Research On The Measurement Of Ventilation Rate And Evaluation Of Local Domain Ventilation

As the development of economy and the improvement of life quality, comfortableand healthy indoor environment has become a public concern.. Ventilation is animportant means to create a desirable indoor environment. Lack of ventilation willresult in a series of health problems. However, excessive ventilation may result in greatenergy consumption. What’s more, part of the supply air cannot be effectively utilizedbecause of the unreasonable air distributions. Under this background, four importantissues during the measurement of ventilation rate and evaluation of ventilation effect inlocal domain are carried out in this thesis. The frame work is as follows:1). Research on the measuring method and device for ventilation rate in air ductswith tracer gas.Firstly, a novel measuring method and system is proposed and the applicability isanalyzed. The term ‘mixing length’ is defined in order to define the influencing factor.On the foundation of the theoretical analysis and numerical simulation, some methodsare advised to reinforce the mixing of tracer gas and air. Based on the research, a deviceis developed and tested, and the results prove the merits of this method. Finally, theapplication of this method is discussed.2). Analysis on the uniformity of indoor distribution and the problems of decaymethod, and introduction of effective ventilation rate.Indoor multi-zone model is built to analyze the uniformity of indoor space. Theresults prove that the slope of the concentration decay is the same in all subzones ifindoor distribution is non-uniform. It indicates that the so called ‘air change rate’ gotfrom the decay method cannot represents the real air change rate of the room. For theroom with fixed outlet, the feasibility of the accurate measuring with decay method isdiscussed. The effective ventilation rate and its advantages in evaluation and measuringare introduced.3). Proposing of an equivalent source model and comprehensive indices for theevaluation of local domain ventilation.The advantages and limitations of local purging flow rate are studied throughcomparative analysis. Based on the Markov Process, the equivalent source model andcomprehensive indices, including the local purging flow rate, equivalent source intensity and extracting potential of contaminant, is proposed to evaluate the effect andpotential of local domain ventilation. A simple calculation method for the indices withCFD tools is introduced.4). Brief analysis on the impact of the unsteady condition on the ventilation effect.The results based on the well-mixing assumption show that the time-averagedinstantaneous ventilation rate (absolute value) is very close to the time-averagedeffective ventilation rate. It indicates that the measured effective rate can be used astime-averaged instantaneous rate during design and evaluation processes.The research progress in this thesis deepens the understanding of room ventilation.Moreover, the conclusions can help to measure and evaluate the room ventilationreasonably, and optimize the design of ventilation for local domain correctly.