ASHRAE OR-10-009-2010 Performance Investigation for the Cleanroom Contamination Control Strategy in an Operating Room《操作室中洁净室污染控制政策的执行调查》.pdf

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1、74 2010 ASHRAEABSTRACTOperating rooms are increasingly turning to contamina-tion control by cleanroom technology for the infectious control.This study presents the numerical approach and field testinginvestigation on performance improvement for a hospitaloperating room with less expenditure. Variabl

2、e speed drivenstrategy has been performed to verify the potential of energy-saving opportunity under contamination standards that it hasbeen designed to fulfill. A physical partition curtain has beenconducted around the high efficiency particulate air (HEPA)filter of an operating room to validate th

3、e improvement of airflow distribution and contamination control. Both numericalsimulation and field measurement of a full-scale operatingroom have been carried out at a district hospital in Taiwan. Theresults from computer simulation revealed that the reductionof face veloctity is feasible and impro

4、vement of airflow couldbe achieved satisfactorily by application of a physical partitioncurtain. Optimal face velocity of HEPA filter could be obtainedthrough compromising of contamination control and energyconsumption as well. Simulation results have been validatedby comparison with the field tests

5、 data of both particle countsand microbial counts.INTRODUCTIONRecent advances in medical technology necessitate regu-lar reevaluation of the heating, ventilating and air-conditioning(HVAC) needs for hospitals facilities. The purpose of theHVAC system for an operating room is not only to achievetherm

6、al comfort but also to remove airborne contamination. Itis vital to perform the surgery in a particle-free environmentand maintain the minimization of contamination. However,little knowledge or quantitative information about energy-efficient HVAC system is available on how to control the envi-ronmen

7、tal variable in the operating room effectively. With costof rising, value of conservation grows. Since HVAC systems ofoperating room operate continuously, it is vital and significantto consider energy-efficient strategies as well as to achieve anacceptable performance for contaminations contort.Rece

8、nt research on operating room ventilation perfor-mance against airborne infection has been investigated thor-oughly by Chow et al. (2005). They also reported that surgicalsite infection due to airborne bacteria is a key factor in devel-oping the HVAC system in the operating room. Anothercomprehensiv

9、e review on the air movement under infectioncontrol focus in operating room has been presented by Pereiraet al. (2005). Their study also identified the control strategieswhich could reduce the risks of airborne contamination inoperating infection. The airborne particles in the infectionprocess and t

10、he microbiological control for the air distributionsystem have been analyzed extensively. Besides, the experi-ment and modeling of airflow pattern as well as the diffusionof contaminants in an operating room was performed by Wool-sey et al. (2004).Computational fluid dynamics (CFD) simulation tech-n

11、ique is a well-known and widely-accepted scientific tech-nique that allows improvement of airflow distribution forcleanroom configuration (Wang et al. 2009). They also iden-tified some option under a limited budget, as well as reducedtrial-and-error effort when modifications of cleanrooms haveto be

12、conducted. Moreover, the CFD codes were successfullyused to simulate the air distribution and contamination decayas well as comparison of indoor particle concentration indifferent rooms (Zao and Zhang 2009). Besides, the biologicalcontaminant control strategies under different ventilationPerformance

13、 Investigation for the Cleanroom Contamination Control Strategy in an Operating RoomFu-Jen Wang, PhD, PE Chi-Ming Lai, PhD, PEMember ASHRAE Member ASHRAETsung-Jung Cheng, PhD, PE Zhuan-Yu LiuStudent Member ASHRAEFu-jen Wang is associate professor and Zhuan-yu Liu is graduate student in the Departmen

14、t of Refrigeration, Air Conditioning and EnergyEngineering, National Chin-Yi University of Technology, Taiwan. Chi-ming Lai is assistant professor in the Department of Civil Engineering,National Cheng-Kung University, Taiwan. Tsung-jung Cheng is associate professor in the Department of Architecture,

15、 Feng Chia University,Taiwan.OR-10-009 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 dig

16、ital form is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 75models in the hospital operating room have been proposed byusing CFD simulation (Zhang et al. 2008). Results showedthat improving air flow distribution could reduce particledeposition on certain critical surfa

