Air Grilles Research Articles

Air dispersal of multi-drug-resistant organisms including meticillin-resistant Staphylococcus aureus, carbapenem-resistant Acinetobacter baumannii and carbapenemase-producing Enterobacterales in general wards: surveillance culture of air grilles

The environmental surveillance of air grilles in clinical areas has not been systematically analysed. Samples were collected from frequently touched items (N= 529), air supply (N= 295) and exhaust (N= 184) grilles in six medical and 11 surgical wards for the cultures of multi-drug-resistant organisms (MDROs): meticillin-resistant Staphylococcus aureus (MRSA), carbapenem-resistant Acinetobacter baumannii (CRAB) and carbapenemase-producing Enterobacterales (CPE), and isolates were selected for whole-genome sequencing (WGS). The contamination rates were correlated with the colonization pressures of the respective MDROs. From 3rd October to 21st November 2023, 9.8% (99/1008) of the samples tested positive, with MRSA (24.2%, 24/99), CRAB (59.6%, 59/99) and CPE (2.0%, 2/99), being the only detected MDROs. The contamination rate in air exhaust grilles (26.6%, 49/184) was significantly higher than in air supply grilles (5.8%, 17/295; P<0.001). The contamination rate of air exhaust grilles with any MDRO in acute medical wards (73.7%, 14/19) was significantly higher than in surgical wards (12.5%, 4/32; P<0.001). However, there was no difference in the contamination rate of air exhaust grilles between those located inside and outside the cohort cubicles for MDROs (27.1%, 13/48 vs 28.8%, 30/104; P=0.823). Nevertheless, the weekly CRAB colonization pressure showed a significant correlation with the overall environmental contamination rate (r= 0.878; 95% confidence interval (CI): 0.136-0.986; P=0.004), as well as with the contamination rate in air supply grilles (r= 0.960; 95% CI: 0.375-0.999; P<0.001) and air exhaust grilles (r= 0.850; 95% CI: 0.401-0.980; P=0.008). WGS demonstrated clonal relatedness of isolates collected from patients and air exhaust grilles. Air grilles may serve as MDRO reservoirs. Cohort nursing in open cubicles may not completely prevent MDRO transmission through air dispersal, prompting the consideration of future hospital design.

Performance improvement of a biotechnology vaccine cleanroom for contamination control

Cleanrooms play an important role in various industries, such as pharmaceuticals, specifically for vaccine cleanrooms by strictly regulating contaminants, temperature, humidity, and pressure to ensure product reliability, particularly in critical areas. This study investigates a biotechnology vaccine cleanroom using a comprehensive field measurement test and numerical simulation analysis. Field measurements were conducted during the at-rest and operational occupancy states. As a result, it was discovered that the operational condition has a higher concentration than the at-rest condition. To mitigate this issue, the numerical simulation improvement strategy employed in this study aimed to reduce the concentration under operational conditions. The strategy proposed in this simulation is determining the ventilation rate and arranging the outlet air grilles. To assess and evaluate the performance of the cleanroom, we utilized ventilation and removal efficiency metrics. These indices served as important metrics for evaluating the cleanroom's efficiency in controlling contaminants. In at-rest conditions, ventilation and removal efficiency were 90.0 % and 86.2 %, respectively. However, under operational conditions, these metrics dropped to 81.3 % and 80.1 %, respectively, in the baseline case. After the proposed improvement design, the ventilation and removal efficiency in the operational condition could improve by up to 6.8 % and 5.2 %, respectively. A proper arrangement of outlet air grilles could control the decrease in concentration. In addition, a higher ventilation rate also could decrease the concentration. However, it caused high energy consumption. Therefore, the ventilation rate must be designed optimally to compromise contamination control and energy saving.

