Contaminant Removal Effectiveness Research Articles

Conversion of a regular patient room to negative pressure at Ancona university hospital (Italy). A combined experimental and numerical investigation

Negative pressure isolation rooms are employed to prevent the spread of infectious diseases to surrounding spaces. This study reports a combined experimental and numerical analysis aimed at reliably assessing the performance of hospital ventilation systems and effectively reducing the risk of airborne infections. The study appraises the enhancement of the safety conditions by retrofitting an existing, positive pressure room ventilation system with a negative pressure and recirculation one. The assessment consisted in experimental measurements of airborne particle concentration and Computational Fluid Dynamics (CFD) simulations with Lagrangian particle tracking of respiratory droplets. The ventilation performance improvement was quantified in terms of recovery rate, contaminant removal effectiveness, particle transfer toward adjacent spaces and probability of infection.Two experimental campaigns were carried out: an ISO standard recovery assessment and a test in real operational conditions. The negative pressure configuration significantly improved the safety inside the patient ward: the recovery rate for droplets with diameter larger than 5 μm increased by a factor three, and the contaminant removal effectiveness after 15 min increased from 45% to 81%. The numerical model for Computational Fluid Dynamics simulation was successfully validated, confirming the ability of the approach to reproduce the undergoing Physics. The negative pressure design eliminated the particle transmission to surrounding spaces, while 2.5% of the emitted respiratory droplets escaped the room in the original existing scenario. The probability of infection after 15 min exposure was reduced by a factor three and peak values reaching 15% were limited to the immediate vicinity of the patients.

Chemical and microbiological assessment of house-filtered water produced by household water filtration systems

Chemical characteristics and microbiological quality of filtered water generated from municipal water using mono-, di- and penta-stage (5-stage) filters, as well as disposed drain water were investigated. With the application of the household water penta filters, the total dissolved solids (TDS) of the filtered water were highly reduced (0.04–0.07 g/L) and, consequently, electrical conductivity also decreased. Furthermore, total hardness was completely removed (0–2 mg CaCO3/L), as well as the chloride content. In the same manner, the nitrate content in the filtered water resulted from the household water penta filters decreased significantly (0.5–0.9 mg/L). Cations, such as Na+ and K+, in the filtered water were greatly affected and were 18–28 and 2 mg/L, respectively. Filtered water generated from the house-water penta filters was not in compliance with the daily amounts of F, Na and K necessary for teenagers and kids, and it might cause a risk of deficiencies. From the microbiological point of view, the penta-stage filter effectively removed total bacterial counts and total coliforms from water making it completely safe for potable and other domestic uses. The home water mono- and di- filters had low effectiveness of contaminant removal.

Impact of displacement ventilation and underfloor air distribution systems on concentrations of indoor particle in different seasons

The particle motion in a room is affected by the thermal environment and the air supply conditions caused by seasonal changes. In the study, a Lagrangian discrete trajectory model combined with the Eulerian fluid method was adopted to simulate the characteristics of indoor airflow and the diffusion of two typical indoor particles with considering different air supply conditions in different seasons. Specifically, the thermal comfort perception, draught rating (DR) of the indoor personnel, and the contaminant removal effectiveness (CRE, ε) of indoor particles under the influences of displacement ventilation (DV) and underfloor air distribution (UFAD) systems were investigated. The results revealed that when considering the indoor thermal comfort under summer and winter air supply conditions, UFAD was found be more effective than the DV system in protecting the temperature difference of indoor personnel. Additionally, the removal effect of PM1 in the breathing area was superior compared to that of the DV system. Regarding the removal effectiveness of PM2.5, the removal performance of both ventilation systems decreased, but the removal effect of the DV system on PM2.5 in the breathing area (with the largest εl of 1.55) was significantly better than that of the UFAD system under winter operating conditions. It is essential for the selection of the ventilation system to consider the thermal comfort of indoor occupants, as different ventilation systems have varying capabilities to remove particles of different sizes. Therefore, choosing an appropriate ventilation system is crucial for enhancing indoor air quality, and the findings of this study provide a basis for improving indoor air quality.

