ASHRAE LV-11-C069-2011 Performance Evaluation of Indoor Environment Parameters for an Unoccupied Operating Room.pdf

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1、 Fu-jen Wang is associate professor and Zhuan-yu Liu is graduate student in the Department of Refrigeration, Air Conditioning and Energy Engineering, National Chin-Yi University of Technology, Taiwan. Chi-ming Lai is assistant professor in the Department of Civil Engineering, National Cheng-Kung Uni

2、versity, Taiwan. Tsung-jung Cheng is associate professor in the Department of Architecture, Feng Chia University, Taiwan. Performance Evaluation of Indoor Environment Parameters for an Unoccupied Operating Room Fu-Jen Wang, PhD, PE Chi-Ming Lai, PhD, PE Member ASHRAE Member ASHRAE Tsung-Jung Cheng,

3、PhD, PE Zhuan-Yu Liu Student Member ASHRAE ABSTRACT The HVAC systems for operating rooms are energy-intensive and sophisticated in that they operate 24 hours per day year-round and use large amount of fresh air to deal with infectious problems and to dilute microorganisms. However, little quantitati

4、ve information has been investigated about trade-off between energy-efficient HVAC system and indoor environment quality especially when the operating room is not occupied. The objective of this study is to present the field measurement approach on performance evaluation of the HVAC system for an un

5、occupied operating room. Variable air volume terminal boxes were conducted to verify the compromise of energy-saving potential and indoor environment parameters including particle counts, microbial counts, pressurization, temperature and humidity. Field measurements of a full-scale operating room ha

6、ve been carried out at a district hospital in Taiwan. Numerical simulation has been applied to evaluate the air flow distribution and concentration contours while conducting the velocity reduction approach in the unoccupied operating room. The results reveal that it is feasible to achieve satisfacto

7、ry indoor environment by reducing the supply air volume (or velocity) in the unoccupied operating room. Optimal face velocity of HEPA filter and percentage of damper opening for the variable air volume terminal boxes could be obtained through compromising of indoor environment quality control and en

8、ergy consumption as well. It will stimulate a more robust investigation of infection-controlled, energy-efficient and environment-comfortable HVAC system specific for unoccupied operating rooms. INTRODUCTION The purpose of the HVAC system for an operating room is not only to achieve thermal comfort

9、but also to control airborne contamination. It is vital and significant to consider energy-efficient strategy as well as to achieve an acceptable performance for contaminations control. A review of distribution patterns and air movement at operating room describing the importance of airborne particl

10、es in the infectious process were provided by Pereira et al. (2005). Comparative analysis of the efficiency of microbiological control of airflow system were demonstrated to identify the control strategy that could reduce the risk of contamination in operating infection. Chow et al. (2005) investiga

11、ted the ventilating performance against airborne infection on an extra-clean operating room. They also reported that the flow velocity at the supply diffuser was identified as one of the most important factors in governing the dispersion of airborne infectious particles. Besides, Landrin et al. (200

12、5) LV-11-C069 2011 ASHRAE 5572011. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions, Volume 117, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is

13、not permitted without ASHRAES prior written permission.conducted the research on the relationship between microbial counts and particle counts in the operating rooms. The results suggested that there was no reason to replace microbial counts with particle counts for routine evaluation of microbiolog

14、ical contamination in conventionally ventilated operating rooms. Furthermore, Cook et al. (2009) reported that vertical laminar flow might not behave predictably when laminar diffusers were used outside of cleanroom environment for which they were primarily designed. Therefore, it was essential to t

15、urn to air motion control to maximize air asepsis in the hospital operating room. Field tests are essential to assure the operating room performs satisfactorily and achieves the contamination standards. The performance investigation for the contamination control strategy in an operating room was con

16、ducted in our previous study (Wang et al., 2010). Both numerical simulation and field measurement of a full-scale operating room were carried out comprehensively. Optimal face velocity of high efficiency particulate air (HEPA) filter could be obtained through compromising of contamination control an

17、d energy consumption. General principles and methods on bio-contamination control of cleanrooms were described extensively in the standard of ISO 14698 (ISO, 2003). Besides, the essential information on measuring equipments and comprehensive procedures for certified testing of cleanrooms were report

