air flow

At sufficiently high Reynolds numbers, the discharge coefficient Cd associated with a sharplycontracting flow through a square-edged opening is, in general, taken to be constant.

Natural ventilation is one of the most fundamental techniques to reduce energy usage inbuildings. However, due to complicated site plans and building layouts, it is difficult todesign optimal layouts for the enhancement of ventilation without knowledge about the flowpatterns. The employment of computational fluid dynamic (CFD) tools in the design processcan give predictive feedback to the designers, allowing them to optimize airflow around thesite to decide on building placement, orientation, and interior space layout.

Before starting to design an HVAC installation for treatment, supply and exhaust of air to and from a building the needs should be listed, transformed to requirements and their consequences analysed. Requirements lead to different amounts of airflow for their fulfilment. These needs for airflow should be calculated. The demand leading to the highest call for airflow will decide the airflow for which the equipment should be dimensioned - the dimensioning airflow.

In this study a series of parametric laboratory measurements were made of the velocitiesoutside, ve, and inside, vi, a full-scale louver positioned in a rectangular opening located in avertical wall forming part of a 1m x 1m x 2m deep model room. The louver parametersexamined, for external incident wind speeds from 0.6 to 2.5 m/s, included louver blade depth(L), aperture (d) and distance from the louver in to room (Rd). For this initial study the bladesof the louvers for each experiment were horizontal with an inclination angle ? of 0.

This paper presents the results of ventilation measurements taken in a non-occupied one-storey dwelling situated in the countryside. The measurements of the ventilation rates in the different rooms have been obtained by the use of tracer gases with the constant concentration technique. Four configurations of ventilation systems have been tested successively. The ventilation systems tested consist of natural air supply and mechanical exhaust. Both 'normal' air supply grilles and self-regulating grilles have been tested.

The prediction of energy use, air flows and temperatures in different rooms of a building andat different climatic conditions is very important, especially when evaluating new conceptsfor heating and ventilation systems in combination with different building envelopeconstructions. A thorough system analysis considering coupled air flow and thermalcalculations becomes very complex if e.g. thermal bridges and dynamic conditions areconsidered.

The two-dimensional turbulent airflow generated by two non isothermal plane wall jets in a compartment is numerically investigated over a wide range of supply airflow rates. The low-Reynolds-number turbulence model of Nagano and Hishida, assembled in a finite-volume-based numerical code, is used after a previous validation study involving several other formulations of the k-e model.

This paper provides a theoretical error analysis of common airflow measurement and control techniques to maintain minimum outside air intake rates in variable air volume (VA V) systems. The results of the error analysis indicate that control strategies using direct airflow measurement from either an averaging Pitot-tube array or an electronic thermal anemometry provided the best ventilation control.

Traditional air-handling unit (AHU) control systems link the position of the exhaust, recirculation, and outdoor air dampers. Laboratory tests of a variable-air-volume AHU using the traditional damper control approach revealed that outdoor air could enter the AHU through the exhaust air damper. This can negatively impact indoor air quality. This paper examines the conditions that lead to this phenomenon and presents a new control system that can help alleviate the problem. The new control system links only the position of the exhaust and recirculation air dampers.

This study investigated the pressure flow characteristics over a number of fullscale modulated louvered windows (MLW). The various MLW parameters included louver inclination angle (8), depth (L), aperture (d) and the ratio of aperture/depth (d/L%). Airflow models were developed using both power law and quadratic model equations. By examining the coefficient of determination (r2) for both model equations, it was evident that the quadratic model equation suggested the best curves fit.