A Probabilistic model of air change rate in a single family house based on full-scale measurements has been developed. The probability of air change rate exceeding certain prescribed limits (risk of improper ventilation or excessive heat flow) is evaluated by utilising the distribution function based on calculated air flow rate. In this way the results are expressed in terms of the R-S model generally used in the safety analysis of structures.
Full scale measurements of air flow velocities, temperature, intensity of turbulence and air exchange rate are carried out on two rooms with different types of ventilation located in the department of architecture at Chalmers University of Technology. The measurements have shown that mixed ventilation gives variable mean flow velocities with a high risk of draught as compared to the room provided with displacement ventilation. Air exchange rate for the room with displacement ventilation is obtained from tracer gas monitor by employing decay and constant emission methods.
The use of local exhaust is considered to be the most effective way to control pollutant dispersion from intense sources, such as in kitchens, in toilets, as well as in copy machine rooms. The optimum air exhaust rate required to prevent pollutants from escaping into the major occupant areas very much depends on the natural air exchange rate(AER) between the hooded room and the major room space. This paper presents a mathematical model and a test procedure of using tracer gas technique to quantify the AER.
The work presented in this paper is aimed at the definition of tracer gas experimental procedures for measuring the air change rate, the age of air and the air change efficiency in real buildings under mechanical ventilation conditions. The measurement procedures, based on the decay method, were validated in a special experimental chamber and implemented in two rooms of a building under real operating conditions. Measurements of volumetric flow rate through the air ducts of two buildings, performed by means of the constant emission rate method, will be shown and commented.
One of the main aspects determining the thermal behaviour of buildings concerns the distribution and circulation of air. Experimentation was undertaken in the context of the investigation of a method of measurement of the natural ventilation of large rooms. The first objective was to endeavour to characterise the atmospheric conditions around the building, namely, conditions related to wind factors, but also those concerned with the location of the building in relation to neighbouring obstacles (other buildings, relief of the ground, etc).
The effect of recirculation on the age of air is described. A new effectiveness measure called the relative air-change effectiveness is defined in such a way that the air distribution pattern in a room may be quantitatively characterized even when the age of the supply air is non-zero. This admits the evaluation of air distribution patterns in single-zone systems that recirculate air, and also multizone systems with or without recirculation.
Login