How and Why Mission-critical Cooling Systems Differ from Common Air Conditioners

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1 Hw and Why Missin-critical Cling Systems Differ frm Cmmn Air Cnditiners White Paper 56 Revisin 3 by Tny Evans > Executive summary Tday's technlgy rms require precise, stable envirnments in rder fr sensitive electrnics t perate ptimally. Standard cmfrt air cnditining is ill suited fr technlgy rms, leading t system shutdwns and cmpnent failures. Because precisin air cnditining maintains temperature and humidity within a very narrw range, it prvides the envirnmental stability required by sensitive electrnic equipment, allwing yur business t avid expensive dwntime. Cntents Click n a sectin t jump t it Intrductin 2 Why precisin air cnditining? 2 Prblems caused by the wrng envirnments Differences between precisin air and cmfrt air cnditining Design criteria System selectin factrs 6 Cst f wnership 9 Cnclusin 10 Resurces 11 white papers are nw part f the Schneider Electric white paper library prduced by Schneider Electric s Data Center Science Center DCSC@Schneider-Electric.cm

2 Intrductin Precisin envirnmental cntrl requirements nw reach far beynd the cnfines f the traditinal data center r cmputer rm t encmpass a larger suite f applicatins, referred t as technlgy rms. Typical technlgy rm applicatins include: 1. Medical equipment suites (MRI, CAT scan) 2. Clean rms 3. Labratries 4. Printer/cpier/CAD centers 5. Server rms 6. Hspital facilities (perating, islatin rms) 7. Telecmmunicatins (switch gear rms, cell sites) Why precisin air cnditining? Infrmatin prcessing is the lifebld f all critical peratins. Therefre yur cmpany s health is dependent n the technlgy rm reliability. IT hardware prduces an unusual, cncentrated heat lad, and at the same time, is very sensitive t changes in temperature r humidity. A temperature and/r humidity swing can prduce prblems ranging frm prcessed gibberish t a cmplete system shutdwn. This can create huge csts fr the cmpany, depending n the length f the interruptin and the value f time and data lst. Standard cmfrt air cnditining is nt designed t handle the heat lad cncentratin and heat lad prfile f technlgy rms, nr is it designed t prvide the precise temperature and humidity set pint required fr these applicatins. Precisin air systems are designed fr clse temperature and humidity cntrl. They prvide high reliability fr year-rund peratin, with the ease f service, system flexibility and redundancy necessary t keep the technlgy rm up and running 24 hurs a day. Temperature and humidity design cnditins Maintaining the temperature and humidity design cnditins is critical t the smth peratin f a technlgy rm. Design cnditins shuld be F (22-24 C) and 35-50% relative humidity (R.H.). As damaging as the wrng ambient cnditins can be, rapid temperature swings can als have a negative effect n hardware peratin. This is ne f the reasns hardware is left pwered up, even when nt prcessing data. Precisin air cnditining is designed t maintain temperature at ±1 F (0.56 C) and humidity at ±3-5% R.H. 24 hurs a day, 8760 hurs a year. In cntrast, cmfrt systems are designed t maintain 80 F (27 C) and 50% R.H. nly during summer cnditins f 95 F (35 C) and 48% R.H. utside cnditins. Usually there is n dedicated humidity cntrl and the simple cntrllers cannt maintain the set pint tlerance required fr temperature, allwing ptentially harmful temperature and humidity swings t ccur. Prblems caused by the wrng envirnment A prly maintained technlgy rm envirnment will have a negative impact n data prcessing and strage peratins. The results can range frm data crruptin t cmplete system shutdwns and failures. 1- High & lw temperature A high r lw ambient temperature r rapid temperature swings can crrupt data prcessing and shut dwn an entire system. Temperature variatins can alter the electrical and physical Schneider Electric Data Center Science Center White Paper 56 Rev 3 2

