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Portable air flow meters are widely used for measuring air flow rates in the field. To cover broad range of flow rates, multi nozzles are generally used. If ASHRAE standard for installing nozzles is applied, the device gets large and heavy, and becomes difficult for compact sizing and handling. In order to overcome this problem, computational fluid dynamic(CFD) simulations were performed to identify the factors that can make the size of the air flow meter smaller. With help of numerical simulation of which the accuracy was verified by the experiment, the necessary area for multi nozzle installation can be reduced by 47%. Based on the modeling of CFD, a portable air flow meter was manufactured and compared with an air flow measurement device that is compliant with ANSI/ASHRAE 51-1999. Nozzles and dampers which affect the length and cross-sectional size of an air flow meter were selected and improved to suit the portable type. A portable small scale multi nozzle flow meter with exit pressure control that was developed in this study has advantages of small size and acceptable accuracy in the field measurement which showed an error of 0.93%. [ABSTRACT FROM AUTHOR]

Outdoor airflow rate, building static pressure, supply air duct static pressure, and relief air plenum static pressure, as controlled variables, are maintained by modulating the speed of the supply and return fans and the position of the outdoor, recirculating, and relief air dampers in an air-handling unit (AHU). The three dampers are often interlinked completely or partially to match independent control inputs with the controlled variables. The traditional damper control has all three dampers interlinked with no control over the relief air plenum static pressure. Reverse relief airflow might occur as the outdoor air damper approaches the closed position. To prevent reverse airflow, one solution is to decouple the relief air damper and maintain positive static pressure at the relief air plenum. Two control methods are available based on the controlloopdesign. The first controlmethoduses the return fan speed to control the relief air plenum static pressure and the relief airdamperto control the building static pressure, and the second control method switches two control inputs. The purpose of this paper is to evaluate the controllability of the reverse relief airflow and building static pressure of these two control methods. The system performance is investigated through steady-state simulations on an AHU at different outdoor airflows using a nonlinear network solution. The simulation results show that both the control methods can well prevent reversere lief air flow. However, the first control method with a constant pressure setpoint may result in negative building static pressure at lower outdoor airflow ratio and either excessivelypositivebuildingstaticpressureorexcessivereturn fan power at higher outdoor airflow ratio. The second control method shows better control over the building static pressure control. A reset pressure scheme should be associated with the first control method when the relief damper is fully open. [ABSTRACT FROM AUTHOR]

Air leakage data from six parallel fan-powered terminal units (FPTUs) that used electronically commutated motors were evaluated to determine if simple models of air leakage could be developed for applications in building energy simulation programs. The data were from an earlier investigation by Edmondson et al. (2011). Units with both 8 and 12 in.(20.3 and 30.5 cm) primary inlets from three manufacturers were evaluated. The analysis included the impact of downstream static pressure, upstream static pressure, and primary airflow on the leakage from the units. Data for downstream static pressures ranged from approximately 0.1 to 0.5 in. w.g. (25 Pa to 125 Pa) and ranged from approximately 0.4 to 2.0 in. w.g. (100 Pa to 498 Pa) for upstream static pressures. Because the original data included some primary airflows outside the expected range of operation of the 8 and 12 in. (20.3 and 30.5 cm) FPTUs, the data set was reduced to include only data in the expected primary airflow operating ranges of these sized units. All the original leakage data were collected with theFPTUfan off and with only primary air flowing through the unit. No attempt was made to quantify how much leakage was coming through differing sources of leakage, such as the seams, penetrations, or backdraft damper. Leakage was found to be primarily dependent on downstream static pressure. A simple regression of leakage and downstream static pressure yielded correlations with Rsquared values from 0.80 to 0.96. Leakage airflow showed little variation with either upstream static pressure or primary airflow when the downstream static pressure was held constant. Three leakage classifications were identified--low, medium, and high--based on the measured data. Correlations that describe the leakage as a function of downstream static pressure for each classification were developed. Calculations for a system with downstream static pressures varying with the square of primary airflow were performed and results presented. These leakage correlations can be used in building simulation models that use mass and energy balance approaches to modeling FPTUs. [ABSTRACT FROM AUTHOR]

The cooling performance of a raised-floor data center is dominated by its ability to deliver adequate cooling airflow to IT equipment through perforated tiles. Although many studies have focused on the design of plenum systems and the use of computational fluid dynamics (CFD) to predict tile airflow rates, very little has been published regarding accurately measuring airflow in existing facilities. We investigate the ability of a commercially available passive flow hood to accurately measure data center tile airflow and find that the built-in back pressure compensation functionality does not workwell. Further, two previously proposed correction methods for data center applications provide reasonable accuracy when applied to fairly restrictive tiles, but are inaccurate for large-open-area tiles. As a solution, we propose a new family of semiempirical two-measurement correction methods for passive flow hoods. Additionally, we construct a high-accuracy powered flow hood (PFH) to validate all of the passivehood methods. The existing and proposed methods are evaluated against bothCFDsimulations and measurements made in an actual data center. The correction method proposed in and recommended by this study yields the highest accuracy-- less than 5% error for scenarios considered. [ABSTRACT FROM AUTHOR]