Long-range air dispersion of Candida auris in a cardiothoracic unit outbreak in Hong Kong

Nosocomial outbreaks of Candida auris, a multidrug-resistant fungus, are increasingly reported worldwide; the mode of transmission has usually been reported to be via direct contact. Some studies previously suggested potential short-distance air dispersal during high-turbulence activities, but evidence on long-range air dispersal remains scarce. To describe a C.auris nosocomial outbreak involving two wards (H7, 5E) in two local hospitals. Samples were taken from patients, ward surfaces (frequently touched items and non-reachable surfaces) while settle plates were used for passive air sampling to investigate possible contributions by direct contact and air dispersal. Epidemiological and phylogenetic analyses were also performed on the C.auris isolates from this outbreak. Eighteen patients were confirmed to have asymptomatic C.auris skin colonization. C.auris was expectedly identified in samplings from frequently touched ward items but was also isolated in two samples from ceiling supply air grilles which were 2.4m high and inaccessible by patients. Moreover, one sample from a corridor return air grille as far as 9.8m away from the C.auris cohort area was also positive. Two passive air samplings were positive, including one from a cubicle with no confirmed cases for four days, suggesting possible air dispersal of C.auris. Whole-genome sequencing confirmed clonality of air, environment, and patients' isolates. This is the first study to demonstrate potential long-range air dispersal of C.auris in an open-cubicle ward setting. Ventilation precautions and decontamination of out-of-reach high-level surfaces should be considered in C.auris outbreak management.

Air Grilles Designed to Prevent Backflows in Natural Ventilation Stacks – Experimental Investigation

Abstract The paper presents the results of the experimental research on the air grills designed to stop backflows in natural ventilation stacks. For each grill pressure drop was measured for different airflow rates, in both flow directions. Two ∅ 100 mm grills working on different principles were tested: one with moving flaps, and one shaped in a way that should greatly increase the hydraulic losses during backflow. For comparison, the ordinary air grill was also tested. The results show that the grill with moving flaps works as intended. With only slightly higher hydraulic losses in the forward direction compared to ordinary grill, it shuts off the backflows almost completely. The other, diffuser-shaped grill doesn’t work as intended. It has very high hydraulic losses in both directions, and the effect of changing the air resistance with the reverse flow is barely noticeable.

Strategies to Enhance Contamination Control Performance through Ventilation Improvement in a Biosafety Laboratory Building

A biosafety level (BSL) laboratory is a set of biocontainment preventative measures used to prevent and isolate hazardous biological agents or their accidental release in a laboratory. It is vital to provide a negative-pressurized environment for disease infection control. The experimental equipment layout may affect the personnel’s exposure to infection. However, the equipment layout and exhaust air grilles were in a fixed position in this investigated BSL. Due to retrofitting, the layout arrangement of HEPA as supply air is investigated numerically. Computational Fluid Dynamics (CFD) simulation is conducted to analyze and determine a better design for contamination control. This study proposes three ventilation arrangements as an alternative design, including vertical arrangement, horizontal arrangement, and L-shaped ventilation arrangements (instead of the supply being arranged in a single line). In addition, the airflow distribution, concentration decay, air of age, ventilation, and removal effectiveness are all examined in the study. The numerical simulation results were verified by a field measurement test. The results revealed that the L-shaped ventilation arrangement for supply air diffusers would achieve better ventilation and removal efficiency. The local mean age of air was also identified as the most satisfactory ventilation performance measure, as it shows the level of contaminant control. It also indicated that ventilation could be improved by arranging the supply air layout with less expenditure through CFD-aided simulation in identifying strategies for best practices for the design stage to reduce the running cost at full operation.

Factors influencing indoor air pollution in buildings using PCA-LMBP neural network: A case study of a university campus

This study investigated indoor air quality (IAQ) and its association with building characteristics and environmental factors in eleven different campus buildings in Gainesville, Florida. Integrated indoor and outdoor sensor systems are built and installed to measure the levels of airborne particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), ozone (O3), relative humidity (RH), and temperature continuously in 10 min intervals for two weeks for each case building. Twenty building-related characteristics were collected through a walkthrough-based survey, HVAC historical data, and construction drawings. Through these data, a PCA-assisted Levenberg-Marquardt Backpropagation (LMBP) neural network model was developed for rapidly and accurately analyzing and predicting the interaction between IAQ and its affecting factors. Factors with significant contributions to indoor exposure were may mostly be determined by outdoor sources. This is evidenced by the strong associations that were found between indoor PM(2.5-10) and O3 values and their corresponding outdoor values and factors, including distance from the major traffic (DFMT), cracks occurring, outdoor temperature, and humidity. Indoor NO2 concentrations were affected by DFMT, indoor O3, indoor RH, number of air grilles, room volume, and window-to-wall ratio. Also, the comparison shows that the PCA-LMBP model outperforms the traditional BP-ANN and multi-linear regression methods. The average values of 1.34, 2.53, and 4.86 were obtained for the root-mean-square error (RMSE) of PCA-LMBP, BP-ANN, and MLR models, respectively. These results can be accordingly referred for the follow-up studies that analyze IAQ in similar building and environmental conditions.