Integrated Phytobial Remediation of Dissolved Pollutants from Domestic Wastewater through Constructed Wetlands: An Interactive Macrophyte-Microbe-Based Green and Low-Cost Decontamination Technology with Prospective Resource Recovery

Macrophytes have the potential to withstand pollutant-induced stress and can be used to clean contaminated water using phyto-extraction, phyto-degradation, phyto-filtration, phyto-stimulation, and phyto-volatilization technique(s). Phytoremediation through constructed wetlands (CWs) for eliminating inorganic and organic pollutants from household sewage and wastewater has attracted scientific attention. CWs are artificially engineered treatment systems that utilize natural cycles or processes involving soils, wetland vegetation, and plant and soil-associated microbial assemblages to remediate contaminated water and improve its quality. Herein, we present a detailed assessment of contaminant removal effectiveness in different CW systems, i.e., free-water surface or surface-flow constructed wetlands (FWSCWs/SFCWs), subsurface-flow constructed wetlands (SSFCWs), and hybrid constructed wetlands (HCWs). Several wetland floral species have been reported as potential phytoremediators, effectively reducing aquatic contamination through biodegrading, biotransforming, and bioaccumulating contaminants. Water hyacinth (Pontederia crassipes) is one of the most resistant macrophytes, capable of tolerating high nitrate (NO3−) and phosphate (PO42−) concentrations. Other aquatic weeds also effectively alleviate biological oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), and pathogen levels and ameliorate the impact of different ionic forms of nitrogen (N), phosphorus (P), and trace elements (TEs). The review primarily focuses on using hydrophyte(s)-microbe(s) associations in different CWs as an essential phytoremediation tool for sustainable management of freshwater ecosystems, ecorestoration, and prospective resource recovery, favoring a circular bioeconomy (CBE).

Investigation on indoor airflow and contaminant dispersion of diffuse ceiling ventilation in heating and cooling modes

This paper systematically investigates the indoor airflow and contaminant dispersion of diffuse ceiling ventilation (DCV) for space heating and cooling. A numerical model of the office with DCV is built and validated. The indoor thermal comfort and air quality (IAQ) under different cases are analyzed. Simultaneously, different indices are employed to determine the influence of exhaust positions and air change rates on the system. The results indicate that DCV can provide a satisfying thermal environment both in heating and cooling modes, and there is no reverse flow from the room to the plenum. Besides, the visualizations of indoor airflow, temperature distributions, and mean age of air (MAA) show the different characteristics during heating and cooling. The ranges of contaminant removal effectiveness (CRE) and temperature effectiveness (TE) are 0.87–1.00 and 0.79–1.55 for heating, respectively. For cooling, they are 0.96–1.23 (CRE) and 0.92–1.06 (TE), respectively. Although the TE for heating is slightly higher than that of cooling, the CO2 concentrations and CRE manifest that DCV performs better for space cooling. Moreover, the results show that the exhaust positions influence TE more than CRE, especially for heating. Within the measured air change rates, it is found that the increase of air change per hour (ACH) can aid to the ventilation effectiveness of DCV. Meanwhile, the linear regression equations between ACHs and MAA are obtained. This research is helpful to reveal the flow mechanisms of DCV and guides the design and operation of the system.

Experimental Study of Indoor Air Distribution and Thermal Environment in a Ceiling Cooling Room with Mixing Ventilation, Underfloor Air Distribution and Stratum Ventilation

A ceiling cooling system integrated with a mechanical ventilation system has been widely used in modern buildings with large sensible cooling loads due to the high thermal comfort level and large energy efficiency. However, there is a lack of systematic research on the influence factors such as ceiling surface temperature and cooling load on the indoor air distribution and thermal environment, and the impact of ventilation system type in the ceiling cooling room is still unclear. Therefore, this paper presented an experimental study of indoor air distribution and thermal environment in a ceiling cooling (CC) room with mixing ventilation (MV), underfloor air distribution (UFAD) and stratum ventilation (SV); the ceiling surface temperature was 17 °C–26 °C and the internal or external cooling load was 41.5 W/m2–69.5 W/m2. The results showed that the vertical air temperature difference and contaminant removal effectiveness were 0.2 °C–0.4 °C and 0.53–0.85 with CC + MV, 0 °C–1.2 °C and 0.68–1.25 with CC + UFAD and 0.3 °C–0.9 °C and 0.50–0.83 with CC + SV, and the corresponding heat removal effectiveness and air diffusion performance index were 0.96–1.11 and 96–100%, 0.9–1.5 and 57–100% and 1.11–1.34 and 71–100%, respectively. Moreover, the difference between mean radiant temperature and air temperature and the predicted mean vote of thermal sensation were from 0 °C to 0.9 °C and between 0 and 0.26 with CC + MV, from −0.1 °C to 2.2 °C and between −0.1 and 0.42 with CC + UFAD and from −0.1 °C to 0.9 °C and between −0.2 and 0.13 with CC + SV. Hence, the ventilation system type clearly affected the indoor air distribution and thermal environment in the ceiling cooling room, and the experimental results would be beneficial for the design and control of a ceiling cooling system combined with a mechanical ventilation system in practice.

