A simplified methodology for the prediction of mean air velocity and particle concentration in isolation rooms with downward ventilation systems

doi:10.1016/j.buildenv.2010.02.015

Building and Environment

Volume 45, Issue 8, August 2010, Pages 1847-1853

https://doi.org/10.1016/j.buildenv.2010.02.015 Get rights and content

Abstract

Calculating the velocity and particle concentration indoor is critical for isolation rooms design. Computational fluid dynamics (CFD) is regarded as a powerful tool aiding in the indoor environment design for isolation rooms by enabling us to predict the velocity and particle concentration distribution in detail. However, CFD method is time-consuming and relatively expensive, especially for actual engineering application. So this study proposes a simplified methodology to predict the mean air velocity and particle concentration in the occupied zone of isolation rooms with downward ventilation systems. The methodology is based on a similarity theory analysis, by which the key similarity criteria are deduced. The correlating equation to calculate the mean air velocity and particle concentration in the occupied zone in isolation rooms is established by multiple linear regression (MLR) which is based on the numerical test results obtained by CFD. The equation correlates the mean air velocity and particle concentration with air supply volume rate, indoor particle generating rate, and other parameters. The calculated results agree with those from measurement and CFD simulations for the studied cases, generating a relative error less than 25%. It could offer the engineers a simpler path to calculate the mean air velocity and particle concentration.

Introduction

Isolation rooms are widely used in clean production workshops, hospital operating rooms and clean wards. For these places, the indoor air flow and particle distribution should be designed carefully to maintain a clean indoor environment. Previous studies suggest that engineering simulations using computational fluid dynamics (CFD) are a valid method for investigating air flow behavior, temperature distribution and particle dispersion in different types of isolation rooms [1], [2], [3], [4].

However, CFD is sometimes time-consuming and relatively expensive, which limits its application in actual engineering applications. Although the cost of CFD is acceptable when studying a limited number of cases for academic research nowadays, a more simplified method is always welcomed for those engineers or designers who are not CFD experts. Besides, in most cases the engineers or designers only concern the mean velocity and particle concentration in the key indoor areas, for example, the occupied zone in isolation rooms. For this purpose, the detailed air flow and particle distribution given by CFD seems unnecessary in terms of deciding the primary schemes for actual application. Furthermore, the indoor environment controlling or decision-making requests the real-time monitoring of air velocity and particle concentration indoor. The CFD calculation does not meet the request as it is hard to response the input parameters (e.g., air flow rate variation, source generating rate variation, and so on) in a short time or real time. A simple methodology that can real time response to the input parameters is necessary for this purpose.

This study therefore presents a simple way to predict the mean air velocity and particle concentration in the occupied zone (Occupied zone is defined as the central part of the room in this study, i.e. up to a height of 2 m and 0.5 m away from each wall [5].) in isolation rooms with downward ventilation systems, as downward ventilation system is regarded to be effective for controlling indoor particles and that current guidelines recommend use of downward ventilation systems for different kinds of isolation rooms [6], [7], [8]. The simple methodology is based on a similarity theory analysis, by which the key similarity criteria are deduced. The correlating equation to calculate the mean air velocity and particle concentration is established by multiple linear regressions (MLR), which is based on the numerical test results obtained by CFD method. The equation correlates the mean air velocity and particle concentration with air supply volume rate, indoor particle generating rate and other parameters. It can be used to aid the engineers or designers to calculate the mean air velocity and particle concentration in a quick and simple way and achieve results with similar precision of CFD method, so as to avoid the complicated computation by CFD software.

Section snippets

Methodology

The methodology consists of three key parts: similarity analysis; numerical test and equation regression.

Verification of the equation

Some cases are studied to verify the simple equations. If the results calculated by using above equations agree with the results calculated by CFD, the simple method is regarded to be working well. Besides, the measured data from the experiment performed in a real isolation room is also employed to compare with the results calculated by the simple equation.

Three new cases out of the 128 cases were again simulated by CFD. Then the results of mean air velocity and particle concentration, together

Discussion

The simple methodology is efficient for predicting the mean air velocity and particle concentration in the studied type of isolation rooms. Zonal model is another kind of simple approach to calculate the velocity, temperature and concentration with few costs. The present methodology would be simpler, as it is a simple algebraic equation which only requires simple input parameters. In this way, the real-time monitoring of mean air velocity and particle concentration in isolation rooms becomes

Conclusion

A similarity analysis is performed to get the key similarity criteria for mean air velocity and particle concentration in the occupied zone of isolation rooms with ceiling air supply and down-side return air flow pattern. Based on the numerical test of CFD, the correlating equation of the key similarity is established. The mean air velocity and particle concentration can be calculated with these correlating equations. The results have a maximal relative error of 27.5% compared with those

Acknowledgement

This work was sponsored by the National Natural Science Foundation of China (Grant No. 50908127).