Improvement of Airflow Distribution and Contamination Control for a Biotech Cleanroom

The biotech cleanroom industry presents a biological basis for living organisms or their components (bacteria or enzymes) to produce helpful medicine. However, biotech industries such as vaccine production need a clean critical environment and contamination control that is always a vital concern for the manufacturing process. This study investigates a biotech cleanroom through a comprehensive field measurement and numerical simulation. The field measurement test results conformed to the design specification to satisfactorily meet with the cleanroom standard of PIC/S and EU GMP. Furthermore, the field measurement data were used as a basic validation and boundary condition for numerical simulation. The numerical simulation results revealed that the concentration distribution in case 1 as a baseline case showed satisfactory results, with a removal efficiency of 75.2% and ventilation efficiency of 80%. However, there was still a high concentration accumulated in certain areas. The improvement strategy was analyzed through non-unidirectional flow ventilation with different face velocities and by adding one return air grille for case 2 and two return air grilles for case 3. The results revealed that case 2 presented the best results in this study, with a removal efficiency of 86.7% and ventilation efficiency of 82% when supplying air velocity at 0.2 m/s. In addition, increasing the supply air velocity to 0.3 m/s could enhance removal ventilation by around 19% and ventilation efficiency by around 5%.

Ventilation Performance Evaluation of a Negative-Pressurized Isolation Room for Emergency Departments.

Due to the emergence of COVID-19 becoming a significant pandemic worldwide, hospitals are expected to be capable and flexible in responding to the pandemic situation. Moreover, as frontline healthcare staff, emergency department (ED) staff have a high possibility of exposure risk to infectious airborne. The ED isolation room will possibly and effectively isolate the infected patient, therefore safekeeping frontline healthcare staff and controlling the outbreak. However, there is still limited knowledge available regarding isolation room facilities specifically for the emergency department. In this study, field measurement is conducted in an ED isolation room located in Taiwan. CFD simulation is employed to simulate and investigate the airflow and airborne contaminant distribution. Instead of high air-change rates (ACH) that purposes for dilution, this study proposes the arrangement of exhaust air grilles to improve the contaminant removal. The results reveal that the exhaust air grille placed behind the patient’s head is optimized to dilute airborne contaminants.

Approaches for effective negative pressure isolation space control to minimize airborne transmission of contaminants in residential homes

Controlling airborne transmission of contaminants including respired viruses such as SARS-CoV-2 is necessary to protect occupants living in the same house with a contagious person. The effectiveness of interventions requiring minor efforts that create a negative pressure isolation zone (IZ) for a contagious person has yet to be systematically tested for residential homes. In this study, ASHRAE Standard 170, which offers guidance for negative pressure isolation space control in healthcare facilities, was used in developing practical and attainable recommendations for residential single-family homes. The relative effectiveness of several control strategies was evaluated through experimentally conducting 17 different test cases in a manufactured single-family house laboratory. These cases were designed based on various heating, ventilation and air-conditioning (HVAC) operating scenarios, intervention measures including closing the IZ door and/or sealing over supply and return air grilles in the IZ, and utilization of bathroom exhaust or portable window fans for pressure control. Four out of 17 test cases were identified as having the potential for strong containment with adequate depressurization in the IZ. The most effective IZ depressurization was achieved through continuously operating the exhaust fan in the bathroom attached to the IZ, by installing a portable window fan that extracted air out of the IZ, and a portable room air conditioner with the AC unit exhaust duct installed in one of the IZ windows.