Evaluation of heating performances of different ventilation methods in an office

In this study, 12 cases were investigated in an office-layout room using experiments and computational fluid dynamics (CFD) simulations. The heating performances of four ventilation methods (i.e. mixing ventilation (MV), stratum ventilation (SV), deflection ventilation (DeV) and impinging jet ventilation (IJV)) were comprehensively compared by various evaluation indexes (i.e. predicted mean vote (PMV), draught rate (DR), vertical air temperature difference (△T), air diffusion performance index (ADPI), energy utilization coefficient (EUC), air change efficiency (ACE) and contaminant removal efficiency (CRE)). Better thermal comfort was found in rooms heated by SV and DeV. The PMV, DR and △T under SV and DeV complied with Category B of ISO 7730:2005, and the ADPI was in full compliance with the stipulation of ANSI/ASHRAE 113-2022. For the energy-saving characteristic, the targeted-occupied-zone ventilation methods (i.e. SV, DeV and IJV) can effectively deliver warm air to the occupied zone, with the EUC values higher than unity and thus providing a good potential for energy saving. SV and IJV showed slightly higher ACEs in the breathing zone. The contaminant removal effectiveness of SV, DeV and IJV was comparable. Under the combined influence of occupant thermal plumes and locations of exhausts, MV showed a high CRE. However, the CRE under MV decreased significantly when the exhausts were not above occupants. In the case of supply air parameters in this study, the entropy-weight method indicated that DeV and SV had a better overall performance for winter heating, followed by IJV and then MV.

Using a retention pond to capture agricultural contaminants from surface waters

To meet the demand of a constantly growing population, agriculture is intensifying, causing an increased use of fertilizers and pesticides. Excessive nutrients transfer to aquatic ecosystems can disrupt the water quality and impact the aquatic life. Pesticides can also have toxic effects on non-target organisms from aquatic systems. The purpose of this study was to evaluate the efficiency of an agricultural retention pond in reducing the supply of nutrients, pesticides and suspended solids to the Nicolet River, a tributary of Lake St. Pierre in the St. Lawrence River. Research combining the study of the fate of a wide range of contaminants in both pond water and sediments, their toxicity to microcrustaceans, microalgae and amphipods, and the effectiveness of contaminant removal, has rarely been carried out in the past. Peak contaminant concentrations occurred one to two months after pesticide and fertilizer applications, and during the months with the highest rainfall. Toxic effects were only observed on microalgae, with suspended solids apparently responsible for this effect through light inhibition on growth rates. However, the pond was not effective in removing this toxicity even if suspended solids were largely removed. Pesticides removal varied widely among sampling dates and pesticide types, with an efficiency reaching 95 % for thiamethoxam, but generally remaining low and often negative (higher concentrations in outflowing water) for other pesticides. On the other hand, the mean fractional removal of suspended solids, phosphorus, and nitrogen based on concentrations was 71 %, 44 % and 22 %, respectively. These are conservative estimations since the removal rates based on loads were above 94 %. The use of retention ponds thus seems an efficient approach to reduce the quantity of fertilizers in rivers draining agriculture areas, but the studied pond was not systematically effective in removing pesticides.

