S. Guffey, West Virginia University, Morgantown, WV.
The most common method of balancing is simply to adjust the damper in each branch in turn until the observed airflow (Q) equals the target airflow (Qt). That procedure is notoriously difficult and time-consuming due to interactions among branches and with the fan. In addition, the common practice of estimating airflows during balancing using centerline velocity pressures (VPcl) adds uncertainty to the process. A new method is proposed to deal with the factors that complicate balancing. The reduction in fan output is estimated from the lowest ratio among the branches of the initial branch airflow (Qo) to the desired airflow (Qt) and from the ratio of the initial fan airflow to the sum of desired branch airflows. The interaction among dampers is countered with factor (F) based on the order of adjustments. The order factor varies from roughly 0.9 for the first damper adjusted to 1.0 for the last. The problem with VPcl is removed by using a target hood static pressure (SPHtarget) as the observed parameter during adjustments.
The value of SPHtarget for each branch is computed from: (1) the value of SPH when measured with all dampers open, (2) the value of F based on the order of adjustment, (3) the ratio of Qo/Qt, and (4) the fan factor based on the estimate of the fan airflow that will exist when the system is balanced. The method is intended to provide the desired relative distribution. The target flow levels are achieved by resetting the fan speed using the fan laws. Simulations on an Excel spreadsheet predict that the method will produce better accuracy for fewer adjustments than the commonly used method. The insertion depths of the dampers should be the minimum possible, making the fan pressure the minimum possible value. Subsequent studies provide experimental verification.
S. Guffey, M. Dodrill, West Virginia University, Morgantown, WV.
This study tested a proposed method for adjusting slidegate dampers to balance exhaust ventilation systems. The proposed method is based on target hood static pressures (SPHtarget) that take into account estimated effects of dampers on the fan, the order of adjustment, and the ratio of the starting branch airflow to the branch airflow goal. It is aimed at achieving a desired relative distribution of airflows; it assumes the fan output will be adjusted after the dampers are adjusted. The method was tested on a working 7-branch, full-sized exhaust ventilation system in the West Virginia University Exposure Assessment Laboratory. The experiment included 1˝ rounds of damper adjustment using the SPHtarget values. Twenty-point Pitot traverses were used to determine the airflow in each branch duct before and after employing the adjustment method. Two radically different target distributions were tested. The initial distribution of airflows was substantially different from both target distributions, providing a high degree of challenge to the methodology. The results matched the range predicted by simulations in a previous study. The amount of fan airflow above the sum of target branch airflows was below 2.2% for all experimental trials, an outstanding result. That accuracy was obtained under excellent measurement conditions. The inaccuracy in the field may be moderately higher due to less ideal measurement conditions.
S. Guffey, V. Balasubramanian, West Virginia University, Morgantown, WV.
The most commonly used method of balancing systems is to adjust each damper in turn until the airflow through its branch equals the desired level. Typically, the airflow through each branch duct is estimated from centerline velocity pressure (VPcl) measurements. To test the effectiveness of that approach, dampers were adjusted on a 7-branch, full-sized experimental duct system. The change in distribution was selected to be challenging. After two rounds of adjusting the dampers using this method, the resulting airflows were determined from full Pitot traverses. The procedure was repeated for the same relative distribution for three different airflow levels (Perfect, Moderate, and High). After adjusting the dampers for a given condition, the percent excess airflow (%FanQexcess) for the system was estimated. It was assumed that %FanQexcess would be greatest when the deviation between the target airflows and the initial airflows was the greatest and least when they were closest. The results varied with the level of the target airflows but not in the expected manner. The excess airflow was about the same for the High airflow (5.3%) and the Perfect airflows (6.56%). The excess for the Moderate case (8.5%.) was the worst. The results probably would have been somewhat worse under the measurement conditions commonly encountered in the field. The pressure in the system also was measured. As expected, the greater the ratio of the initial fan airflow to the target fan airflow the greater the pressure in the system.