18、ed in NEBB (1996). Furthermore, operating rooms required efficient HVAC system to secure the highly demanding indoor environment conditions. Balaras et al. (2007) reported that there were still opportunities for energy conservation without sacrificing overall thermal comfort through the summarized f

19、ield test data of indoor thermal conditions from 20 operating rooms. Besides, the common variable air volume (VAV) system was based on the constant static pressure in the main duct and the VAV units including the controller, air flow measureing equipment and the dampers. The fundamentals for a press

20、ure controlled VAV system design which took good indoor environment, and energy efficiency into account were presented comprehensively (Engdahl et al., 2003). Karunakaran et al. (2010) also conducted the research aimed to achieve enhanced energy conservation and better thermal comfort for space cond

21、itioning with the application of VAV system. Computational fluid dynamics (CFD) techniques were used routinely to predict airflow patterns and distributions of temperature and concentration for indoor environments (Sorensen et al., 2003). Wang et al. (2009) improved airflow distribution for cleanroo

22、m configuration using CFD simulation. Some options under a limited budget were identified with less trial-and-error effort when modifications of clearooms had to be conducted. Besides, Zhang et al. (2008) conducted the investigation of biological contaminant control stratgies under different ventila

23、tion models in the operating room by using CFD simulation. Results showed that improving airflow distribution could reduce particle deposition on certain critical surface. Furthermore, Chow et al. (2005) investigated the effect of medical lamp position and diffuser supply velocity on ventilation per

24、formance in an operating room. The dispersion of infectious particles from both surgical staff and patient was simulated through CFD analysis as well. Besides the influence of persons movements on contaminant transport during operation was examined by Brohus et al. (2006). A significant risk of cont

25、aminant transport from less clean zone to the ultra-clean zone was found. Results revealed it was possible to simulate the influence of movements using a relatively simple CFD model. Although many researches have been done on field measurement as well as for CFD simulation for operating rooms, littl

26、e quantitative information was available on compromise of indoor environment quality and energy saving potential especially when the operating room was not occupied. In this study, the field measurement approach on performance evaluation of the HVAC system for an unoccupied operating room will be in

27、vestigated. Fan-powered variable air volume terminal boxes were conducted to verify the compromise of energy-saving potential and indoor environment parameters including particle counts, microbial counts, pressurization, temperature and humidity. Different opening percentage of fan-power terminal bo

28、x were also examined to verify the potential of energy-saving opportunity and the varation of indoor environment parameter when the operating room was unoccupied. Both field measurement and numerical simulation of a full-scale operating room will be carried out in a district hospital. Besides, the e

29、ffects by reducing the face velocity of HEPA filters will be examined using CFD simulation and concentration decay method through compromising of indoor environment quality control and energy consumption as well. HVAC SYSTEM DESCRIPTION 558 ASHRAE TransactionsThe schematic diagram of HVAC system for

30、 the investigated operating room area is shown in Figure 1. There are 9 operating rooms which connected to an air handling unit (AHU) through main duct at 3rd floor of the hospital. Supply air flow from AHU is provided to each branch duct of the operating room. Fan-powered VAV terminal box is equipp

31、ed at each branch duct to regulate the thermal environment requirements for the operating rooms. The opening percentage of regulating damper is modulated according to the set point of operating room under various cooling load condition. An variable speed driven fan of the AHU is equipped to provide

32、energy-saving operation specific for various operating room occupancy. The inverter of supply fan can be regulated based on the static pressure sensor installed at the outlet of AHU in the main duct system. The layout of the investigated operating room is shown in Figure 2. Some medical equipment in

33、cluding anesthesia system, surgery appliance, cabinet and trolley were sketched in the layout as well. The dimension of the operating room is at length of 6.0m (19.8ft), width of 5.1m (16.8ft), and height of 3.0m (9.9ft) respectively. The investigated operating room with cleanliness level 10,000(ISO

34、 class 7) is equipped with 6 pieces of high efficiency particulate air(HEPA) filters at the filtration efficiency over 99.97% (above 0.5m). The supply air coverage area at the dimension of 3.8m2.4m (12.5ft7.9ft) consists of 6 pieces of HEPA filters with a medical lamp located at the center of HEPA f