Promotion Mechanism of Atrazine Removal from Soil Microbial Fuel Cells by Semiconductor Minerals

In recent years, soil microbial fuel cells (Soil-MFCs) have attracted attention due to their simultaneous electricity production and contaminant removal functions, but soil electron transfer resistance limits their contaminant removal effectiveness. To overcome the above-mentioned drawbacks, in this study, a dual-chamber Soil-MFC was constructed using atrazine (ATR) as the target contaminant, and the electrochemical performance of Soil-MFC and ATR removal were enhanced by semiconductor mineral addition. Analysis of atrazine was performed in soil using HPLC and GC-MS, and analysis of metallic minerals using XPS. Anodic microorganisms were determined using high-throughput sequencing technology. The results showed that the addition of Fe3O4 increased the maximum output voltage of the device by 2.56 times, and the degradation efficiency of atrazine in the soil to 63.35%, while the addition of MnO2 increased the internal resistance of the device and affected the current output, and these changes were closely related to the ion dissolution rate of the semiconductor minerals. In addition, the addition of both minerals significantly increased the relative abundance of both Proteobacteria and Bacteroidota, and Fe3O4 simultaneously promoted the significant enrichment of Firmicutes, indicating that the semiconductor minerals significantly enhanced the enrichment of electroactive microorganisms near the anode. The structural equation modeling indicated that the semiconductor minerals achieved efficient degradation of ATR in the soil through a synergistic mechanism of metal ion leaching and microbial community structure changes. The detection of ATR and its degradation products in soil revealed that the degradation of ATR mainly included: (1) hydrolysis of atrazine by microorganisms to generate dehydroxylated atrazine (HYA); (2) reduced to diethyl atrazine (DEA) and diisopropyl atrazine (DIA) by extracellular electron reduction and re-dechlorination and hydrolysis to HYA. Semiconductor minerals make an important contribution to promoting microbial activity and extracellular electron reduction processes. The results of this study strengthen the power production and ATR removal efficiency of the Soil-MFC system and provide important theoretical support for the on-site removal of organic pollutants and the sustainable application of converting biomass energy into electricity.

Onsite measurement and dilution-based infection risk assessment for a new mobile negative pressure isolation room (MNPIR) as a solution to minimize cross-infection

This study proposes an onsite measurement protocol and infection risk assessment using tracer gas tests based on the dilution-based method to evaluate the ventilation system's performance in the mobile negative pressure isolation room (MNPIR) and minimize infection risk for health care workers (HCW). The dilution-based infection risk assessment is better in determining spatial distribution of infection risk compared to the Wells-Riley model. The study shows that ventilation effectiveness to reduce the infection risk for HCWs can be reviewed using four onsite measurement protocols and a dilution-based infection risk assessment. Optimizing the SA and EA installation locations is key to reducing the cross-infection risk of HCWs, and the contaminant removal effectiveness (CRE) index averaged 2.6, indicating adequate ventilation efficiency. By applying an appropriate ventilation system, the infection risk in HCW spaces was reduced to 50% or less of the average risk (by the Wells-Riley model). The proposed approach allows for quantitative evaluation of infection risk by location and exposure time, demonstrating that the MNPIR can effectively minimize infection risk for HCWs. The study suggests follow-up research on cooling and heating strategies that consider both patient comfort and effective ventilation performance in the MNPIR.

Efficient Ventilation Configurations for an Isolation Ward in View of Reducing the Potential Contamination of Its Occupants

The rise of respiratory infections, such as the SARS epidemic in 2003, and the H1N1 influenza epidemic in 2011, highlighted the importance of efficient ventilation in healthcare facilities. The novel SARS -Cov-2 disease has sparked many concerns over the ventilation performance of multi-bed isolation wards and their ability to suppress airborne infectious contamination. The study is primarily based on suggesting ventilation improvements for a locally acquired multi-bed intensive care isolation unit. The study via ANSYS -fluent incorporates a k-ε turbulent model that is used to analyze exhaled CO2 particle tracks of 4 human models. Three ventilation strategies, namely, Displacement, Stratum, and Curtain -Air-jet are initially considered and evaluated based on two indoor air quality indices (IAQs), namely, air change efficiency and contaminant removal effectiveness. Stratum ventilation comfortably exhibits unidirectional flow characteristics with an air change efficiency of 0.946, which was obtained through ANSYS -CFX while each suggested configuration is capable of achieving a contaminant removal effectiveness value greater than 1 which depicts that the contamination source is not in a perfect mixing zone. Results provided inconclusive evidence to draw correlations between the two IAQ indices and thus it is confirmed that these indices solely depend on the type of ventilation strategy. Contaminant concentration on health care worker breathing plane and exhaled particle tracking for 4 minutes in each analyzed configuration revealed that both Stratum and Curtain air-jet models improve the escaped particle efficiency by 25% and 29% respectively compared to the base model. These models are further compared against reference values specified by guidelines to evaluate their suitability for real-world operation. KEYWORDS: Ventilation, efficiency, ANSYS, isolation, airborne particles, Displacement, Stratum, Curtain -Air-jet

