1、330 2010 ASHRAEABSTRACTThe authors have been working on the development ofconstituent technologies that will contribute to saving energyin air cooled packaged air-conditioners, in order to reduceenergy consumption in A/C facilities used in data centers, andhave developed an A/C for data centers that
2、 incorporates thesetechnologies. In the development of constituent technologies,based on the unique characteristics of year-round coolingoperations in data centers, the authors endeavored to increasethe efficiency of compressors in outdoor conditions at mediumand low temperatures, and to expand the
3、scope of low pressureratio operations. The authors have also developed savingenergy technologies that take into account A/C operating con-ditions and installation conditions; for example, preventingreduced operating efficiency resulting from long refrigerantpipes by installing the compressor in indo
4、or units; preventingexcessive cooling with A/C control using multiple temperaturesensors placed in the vicinity of IT equipment; and avoidingunnecessary humidification through high sensible heat designthat takes into account the heat load characteristics of datacenters. Air conditioners that incorpo
5、rate these saving energytechnologies reduce annual power consumption by about 40%under Tokyo meteorological conditions compared to conven-tional computer room A/Cs.INTRODUCTIONIn recent years, there has been a trend toward increasedvolumes of power consumed at data centers, and this hasbecome a prob
6、lem from the perspective of reducing energyconsumption. According to a survey report by the U.S. Envi-ronmental Protection Agency, in data centers that house largenumbers of IT equipment, the volume of power consumed bythe IT equipment is about the same as that consumed bydevices on the facilities s
7、ide, including A/Cs, lighting, andpower equipment. In order to reduce the power consumptionat data centers, it is therefore important to not only promoteincreased saving energy in IT equipment, but also to increasethe operating efficiency of facility side equipment, and partic-ularly A/Cs, which con
8、sume large amounts of power.The authors focused on air cooled packaged air-condi-tioners, which are used in many data centers in Japan, and havebeen working on the development of constituent technologiesthat will contribute to saving energy in this equipment. Wehave succeeded in developing an A/C fo
9、r data centers thatincorporates these technologies. In this paper, we will intro-duce these saving energy technologies and the operating effi-ciency characteristics of the newly developed A/C, along withthe results of field survey.Constituent Technologies Saving Energy in Data Center A/CData center
10、A/Cs are used for cooling all year round. Forthis reason, it is important to increase operating efficiencyunder medium and low outdoor temperature conditions, whichoccur frequently throughout the year, as opposed to highoutdoor temperature conditions, which are generally empha-sized in the design of
11、 A/Cs. Furthermore, because IT equip-ment are the main target of cooling operations, latent heat loadalmost never arises; rather, “sensible heat” is the controllingfactor. In these development activities, we worked on devel-oping the following technologies, based on these unique char-acteristics of
12、data centers.Development of a High-Efficiency Air Cooled Packaged Air-Conditioner for Data CentersKeisuke Sekiguchi, Dr. of Eng Shisei Waragai, Dr. of EngTsuneo Uekusa, Dr. of Eng Kenji YamasakiKeisuke Sekiguchi is a research engineer and Shisei Waragai is a senior manager at the Research and Develo
13、pment Headquarters of NTTFacilities, Inc., Tokyo, Japan. Tsuneo Uekusa is a executive manager in the Accounts and Finance Department at Nippon Telegraph and Tele-phone West Corporation, Osaka, Japan. Kenji Yamasaki is a senior manager in the Air Conditioning Design Department of Hitachi Appli-ances,
14、 Inc., Shizuoka, Japan.OR-10-036 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 digital f
15、orm is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 331Compressor efficiency improvementExpanded scope of low pressure ratio operationsHigh sensible heat design in an indoor unitWe also incorporated the following technologies toprevent reduced operating efficiency resu
16、lting from A/Cinstallation conditions and issues during data center applica-tions that would result in local excessive cooling operationsdue to the uneven distribution of heat volumes generated by ITequipment.Prevention of excessive cooling through A/C controlusing multi-point sensorsHigh-efficiency
17、 equipment configurations when install-ing long refrigerant pipesCompressor Efficiency ImprovementThe inverter driven scroll compressor installed in this A/C (Figure 1) takes into account year-round cooling operationsby using a release valve that is expected to improve thecompressor efficiency when
