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displacement ventilation

Thermal comfort in a mixing ventilated room with high velocities near the occupied zone

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.

Computation of airflow in a displacement ventilation/chilled ceiling environment

This study is to validate a CFD model of displacement ventilation combined with chilled ceiling and determine if this combination may create draught risk or influence badly indoor air quality.

An example of verification, validation, and reporting of indoor environment CFD analyses

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.

Numerical investigation of transient buoyant flow in a room with displacement ventilation and a chilled ceiling system

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.

Displacement ventilation environments with chilled ceilings: thermal comfort design within the context of the BS EN ISO 7730 versus adaptive debate.

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.

A critical review on the performance and design of combined cooled ceiling and displacement ventilation systems.

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.

Experimental and numerical investigation of temperature distribution in room with displacement ventilation.

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.

Displacement ventilation application for hot and humid climate.

Discusses the possible use of displacement ventilation systems in warmer climates.

Displacement ventilation versus mixing ventilation - comparison of energy use.

There are basically two ventilation principles that can be utilised in a room: mixing ventilation (denoted MV) and displacement ventilation (denoted DV). In MV, air with high velocity is supplied outside the zone of occupancy, which ideally gives uniform temperature and concentration in the room. In DV, cool air with low velocity is supplied in the lower part of the room. Contaminated air and heat is transported towards the ceiling by the convection currents set up by heat sources, where is is extracted.

Virtual reality presentation of temperature measurements on a diffuser for displacement ventilation.

The instantaneous temperatures close to a diffuser for displacement ventilation have been measured by using a whole-field measuring method. The air temperature was measured indirectly by using infrared thermography with a digital infrared camera and a measuring screen. By moving the measuring screen the whole field around the diffuser was measured. A method has been developed for combining the tow-dimensional measurements to produce a three dimensional representation.

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