References (23)

S.C. Hu et al.
Design and evaluation of a minienvironment for semiconductor manufacture processes
Building and Environment
(2002)
H. Qian et al.
Dispersion of exhalation pollutants in a two-bed hospital ward with a downward ventilation system
Building and Environment
(2008)
J. Liu et al.
Numerical simulation on a horizontal airflow for airborne particles control in hospital operating room
Building and Environment
(2009)
W.K. Chow et al.
Numerical studies on the indoor air flow in the occupied zone of ventilated and air-conditioned space
Building and Environment
(1996)
E.L. Gyenge
Dimensionless numbers and correlating equations for the analysis of the membrane-gas diffusion electrode assembly in polymer electrolyte fuel cells
Journal of Power Sources
(2005)
B.E. Launder et al.
The numerical computation of turbulent flows
Computer Methods in Applied Mechanics and Engineering
(1974)
B. Zhao et al.
Numerical investigation of particle diffusion in clean room
Indoor and Built Environment
(2005)
ASHRAE
HVAC design manual for hospitals and clinics
(2003)
CDC
Guidelines for environmental infection control in health-care facilities
(2003)
ICCS
ISO/TC209 standard
(1993)

IEST-RP-CC012.1

Considerations in cleanroom design

(1998)

Cited by (13)

