English

Analysis of temperature trends for the last 100 years in several large U. S. cities has indicated that since -1940 there has been a steady increase in downtown temperatures of O. l-0.5°C per decade (-0.5°C for larger cities like Los Angeles and 0.1°C for smaller cities). Typically, electricity demand in cities increases by 2-4%/°C, hence, about 5-10% of the current urban electricity demand is spent to cool buildings just to compensate for the urban heat island effect. Downtown Los Angeles, for example, is now 3°C warmer than in 1940 leading to an increase in electricity demand of 1500 MW.

This paper presents the results from the monitoring of a low energy building, namely, the Portland Building University of Portsmouth - UK) during February and July 1997. The BMS Research Group at the University of Portsmouth has instrumented the building so that its performance can be compared with the predictions obtained at the design stage. The Building has been operational since July 1996 and the monitoring exercise commenced in January 1997. Sensors monitor air temperature, air relative humidity and slab temperature in selected areas of the building.

This investigation is part of project NATVENT TM, a concerted action of nine institutions of seven European countries under the Joule-3 program. It aims to open barriers that blocks the use of natural ventilation systems in office buildings in cold and moderate climate zones. The choice to apply natural ventilation in office buildings is very arbitrary; it depends very much on the personal preference of the architect or taken for budgetary reasons, even sometimes not considered at all.

The air flow in a Passive Downdraught Evaporative Cooling (PDEC) tower has been modelled using a Computational Fluid Dynamics (CFD) code. Water is injected into dry warm air and the interaction between the water and the air is represented using a particle transport model. This models the transfer of mass, momentum and heat between the water particles and the air in addition to predicting individual particle trajectories.

The results presented here supply values for the room ventilation efficiency of a number of configurations covering as many as possible of the ventilation systems encountered in actual practice. The study is based on experimental results and numerical simulation. Using a few configurations experimented-on, simulations were performed using CFD code, which in particular allowed the reliability of calculations to be checked. The simulation tool was then used in such a way as to arrive at results that could be applied in practice.

The purpose of this research is to give an overall prospect of the performance of 4 kinds of ventilation systems for dwellings using numerical simulation under various conditions. The total number of combinations of various parameters for the calculation is 174. Calculations for pollutant concentration, humidity and condensation, interior pressure and airflow rate, heat energy by ventilation, etc. are performed hourly through the heating season.

This paper presents an analysis of different possibilities of representing mass transfers in zonal models. In this aim, formulations derived from the Navier-Stokes equations or from Euler's theorem are obtained. The models which result from them and empirical models are compared so that to define the best compromise between simplicity, accuracy and easy convergence.

Trouble shooting air distribution problems in mechanically ventilated offices often has to be carriedout in limited "after hours" periods. The method of applying a pulse of tracer to the fresh air supplyhas been found to be too time consuming to map the local mean age of air over complex floor plans.In response an automated gas chromatograph has been developed to make air change efficiencymeasurements in real time using the method of homogeneous emission.

Concentrations of indoor air contaminants are normally calculated by assuming that they fullyfollow airflow paths in a room. This assumption is also used to predict the local residence timeof contaminants in a room, which may further be used to characterise the ventilation effectiveness.In this paper, a different methodology has been adopted, in which indoor airborne particles do notalways follow the main airstream induced by the ventilation system. Dispersion of particles ispredicted by a drift-flux model.