3 characteristics f electrnic chips and ther bard cmpnents, causing faulty peratin r failure. These prblems may be transient r may last fr days. Even transient prblems can be very difficult t diagnse and repair. 2- High humidity High humidity can result in tape and surface deteriratin, head crashes, cndensatin, crrsin, paper handling prblems, and gld and silver migratin leading t cmpnent and bard failure. 3- Lw humidity Lw humidity greatly increases the pssibility f static electric discharges. Such static discharges can crrupt data and damage hardware. Differences between precisin air and cmfrt air cnditining 1- Sensible heat rati A heat lad has tw separate cmpnents: sensible heat and latent heat. Sensible heat remval r additin causes crrespnding changes in air-dry bulb temperature. Latent heat is assciated with the increase r decrease in the misture cntent f the air. The ttal cling capacity f an air cnditiner is the sum f the sensible heat remved and the latent heat remved. Ttal Cling Capacity = Sensible Cling + Latent Cling The sensible heat rati is the fractin f the ttal cling that is sensible. Sensible Heat Rati (SHR) = Sensible Cling Ttal Cling In a technlgy rm, the cling lad is made up almst entirely f sensible heat cming frm IT hardware, lights, supprt equipment, and mtrs. There is very little latent lad since there are few peple, limited utside air, and usually a vapr barrier. The required SHR f an air cnditiner t match this heat lad prfile is very high, Precisin air cnditining is designed t meet these very high sensible heat ratis. In cntrast, a cmfrt air cnditiner typically has a SHR f , thereby prviding t little sensible cling and t much latent cling. The excess latent cling means that t much misture is cntinually being remved frm the air. In rder t maintain the desirable 35-50% relative humidity band, cntinuus humidificatin wuld be necessary, which by definitin cnsumes large quantities f energy. Figure 1 Sensible heat rati (SHR) Precisin Air Cnditining SHR Cmfrt Air Cnditining SHR Sensible Heat Rati (SHR) Schneider Electric Data Center Science Center White Paper 56 Rev 3 3

4 2- Precise temperature and humidity Precisin air cnditiners have the sphisticated, fast-acting, micrprcessr-based cntrls necessary t react quickly t changing cnditins and maintain the tight tlerances required fr a stable envirnment. Precisin air systems usually include multiple stages f cling and heating, a humidifier, and a dedicated dehumidificatin cycle, allwing them t satisfy any and all temperature and humidity cntrl requirements. Cmfrt air cnditiners generally have basic, limited cntrls unable t react quickly enugh t maintain the required tlerance. Cmfrt systems d nt usually include heat r the humidificatin/dehumidificatin cycles necessary fr a stable technlgical envirnment. The cmpnents, if available, are frequently add-ns and nt part f an integrated system. 3- Air quality Precisin air cnditiners perate at a high air flw rate per unit heat remved, generally, 160 CFM (76 Lps) per kw r greater. This high vlumetric rate mves mre air thrugh the space imprving air distributin and reducing the chance f lcalized ht spts. Mdern technlgy equipment generally cnsumes arund 160 CFM fr each kw f electrical pwer cnsumptin, s it is imprtant that this quantity f cl supply air be available at the equipment inlet. If it is nt, the equipment will btain sme f its air frm ther areas f the rm, ften resulting in dangerusly high inlet temperatures. The high CFM / kw f precisin cling equipment als allws mre air t mve thrugh filters, ensuring a cleaner envirnment. Precisin air cnditiners typically use a mderate- t high-efficiency, deep-pleated filter bank, t minimize airbrne particles. Cmfrt air cnditiners perate at a much lwer CFM / kw (40-54 Lps / kw). Lw CFM can lead t pr air distributin and mre airbrne cntaminants. Filters fr cmfrt air cnditiners are usually flat, lw-efficiency media that d nt remve a sufficient percentage f airbrne particles. 4- Hurs f peratin Precisin air cnditiners are designed and built t run nn-stp 8760 hurs a year. The systems are designed - with cmpnents selected and redundancy incrprated - t ensure minimal dwntime. System cntrls maintain rm cnditins fr the full range f utside ambient cnditins, summer r winter. Cmfrt air cnditiners are designed t run during summer days, up t an expected maximum f 1200 hurs per year. The system is nt designed r expected t perate nnstp, year rund. Neither the cntrls nr the refrigeratin system is designed fr zer dwntime r winter peratin. Design criteria 1- Lad density Due t the high equipment cncentratin, the lad density within a technlgy rm can be five times higher than that in a typical ffice. Systems must be designed t handle this extremely high-density lad. Sensible capacity and air distributin are very imprtant. Lad Density Office 5 15 watts / sq. ft. ( watts / sq. m) Technlgy Rm watts / sq. ft. (538 2,153 watts / sq. m) Schneider Electric Data Center Science Center White Paper 56 Rev 3 4