Contaminant removal effectiveness evaluation of ventilation, UR-UVGI, and air cleaner using CFD in negative pressure isolation ward

A negative pressure isolation ward (NPIW) is designed to create negative pressure to prevent the spread of airborne viruses. Therefore, it is necessary to increase the contaminant removal effect in the NPIW. To reduce indoor air contaminants, upper room-ultraviolet germicidal irradiation (UR-UVGI) and air cleaner are being used. Unlike the UR-UVGI, the air cleaner generates airflow. Therefore, the contaminant removal effect may differ according to the ventilation methods. This study is to compare ventilation, UR-UVGI, and air cleaner contaminant removal effects using CFD and Contaminant Removal Effectiveness (CRE) in the NPIW. As a result, the CRE of the ceiling and wall exhaust methods were different, and the CRE of the URUVGI and air cleaner cases were also different according to the two ventilation methods. Therefore, when applying UR-UVGI and air cleaner, it is necessary to consider the ventilation method.

Ventilation effectiveness in classroom infection risk control

The benefits of a good ventilation in classrooms are a well-studied topic regarding health and learning outcomes. However, many studies still show poor results regarding air quality, air change rate and air velocities. In this paper, typical Estonian classroom air distribution solutions were studied in an air distribution laboratory at Tallinn University of Technology. The air change efficiency was measured with CO2 tracer gas concentration decay method. For determining the contaminant removal effectiveness, continuous dose method was used to create a constant contaminant source. In addition, by using air velocity probes, we conducted draught measurements in the mock-up classroom. Tests were conducted using dedicated room-based air handling unit and thermal mannequins for imitating heat sources from students. We found that all solutions studied ensured the air change efficiency roughly corresponding to fully mixing air distribution, but local ventilation effectiveness values of contaminant removal showed large variation from 0.6 to 1.7 stressing the impact of source location. Grouped ceiling supply circular diffusers and single vertical supply grille air distribution commonly used in renovated educational buildings resulted in higher draught risk on the border of the occupied zone. High air velocities recorded in some areas of the classroom perimeter, well explain why draught is considered as one of the main reasons why the airflow rates are reduced, or supply air temperatures are lifted compared to designed values. Perforated duct diffusers resulted in acceptable air velocities. In conclusion, local ventilation effectiveness of contaminant removal showed that fully mixing is not a case with a point source, although air change efficiency determined with equally distributed source showed fully mixing conditions. Therefore, in those cases, the air change rate should be increased to achieve the same ventilation effectiveness. Based on the experiments conducted, a point source ventilation effectiveness measurement method for the breathing zone is proposed. This value determined at least with two source locations can be used in infection risk-based ventilation design.

Effect of active chilled beam layouts on ventilation performance and thermal comfort under variable heat gain conditions

The active chilled beam system has been popularly used in office and meeting rooms. There are very few studies of their terminal configuration on the thermal comfort and ventilation performance of systems with different heat gains. A comparative experimental study was implemented in mock-up office and meeting rooms to provide a comprehensive evaluation of the airflow patterns, air distribution, ventilation effectiveness, and local thermal comfort of the 4-way system. Four different terminal layouts with two types of the chilled beams (600 unit and 1200 unit sized 0.6 m × 0.6 m and 1.2 m × 0.6 m, respectively) were tested at three heat gain levels: low (46W/m2) and medium (66W/m2) heat gains in the office room, and high (92W/m2) heat gain in the meeting room. The results revealed that the terminal layouts and heat gain levels had significant effects on air distribution and local thermal comfort. The increased heat gains generated lower heat removal effectiveness, worse indoor thermal uniformity, and increased risk of draught. Generally, the 1200-unit system performed better than that with 600 units for heat removal effectiveness and contaminant removal effectiveness. In terms of local thermal comfort, the 600-unit system generally provided higher performance than that with the 1200-unit system. The practical recommendations for the system design and operation stages are provided based on the operating range of the 4-way systems under variable terminal layouts and heat gain conditions.

