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.
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.
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.
One of the reasons for using displacement ventilation is that it may provide better indoor air quality in the occupied zone than conventional mixing ventilation. It is therefore important to understand the importance of the system on this aspect. A validated CFD model was employed to generate concentration distribution data for CO2, radon and moisture in a Hong Kong shop with displacement ventilation. Analysis found that the concentration distribution affected by factors such as the source type and location, its associated plume strength and human body convection, etc.
This paper deals with the performance evaluation of three types of low-level ventilation systems: the wall displacement ventilation, the floor displacement ventilation and the impinging jet ventilation systems. The comparison between the performances of these three systems is based on air movement, comfort assessment, mean age of air and ventilation efficiency for contaminant removal. Data from measurements and CFD simulations are used for comparisons.
A new method of transport process visualisation is suggested to analyse the fluid flow and heat transfer structures. A two-dimensional displacement ventilation flow model is comprehensively investigated. Results demonstrated that the streamline and heatline visualising means macroscopically exhibit the nature of momentum and heat transfer philosophy, providing a direct insight to see the IAQ.
Today there is an increasing focus on the importance of a proper ventilation system to obtain good working conditions in the term of air and thermal quality to ensure high productivity. Different ventilation principles are used, e.g., mixing ventilation and displacement ventilation. In order to ensure that the ventilation system meets the demands it is important to know which parameters that influence the performance of the system. In this work the mixing ventilation principle was investigated.
Describes how a nodal model was developed intended to represent room heat transfer in displacement ventilation and chilled ceiling systems. Precalculated air flow rates were used to predict the air temperature distribution and the division of the cooling load between the ventilation air and the chilled ceiling. A network of ten air nodes is used to separately represent the air movements in the plumes and the rest of the room. Calculation of the capacity rate parameters is done by solving the heat and mass balance equations for each node using measured temperatures.
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