Investigation of Airflow Distribution and Contamination Control with Different Schemes in an Operating Room

Controlling contamination via proper airflow distribution in an operating room becomes vital to ensure the reliable surgery process. The heating, ventilation, and air conditioning (HVAC) systems significantly influence the operating room environment, including temperature, relative humidity, pressurization, particle counts, filtration, and ventilation rate. A full-scale operating room has been investigated extensively through field measurements and numerical analyses. Computational fluid dynamics (CFD) simulation was conducted and verified with the field measurement data. The simulation was analyzed with three different operating room schemes, including at-rest conditions (case 1), normal operational conditions with personnel (case 2), and actual conditions with personnel inside and some medical equipment blocking the return air (case 3). The concentration decay method was used to evaluate this study. The results revealed that the contamination concentration in case 1 could be diluted quickly with the average value of 404 ppm, whereas the concentration in case 2 slightly increased while performing a surgery with the average value of 420 ppm. The return air grilles in case 3, blocked by obstacles from some medical equipment, resulted in the average concentration value of 474 ppm. Other than that, the contaminant dilution could be obstructed dramatically, which revealed that proper and smooth airflow distribution is essential for contamination control. The ventilation efficiency of case 2 and case 3 dropped around 6% and 17.91% compared to case 1 in the unoccupied and ideal condition. Ventilation efficiency also decreased along with decreasing the air change rate per hour (ACH), while with increasing ACH, the ventilation efficiency in case 3 actually increased, approaching case 2 in the ideal condition.

Coughed droplet dispersion pattern in hospital ward under stratum ventilation

This study aims to investigate the characteristics of coughed droplet dispersion in hospital wards under stratum ventilation (SV). The dynamic dispersion process of the coughed droplets and the spatial distribution of the droplets in a two-bed ward under SV are investigated, considering the initial size and evaporation of the droplets. For SV, the supply air grilles are on the wall opposite the patients with the centre height at 1.5 m above the floor, the exhaust diffusers are on the lower part of the wall near the patients, and the air change rate is 12 ACH. For comparison, displacement ventilation (DV) and mixing ventilation (MV) are also discussed. The RANS-based RNG k-ε model is applied to solve the flow field. The Lagrangian approach is applied to solve the droplet motion. The exposure risk in the ward is less under SV because (a) The horizontal airflow leads to a strong deposition at the initial dispersion stage that decreases droplet concentration. With the infector in the supine and sitting positions, 68% and 49% of the coughed droplets are deposited on indoor surfaces in 10 s, respectively. (b) The air jet directly supplied to the breathing zone dilutes local droplet concentration. Compared with DV and MV, SV has better control over the 50 μm diameter droplet because the higher airflow velocity under SV could increase the deposition of the 50 μm diameter droplet. Controlling the droplet dispersion in the initial stage is more efficient to improve the infection control performance of SV.

The effects of acoustical ceiling panel type and penetrations forservices on vertical sound isolation inside buildings

Attenuation of sound transmitting between rooms oriented over one another inside buildings is studied. Transmission loss and sound transmission class were measured by an independent, accredited, acoustics laboratory with and without a variety of modular acoustic ceilings suspended under a baseline concrete floor structure. Ceiling panel material types include stone wool, fiberglass and mineral fiber. Ceilings were tested with and without the presence of service penetrations for supply air diffusers, return air grilles and light fixtures. Some ceilings were also scanned with a sound intensity probe and the resulting color sound maps are used as supplemental method of evaluating both isolation and absorption performance of the individual components of the ceiling systems. Results show that while the effects of ceiling panel type on absorption performance, and thus room acoustics, is substantial, the material type and weight of the ceiling panels do not substantially affect the overall isolation performance of the floor-ceiling assembly.

The effects of acoustical ceiling panel type and penetrations for services on vertical sound isolation inside buildings

Attenuation of sound transmitting between rooms oriented over one another inside buildings is studied. Transmission loss and sound transmission class were measured by an independent, accredited, acoustics laboratory with and without a variety of modular acoustic ceilings suspended under a baseline concrete floor structure. Ceiling panel material types include stone wool, fiberglass and mineral fiber. Ceilings were tested with and without the presence of service penetrations for supply air diffusers, return air grilles and light fixtures. Some ceilings were also scanned with a sound intensity probe and the resulting color sound maps are used as a supplemental method of evaluating both isolation and absorption performance of the individual components of the ceiling systems. Results show that while the effects of ceiling panel type on absorption performance, and thus room acoustics, is substantial, the material type and weight of the ceiling panels do not substantially affect the overall isolation performance of the floor-ceiling assembly.

