1、118 2010 ASHRAEABSTRACTThis is an analysis of electrical and water consumption forcooling systems involving refrigeration with dry coolers, watereconomizers and air economizers combined with steam, ultra-sonic and evaporative humidifiers on telco/data centerslocated at various cities throughout the
2、United States.Air economizers with evaporative humidifiers are the mostenergy efficient model, although the savings are quite small fortropical locations. Air economizers are often able to satisfycooling requirements without any refrigeration and are alsoable to reduce refrigeration load for additio
3、nal time. Theseperiods when refrigeration is not required have improved reli-ability uptime and provide low risk opportunities for chillerplant servicing. The Air economizer system also consumes lesswater than water economizer or refrigeration only systems.Water economizers are less effective than a
4、ir economizersat improving energy efficiency and reducing refrigerationdependency. The modeled dry cooler did not provide any sav-ings versus refrigeration only.Evaporative humidifiers are more efficient than ultrasonichumidifiers and much more efficient than steam humidifiers.Air economizers with s
5、team humidifiers are an energywasteful design. More power is consumed by the steam humid-ifiers than is saved by the air economizers.INTRODUCTIONThis article analyzes electrical and water consumption forfour different cooling systems combined with three differenthumidification systems on hypothetica
6、l telco/data centerslocated at 262 cities throughout the United States.The four analyzed cooling systems include refrigerationonly, refrigeration with dry coolers, refrigeration with watereconomizers, and refrigeration with air economizers. Thesecooling systems do not represent every conceivable mod
7、el, butthey do represent the most common configurations.The three analyzed humidifiers include steam, ultrasonicand evaporative.Equipment, installation, and maintenance costs are notdirectly addressed.DATABASENOAA Hourly United States Weather Observations 1990-1995 Database has been used to determin
8、e weather conditionson an hourly basis for these consumption calculations. Theresults are based upon calculations repeated for every hour forthe six year period from the beginning of 1990 until the end of1995. Weather data records include station, date, hour of day,dry bulb temperature, relative hum
9、idity, barometric pressure,humidity ratio, wet bulb temperature, and enthalpy. Theweather data also included solar radiation data, but this datawas too inconsistent to be relied upon.Appendix A contains Transact SQL source code forcreation of all tables, stored procedures and functions andis availab
10、le on-line at http:bruceAppendixA.pdf.Water and moist air property functions were derived fromequations and tables within “Psychrometrics” (ASHRAE2005a).Refrigerant property functions were derived from“Refrigerant 134a (1,1,1,2-Tetrafluoroethane) Properties ofSaturated Liquid and Saturated Vapor” Ta
11、ble (ASHRAE2005b).The motor efficiency function is based upon NEMA MG14-pole squirrel cage TEFC Premium efficiency motors. TheConsumption Analysis of Telco and Data Center Cooling and Humidification OptionsBruce A. HellmerMember ASHRAEBruce A. Hellmer is a professional engineer with Tier IV Consulti
12、ng Group, Lees Summit, MO.OR-10-014 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digita
13、l form is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 119VFD efficiency function assumes load independent losses of1.8% of full load and load dependent losses of 0.6% of actualload.BUILDING LOADSEquipment continuously releases one MW of heat withinthese hypothetical t
14、elco/data centers. This one MW heat loadwas selected to make scaling the results easy.Internal heat loads:Telco, data and conditioned electrical power distributionequipment: 1 MWLighting: 20 kWMiscellaneous: 10 kWPeople: 25 at 450 Btu/h (0.132 kW) each, latent loadwas disregardedBuilding characteris
15、tics:Height 18 ft (5.5 m)Length: 140 ft (42.7 m)Width: 140 ft (42.7 m)Equipment space: 10,000 ft2(929 m2) at 100 W/ft2(1076 W/m2)Support space: 9600 ft2(892 m2)Roof R-factor: 30 Btu/h ft2F (170 W/m2C)Exterior wall R-factor: 20 Btu/hft2F (114 W/m2C)The solar heat gain for each location has been calcu
16、latedfor the roof and the north, south, east and west walls for eachhour of the day and for each month of the year using the trig-onometric equations in “Fenestration” (ASHRAE 2005d).Heat transfer through the buildings exterior envelope hasbeen calculated using sol-air temperatures derived from sola
