Air-Flow Redistribution in Exhaust Ventilation Systems Using Dampers and Static Pressure Ratios

Guffey, Steven E.

doi:10.1080/1047322x.1993.10389188

Cited by 7 publications

(15 citation statements)

References 3 publications

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“…This can be done using orifices whose resistances to flow can be predicted or by using estimates of X damper determined experimentally for common damper types, such as the estimates published by Crowder and Loudermilk (2) and Idel'chik. (3) In addition, the Static Pressure Ratio Method (1) uses resistances to predict the ratio of the hood static pressure to the static pressure just upstream of the junction fitting for each branch duct and then bases adjustment of dampers on achieving the predicted ratios. The difficulty in each case is in predicting the values of X damper that are required to achieve the desired distribution of airflows.…”

Section: Strategies For Adjusting Dampersmentioning

confidence: 99%

“…The effect on the fan airflow of increased system resistance as dampers were adjusted was simulated by modeling the relationship between the resistance of the system (X system ) and the airflow level produced by the fan (Q fan ) at a fixed rotation rate. The resistance of an entire system can be approximated by: (1,2) X system = TP fan VP fan inlet (24)…”

Section: Example System and Computationmentioning

confidence: 99%

“…(1) For that reason, it is likely that nearly all dampers are adjusted using trial and error methods. That is, one adjusts and readjusts the damper while comparing the observed pressure or flow to the level desired for that damper.…”

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confidence: 99%

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A Goal Method and a Target Method for Balancing Exhaust Ventilation Duct Systems with Dampers

Guffey

2007

Journal of Occupational and Environmental Hygiene

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This work presents and discusses two approaches to adjusting dampers, here called the Goal and Target Methods. A form of the Goal Method is commonly employed but has not been clearly described or discussed elsewhere. The Target Method is a novel variation of so-called "proportional" methods. Detailed step-by-step procedures for each are presented. It is likely that the most common method of balancing the airflows in ventilation systems is simply to adjust the damper in each branch in turn until the observed airflow for each branch duct (Qbr) equals the goal airflow (Qbr-goal). This is a simple Goal Method. It is difficult and time-consuming due to interactions among branches and with the fan. As one adjusts a damper to reduce airflow in that duct, all other airflows increase. As each damper is inserted, the overall resistance of the system increases, reducing fan output. The Target Method uses target values of centerline velocity pressure (VPcl) or hood static pressure (SPh) computed from the measured values of VPcl and SPh multiplied by factors intended to account for (a) initial Qbrand Qbr-goal, (b) the interactive effects of dampers on branch airflows, and (c) a model that predicts the reduction in fan airflow due to the dampers. Simulations on a computer spreadsheet predict that the Target Method will produce better accuracy for fewer adjustments than the goal method, but it is more computationally difficult.

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Section: Strategies For Adjusting Dampersmentioning

confidence: 99%

Section: Example System and Computationmentioning

confidence: 99%

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A Goal Method and a Target Method for Balancing Exhaust Ventilation Duct Systems with Dampers

Guffey

2007

Journal of Occupational and Environmental Hygiene

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“…(1) Some ventilation authorities argue against the use of dampers, favoring "balance by design" to achieve desired airflows. In particular, Caplan (2) stated that it was often difficult to adjust dampers properly and that the dampers themselves could encourage blockages.…”

Section: Introductionmentioning

confidence: 99%

“…A portion of the airflow can be shifted from one branch duct to another by changing the relative resistance to flow of the two pathways. (1) This can be done by strategic substitution of members (e.g., elbows with different resistances), but that can be discouragingly costly and disruptive. Ventilation system owners are more likely to take timely corrective actions if there is a nondisruptive and less expensive way to shift airflows among branches.…”

Section: Introductionmentioning

confidence: 99%

Experimental Validation of a Target Method for Balancing Exhaust Ventilation Duct Systems with Dampers

Dodrill

Guffey

2008

Journal of Occupational and Environmental Hygiene

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This study tested the "Target Method" for adjusting ventilation systems. The Target Method is based on target hood static pressures (SPh(target)) computed in a manner designed to take into account the estimated effects of dampers on the fan, the order of damper adjustments, and the ratio of the prebalancing branch airflows to their goals. It is aimed at achieving a desired relative distribution of airflows even if the fan output is far from ideal. The method assumes the fan output will be adjusted after the dampers are adjusted. The method is expected to produce lower fan pressure requirements than some commonly used methods. The method was tested on a working seven-branch, full-sized exhaust ventilation system in the West Virginia University Exposure Assessment Laboratory. Two radically different target distributions were tested with two replications apiece. Both target distributions of airflows were substantially different from the initial distribution, providing a high degree of challenge to the methodology. For each distribution, SPh(target) values were computed for the first round of adjustments. Each damper was adjusted until the observed value of the hood static pressure was nearly equal to that damper's computed SPh(target) value for that distribution. Each of the other branch dampers was adjusted similarly in turn. After the first round of adjustments, the median ratio of SPh to SPh(target) provided the targets for the partial second round of adjustments. Twenty-point Pitot traverses were used to determine the airflow in each branch duct both before and after employing the adjustment method, providing the basis to determine the success in reaching each of the two desired distributions. The percentage of excess airflow (assuming ideal adjustment of the fan speed) was below 2.2% for all experimental trials. An unpublished study by Vivek Balasubramanian showed that excess airflow was 4.8% to 8.5% in the same experimental system after two full rounds of adjustment using the customary Target Method. Under poor measurement conditions, the greater uncertainty of pressure measurements would likely produce somewhat higher excess airflows.

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A novel flow-guide device for uniform exhaust in a central air exhaust ventilation system

Tong

Gao

Luo

et al. 2019

Building and Environment

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Exhaust ventilation system with one central fan and multiple terminals has been widely used for the heat and contaminant removal in building environment. Conventional design without pressure balancing leads to uneven distribution of exhaust airflow rate among the multiple outlets. Existed balancing methods usually uses dampers (constant-air-volume valve or regulating valve), tapered duct, or varied inlet area. However, these methods result in higher fan energy consumption, or complicated construction and on-site commissioning. In this paper, a flow-guide device was developed for adjusting the pressure distribution of duct branches. This new device is integrated with the interflow Tee-junction and does not need any commissioning or regulating. The resistance performance of the device responding to the structural parameter was derived using the CFD simulation and experiment. The negative direct resistance featured by the device was found to effectively benefit exhaust at the outlets farther away from the central fan. The ductwork hydraulic model based on the Bernoulli's law of airflow and the fitted resistance correlations were further proposed to fulfill the parametric design. Finally, full-scale test was carried out for a central exhaust system installed with the flow-guide devices referring to a factory workshop with 30 heat and contaminant sources. Compared to the system without the devices, the total rate of the system increased by 25%. Discrepancy of exhaust rate decreased by 78% and uneven degree decreased by 82%, which well meets the engineering balancing requirement. Meanwhile, total resistance of the system reduced 23.8% owing to the negative loss the devices bring.

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Air-Flow Redistribution in Exhaust Ventilation Systems Using Dampers and Static Pressure Ratios

Cited by 7 publications

References 3 publications

A Goal Method and a Target Method for Balancing Exhaust Ventilation Duct Systems with Dampers

A Goal Method and a Target Method for Balancing Exhaust Ventilation Duct Systems with Dampers

Experimental Validation of a Target Method for Balancing Exhaust Ventilation Duct Systems with Dampers

A novel flow-guide device for uniform exhaust in a central air exhaust ventilation system

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