C. Prevost, L. Bouilloux, R. Colin, IRSN, Gif sur Yvette, France.
The Institute for Radiological Protection and Nuclear Safety (IRSN) carries out research and analysis within the fields of nuclear safety, protection against ionizing rays, control and protection of nuclear materials. The purpose of the present study consists in quantifying the intensity of polluting agents propagation phenomenon when a gloves box is used under incident conditions that is, in this case, the breakage of static confinement by a sudden gloves or bags breakdown. The knowledge of the confinement efficiency is of primary importance because it conditions the concentration in radioactive element likely to be breathed by an operator. In nuclear industry, the operator protection is normally assumed by the dynamic confinement technique that consists in creating, at the level of the opening of the enclosure, an airflow directed toward the interior of this one, with a sufficient velocity value in order to limit the diffusion of the airborne contamination towards outside. The present paper concerns applications of gas and aerosol tracer techniques in order to determine coefficients of back dissemination of a polluting agent in many different normal or accidental configurations and in particular when an experimental manikin is used to simulate the presence of an operator at his working station. Tracers techniques are applied to understand the behavior of pollutants such as gases or particles of various size distributions, ranging between 0.18 µm and 5 µm (aerodynamic diameters) near the opening when a glove or other equipment of the ventilated box is broken. Finally, results highlight the presence of a significant back dissemination of a polluting agent whatever is its nature, and one determines useful data to precisely evaluate the concentrations inhaled by an operator since the internal pollutant flow rate known.
M. Pavelek, E. Janotkova, Brno University of Technology, Brno, Czech Republic.
The contribution deals with the application of interferometry in research on nonisothermal air jets. The research was carried out using scale models with a Mach-Zehnder interferometer and our own software, Interfer-Visual. The contribution contains examples of visualized nonisothermal jets from slot and circular outlets in free spaces and spaces containing barriers. The results comprise interferograms of jets and flow fields, which provide both qualitative and quantitative information about air jets. The focus is, above all, on the evaluation of air jet shapes, temperatures in jets, and enthalpy in jets. A knowledge of air jet shapes is very important to the practical use of outlets. For nonisothermal air jets from outlets in free spaces, the expansion angle in the main zone of slightly nonisothermal air jets and the trajectory of the jet axis of strongly nonisothermal air jets are important. The C-value of air outlet can be effectively defined from the expansion angle of the main zone of slightly nonisothermal air jets. A knowledge of local temperature distribution in nonisothermal air jets serves for a detailed understanding of heat processes in the jets. The enthalpy distribution in nonisothermal air jets can be useful not only for jet power balance, but for research into other air jet parameters like velocity, volumetric flow, or mean jet temperature. From the distribution of volumetric flow it is possible consecutively to evaluate the suction of air from the surrounding atmosphere to the jet. The data obtained are useful for a more profound understanding of air jets, as well as for practical use in the field of ventilation, air conditioning and warm-air heating.
F. Bonthoux, INRS, Vandodeuvre, France; E. Belut, INRS, Vandoeuvre, France; M. Bruchhausen, F. Lemoine, LEMTA, CNRS UMR 7563, Vandoeuvre, France.
Machining, especially in the hard metal industry, is an important source of workers’ exposure to inhalable contaminants, such as cobalt, presenting a health hazard. The design of precise and efficient close capture exhausts systems is henceforth of absolute necessity. CFD (computational fluid dynamics) is believed to be of extremely valuable help to this design process, but its application to rotating machinery induced two-phase flows still requires development and experimental validation. To that purpose, an experimental device was designed, which aimed to generate an emission of solid particles under conditions similar to those of machining but in a perfectly controlled environment. It consists in a feeding system injecting continuously spherical glass particles against a rotating cylinder, which ejects these particles by friction, hence creating a stable particle stream with a controlled flow rate. The jet properties, such as particles velocities, size distribution, and concentrations, were measured experimentally using phase doppler anemometry (PDA) technique. Measurements results, as well as experimental facilities and measurements techniques, are presented here. These results are intended to be used as input and validation data for further numerical investigations.