17、rheat gain for a light colored surface using the methoddescribed in “Nonresidential Cooling and Heating LoadCalculations” (ASHRAE 2005c). Return air grilles are locatedat ceiling so the bottom of roof is exposed to air at return airconditions. The inside of exterior walls is exposed to air atroom ai
18、r conditions.STANDARD OPERATING CONDITIONSThe most sensitive equipment should operate in a Class 1environment with the following recommended conditions(ASHRAE 2004):Dry-bulb temperature: between 68 and 77F (20 and25C)Relative humidity: between 40 and 55%Dew-point temperature: below 62.6F (17C)ASHRAE
19、 Technical Committee 9.9 has revised theserecommended conditions in its recent Second Edition(ASHRAE 2009):Dry-bulb temperature: between 64.4F and 80.6F (18and 27C)Relative humidity: below 60%Dew point temperature: between 41.9F and 59F (5.5and 15C)This energy analysis is not intended to address ene
20、rgysaving associated with operating at elevated space tempera-tures; thus these assumed operating conditions target themiddle of the recommended temperature range:Cold aisle, zone and room temperature setpoints: 72F(22.2C)Return air temperature: 80F (26.7C)Cold aisle, zone and room relative humidity
21、 setpoints(low limit): 40%Maximum supply humidity ratio corresponding to aroom temperature of 72F (22.2C) and a relativehumidity of 55%.AIR HANDLERSLarge central station air handlers were modeled. These airhandlers were utilized because they are easily equipped withair economizers and evaporative hu
22、midifiers. ComputerRoom Air Handlers (CRAHs) can be equipped with air econ-omizers, but this would generally require that they be locatedadjacent to exterior walls or below roof penetrations. CRAHsare also not generally available with ultrasonic or evaporativehumidifiers.Large central station air ha
23、ndlers may be good modelswith respect to electrical and water consumption for moresmaller air handlers, such as CRAHs, so long as the supply fankWh values are adjusted to reflect the different bhp/cfm ratios.Air handler characteristics:Quantity: six, four essential and two redundantTags: AH1, AH2, A
24、H3, AH4, AH5 and AH6Mass flow rate: 182,343 lb/h (50.65 kg/s)Volume flow rate: about 40,000 cfm (18.88 m3/s) fornear sea level installationsExternal static pressure: 2.0 inWC (498 Pa)Coil face velocity: 488 fpm (2.48 m/s)Coil size: 82 ft2(7.62 m2) for near sea level installationsPre-filters: 2 in. (
25、50.8 mm), 30% (MERV 7) pleated Final-filters: 80% V-typeFilter mid-life pressure drop: 1.25 inWC (312 Pa)All air handler fans operate continuously with their fanspeeds modulating together to maintain a 1.5 inWC (373 Pa)pressure in a common supply header. This common supplyheader pressure is not flow
26、 dependent, thus its portion of fanpower is proportional to the mass flow rate. The remainder ofthe fans developed pressure is frictional, thus its portion of fanpower is proportional to the cube of the mass flow rate.Zone dampers for takeoffs from common supply headerwill modulate to satisfy their
27、cold aisle, zone or room temper-ature demands. 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either prin
28、t or digital form is not permitted without ASHRAEs prior written permission. 120 ASHRAE TransactionsMINIMUM OUTDOOR AIRThe buildings include a redundant pair of 1 MW batteryrooms at 800 ft2(74 m2) each. These battery rooms require1.0 cfm/ft2(0.0051 m3/sm2) or a total of 1600 cfm (0.755 m3/s) of exha
29、ust air. The battery room exhaust is made up with airtransferred from other building spaces. Restroom and otherexhausts add an additional 400 cfm (0.1888 m3/s) for abuilding total of 2000 cfm (0.944 m3/s) of exhaust. More than2000 cfm (0.944 m3/s) of outdoor air must be introduced intothe building b
30、y the air handlers in order to makeup exhaust andslightly pressurize the building.Air handlers are assumed to draw at least 2% of their flowrate as outdoor air. This flow rate is equivalent to more than2000 cfm (0.944 m3/s) for the entire building.REFRIGERATION ONLYThis design operates refrigeration
31、 throughout the entireyear. See Figure 1 for schematic diagram and Figure 2 forpsychrometric chart.REFRIGERATION WITH DRY COOLERSEach dry cooler utilizes a fluid cooler, an air handler cool-ing coil, and a coolant pump. The dry cooler in this model canbe operated simultaneously with chiller operatio
32、n. See Figure 3for schematic diagram.After executing model with many configurations, an airhandler cooling coil with low air friction losses was selected.An air handler coolant coil with a high air pressure drop willburden their air handler fans all year long. A generously sizedfluid cooler was sele
