ASHRAE OR-05-12-4-2005 Reliability Engineering for Datacom Cooling Systems《数据通信的冷却系统的可靠性工程》.pdf
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1、OR-05-1 2-4 Reliability Engineering for Datacom Cooling Systems Donald L. Beaty, PE Member ASHRAE ABSTRACT A metric that is paramount in todays datacom (data processing and telecommunications) facilities is reliability. It is a requirement that is often quant$ed by the facility decision makers. As l
2、oad densities increase, the challenges to plan, implement, and operate reliable cooling systems to satis there is little focus on investing in designs that minimize human error. QUALITATIVE VARIABLES THAT IMPACT COOLING SYSTEM RELIABILITY Overview and Baseline To illustrate the extent of the impact
3、that qualitative vari- ables have on the reliability of a cooling system, let us consider a project design needing CRAC units to handle a 1 O-ton sensi- ble load. In the subsections below, we will look at groupings of scenarios derived from changing the emphasis of a single variable and how that cha
4、nge impacts the overall cooling system reliability. The groupings will focus on the following variables: Equipment location Commissioning process Implementation of redundant units Maintenance and operation The focus behind the description of the scenarios in these groupings is to demonstrate how imp
5、roving the overall cool- ing system reliability is not a simple challenge that is met by implementing a single solution but, rather, that it requires an engineered approach including a holistic consideration of a wide variety of variables and an implementation strategy to ensure that each one is pro
6、visioned with the common goal in mind. Group 1: Impact of Equipment Location in this first group ofscenarios (Group i), we will compare the impact that the location of the equipment being used may have on the overall cooling system reliability. The first scenario under this group will also be used a
7、s a baseline for ali subsequent groups. Scenario la (Baseline). A new CRAC unit, optimally located and commissioned, and currently has been in operation for 80 hours under full load (i.e., broken in). Scenario lb. Same as Scenario la but the unit is installed in an undesirable location, resulting in
8、 less than recommended clearances and very difficultkomplex piping and wiring configurations (Figure 3). Scenario IC. Same as Scenario la but with physical obstructions and other producers of turbulence to air- flow paths on the supply and/or return airflow side (Fig- ure 4). Figure 3 Vertical stanc
9、hions blocking front access to CRAC unit. ASHRAE Transactions: Symposia 949 Figure 4 Piping blocking supply airflow path. Scenarios la through IC are simplistic but are helpful to demonstrate the variation in reliability and performance that can commonly occur independently from a focus solely on “s
10、ingle point of failure.” As indicated by the scenarios, the location of the equipment from both a connectivity, clearance, and airflow path standpoint. all can have a significant impact on the reliability of the cooling system as a whole. Group 2: Impact of Commissioning Process Commissioning is oft
11、en thought of as simply “extensive start-up and testing,” but true commissioning is far broader and more important than simply testing. ASHRAE defines commissioning as: The process of ensuring that systems are designed, installed, functionally tested, and capable of being oper- ated and maintained t
12、o perform in conformity with the design intent. This process could easily be renamed as the “critical process” or “roadmap to successful reliability.” ASHRAE provides a good source for information on the process of commissioning, including ASHRAE Guideline 1- 1996, The HVAC Commissioning Process. In
13、 this guideline, commissioning begins with the initial planning phase and continues on through the design, construction, start-up, accep- tance, and training. In other words, it should be applied throughout the life of the building. The following is another group of scenarios (Group 2) where Scenari
14、o 2a is exactly the same as Scenario la in the previous group (Group i). However, the variable that impacts the reliability in this group has to do with the level of the commissioning process that is performed. Scenario 2a (Baseline). A new CRAC unit, optimally located and commissioned and currently
15、 has been in operation for 80 hours under full load (i.e., broken in). Scenario 2b. Same as Scenario 2a including a complete commissioning process but the unit started serving criti- cal load without the benefit of any full-load hours of break in or bum in (therefore exposed to the risk of infant mo
16、rtality as described by Galm 2003). Scenario 2c. Same as Scenario 2a but the commission- ing process did not include a load bank to apply a full cooling load for the prefunctional and functional testing that occurs with the ASHRAE-defined commissioning process. Scenario 2d. Same as Scenario 2a but n
17、o commission- ing was performed; instead, just the traditional factory start-up procedures and standard punchlist were used. Scenarios 2a through 2d are also simplistic but are helpful to demonstrate the variation in reliability and performance that can commonly occur simply by varying the commissio
18、ning effort from comprehensive to none. Group 3: Impact of Implementation of Redundant Units The following is another group of scenarios (Group 3) where Scenario 3a is exactly the same as Scenario la in Group 1 but now is used as a baseline to compare a still different set of variations that impact
19、reliability. This time, the variations have to do with the addition of redundant units and why that method does not automatically equate to an improvement in the overall reliability of the system. Scenario 3a (Baseline). a new CRAC unit, optimally located and commissioned, and currently has been in
20、operation for 80 hours under full load (i.e., broken in). Scenario 3b. Two new CRAC units each equal in size to the CRAC unit in Scenario 3a but the locations of the units are such that a failure of one unit will not provide adequate capacity to the intended load. Scenario 3c. Two new CRAC units, ea
21、ch equal in size to the CRAC unit in Scenario 3a, but the units are nut calibrated to work cohesively and do not have sufficient controls or mechanisms to effectively operate as a reli- able, redundant system. Scenario 3d. Two new CRAC units, each equal in size to the CRAC unit in Scenario 3a, but n
22、o commissioning was performed and, instead, just the traditional factory start-up procedures and standard punchlist were used. Scenarios 3a through 3d provide some sense of the vari- ation in reliability even if redundant units are added. Redun- dant units are often thought of as the simple solution
23、 to increasing the reliability of a system, but, as indicated in the scenarios above, the decision to utilize a redundant system still requires an implementation process focused on meeting the overall goal of improved reliability. 950 ASHRAE Transactions: Symposia Group 4: Impact of Maintenance and
24、Operation In the final group of scenarios (Group 4), once again Scenario 4a is exactly the same as Scenario 1 a in Group 1 but now is used as a baseline to compare how maintenance and operation variations can impact system reliability. Scenario 4a (Baseline). A new CRAC unit, optimally located and c
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