P. Lagus, Lagus Applied Technology, Inc, Escondido, CA.
As early as 1984, inleakage measurements were undertaken for control rooms and other structures associated with the chemical process industry. The driving force for these measurements was the need to locate so-called “temporary safe havens” within the plant environment. These safe havens are intended to provide a habitable environment for the plant personnel during a toxic release. In 2003, the United States Nuclear Regulatory Commission requested data on the inleakage characteristics of all operating nuclear power plants in the United States. Essentially, this request required all operating plants to measure the inleakage into the control room. In both the chemical process industry and the nuclear power generation industry, inleakage testing has been undertaken using tracer gas techniques that are based on ASTM Standard E 741 ” Standard Test Method for Determining Air Change Rate in a Single Zone by Means of a Tracer Dilution.” In the chemical process industries, the response to emergency conditions is to isolate the control room and place the ventilation system into a recirculation mode. This creates a so-called “neutral pressure condition” in the control room. Within the nuclear power industry, the majority of control rooms respond to a radiation emergency by pressurizing the control room with filtered outside air. A lesser fraction of these control rooms isolate and recirculate as in the chemical process industry. For a chemical release emergency, most nuclear power plant control rooms isolate and recirculte as in the chemical process industry. In this paper, we provide a description of the techniques used to measure inleakage for both neutral pressure and pressurized control rooms. Measured inleakage data for both control room types will be presented to illustrate the range of inleakage values that have been found in actual practice. The safety significance of these measured values will also be discussed.
L. Zhao, The Ohio State University, Columbus, OH.
Ventilation systems play critical roles in air velocity distribution, which directly affects animal and human workers’ comfort, heath, and productivity. Because of long-standing difficulties in low-speed, indoor airflow measurement, it has been difficult to comprehensively evaluate the performance of typical ventilation systems. In this study, full-scale airflow patterns and detailed air velocity distribution in three different ventilation systems were measured using a particle image velocimetry (PIV) system in a mechanically ventilated room under controlled conditions. It was found that airflow patterns and air velocity distribution in a enclosed space vary significantly as a result of ventilation systems, especially in the animal-occupied zones. Air inlet location affects the air velocity distribution as expected. In addition, air outlet locations affect air velocity distribution in animal-occupied zones significantly. Therefore, air outlet locations should also be considered for ventilation system design.
K. Hall, Tallinn University, Tallinn, Estonia.
This case study deals with the renovation project of ventilation in the Natural Science Building of Tallinn University of Technology, covering the established aims and principles of technical solutions, in general, and results of monitoring. The reconstruction project involved the task of creating a new ventilation system for required indoor climate of laboratories, avoiding dissemination of harmful materials to rooms. In addition, it was required to keep the operations costs at approximately an acceptable level. There are two separate central supply-exhaust air ventilation systems for general air exchange and for local ventilation systems. Both systems have recuperative indirect heat recovery units with a circulating fluid medium. To extract dangerous and abrasive materials, additional separate local systems were provided. Automation of ventilation systems is characterized by a short-time response operation. The system of automation has several additional functions, such as to ensure the minimum main air exchange rate in the rooms (so-called standby conditions), signaling about system disturbances and noneconomical operation in some of the rooms to guarantee the required level of CO2 concentration or indoor air temperature. To assess the operating systems and to achieve the established aims, special testing of joint work between fume cupboards and main ventilation was conducted, using airflow smoke to emphasize the effect. During this monitoring, CO2 concentration in the rooms and the air speed values in the fume cupboard openings were investigated. Results of monitoring demonstrate that investments for these ventilation systems were justified and the installed ventilation systems corresponded to our technical and sanitary-hygienic expectations.