33、cted to support free cooling at elevatedoutdoor air temperatures. Although dry coolers may operate toreduce refrigeration loading, no energy is saved while simul-taneously operating dry coolers and refrigeration.Fluid cooler characteristics:Quantity: six, one per air handlerTags: DC1, DC2, DC3, DC4,
34、 DC5 and DC6Materials: copper tubes and corrugated fins, stainlesssteel frameCoil size: five at 54 in. width 90 in. length (1.372 mwidth 2.286 m length)Coil rows: 6Coil fin pitch: 14 per in. (550 per m)Coil circuiting: singleAir flow rate 88,000 cfm (41.6 m3/s)Entering air temperature: 26.0F (3.3C)
35、dbLeaving air temperature: 38.6F (3.7C) dbCoolant: 40% Propylene Glycol in waterCoolant flow rate: 300 gpm (19.0 l/s)Entering coolant temperature: 52.8F (11.6C)Leaving coolant temperature: 44.0F (6.7C)Coolant pressure drop: 5.8 ft HD (17.34 kPa)Capacity: 1,213,640 Btu/h (355.5 kW)Fans: ten 36 in. (0
36、.914 m) propellersFan power: ten at 2.0 bhp (1.492 kW)Motor size: ten at 2 hp (1.5 kW)Air handler cooling coil characteristics:Materials: copper tubes and corrugated fins, stainlesssteel frame and drain panRows: 6Fin pitch: 8 per in. (315 per m)Circuiting: singleEntering air temperature: 80.0F (26.7
37、C) db/60.0F(15.6C) wbLeaving air temperature: 53.6F (12.0C) db / 49.3F(9.6C) wbAir pressure drop: 0.76 inWC (189 Pa)Entering coolant temperature: 40.0F (4.4C)Leaving coolant temperature: 48.3F (9.1C)Coolant pressure drop: 36.3 ftHD (109 kPa)Capacity: 1,155,346 Btu/h (338.61 kW)Pump characteristics:D
38、esign flow rate: 300 gpm (19.0 l/s)Developed pressure: 50.0 ft of head (149 kPa)Pump power: 5.16 bhp (3.85 kW)Motor size: 7.5 hp (5.6 kW)The dry cooler season has two control modes. The coldestmode controls the fluid cooler fans to maintain the air handlercooled air temperature at a setpoint of 50F
39、(10.0C). Whenthe coldest mode is no longer able to satisfy its setpoint, thecool mode with elevated air handler supply air temperaturescauses zone dampers to open more requiring the air handlersupply fans to speed up. Results from the model indicated thatair handler capacity may be exceeded trying t
40、o operate the drycooler above an outdoor dry-bulb temperature of 42F(5.6C); so this temperature is used for changeover to refrig-eration. See Figure 4 for psychrometric chart.REFRIGERATION WITH WATER ECONOMIZERSEach water economizer utilizes a cooling tower, a flat-plate heat exchanger, indoor cooli
41、ng coils, a condenser waterpump and a chilled water pump. The heat exchanger iscircuited in parallel with the chiller and it isolates the chilledwater system from contaminates introduced by the coolingtower into the condenser water. The water economizer in thismodel shares a cooling tower, air handl
42、er cooling coils, acondenser water pump and a chilled water pump with thechiller train and thus the chiller and economizer cannot beoperated simultaneously. See Figure 5 for schematic diagram.Chilled water circuiting of a heat exchanger in series andahead of the chiller so that the chiller and econo
43、mizer couldoperate simultaneously was considered but not modeled.Series chilled water circuiting together with series condenserwater circuiting would result in condenser water temperaturesthat are near or below the chilled water temperature; whichwould be too cold and in violation of the chiller man
44、ufacturersrecommendations. Series chilled water circuiting togetherwith an additional cooling tower and condenser water pump 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal u
45、se only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 121Figure 1 Entire facility with refrigeration only. 2010, American Society of Heating, Refrigerating and Air-Conditioning En
46、gineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. 122 ASHRAE TransactionsFigure 2 Psychromet
47、ric chart, refrigeration only.Figure 3 Air handler with dry cooler.Figure 4 Psychrometric chart, refrigeration with dry cooler.Figure 5 Chiller with water economizer. 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transacti
48、ons 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 123dedicated to the economizer would be expensive, have a shortoperating season and
49、 would not save much energy. The addi-tional power consumed by the economizers cooling tower,condenser water pump and the chilled water pump that mustpump through both a heat exchanger and a chiller may closelyapproach or exceed the power saved by the reduced chillerload during this period with very efficient chiller operatingconditions.Chillers with an integrated water economizer were notmodeled. This water economizer option is sometimes called“free cooling” and may be less expensive than the modele
