IJV3

The air conditioning of large non-domestic buildings is becoming an increasing trend, even in moderately mild climatic zones. This is often needed to avoid overheating that results from high internal heat gains and solar radiation. This paper describes work, undertaken in the United Kingdom, aimed at minimizing the need for conventional air conditioning in such buildings.

The work described in this paper formed part of the European UrbVent project on urban ventilation.Measurements of wind speed, wind direction, and air temperature were made at four different heights, inside a pedestrian street canyon in the centre of Athens, Greece, and at the top of the canyon. In addition, infrared radiation on the canyon faades was measured. Experimental data were collected at intervals of 30 seconds. The dimensions of the canyon were: height/width=2.3, length/height=50/23=2.2 with an orientation of 12 degrees from North.

This paper introduces a concept of robustness of an air distribution method, which is defined as being capable of meeting the ventilation requirements during varying operational conditions. The robustness performance may be particularly important when the system allows individual control of the supply air parameters. As a preliminary example, plenum-based (ductless) air distribution methods are studied using computational fluid dynamics.

Ventilation towers are often incorporated into the design of naturally-ventilated buildings. These towers increase the physical height of the building and thereby potentially enhance the buoyancy-induced air velocity. However, acoustic baffles, insect meshes, etc., placed within the towers result in pressure losses that effectively reduce the area of the flow path, thereby restricting the rate of airflow.

This research grows out of a desire to find a Solar-Wind Generated Roof Ventilation System for low-cost dwellings located in high building density urban areas where horizontal air movement is restricted. A general purpose computational fluid dynamics (CFD-ACE+) program was utilised to explore, analyse and develop a roof model based on its aerodynamics and thermal performance to obtain optimum wind pressure and temperature differences. Comparisons were made with physical scale models.

This paper reviews the current literature on discharge coefficients (CD) of openings and compares different studies for wind-driven cross-ventilation. Considerable variation of discharge coefficients with opening porosity, configuration (shape and location in the faade), wind angle and Reynolds number is shown. Consequently, the use of a constant CD value such as that given in textbooks or other sources might be an invalid simplification.

To accurately estimate the natural ventilation of outdoor spaces surrounded by low-rise buildings using a wind tunnel requires correct representation of the natural wind regime combined with appropriately scaled building models and testing method. Existing outdoor ventilation studies are largely based on wind speed and estimated air change rates. Wind speeds mainly influence: peoples comfort, safety in pedestrian areas, the heat transfer between outdoor surfaces and airflow, and evaporation from wet surfaces.

Top down natural ventilation systems, usually referred to as ‘windcatchers’, have been used recently in modern non-domestic buildings in the UK. These systems combine inlet and outlet into a single roof mounted terminal, which is split into sections. Literature exists on theoretical, scale modelling and wind tunnel tests to evaluate the performance of the systems; however there is a scarcity of performance in-use tests. This paper presents the results of air exchange rate tests using the tracer gas decay method carried out in three operational buildings with windcatchers.

This paper presents a three-dimensional zonal model, ZAER, for heat transfer and air flow calculations. It is based on an intermediate approach between single-air-node and CFD models. The indoor air volume is divided into macroscopic homogeneous zones. Heat and mass balance equations are written for each zone, while the mass flow rates across the interfaces are calculated by power pressure laws. The simulation tool ZAER allows the determination of temperature fields and air flow distributions inside unconditioned buildings, taking into account external boundary conditions.

A zonal model is an intermediate approach between computational fluid dynamics (CFD) and single-room models. It can give results faster than CFD and be more accurate than single-zone models. It has been used to provide some global information regarding thermal and flow parameters within a room. In this review, due emphasis is given to the commonly used pressurized zonal model - the power law. Qualitative validations show that the power law model reasonably predicts well for natural convection.