18、the outdoor temperature is low.The release valve prevents excess compression that arises inlow pressure ratio operating conditions. A compressor simu-lator is used to determine the installation position so as tominimize annual power consumption.In order to further improve compressor efficiency, wead
19、opted a new DC inverter motor, thus eliminating the need forexcitation power in the rotor and the asymmetric scroll wrap,which reduced leakage loss. By using these technologies, wewere able to improve compressor efficiency in pressure ratiosfor all operating conditions compared to conventional A/Cs(
20、Figure 2). Notably, improvements at low pressure ratiosresulted in a 50% increase in compression efficiency at a pres-sure ratio of 1.5.Expanded Scope of Low Pressure Ratio OperationsIn the case of conventional A/Cs, the minimum pressureratio under which operations were possible (the “minimumallowab
21、le pressure ratio”) was comparatively high, at about1.5, so even when the outdoor temperature was low, it wasnecessary to maintain a high condensation pressure, which inturn resulted in extremely high power consumption in thecompressor. In contrast, the new A/C reduces the minimumallowable pressure
22、ratio to 1.2, thereby expanding the scope ofcompressor operations (Figure 2). Whereas in the case ofconventional A/Cs, the condensation pressure remainedalmost the same when the outdoor temperature dropped lowerthan about 15C (59F), the new A/C can be operated evenwhen the condensation pressure is r
23、educed further, even withoutdoor temperatures common in winter months (Figure 3).Figure 4 shows an example of cooling conditions in arefrigerating cycle during low outdoor temperatures. In thecase of conventional A/Cs, the pressure ratio is high, and thecompressor consumes large volumes of power, bu
24、t the new A/C can operate at low condensation pressures, so the pressureratio is lower, and the compressors power consumption can bereduced.Figure 1 High-efficiency compressor technologies.Figure 2 Compressor efficiency.Figure 3 Condensation pressure 1 = outdoor temperatureof 35C (86F). 2010, Americ
25、an 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 digital form is not permitted without ASHRAEs prior wr
26、itten permission. 332 ASHRAE TransactionsFurthermore, reducing the condensation pressureincreases specific enthalpy for the refrigerant in the evaporator(Figure 4). As a result, the new A/C can ensure a fixed level ofcooling performance even when the compressor rotatingspeed is decreased and the vol
27、ume of refrigerant circulation isreduced. This can further reduce the A/Cs power consump-tion.High Sensible Heat Design in an Indoor UnitMost of the heat load in data centers is sensible heat loadgenerated by IT equipment; the latent heat load generated byhuman bodies and the outdoor atmosphere is m
28、uch lower thanin regular offices. For this reason, the A/Cs designed to be highSHF are saving energy because there is no unnecessary humid-ification or dehumidification. Many computer A/Cs have aSHF of about 0.9, however, so A/C operations in standard datacenter include dehumidification. For example
29、, even if the airis humidified to prevent static electricity, the A/C may bedehumidifying the room at the same time.The new A/C, on the other hand, has been designed withthe SHF increased to about 1.0, so under standard operatingconditions, the A/C is almost never dehumidifying the room;unnecessary
30、humidification is thus avoided, and energyconsumption is reduced.High-Efficiency Equipment Configurations When Installing Long Refrigerant PipesIn many cases, air cooled packaged air-conditioners foroffices have compressors installed in the outdoor unit, in orderto make the indoor unit more compact,
31、 or to enable installationof multiple indoor units. Some computer room A/Cs are devel-oped based on the design of the outdoor unit for these office A/Cs, in order to minimize costs, and so have the compressorsinstalled in the outdoor unit. The new A/C has adopted a struc-ture in which the compressor
32、s are installed in the indoor unit.The unique features of this type of A/C are shown in Table 1.One of the main advantages in actual operation is that byinstalling the compressor in the indoor unit, loss of operatingefficiency and cooling performance due to the length of refrig-erant pipes is kept t
33、o a minimum. Figure 5 shows the ratio ofchanges in cooling performance vs. the length of the refriger-ant pipes, in both the new A/C and computer room A/Cs thathave the compressor installed in the outdoor unit. In the caseof the computer room A/Cs, cooling performance dropsdramatically as the length