J. Bennett, NIOSH, Cincinnati, OH.
The protection of building occupants from hazardous outdoor releases can involve many strategies of varying cost and complexity. One method is known as “shelter-in-place,” in which a space within the building is isolated to a practical degree from ambient and the remaining building air. The design of such a space involves decisions about size and level of permeability. An obvious issue is the comfort and health of occupants during the event. Because a design cannot satisfy all needs entirely, engineering the space becomes an optimization problem. This research provides an analytical framework for considering the effects of the variables volume, air exchange or ventilation rate, concentration, and time. Intuition suggests that the room should be as large as possible to keep the balance of O2 and CO2 at safe levels. However, the current work quantifies the optimal room size using a systems analysis of a three-compartment building model consisting of ambient, building, and safe-room zones. The results provide the optimal safe-room volume as a function of ambient, building, and safe-room concentrations, ambient/building and building/safe-room air exchange rates, contaminant generation rate within the safe-room, and building volume. Also, the analysis can be used to rank the importance of the variables affecting safe-room concentration so that control efforts can be efficiently applied. This information will be helpful in choosing among existing rooms to use for shelter, making room modifications, or for designing a new space.
S. Soares, IRSN, Gif sur Yvette, France.
In the nuclear industry, the response of a ventilation network to accidental disturbances, either mechanical (fan failure, damper blockage, etc.) or thermal (fire, etc.) is difficult to evaluate when the network becomes complex. In order to determine and analyze the consequences of these disturbances on the radioactive materials confinement, a code called SIMEVENT has been developed. Among the external parameters likely to affect a ventilation network, the wind effect is actually basically modeled due to a lack of qualified data concerning the wind impact on complex building’s geometries and the interaction between wind and chimney exhaust. In view of the network’s complexity and the installations diversity, a research program including experimental and model studies has been launched to assess the pressure coefficients due to wind on different chimneys and reference buildings geometries. Different chimney terminals have been placed in a wind tunnel (the variables are the incline angle, wind velocity, and airflow in the duct); for each angle, the evolution of the pressure coefficient versus wind velocity is determined and is characteristic of a chimney terminal geometry. Two types of scale-model have been chosen for representing either nuclear power plants or plants and laboratories buildings. The different values of wind pressure coefficients have been measured on both scale models placed in a wind tunnel. The modeling of wind influence on the networks consists then in fixing measured wind pressure coefficients at all air inlets and outlets in the code; then, SIMEVENT calculates the consequences on pressure and flow rate values inside the whole building, for the normal operating mode or degraded ones (such as fan failure or appearance of fissures on walls).
Finally, the use of such a code allows the evaluation of contamination release in environment due to degraded operating modes in ventilation networks, integrating the influence of wind.
T. Smith, Exposure Control Technologies, Inc., Cary, NC.
The desire to save energy in laboratories by reducing the volume of tempered air exhausted from chemical fume hoods has increased use of variable air volume (VAV), ventilation systems. VAV systems can provide significant opportunities for energy savings in laboratories, but they are complex systems comprised of numerous interacting components, including sensors, actuators, and computerized controls that must accurately adjust flow in response to user demand. As will be demonstrated in this paper, improper response of a VAV system and inability to provide stable control of flow can significantly affect hood performance or the ability of the fume hood to provide desired containment. The tests described in currently published standards are inadequate to evaluate VAV performance. To ensure that VAV systems provide the opportunity to save energy without jeopardizing hood performance, a series of tests may be added to the ASHRAE 110 “Method of Testing Performance of Laboratory Fume Hoods.” The additional VAV tests are necessary to verify proper operation, define operating conditions, and identify potential problems. This paper provides a description of VAV fume hood systems, examples of how improperly operating VAV systems affect hood performance, and a description of recommended methods to evaluate performance of VAV fume hood systems.
Posted May 30, 2006