Improving Thermal Comfort in Aircraft Cockpit Based on Optimization of Supply Air Grille

Pilot’s thermal comfort and performance are directly affected by air flow field and temperature field in cockpit. A three-dimensional cockpit model of a certain civil aircraft is established, and the distribution of air velocity and temperature is obtained with the method of computational fluid dynamics (CFD). Aiming at the problems of high local air speed and uneven temperature distribution in the cockpit, two new supply air grilles are proposed. The results show that one of the grilles can obviously optimize air flow field and temperature in the cockpit and improve the thermal comfort of the pilots.

Nosocomial Outbreak of Coronavirus Disease 2019 by Possible Airborne Transmission Leading to a Superspreading Event.

BackgroundNosocomial outbreaks with superspreading of COVID-19 due to a possible airborne transmission has not been reported.MethodsEpidemiological analysis, environmental samplings, and whole genome sequencing (WGS) were performed for a hospital outbreak.ResultsA superspreading event involving 12 patients and 9 healthcare workers (HCWs) occurred within 4 days in 3 of 6 cubicles at an old-fashioned general ward with no air exhaust built within the cubicles. The environmental contamination by SARS-CoV-2 RNA was significantly higher in air grilles (>2m from patients’ head and not reachable by hands) than high-touch clinical surfaces (36.4%, 8/22 vs 3.4%, 1/29, p=0.003). Six (66.7%) of 9 contaminated air exhaust grilles were located outside patient cubicle. The clinical attack rate of patients was significantly higher than HCWs (15.4%, 12/78 exposed-patients vs 4.6%, 9/195 exposed-HCWs, p=0.005). Moreover, clinical attack rate of ward-based HCWs was significantly higher than non-ward-based HCWs (8.1%, 7/68 vs 1.8%, 2/109, p=0.045). The episodes (mean ± S.D) of patient-care duty assignment in the cubicles was significantly higher among infected ward-based HCWs than non-infected ward-based HCWs (6.0±2.4 vs 3.0±2.9, p=0.012) during the outbreak period. The outbreak strains belong to SARS-CoV-2 lineage, B.1.36.27 (GISAID Clade GH) with the unique S-T470N mutation on WGS.ConclusionThis nosocomial point source superspreading due to possible airborne transmission demonstrated the need for stringent SARS-CoV-2 screening at admission to healthcare facilities and better architectural design of the ventilation system to prevent such outbreaks. Portable high-efficiency particulate filters were installed in each cubicle to improve ventilation before resumption of clinical service.

Air heating system design for a sub-Arctic climate using a CFD technique

The thermal comfort in a residential building equipped with an air heating system and located in a sub-Arctic region was investigated with computational fluid dynamics (CFD) software. The predicted percentage of dissatisfied (PPD) was used to identify flaws with the heating system during winter conditions. New scenarios were simulated and compared to each other to see potential improvements of the thermal indoor climate. Comparison was done by combining the discomfort spaces inside rooms, the level of the discomfort and the time spent in these spaces. The discomfort covered 8–38% of the interior volume depending on the test case.The results provide the necessary means to create a satisfactory thermal indoor climate if an air heating system is to be utilized in sub-Arctic regions during the winter. The correct heat demand for each floor and appropriate placement of the supply devices are required. Adding air transfer units or grilles in rooms from which exhaust air is removed further improves the comfort. The results also show the strength of using CFD technique when investigating the indoor discomfort with PPD, and how a fair assessment can be done by combining the PPD with time.

