Methodology for the Evaluation of Natural Ventilation in ... - Cham

helium-air bubbles were created using this generator. This media proved useful in its long hangtime; the bubbles disappeared when they burst when colliding with a surface. However, thegeneration rate of the small (2-3 mm diameter) bubbles was approximately 5-10 per second. Fora large volume room, this rate was insufficient to track airflow patterns accurately within thespace. In the reduced-scale models, the small volume of space did not allow the bubbles to travela great distance before bursting on impact with a surface, particularly with the buoyancy-drivenflow.Draeger smoke pencils were used for much of the localized airflow within the prototypebuilding, but these were found to dissipate too quickly within the model. They were able toshow localized airflow patterns within the occupied space, as the measured air velocities werewell below 0.5 m/s. Since they were being used for localized flow, the flow visualizationexperiments could be carried out during occupied hours, when heat loads due to the occupants,lights, and office equipment were present. This provided realistic airflow patterns for anoccupied commercial office building. By determining localized airflow patterns at various heightand locations throughout the prototype building, an understanding of the overall airflow patternswas obtained. Though useful for localized flow patterns within the prototype building, thesmoke pencils dissipated more quickly in the reduced-scale air model. The velocities that wererecorded for the scale model were 0.2-0.8 m/s, causing a much faster dissipation of the smokepencils. In the prototype building, the smoke dissipated quickly at the windows, but was visibleenough to show the flow direction. In the occupied space of the prototype building the measuredair velocities ranged from still to 0.5 m/s within 1 meter of an open window. Therefore, anotherapproach was created, to try to produce a relatively steady stream of ‗smoke‘, at multiple inletlocations. This was done using a fogger machine that initially uses heat to produce fog, whichwas then attached to a series of tubes to decrease the inlet velocity and cool down the fog media.The fogging machine has its own benefits and drawbacks. One of the problems with foggingmachines is the difficulty in controlling the amount of media that is being generated by thefogger. Too much smoke can obscure airflow patterns, thereby making them indistinguishable.The fog machine produces a visible fog by heating up a glycerin-based solution, which exits thefog machine at 45°C. An apparatus was created in order to cool down the fog that was producedto the inlet air temperature of the model and then introduce the fog in through the windowopenings. A series of small nozzles was attached to a long tube that extended the length of thefaçade of the model. The nozzles were spaced so that each one supplied fog to each window.This apparatus worked for the single and two-zone cases, but was removed for the full-modelexperiments, as it did not allow adequate amounts of fog into the model. The use of a remotecontrol device to provide small spurts of fog, rather than one constant stream also helped incontrolling the amount of fog being introduced. Care was taken to ensure that the intermittent fogbeing introduced into the model was not introduced with significant velocity, which woulddisrupt or alter the airflow patterns.Three independently controlled 9-watt compact fluorescent lamps were used in the reduced-scaleair model to provide some amount of illumination used to capture the airflow patterns. Theselamps were chosen for their lumen output and their low heat output. It was important to limit theamount of additional heat added to the model, as additional heat sources would influence theflow patterns within the model. The compact fluorescent lamps combined with a Canon S4080