35、ilter coverage at the dimension of 0.6m 0.6m (2ft2ft) for lamp holder. The operation table located at the center of operating room just under the coverage of HEPA filter. Three return air grilles and one exhaust air grilles with the dimension of 0.5m 0.3m (1.6ft1.0ft) are located at four corners of

36、the operating room about 0.3m above the ground level. Specified design condition for the operating room temperature 222 (72 ), humidity 455(%RH) and the pressurization of 62 Pa. The colony forming unit(cfu) for microbial counts less than 100 cfu/m (3 cfu/ft) is specified. Figure 1 Schematic diagram

37、of the HVAC system for operating room Figure 2 Layout of the investigated operating room 2011 ASHRAE 559FIELD MEASUREMENT To examine the indoor environmental parameters including temperature, humidity, pressurization particle count and microbial counts of this investigated operating room during unoc

38、cupied period, comprehensive field measurements were carried out at specified sampling locations. It was quite common for the HVAC system of operating room operated at full load condition even when it was unoccupied. By adjusting the opening percentage of damper for fan-powered unit, the filed measu

39、rement of energy consumption for AHU as well as the field test data of operating room were recorded simultaneously to evaluate the energy saving potential without sacrificing contamination control and indoor thermal requirement. All of the experiments were done during holiday in order not to interfe

40、re the normal operation procedure of the hospital. The specifications of apparatus for field measurement were summarized in Table 1. The particle counts and microbial counts of ten sampling points were carried out at specified sample locations of the operating room. Quantities tests of airborne part

41、icle counts were performed with a Met-One Model 3313 particle counter, sensitive to particles larger than 0.5m. Three times of measuring at each sampling location were conducted for accuracy and repeatability. The sampling flow rate for particle counter operated at 28.3 l/min (1 ft/min) with samplin

42、g period of 1 minute. Microbial counts were conducted as well with a Merck MAS-100 impaction sampler. The active sampling methods impacted the microbe-carrying particles onto an agar surface with 100 liters (3.53 ft) of sampling air per minute. Bacteria were incubated for 48 hours at 35 (95 ) in an

43、incubator, colonies were counted and hence the number of colony forming unit (cfu) could be ascertained accordingly. A TSI Model 8386A digital manometer was employed to monitor the pressure difference of the operating room closure for contamination control concern during conducting the face velocity

44、 reduction approach. The variation of temperature and humidity at return air grille were recorded by a multi-channel data logger (YOKOGAWA, Model MV100) with several temperature and humidity transmitters. Tests of temperature at accuracy of 0.2 and humidity at accuracy of 2% RH were performed contin

45、uously for at least one hour under different measurement case. The power consumption of the AHU system was measured using a power meter (HIOKI, model 3/69) with an uncertainty of 0.2% of the full scale. Table 1. Apparatus for field measurement Apparatus Model Probe Operative range Accuracy TSI-9555-

46、P Anemometer and manometer 0.25 -30 (m/s) -1245-3735 Pa 1% 1 Pa ALNOR-8386A Array anemometer 25 2500 (ft/min) 3% YOKOGAWA-MV100 PT-100 and humidity sensor 0 - 100 ( ), 0 - 100 (%RH) 0.2, 2%RH Met One-3313 Air dust particle counter 0.3,0.5,1,3,5,10 m 5%Merck-MAS-100 Impact microbial sampling 0 - 1000

47、 (liters/min) 4% HIOKI-3169-20/21 Power meter 0 - 600 Vrms, 0.5A5000A 0.2% NUMERICAL SIMULATION To evaluate the energy-saving potential and indoor environmental parameter under different face velocity of HEPA filter when the operating room was unoccupied, a commercial CFD code, STAR-CD (2001), was u

48、sed to simulate the airflow distribution and concentration contour of the operating room. The governing equations solved by STAR-CD include the three-dimensional time-dependent incompressible Navier-Stokes equation, time dependent convection diffusion equation and k- turbulence equations. These form

49、ulated equations can be found in the STAR-CD users manual (2001) as well as any CFD text books and will not be repeated here. The well-known finite control volume method with a Pressure Implicit with Splitting of Operator (PISO) algorithm was adopted to solve all the governing equations simultaneously. After solving the 560 ASHRAE Transactionsvelocity field, the transient simulations of concentration field were conducted and concentration decay method based on mass concentration equation could be obtained accordingly. It was assumed that the air flow field