Investigation on the contaminant distribution with improved ventilation system in hospital isolation rooms: Effect of supply and exhaust air diffuser configurations

This study, that is practice-based learning in a real hospital construction project, has evaluated the ventilation performance of three strategies in the protection of health care workers and HVAC control for airborne infectious diseases induced by contaminated exhaled air from patients in a negative pressure isolation room. This paper examines air flow path and airborne pollutant distribution by computational fluid dynamics modeling and field measurement. In hospitals, the risk of virus diffusion mainly depends on air flow behavior and changes in direction caused by supply air and exhaust air locations. An improved isolation room ventilation strategy has been suggested, and is found to be the most efficient in removing contaminants based on the observations and simulation results from three ventilation systems. The results show that ventilation systems utilizing the “low-level extraction” technique are very effective at removing pollutants in the human breathing zone. A new clean isolation room ventilation strategy has been developed that employs two exhaust air grilles on the wall behind the bed at low floor level, coupled with a fan filter unit, and is found to have the highest pollutant removal efficiency.

Development of outdoor pollution free zone by fan-assisted devices

Vertical City Air Purification System was designed to reduce the aerosol counts at the playground next to a major traffic road. Columns with air grilles are arranged in circle to create a close loop system. Computational simulation is adopted to study three scenarios. The first simulation covers conventional wind block technology, where strong wind speed is created between columns to stop pollutants from entering the premise. However, it is observed that polluted air can enter the development from the head above. Hence, two other options are created, one with supply air directing to the centre of the development, the other with underfloor air supply. It is studied that at outlet velocity of 6.5 m/s, the underfloor system can contribute to around 40% pollution reduction using MERV13 filter, which is more than 24% better than the baseline. Traditionally, outdoor pollution mitigation deems to be contributing insignificantly. The positive simulation result marks a potential for future outdoor pollution mitigation development.

Effects of noise flanking paths on ceiling attenuation class ratings of ceiling systems and inter-room speech privacy

Continuous plenums above suspended, modular ceilings and partial-height walls in buildings can result in inter-room speech privacy and annoyance problems, especially when noise flanking paths via air diffusers, grilles, and lights exist. However, testing of the effects of ceiling system noise flanking paths is limited in the industry. Multiple ceiling systems comprised of various noise flanking paths through air diffusers, grilles, and lights were tested in an independent, accredited, acoustics laboratory according to ASTM International (ASTM) E-1414 and E-413. Additionally, recorded speech was played back in the test chamber source room and binaurally recorded in the test chamber receiver room. The results show that wideband ceiling attenuation class (CAC) decreases by 10 decibels (dB) and 1/3 octave band normalized ceiling attenuation (Dn,c) decreases by 15 to 22 dB in the higher frequency bands when common noise flanking paths are introduced into a ceiling system with CAC-37 ceiling panels. Subjective listening during the course of these tests shows that a ceiling system comprised of CAC-37 panels and typical noise flanking paths (that drop the system rating down to CAC-27) did not provide speech privacy. Intelligibility of recorded speech transmitting into the receiver room was high.

Developing an innovative fan dry coil unit (FDCU) return system to improve energy efficiency of environmental control for mission critical cleanrooms

Traditional wall-return re-circulation air systems with ceiling-supply and wall-return air grilles are fairly common in non-unidirectional airflow industrial cleanrooms. Such re-circulation systems normally have longer airflow circulation pathways, which inherently induced higher airflow resistance, resulting in higher fan power demand per unit of airflow rate delivered. To overcome the airflow resistance, Fan Filter Units (FFUs) used in the traditional wall-returned re-circulation system are designed to operate with high external pressures, which also induce high negative pressures in supply air plenums (SAP). The negative pressures within SAP can increase the risks of infiltration of outdoor air and contaminants. A longer airflow pathway corresponds to a higher level of negativity of the air pressure inside the supply air plenum, thus inducing higher risks of cross-contamination. To overcome the above-mentioned drawbacks, a new re-circulation system using fan dry coil unit (FDCU) was proposed. This new system exhibits shorter air re-circulation paths while providing effective environmental controls (e.g., removal rate of 0.1μm particle and temperature control) for a cleanroom. In this study, experiments were conducted in a full-scale cleanroom to investigate the energy performance of applying the innovative FDCU-return system, compared to a traditional wall-return system. Results showed that the FDCU-return system can increase energy efficiency and reduce the electric energy consumption by more than 4% compared to the wall-return system.