h/yr x EUR 0.08/kW x 10 % = EUR 1200/yr
The costs for a major revision in such a system, adding a 90 litre tank near a critical consumer and a shut-off valve for a sparsely used branch, replacing 20 metres of pipework, 10 hoses and disconnectors is about E UR 2000, so the payback period is a profitable 1.7 years. Often the costs are lower, when only some pressure readjustment needs to be done, but in every case there has to be thorough considerations about the lowest tolerable pressure meeting the needs.
Economics are a driving force to revise compressed air systems. A major obstacle is a lack of knowledge and/or of skilled staff responsible for compressed air systems. Technical staff may be aware that the compressed air is expensive, but the inefficiencies are not readily obvious, and the operator may lack staff with sufficient in-depth experience.
Initiatives in many countries of the EU for spreading compressed air knowledge strongly promoted the implementation, creating a 'win-win-win' situation: the owner of the compressed air systems wins lower overall costs, the supplier of compressors and other devices wins higher revenues and the environment wins lower power station emissions.
修改壓縮空氣系統和壓力調整及管路更新的成本不是很容易估算而且每一座工廠的情況都不一樣。舉例一座50kW的中型系統的節省估計如下式
這套系統主要修改式增加了一套90公升的儲氣筒在一關鍵使用地點、在很少用的一股之線裝了一套關斷閥門、更新20公尺長的管路、調皮管及接頭成本大約是2000歐元計算回收年為1.7年。如果只是做壓力調整，其成本不會太高，但必須徹底考量要有的最低可容忍的壓力，以符合作業需求。
經濟性是更新壓縮空氣系統的驅動力。其主要障礙是:缺乏壓縮空氣系統相關知識及對系統有功夫的技術人員。技術人員了解壓縮空氣很貴，但對於無效率可能就較模糊，以及操作人員普遍都不是很有足夠經驗的技術人員。
歐盟倡議將壓縮空氣系統的知識廣泛推廣應用創造三贏局面:業者解省整體成本；壓縮機與設備供應商贏得較高利潤；環境贏得低的電力生產汙染排放。
Energy Efficiency (2009) 3.7.1