A study on contaminant leakage from Airborne Infection Isolation room during medical staff entry; Implementation of walking motion on hypothetical human model in CFD simulation
2024, Journal of Building Engineering
The recent outbreak of respiratory infectious diseases such as Middle East Respiratory Syndrome (MERS) and Coronavirus Disease-19 (COVID-19) highlights the critical role of Air Infection Isolation (AII) rooms in preventing the spread of disease. However, the risk of contaminant leakage from the AII room during medical staff interactions remains a significant challenge. This study advances our understanding by employing Computational Fluid Dynamics (CFD) simulations with a novel approach. While CFD simulations mitigate some limitations of field experiments, such as measurement resolution and variable changes, their accuracy is often limited by the oversimplification of models, particularly in representing human models and movement. Unlike prior studies, we incorporate minimal simplification, featuring a human model with Personal Protective Equipment (PPE) and realistic walking motions. This study explores four distinct scenarios with varied human movements, offering a comprehensive analysis of airflow and contaminant dispersion in AII rooms. The results indicated significant differences in airflow patterns and contaminant distribution when realistic walking motion was implemented in the human model, as opposed to simplified movement models. The contaminant leakage from the AII room ranged from 20.6 % to 28.6 %, suggesting that prior studies may underestimate infection risks due to oversimplified human models and motions. These findings underscore the importance of implementing realistic human models and motions in CFD simulations for accurate infection risk assessment in AII rooms. Additionally, our study opens pathways for future research to explore more complex human interactions in clinical settings, enhancing infection control strategies.
Downward piston ventilation assisted with a localized - Chair exhaust for mitigation of pathogen transport in educational spaces
2022, Journal of Building Engineering
Citation Excerpt :
The system's operation is based on the push-pull principle. DPV systems generate a downward parallel flow of cool clean air from ceiling level, leading to a low-turbulence downward displacement of air in the space, which is exhausted through low-level diffusers commonly distributed around the room periphery [10]. The unidirectional airflow pattern controls airborne particulate contamination by direct entrainment and removal [11] where the supplied air pushes down the contaminants that are removed at floor level and minimize their spread in the space [8].
This study proposes the integration of a localized - chair exhaust (LCE) device and a downward piston ventilation (DPV) in an educational space. The main aim is to assess the proposed system ability in providing a safe educational space similar to the case implementing the 2 m distancing between students at lower energy consumption. This allows the decrease of the DPV high supply flowrate without jeopardizing the protection level compared to the standalone DPV. A three-dimensional computational fluid dynamics (CFD) model of the educational space with DPV + LCE combination was developed as simulator software. The CFD model was validated experimentally and a parametric study was conducted to determine the best DPV supply airflow rate when assisted with LCE. The DPV flowrate should be capable of (i) preserving high protection levels, (ii) maintaining acceptable thermal comfort levels, while (iii) reducing the energy bill burden. Hence, an infected student was assumed sitting in the middle of the space and the exposure levels of the surrounding students were evaluated using the intake fraction (iF) index. It was found that for a practical use in educational spaces, the DPV system should be operated at 60 l/s per person with LCE at 20 l/s to maintain the high protection potential of the DPV system at 51% energy savings in the overall system energy consumption. Furthermore, the energy performance of the proposed system was compared to that of other ventilation systems implemented in educational spaces while offering same or better protection levels.
Comparison of air change efficiency, contaminant removal effectiveness and infection risk as IAQ indices in isolation rooms
2013, Energy and Buildings
Citation Excerpt :
It is ever more frequently used to design operating theatre ventilation systems [13–15], general hospitalisation rooms [16,17] and hospitalisation rooms for isolation patients [11,18,19]. Recent works attempt to shed light on the best disposition of air inlets and outlets in order to minimise the infection risk [18,20–23]. No consensus exists, however, in this respect and some authors even question the current recommendations of the Centres for Disease Control and Prevention [24].
An effective design of the ventilation system of the isolation rooms for infectious patients can reduce the risk of spreading infections. However, no consensus exists regarding the placement of the air inlets and outlets which minimises the risk of spreading infection. In this work, we use computational fluid dynamics (CFD) to evaluate the ability of the ventilation system to minimise the risk of infection in the rooms of isolated infectious patients. We analyse the influence of the position of the air inlets and outlets. We take into account the deposition and viability of the infectious particles. To compare the different configurations quantitatively, three types of indices are employed: those which quantify the capacity to renew the air; those which quantify the capacity to remove a contaminant and those which quantify the risk of airborne infection. These three types of indices are applied to the entire isolation room and in specific zones of the room in order to evaluate the quality of the ventilation globally and locally respectively. Likewise, using different air diffusers we demonstrate the importance of the diffuser on the air flow pattern and, therefore, on the quality of the ventilation.
Analyzing grid independency and numerical viscosity of computational fluid dynamics for indoor environment applications
2012, Building and Environment
Citation Excerpt :
The selection of the grids to be tested and the determination of the grid-independent solution, however, mostly count on a CFD user’s experienced judgment. Roache [9,10] proposed a grid convergence index (GCI) to quantitatively evaluate the grid-induced error, which however received little attention in the field [16]. The GCI based approach provides a sound estimation of grid-induced error, but a standardized procedure need to be developed that includes the selection of variables and variable locations for comparison and the determination of numerical error introduced by grid size.
Computational fluid dynamics (CFD) has been introduced to indoor environment study for decades. Analysis of CFD results will first require the reach of a grid-independent CFD solution to eliminate the false information induced by numerical causes, e.g., grid and numerical scheme. Judging a grid-independent solution has been mostly experience-based, leading the necessity of developing an objective and easy-to-use criterion for grid independency evaluation. This paper presents a new approach to assessing the grid independency of CFD modeling for indoor environment applications. A normalized root mean square error (RMSE) index is developed from the grid convergence index (GCI) concept in literature to evaluate the overall differences of predicted results with varying grid resolutions. The paper further introduces the use of numerical viscosity analysis method to verify the grid-independent solution of a CFD analysis, which also provides fundamental insight into the grid-induced error in numerical solutions. Although initially developed for indoor environment applications, the proposed RMSE index along with the numerical viscosity analysis method can be applied to most general CFD studies and has great potential of being incorporated into commercial CFD software to provide user a more accurate and objective alternative of checking grid independency of CFD simulation.
Preventing the entry of outdoor particles with the indoor positive pressure control method: Analysis of influencing factors and cost
2011, Building and Environment
Citation Excerpt :
The total number of cases is 972. A correlating equation to calculate the satisfied superfluous air exchange rate was established by multiple full quadratic regressions method which has been used in several studies [15]. To ensure the quality of the regressions, all the parameters were normalized by dividing by a reference value.
Maintaining positive pressure indoors with a mechanical ventilation system is a popular control method for preventing the entry of outdoor airborne particles. This paper analyzes the factors which affect the satisfied superfluous airflow rates of positive pressure control. Through modeling a large amount of cases with a validated model, the factors, e.g. temperature difference, outdoor wind velocity, effective air leakage gaps in the envelopes, the area of the air leakage and the room, were analyzed. Based on the theoretical model, a correlating equation to calculate the satisfied superfluous airflow rate was established by multiple full quadratic regressions. The correlating equation is simple for engineers or designers to use to determine the satisfied superfluous airflow rate. This paper also aims to find which method, pressure control or indoor air cleaning, costs less to prevent the same amount of outdoor-originated particles from entering indoor environments. Generally speaking, indoor air cleaning control method requires less supply airflow rate than positive pressure control method for reducing the concentration of indoor particles with outdoor origin. An exception for this is a situation with a very low indoor/outdoor particle concentration (I/O ratio) requirement.
Constructing prototypical building models based on the similarity theory coupled with entropy weight method
2020, Science and Technology for the Built Environment

View all citing articles on Scopus

View full text

A simplified methodology for the prediction of mean air velocity and particle concentration in isolation rooms with downward ventilation systems

Abstract

Introduction

Section snippets

Methodology

Verification of the equation

Discussion

Conclusion

Acknowledgement

Building and Environment

Building and Environment

Building and Environment

Building and Environment

Journal of Power Sources

Computer Methods in Applied Mechanics and Engineering

Numerical investigation of particle diffusion in clean room

Indoor and Built Environment

HVAC design manual for hospitals and clinics

Guidelines for environmental infection control in health-care facilities

ISO/TC209 standard

Considerations in cleanroom design