5 Office Area Technlgy Rm Figure 2 Lad density 2- Temperature and Humidity Design gal cnditins shuld be F (22-24 C), 35-50% R.H. 3- Air Quantity The high CFM / kw (Lps / kw) inherent t precisin systems cntributes t the high sensible heat rati, imprves air distributin, and increases filtratin rates. The high CFM des nt cause discmfrt t persnnel as it is distributed under the raised flr and drawn up thrugh equipment and int the space arund the rm. 4- Air Cleanliness Withut filters, airbrne dust can damage equipment. Filters shuld be deep pleated fr mderate t high efficiency. Filter sizing is als imprtant; the filter must perate with face velcities lw enugh t be effective. Regular filter changes are necessary. 5- Vapr Barrier Because almst all cnstructin materials are transparent t misture, a well-designed technlgy rm must include a vapr barrier. Withut a vapr barrier, the technlgy rm will lse humidity in the winter and will gain it in the summer. This makes humidity set pint cntrl very difficult and increases the run times f energy-expensive cmpressrs and humidifiers. T create an effective vapr barrier, ceilings shuld be sealed with a plyethylene film, cncrete walls shuld be painted with a rubber r plastic base paint, drs shuld seal tightly, and all pipes and cable penetratins shuld be sealed. 6- Outside Air Requirements Technlgy rms tend t be sparsely ppulated and d nt require much utside air fr persnnel. Outside air shuld be minimized t limit the latent lad brught int the rm. A quantity f 20 CFM (9.4 Lps) per persn is currently sufficient t satisfy Indr Air Quality (IAQ) cncerns in the U.S. Schneider Electric Data Center Science Center White Paper 56 Rev 3 5

6 7- Redundancy Redundancy is achieved by perating additinal equipment t prvide 100% f the required cling capacity even after a unit shutdwn r failure f ne r mre units. The cst f redundancy shuld be weighed against the prjected cst f technlgy rm dwntime. Figure 3 Redundancy 52 kw 52 kw 52 kw 70 kw 70 kw Handles the 104 kw lad Redundant Unit 140 kw capacity is 35 kw verlad The difference between redundancy and ver capacity shuld be nted. A 70 kw lad with 3 x 52 kw systems r 4 x 35 kw systems prvides redundancy. A run-time-based rtatin f equipment peratin and a cntrls interface that prvides autmatic start up are required fr standby equipment t be cnsidered redundant. 9- Security The security f the air cnditiners is as imprtant as that f the technlgy rm hardware since the hardware cannt perate withut them. The indr units must be lcated within the technlgy rm and shuld be subject t the same restricted access as the IT hardware. The utside heat rejectin equipment shuld be placed n a rf r sme ther secure area within the facility. System selectin factrs Related resurce White Paper 25 Calculating Ttal Cling Requirements fr Data Centers 1- Lad calculatins Heat in technlgy rms is generated by hardware, lights, peple, utside air, transmissin lads, sun, and supprt equipment (PDUs, UPS, etc.). As a rule f thumb, use 15 sq. ft. / kw (1.39 sq. m. / kw) fr lad calculatins. Fr a mre detailed lad calculatin see White Paper 25, Calculating Ttal Cling Requirements fr Data Centers. 2- Unitary systems a- Air cled Schneider Electric Data Center Science Center White Paper 56 Rev 3 6

7 Air Cnditiner Air Cled Cndenser Figure 4 Air cled system System cnfiguratin Refrigeratin system is split between indr air cnditiner and utdr air-cled heat rejectin unit. Cmpressrs can be lcated in the indr r utdr equipment. Fr security and maintenance, cmpressrs are usually lcated in the indr unit. Refrigerant pipelines (tw per cmpressr) intercnnect tw halves f the system. Refrigerant piping design is critical. The design must address pressure lsses, refrigerant velcities, il return, and traps. Qualified expert cntractrs shuld install the service unit. Excellent fr multiple units and expanding installatins. Each system is a selfcntained, stand-alne mdule. b- Water cled Cling Twer Air Cnditiner Figure 5 Water cled system Pump Package System cnfiguratin Indr air cnditiner is a cmplete, self-cntained refrigeratin system. Heat is rejected t a clant water supply via a heat exchanger in the indr unit. The clant water is then usually pumped t a cling twer and re-circulated. Other water surces such as wells als can be used. Cling twer shuld be winterized in cld and temperate climates. Twer shuld be designed with redundancy, r an emergency back-up water supply shuld be available. Schneider Electric Data Center Science Center White Paper 56 Rev 3 7

8 Water treatment is required when a cling twer is used. Water pipe design is a lt less critical and easier t install than refrigerant piping. The refrigeratin system arrives factry charged and tested. c- Glycl cled Air Cnditiner Dry Cler Figure 6 Glycl cled system Pump Package System cnfiguratin Indr unit is similar t water-cled system. A glycl slutin is circulated in place f water and the heat rejectin ccurs in an utdr liquid t air heat exchanger r "dry cler. Dry clers are lwer maintenance than cling twers. Presents excellent pprtunities fr heat recvery applicatin. System E.E.R. is lwest f three unit types. Multiple units can be linked t single large dry clers and pump packages. Be aware f redundancy requirements if this is dne. d- Free-cling glycl System cnfiguratin Prduct is identical t glycl-cled but als includes an additinal free-cl cil fr energy savings. When the utside temperature drps, cl glycl slutin is run thrugh the supplementary free-cl cil and cling is btained withut running the cmpressrs. Presents excellent perating cst reductins in apprpriate climates. Extra cil means mre blwer mtr HP. Lk fr systems with larger free-cl cils fr mre cst savings. Free-cl cils shuld be installed befre the DX cil fr assisted capacity during mild, ambient temperatures. e- Supplementary chilled-water cil System cnfiguratin A supplementary chilled-water cil can be included in a DX system t prvided cmplete redundancy in a single unit. Unit may perate as a chilled water system with 100% mdular DX back up in the event f an emergency. Unit may act as a DX system with emergency central plant chilled-water back up if required. Schneider Electric Data Center Science Center White Paper 56 Rev 3 8