Airplane cabin mixing ventilation with time-periodic supply: Contaminant mass fluxes and ventilation efficiency.

Airplane cabin ventilation is essential to ensure passengers' well-being. The conventional ventilation method is mixing ventilation with a statistically steady supply, which, according to former studies, has reached its limits regarding, for example, the ventilation efficiency. However, the effect of a statistically unsteady (time-periodic) supply on the mixing ventilation efficiency has remained largely unexplored. This research uses computational fluid dynamics (CFD) with the large eddy simulation (LES) approach to study isothermal time-periodic mixing ventilation in a section of a single-aisle airplane cabin model, in which the air exhaled by the passengers functions as (passive) contaminants. Two time-periodic supply strategies are evaluated. The induced time-periodic airflow patterns promote an efficient delivery of fresh air to the passenger zone and affect the passengers' expiratory plumes. This results in increased mean contaminant mass fluxes, causing a strong reduction of the mean contaminant concentrations in the passenger zone (up to 23%) and an increased contaminant extraction from the cabin. Mean velocities increase with up to 55% but remain within the comfortable range. It is shown that the ventilation efficiency improves; that is, the contaminant removal effectiveness and air change efficiency (in the full cabin volume) increase with up to 20% and 7%, respectively.

Ventilation indices for evaluation of airborne infection risk control performance of air distribution

Air distribution is an effective engineering measure to fight against respiratory infectious diseases like COVID-19. Ventilation indices are widely used to indicate the airborne infection risk of respiratory infectious diseases due to the practical convenience. This study investigates the relationships between the ventilation indices and airborne infection risk to suggest the proper ventilation indices for the evaluation of airborne infection risk control performance of air distribution. Besides the commonly used ventilation indices of the age of air (AoA), air change effectiveness (ACE), and contaminant removal effectiveness (CRE), this study introduces two ventilation indices, i.e., the air utilization effectiveness (AUE) and contaminant dispersion index (CDI). CFD simulations of a hospital ward and a classroom served by different air distributions, including mixing ventilation, displacement ventilation, stratum ventilation and downward ventilation, are validated to calculate the ventilation indices and airborne infection risk. A three-step correlation analysis based on Spearman's rank correlation coefficient, Pearson correlation coefficient, and goodness of fit and a min-max normalization-based error analysis are developed to qualitatively and quantitatively test the validity of ventilation indices respectively. The results recommend the integrated index of AUE and CDI to indicate the overall airborne infection risk, and CDI to indicate the local airborne infection risk respectively regardless of the effects of air distribution, supply airflow rate, infectivity intensity, room configuration and occupant distribution. This study contributes to airborne transmission control of infectious respiratory diseases with air distribution.

Single-stage or two-stages bio-electrochemical treatment process of drainage from soilless tomato cultivation with alternating current

This work substantially extends knowledge on the possibilities of treating drainage from full-technical scale soilless tomato cultivation. Experiments were carried out in one stage bio-electrochemical reactor and separate biological and electrochemical reactors connected in series, with using alternating current. The study aimed to determine: the effect of single-stage, two-stages wastewater treatment process and hydraulic retention time (HRT) on the effectiveness of contaminant removal and organic substrate consumption, the contribution of biological and electrochemical processes and on the kinetics of contaminant removal. The use of coupled biological and electrochemical processes in one reactor (R1) showed the highest efficiency nitrogen removal, reaching 62.7 % (HRT = 1d) and 89.8 % (HRT = 7d), respectively. The separation of biological (R2-I) and electrochemical processes (R2-II) demonstrated the first one (R2-I) to be mainly responsible for denitrification (TN removal effectiveness at 51.9 % compared to 54.9 % effectiveness of the whole system). In single R1, the concentration of phosphorus in the effluent reached 2.32 ± 0.47 mg P∙L−1 (97.1 %; HRT = 1d) and 1.16 ± 0.06 mg P∙L−1 (98.3 %; HRT = 7d). In R2 enabled reducing phosphorus concentration in the effluent to 0.18 ± 0.07 mg P∙L−1 (99.8 %). The study showed that using of alternating current proved viable in increasing the rate and effectiveness of denitrification, but only if we apply electric current simultaneously with external source of organic carbon.

