PR1989

Rising moisture from the ground has caused quite a lot of damage on foundations of Swedish buildings. It is in some constructions possible to prevent this by mechanical ventilation below the floor or below the concrete slab. This paper will present a model for coupled air flow and heat conduction for mechanically ventilated foundations. The presented model uses analytical expressions for the air flow in an air-permeable layer below a rectangular building. Analytical double-periodic functions of elliptic type are used.

The paper describes the development in airflow simulations in rooms. The research is, as other areas of flow research, influenced by the decreasing cost of computation which seems to indicate an increased use of airflow simulation in the coming years. It is shown that velocity and temperature distribution can be predicted in small rooms of simple geometry as well as in large areas with a complicated geometry, such as theatres, atriums and covered shopping centres.

This paper describes a set of experiments conducted in a three bedroom house in order to identify the leakage distribution of the building and the air flow rate through the on-purpose designed opening of the interior doors. Starting from the depressurization test in every zone, we were unable to track all the flow equation of every specific identified connection. We therefore propose to characterize the leakage between two zones by a unique general connection. Its flow behavior (K,n) is determined by an optmization under constraints of the results of the various tests.

The distribution of wind pressure on a building envelope is governed by the size and shape of the structure and the turbulence characteristics of the wind. Observation of the mean wind pressures shows that surfaces are divided into pronounced zones of positive and negative pressure. The turbulence gives rise to fluctuating pressure components of appreciable magnitude. This fact changes the prerequisites of the ventilation for a given volume. The pressure in the cavity behind the facade materials depends on the external pressures over the facade.

In order to be validated, the computer programs simulating the air flows in multizone buildings need several measured data sets to be compared with. Such a set was measured on the LESO, a mid-sized administrative building. This set contains: a) The permeability coefficients (C,n) of the building obtained by guarded zone pressurization b) Pressure coefficients Cp measured in windtunnel and on the real building c) Tracer gas air flows measurements d) Corresponding weather data for two periods of 10 days on the non inhabited building.

Ventilation, infiltration, indoor air flows and air exchanges determine two aspects of fast growing interest: the energy balance of buildings and the indoor environment. Whilst in the wages of the energy crisis RD (research and development) & D (demonstration) in the different areas had been focused on rational energy use now with view on the public awareness of the environmental situation (outdoors and indoors) also the aspect of indoor air quali ty stimulates widespread RD&D activities.

VAV - air conditioning system makes it possible to control indoor conditions even when the heat loads are changing. But this is possible only when each part of the system works as it is intended to work. When the air flow varies in a large range, it can cause situations, where pressure loss of some flow dampers are out of their operating range. This is possible especially whenthe system is large and the velocities are high. This means that the air flow is not correct. Also increasing noise levels may appear.

This paper describes a simulation program which was developed for the modelling of air-conditioning systems and conditioned spaces in industrial buildings. The program can be used for a design of systems for new buildings and for analysis of existing ones. By viewing the building as a dynamic entity, it is possible to investigate how thermal capacity of the building elements acts on both the conditioned space and the performance of the air-conditioning system. The program simulates three important aspects of a building.

The use of passive perfluorocarbon technique for air flow measurements has been developed and tested. The building and testing of the system took approximately one year. The reproducibility of the analysis was tested during the period. The results show that the relative standard deviation of the analysis for parallel samples is less than 7 % for each tracer in most of the cases. A drift of calibration was noticed, but it can be allowed for by using reference samples with known amounts of tracers. The accuracy of the method was tested in controlled laboratory conditions.

The indoor climate and ventilation were measured in 50 dwellings with various ventilation systems. The health and comfort of people living in the dwellings were studied with a simultaneous questionnaire. The ventilation rates measured with a tracer gas using the decay method varied from 0.1 to 1.2 m³/hm³, with an average of 0.5 m³/hm³. The ventilation rate in the bedroom was usually lower than the mean ventilation rate of the dwelling. The ventilation rates measured in a two-week period with the passive perfluorocarbon method varied from 0.2 to 1.9 m³/hm³, with an average of 0.8 m³/hm³.