34、 of the refrigerant pipe increases,with a decrease of about 13% for 160 m (175 yd). The new A/C shows almost no decrease in cooling performance evenwhen the refrigerant pipes are 160 m (175 yd) long. Increasedlength of the refrigerant pipes causes refrigerant pressure lossthat results in increased p
35、ower consumption, but this increaseis almost entirely independent of the compressor installationposition. This means that in terms of operating efficiency, thenew A/C offers the advantage of minimal reductions in cool-ing performance due to refrigerant pipe length.Prevention of Excessive Cooling Thr
36、ough A/C Control Using Multi-Point SensorsHeat volumes generated by IT equipment differ depend-ing on the type of device, and vary depending on operatingrates. As a result, temperatures vary dramatically in datacenter machine rooms that house many IT devices. In somecases, the A/C temperature settin
37、gs are lowered to take intoaccount these variations in room temperature, and the lower A/C intake air temperatures result in huge increases in the A/Cspower consumption (Figure 6).Figure 4 P-h line drawing during low outdoor temperatures.Table 1. Unique Features of A/C with Compressor Installed in I
38、ndoor Unit1. Minimal reduction in operating efficiency due to refrigerant pipe length2. Minimal reduction in cooling performance due to refrigerant pipe length3. Minimal concerns about condensation on the refrigerant pipe4. Small refrigerant pipe diameterFigure 5 Reduction in cooling performance due
39、 to refriger-ant pipe length. 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 digital form
40、 is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 333The new A/C uses multi-point temperature sensors tocontrol the A/C. By installing the temperature sensors forcontrol near the IT equipment, the room temperature can beincreased to the maximum allowable operating tempe
41、raturefor the IT equipment (Figure 7). This way, the A/Cs intaketemperature increases, thereby reducing the A/Cs powerconsumption. In standard data centers, the A/Cs intake airtemperature can be increased by an average of 1 to 3C (1.8 to5.4F), which can be expected to reduce the A/Cs powerconsumptio
42、n by about 2 to 6% per year.Comparison of Average Annual Operating EfficiencyHere, we will compare the operating efficiency forconventional A/Cs and the new A/C featuring the savingenergy technologies introduced above. Figure 8 shows A/Coperating efficiency estimated using values measured in a test-
43、ing room, and times for outdoor temperatures based on stan-dard meteorological data for Tokyo. The other conditions areshown in Table 2.For this comparison, we assumed that the air flow fromthe A/C was distributed through the raised floor, and that theexternal static pressure of the indoor fan was 1
44、20 Pa. A/C oper-ating efficiency divided cooling heat volume by A/C powerconsumption, and A/C power consumption was calculated asthe total power consumption for the compressor and otherelements of the freezing cycle, in addition to the indoor andoutdoor fans and the A/C control devices. Figure 8 sho
45、ws thatthe new A/C has a higher operating efficiency than conven-tional A/Cs under all outdoor temperatures. There is a partic-ularly noticeable difference during the intermediate period 10to 25C (50 to 77F), which is the most common outdoortemperature: the operating efficiency for conventional A/Cs
46、 isjust under 3, while the operating efficiency for the new A/C isbetween 4 and 5.Table 3 shows the annual averages estimated based on theoperating efficiency characteristics in Figure 8. As the basisfor times during which outdoor temperatures occur, we usedvalues tabulated at 1C intervals from mete
47、orological data forTokyo and New York. The average annual operating efficiencyfor conventional A/Cs was 2.5 in Tokyo and 2.6 in New York,as compared to 4.2 in Tokyo and 4.4 in New York for the newA/C. This can be expected to achieve reductions in annualpower consumption of about 40% in Tokyo, and ab
48、out 42% inNew York, where low outdoor temperatures are morefrequent.Field Survey for the New A/CWe installed the new A/C in an actual data center to checkoperating conditions and measure operating efficiency. Thedata center was located in Tokyo, and the measurement periodwas one year, from September
49、 2007 to August 2008. Theindoor unit was installed on the 5th floor and the outdoor uniton the roof of an 8-floor building, and the refrigerant pipe wasapproximately 80 m (87.5 yd) long. In order to determine theA/Cs operating efficiency, we calculated cooling perfor-mance based on the difference in refrigerant specific enthalpyFigure 6 Image of room temperatures during regular oper-ation.Figure 7 Image of room temperatures using multi-pointtemperature control.Table 2. Conditions for Estimates of Operating EfficiencyIndoor unit intake air temperature 24C db (75.2F d