Comparison of Indoor Air Distribution in a Ceiling Cooling Room with Different Mechanical Ventilation Systems

This paper presents an experimental study concerning the influence of ventilation system type on indoor air distribution in a ceiling cooling (CC) room with mixing ventilation (MV), underfloor air distribution (UFAD) and stratum ventilation (SV) when the internal or external cooling load was increased from 41.5 W/m2to 69.5 W/m2. The distributions of indoor air temperature, air velocity and contaminant concentration were measured and evaluated by the vertical air temperature difference, turbulence intensity and contaminant removal effectiveness, respectively. The results show that when the ceiling surface temperature increased from 17.0°C to 26.0°C, the vertical air temperature differences, turbulence intensities and contaminant removal effectiveness were 0.2°C-0.4°C, 27%-34% and 0.53-0.85 with CC+MV, 0.2°C-1.2°C, 27%-43% and 0.68-1.25 with CC+UFAD and 0.3°C-0.9°C, 24%-40% and 0.5-0.83 with CC+SV. The CC+MV had the most uniform distributions of indoor air temperature and velocity, whereas the CC+UFAD had the most non-uniform distribution of indoor contaminant concentration.

Experimental investigation on the ventilation performance of diffuse ceiling ventilation in heating conditions

This paper aims to investigate the performance of diffuse ceiling ventilation (DCV) in heating mode by a full-scale chamber. Eleven cases combined with different exhaust positions, supply air change rates, internal heat source intensities, and the type and location of contaminant sources were tested. The contaminant removal effectiveness (CRE) and temperature effectiveness (TE) were utilized to evaluate the ventilation effectiveness of DCV. It is found that thermal discomfort due to vertical temperature differences or draught is negligible for all tested cases. The results demonstrate that the effect of exhaust positions on CRE depends on the existence of internal heat source. With the presence of heat source, the room air can reach a good mixing, and the effect of exhaust positions is therefore limited. Nevertheless, when there is no internal heat source, the lower position can force the supply air to enter the occupied zone and improve ventilation performance. Increased air change rates can significantly improve indoor air quality, but have a little influence on ventilation effectiveness. CRE is strongly influenced by the internal heat source intensity and the contaminant source type. With the increase of heat source intensity, CRE increases notably from 0.28 to 0.82. As for different contaminant source types, CRE is about 1.3 under the active source (with heat), but only 0.68 and 0.82 under the passive source (without heat). This study is beneficial to the further design and optimization of DCV for its broader heating application.

Regional flow motion and heat energy balance analysis of a 10,000 class pharmaceutical cleanroom with secondary return air conditioning system

• Cleanroom with the secondary return system was modeled with airflow and energy network. • The air change rate has a notable influence on the mean age of air globally and locally. • The air change rate has a small effect on contaminant removal effectiveness and air change efficiency. • Promotion of return air volume in the occupied area could reduce local pollutant concentration levels; • Computational fluid dynamics procedure was validated by the on-site measurements. Improving air quality in occupied area has always been the core focus of ventilation design in cleanrooms. A 10,000 class pharmaceutical cleanroom, with secondary return system, was firstly introduced. Full computational fluid dynamics procedure validated by on-site measurements was then applied to model such cleanroom airflow and particle transport. Energy balance of this ventilation system was also analyzed. Details of room airflow and contaminant fields for the specific zone (above the device and around the human body) were subsequently analyzed concerning the effect of delivering ventilation flow rate and return air volume. Representative parameters, mean age of air, contaminant removal effectiveness, and air change efficiency at the occupied zone and the whole space were evaluated. Results demonstrate that promotion of the return air volume in the occupied area could appropriately reduce pollutant concentration level. Moreover, an increase in ACH (air change rate per hour) did not always shorten the local age of air near the equipment. For a large ACH, it not only will raise the dust around the machine again, it will also cause uncomfortable flow draft. Additionally, when ACH = 20 h − 1 and 25 h − 1 were achieved respectively, the age of air was reduced by 32% and 21.4% in the whole room and further done by 31.1% and 23.5% in the occupied zone; with identical changes, room air change efficiency (RACE) was achieved at 49.3 % and 50.4 %, respectively. It shows that the increase of ACH seems to have little effect on the air change efficiency. When ACH increases from 15 h −1 to 20 h −1 , the efficiency of pollutant removal at the occupied zone will not be significantly improved ( ε = 1.78).