modelling

At present, Computational-Fluid-Dynamics (CFO) with the 'standard' k-e model is a popular method for numerical simulation of room airflow. The k-e model needs a lot of computing time and large a computer. This paper proposes a new zero-equation model to simulate three dimensional distributions of air velocity, temperature, and contaminant concentrations in rooms. The method assumes turbulent viscosity to be a function of length-scale and local mean velocity.

Convective heat transfer from internal room surfaces has major effect on the thermal comfort, air movement and heating and cooling loads for the room. Recent studies have shown that the values of convective heat transfer coefficient used in building thermal models greatly influence the prediction of the them1al environment and energy consumption in buildings. In computational fluid dynamics ( CFD) codes for room air movement prediction accurate boundary conditions are also necessary for a reliable prediction of the air flow.

The numerical evaluation of room air movement is made by systematic discretization of space and the dependent variables. This makes possible to replace the governing differential equations with simple algebraic equation. The dynamic model of the temperature is based on the energy balance equation, considering a given flow field. The temperature in a given control volume depends on the temperatures of its corresponding neighbours. This form of the model is. not appropriate for control theory.

A two-dimensional turbulence k-e model is used to predict distribution of air velocity, temperature and turbulence kinetic energy in an air-conditioned room using ceiling air supply. Mixing characteristics of the airflow are analyzed under different air supply velocities and temperatures. A modified Archimedes number is correlated with the parameter ·characterizing heat transfer, ventilation system, and turbulence kinetic energy of room air flow. Significant correlations have been shown.

In this paper ventilation strategies are examined in order to improve the thermal performanceof an attached sunspace of a two-storey semi-detached house in the area of Athens Greece.The ventilation strategies examined are cross and single-sided ventilation through the verticalwindows of the sunspace. Simulations were conducted implementing multizone ventilationmodel COMIS coupled with the thermal simulation model Suncode.

Cheap 3D models for visualization of room ventilation applications are now available. VRML (Virtual Reality Modelling Language) is found to be a good format to describe buildings, rooms and furniture. A 3D model in VRML can be placed on an World Wide Web www page and others can see the model in "Walk Through" mode. Use of VRML is described with examples as for instance in planning of measurements and as a basis for geometry in CFD calculations. The advantage of 3D and VRML is that it is much easier to see, find and correct problems than using traditional drawings.

Previous full scale experiments gave us a global and qualitative understanding of the gas circulation in a ventilated room in case of fire. In order to go thoroughly in the knowledge of these phenomena, we have built a scale model to perform more precise temperature measurements and more complete tracer gas experiments. The results show the existence of two zones when the air inlet is near the floor. At the opposite, when it is near the ceiling the room can be considered as a one single zone.

The efficiency of a kitchen ventilation system is usually determined by its ability in heat and effluent removal. The main part of a ventilation system is the hood, with its face (or capture) velocity. Heat generation associated with the cooking process is the main factor that affects the thermal comfort. The heat removal capability is studied under different capture velocities so as to determine the minimum requirement for efficient removal of heat and effluent.

Infiltration has traditionally been assumed to affect the energy load of a building by an amount equal to the product of the infiltration flow rate and the enthalpy difference between inside and outside. Results from detailed computational fluid dynamics simulations of five wall geometries over a range of infiltration rates show that heat transfer between the infiltrating air and walls can be substantial, reducing the impact of infiltration.

Simulations have been performed to investigate the performance of intelligent algorithms for control of indoor air quality through natural ventilation strategies whilst simultaneously meeting the requirements of thermal and visual comfort. The proposed control algorithms are founded on the knowledge base of the building physics and support the control of natural ventilation through control of the window opening, whilst simultaneously controlling the lighting, heating and cooling systems of the building.