17、ce. Furthermore, the inte-grated effect of medical lamp position and diffuser dischargevelocity on ventilation performance in an operating room hasbeen investigated (Chow et al. 2006). The dispersion of infec-tious particles from both surgical team and patient were simu-lated through CFD analysis as

18、 well.Field-measurement is essential to assure the operatingroom performs correctly and achieves the contamination stan-dards. The biological contamination control strategies underdifferent models in operating room has been simulated andthen compared with filed measurement, to check the accept-able

19、level of consistency (Zhang et al. 2008). Besides, bioaero-sol characteristics related to human dispersion were evaluatedextensively based on field tests data in hospital cleanroomwith different class levels (Li and Hou 2003). Furthermore,particle counts and microbial counts during 105 operatingproc

20、edures under laminar air flow condition were surveyedand investigated to assure the high air quality in operatingroom (Hansen et al. 2005). Some valuable informationdescribing cleanroom measurement to evaluate the overallperformance of cleanroom can be found in literature (IEST.1993). General princi

21、ples and methods on bio-contaminationcontrol of cleanroom are described extensively in the stand ofISO. 14698 (ISO 2003). Besides, the essential information ondesign consideration, equipments and comprehensive proce-dures for certified testing of cleanrooms were reported inNEBB (1996).Although much

22、research has been done on CFD simula-tion as well as for field measurement for operating rooms, littlequantitative information is available on compromise ofcontamination control and energy saving potential. In thisstudy, the strategic approach on performance improvement ofthe HVAC system for an oper

23、ating room will be investigated.Variable speed driven strategy was also performed to verifythe potential of energy-saving opportunity under specifiedcontamination standards. A physical partition curtain has beenconducted auxiliary around the HEPA filter of an operatingroom to validate the improvemen

24、t of air distribution andcontamination control. Both numerical simulation and fieldmeasurement of a full-scale operating room will be carried outin a district hospital in Taiwan. The performance of contami-nation control could be evaluated comprehensively not onlyby airflow distribution but also con

25、centration profile underdifferent curtain length and different face velocity provided byinverter-driven fan unit. Besides, the variation of temperatureand humidity for the operating room will be monitored on siteto evaluate the effect induced by reducing the face velocity ofHEPA filters.SYSTEM DESCR

26、IPTIONThe schematic diagram of HVAC system for the investi-gated operating room is shown in Figure 1. Supply air flowfrom outside air handling unit (OAHU) is provided to the oper-ating room through 12 pieces of HEAP filters above surgerytable. Return air flow is recirculated through four return airg

27、rilles located at four corners of the operating room byconducting constant air volume (CAV) recirculating air hand-ing unit (RAHU). An inverter with variable frequency driveswas installed to examine the performance variation andenergy-saving potential under different face velocity of HEPAfilter. The

28、 investigated operating room with the dimension oflength 6.2 m (20.3 ft), width 4.8 m (15.7 ft), and height 3.7 m(12.1 ft) respectively.This investigated operating room with cleanliness levelclass 10,000 (ISO class 7) is equipped with 12 pieces of highefficiency particulate air (HEPA) filters at the

29、 filtration effi-ciency over 99.97% (above 0.5 m). The supply air coveragearea consists of 12 pieces of HEPA filters at 1.2 m 0.6 m (4 ft 2 ft) with a medical lamp located at the center of HEPA filterscoverage. Specified design conditions are temperature 20 2C (68F), humidity 55 5 (% RH) and the pre

30、ssurization of10 2.5 Pa. The colony forming unit (cfu) for microbial countsless than 175 cfu/m3(5 cfu/ft3) is specified. To establish theexact geometrical model for simulation, three surgical staffmembers and some equipment including surgery appliance,cabinet and computer were assumed in the operati

31、ng room.The patient lies on the operating table just under two medicallamps. The full-scale geometric layout of the investigatedoperating room is shown in Figure 2. A physical partitioncurtain with length of L around the HEPA filter coverage isassumed to investigate the performance improvement ofair

32、flow distribution and contamination control.Figure 1 Schematic diagram of the investigated operatingroom. 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

33、 reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. 76 ASHRAE TransactionsNUMERICAL SIMULATIONThe Computational fluid dynamics (CFD) technique hasbeen proven to be very powerful and efficient in parametricstudies of