9 Unit may use chilled water when available. Fr instance, if chiller runs primarily t supprt a manufacturing prcess in a factry r t supprt summertime cmfrt systems, and switch t DX when chilled water is rutinely n lnger available. f- Chilled water Air Cnditiner Central Chiller Figure 7 Chilled water system System cnfiguratin Chilled water is supplied frm a central chiller t packaged units in the technlgy rm. The refrigeratin system is cntained in the packaged chiller. Indr air cnditiners cntain cntrls, chilled-water cil, chilled-water cntrl valve, blwers, filters, humidifiers and reheat. Chilled-water temperature shuld be as high as pssible t keep a high sensible heat rati (47 F / 8.33 C r higher). Redundancy shuld be extended t central chilled plant and pump packages. Central plant shuld be winterized fr year-rund peratin. May require perating persnnel in sme cities. D nt cmbine with cmfrt cling chillers since chilled-water supply temperatures shuld differ (42 F / 5.6 C fr cmfrt, 47 F+ / 8.3 C+ fr technlgy rm). Cst f wnership 1- Operating csts Technlgy rm air cnditining csts are typically ten times higher per square ft than ffice r cmfrt air cnditining. This is because f year-rund rather then seasnal peratin and the greatly increased heat lad density. Hwever, precisin air cnditining perating csts are far less than cmfrt air cnditining if bth systems are applied t a technlgy rm. Precisin air cnditining csts are lwer than cmfrt air cnditining fr cmparable use because f the fllwing: Under-flr system - A high sensible heat rati eliminates ver-dehumidificatin and subsequent humidifier peratin. High Energy Efficiency Rati (E.E.R). With the versized cils, high CFM, and heat pump duty cmpressrs, cmputer grade systems have higher sensible cling energy efficiency ratis than cnventinal cmfrt cling. Precisin air equipment is designed with high-efficiency cmpnents fr year-rund peratin. Lk fr the fllwing: Oversized, shallw cling cil Schneider Electric Data Center Science Center White Paper 56 Rev 3 9

10 High efficiency blwer mtrs Steam canister humidifiers Heat pump duty rated cmpressr High S.H.R. s Dedicated dehumidificatin cycle Lw FLA 100,000 HR L rated bearings Extended warranties 2- Service csts The largest csts incurred during the service r repair are generally in technlgy rm dwntime. Fr this reasn, redundancy shuld always be designed in first. Hwever, t further reduce this expsure, equipment can be selected with features that will reduce required service and repair time dramatically. Lk fr the fllwing: Blt in refrigeratin cmpnents. Cmpressr and filter dryer shuld be remvable withut gas trches. Primary and secndary engineering drain pans. Quick-change canister humidifier. Cmpnents shuld be ut f the air stream in a separate mechanical sectin. Remvable fan deck assembly. Clr-cded and numbered electrical wiring. Mtr start prtectrs instead f fuses. Easily remvable and/r hinged access panels. Run-time-based maintenance calls. Cnclusin Technlgy rms huse sensitive electrnics that need precise envirnmental cnditins t run ptimally. By prviding the envirnmental stability that this type f electrnic equipment requires, precisin air cnditining helps yur business avid expensive system shutdwns and cmpnent failures. Abut the authr Tny Evans is an engineer with APC by Schneider Electric in West Kingstn, RI. He has 14 years f experience in pwer and cling system design and is a member f ASHRAE Technical Cmmittee 9.9 (Missin Critical Facilities, Technlgy Spaces, & Electrnic Equipment). Schneider Electric Data Center Science Center White Paper 56 Rev 3 10

11 Resurces Click n icn t link t resurce Calculating Ttal Cling Requirements fr Data Centers White Paper 25 White Paper Library whitepapers.apc.cm TradeOff Tls tls.apc.cm Cntact us Fr feedback and cmments abut the cntent f this white paper: Data Center Science Center DCSC@Schneider-Electric.cm If yu are a custmer and have questins specific t yur data center prject: Cntact yur Schneider Electric representative Schneider Electric Data Center Science Center White Paper 56 Rev 3 11