Submitted by Maria.Kapsalaki on Thu, 05/28/2015 - 11:35
The mixing of a tracer gas with zonal air was compared between two zones in an unoccupied test building in both the horizontal and vertical direction. A constant injection of sulphur hexafluoride (SF6) tracer gas was released into each zone separately and its concentration was measured at different positions within the zone. Variations in concentration were observed for different horizontal positions in the southern zone indicating incomplete mixing.
The increasing incidence of airborne transmitted diseases indoors has prompted the attention ofstudying expiratory droplet dispersion and transport in built environments. Droplet dispersion in aroom under the conventional well-mixed and displacement ventilation is simulated. In this work, asource (i.e. a patient) and a receptor (i.e the susceptible object) were located in a mechanicalventilated room. This study evaluated droplet dispersion and mixing under well-mixing anddisplacement ventilation scheme.
The paper will discuss design models for the air distribution system in an office with twopersons. The comparisons are made between mixing ventilation and displacement ventilationand they are based on a maximum velocity assumption and a restricted vertical temperaturegradient in the room. The comparison is extended by considering both the local discomfortcaused by draught rating (DR) and the percentage of dissatisfied due to the temperaturegradient (PD).
Mixing ventilation and displacement ventilation were compared in an intervention study inclassrooms. Particles, cat allergen and CO2, were measured in classroom air at different levelsabove the floor, during regular lessons. With mixing ventilation, the particle concentrationtended to decrease with height, with a stronger gradient occurring for larger particles. Withdisplacement ventilation, the particle concentration increased with height, except for particles>25 m. The displacement system thus tended to have a slight upward displacement effect onmost of the particles.
The influence of uniformly distributed cooling load is investigated on the air velocity in theoccupied zone. The experiments have been carried out in a scaled test room of 6 6 2 mwith a scale factor 1:1.5. The room is equipped with nine vortex inlets. The inlets areuniformly distributed; every inlet supplies a cubical volume to remove the maximum possiblecooling load with a minimum airflow rate. The air supply rates based on floor area are set to30 m/(h m2). The cooling load generated by mannequins is uniformly distributed and variesbetween 0 and 180 W/m2.
Existing technical recommendations and standards regarding natural ventilation in Portugalestablish one air change rate, ACH, in main rooms (bedrooms and living rooms) and fourACH in service rooms (kitchens and bathrooms).
This paper considers the predictions obtained using a recently developed ventilation parameter (VP) for evaluating the ventilation performance which combines the indices for indoor air quality and thermal comfort. This ventilation parameter is used to analyse the changes in ventilation performance with changes in the position of workstation in a room ventilated using mixing ventilation.
This paper examines thermal mixing of outdoor and return airstreams in typical air-handling units equipped with parallel blade dampers. The mixing of the two airstreams in rectangular and square mixing chambers is studied for eight different dampers and blade orientations. Testing is conducted at a total supply air of 16000 CFM with outdoor flow percentages of 15% and 30%. The temperature differential between the outdoor and return airflows is kept at 40F. Damper blades with chords of 4 and 6 inches are tested.
The mixing of different air streams is a process commonly found in air handling systems. One of the most common examples of this process is found in the air handling unit mixing box where outdoor air is mixed with return air. In the adiabatic mixing process, the energy leaving the mixing box equals the energy entering the mixing box. In order to calculate the energy in the mixed air stream, it is only necessary to know the energy in the outdoor and the return air streams. As a result, it is not necessary to consider whether the mixing process is ideal or not.
The evolution of the temperature profile in a warm room driven by a natural ventilation flow which develops when the room is connected to a cold exterior by two openings at different vertical heights is explored. With the openings at the top and base of the room, we find the classical displacement ventilation regime provides a leading order description of the flow. With openings at the centre and top of the room, the ventilation is hybrid, with the lower part of the room being well-mixed, and the upper part being stratified by an upward displacement ventilation flow.