This paper analyses through CFD simulation results the removal effectiveness in an office cooled by a chilled ceiling combined with either mixing or displacement ventilation. For passive pollutant sources, both systems provide similar air quality. For active pollutants and when a large volume of all fresh air is supplied, displacement ventilation has better performance.
Measurements were carried out in a test chamber with displacement ventilation to know the vertical distribution of airborne particles generated by two human subjects having an activity representative of that of people working in an office. Particle concentration was observed as increasing with height. A threshold size of particles was found at 5 to 10 microns above which the displacement effect of particles by air flow started to decline. Negative concentration gradients were observed for large particles at the lowest ventilation rate, when the air flow does not displace them.
Experimental results on the thermal conditions around a ventilated chair (with air supply openings in its base) are provided. They concern air velocities, temperatures and thermal comfort for a seated person. Results are commented compared to those obtained in a room with displacement ventilation with wall-mounted diffuser.
Experimental results in a testing room with mixing ventilation were used to define two new ways of designing the inlet airflow in order to ensure comfort. The first way uses the assumption that air velocities are only a function of the Archimedes number, which provides curves showing air velocity in the occupied zone as function of inlet air temperature and velocity. The second way results from an analytical calculation of the penetration length of the air jet in the room and the distance where it enters the occupied zone.
A procedure to verify, validate and report CFD analyses in indoor environment applications has been developed. The process on how to use this procedure is explained through the example of CFD modeling of an office with mechanical displacement ventilation.
Flow and heat transfer calculations have been operated in a typical office room equipped with a displacement ventilation and a chilled ceiling system. Results show quasi-periodic flow when the values of internal thermal loads are high. They also show lateral oscillations of the plumes above heat sources which create after impact on the cold ceiling recirculating flows in the room.
Describes the current design standard BS EN ISO7730 - 'Moderate thermal environments - determination of the PMV and PPD indices and specification of the conditions for thermal comfort'. States that it is based on Fanger's work and comprises a steady-state human heat balance model that leads to a prediction of the sensation of human thermal comfort for a given set of thermal conditions. Questions the applicability of this standard when confronted with the more complex environment of a chilled ceiling operated in combination with displacement ventilation.
The subject of this study is the design of cooled ceiling and displacement ventilation systems in buildings. States that good design of CC/DV systems can lead to better indoor air quality and thermal comfort in comparison to widely used VAV mixing systems. A key design parameter is the cooling load removed by the displacement ventilation. Due to a small vertical temperature gradient, a low DV has a positive effect on thermal comfort, but also has a negative effect on indoor air quality because of the increased mixing of room air.
Describes an improved form of the standard k-epsilon model for buoyant room flows and gives an assessment of the results. The improved model is based on the generalized gradient diffusion hypothesis of Daly and Harlow. Compares the results from the computations for three-dimensional flow with temperature measurement performed by the authors in a laboratory room with displacement ventilation. A good agreement is shown by the numerical results, better than the results from the standard model.