34、airflow distribution and concentration profile. In thisstudy, a commercial CFD code, STAR-CD (2001), was used tosimulate the airflow distribution and concentration contour ofthe operating room accordingly. It will examine the improve-ment of operating room configuration without interfering withnorma

35、l processes. The governing equations solved by STAR-CD include the three-dimensional time-dependent incompress-ible Navier-Stokes equation, time dependent convection diffu-sion equation and k- turbulence equations. These formulatedequations can be found in the STAR-CD users manual (2001)as well as a

36、ny CFD text books and will not be repeated here. Thewell-known finite control volume method with a PressureImplicit with Splitting of Operator (PISO) algorithm wasadopted to solve all the governing equations simultaneously.After solving the velocity field, the transient simulation ofconcentration fi

37、eld was conducted and concentration decaymethod based on mass concentration equation accordingly.To evaluate the energy-saving potential under differentface velocity of HEPA filter, the performance improvementstrategy with a physical partition curtain was proposed and ana-lyzed by numerical simulati

38、on. It was assumed that the air flowfield is homogenous, isotropic and three-dimensional. Thetemperature and face velocity of the HEPA filters have beenmeasured through field tests using a multi-function hot-wiredanemometer to provide reliable measurement data as theboundary conditions of CFD simula

39、tion. Furthermore, all ofthe boundary conditions for solution domain were clearly de-fined according to the actual field tests data to carry out theaccurate solutions. The face velocities of HEPA filter were keptat 0.2 m/s (40 fpm), 0.25 m/s (50 fpm) and 0.3 m/s (60 fpm) andcould be achieved by on-s

40、ite adjusting the frequency of inverterat field test stage. The supply air temperature was maintainedat 288 K (15C or 59F). All the persons including surgery staffand patient are modeled as heated cuboids with a size and con-vective heat output that correspond to the actual level of heatsupply repor

41、ted in literature (Chow et al. 2006). Typically, theno-slip condition was applied on the solid walls and physicalpartition curtain around HEPA filter since they were not perme-able. The concentration-decay simulation was adopted by assum-ing the initial contamination concentration of CO2at 3000 ppmi

42、n the operating room. Background CO2concentration levelwas presumed at 415 ppm according to CO2 concentration ofoutdoor provided by Environment Protection Administrationof Taiwan. Numerical simulation of different approaches toimprove performance of the operating room was conductedand assessed compr

43、ehensively. All the calculation based onnumerical simulation will be compared and analyzed with fieldtest data of particle counts as well as microbial counts.FIELD MEASUREMENTField tests were conducted not only to provide reliabledata for simulation but also to verify the simulation results forasses

44、sment of performance improvement of the operatingroom. The particle counts of eight sampling locations werecarried out at specified position of the operating room. Quan-tities tests of airborne particle counts were performed with aMet-One Model 3313 particle counter, sensitive to particleslarger the

45、n 0.5 m. Three times of measuring at each samplinglocation were conducted for accuracy and repeatability. Thesampling flow rate for particle counter operates at 28.3 l/min(1 ft3/min) with sampling period of 1 minute. Furthermore, toverify the numerical results on concentration of contamina-tions and

46、 ventilation performance, microbial counts have beenconducted as well with a Merck MAS-100 impaction sampler.The active sampling methods impact the microbe-carryingparticles onto an agar surface with 100 liters (3.53 ft3) ofsampling air per minute. Bacteria were incubated for 48 hoursat 35C (95F) in

47、 an incubator, colonies are counted and hencethe number of colony forming unit (cfu) can be ascertainedaccordingly. The impaction sampler was disinfected and waswiped with alcohol before every measurement.A TSI Model 8386A digital manometer was employedto monitor the pressure difference of the clean

48、room closurefor contamination control concern during reducing the facevelocity. The variation of temperature and humidity at returnair grille were recorded by a multi-channel data logger(YOKOGAWA, Model MV100) with several temperature andhumidity transmitters. Tests of temperature at accuracy of0.2C

49、 and humidity at accuracy of 2% RH were performedcontinuously for at least one hour under different measure-ment case. All instruments used in this study were calibratedregularly according to the manufactures instructions.Figure 2 Geometric model for simulating the operatingroom. 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 is not permitted witho