当目标是尽量减少室内污染物的平均暴露时，通风系统的目标是尽快将污染物从通风空间中清除。污染物在通风空间的停留时间越短，暴露于污染物的程度越低；因此，污染物越早到达排气管，通风就越好。因此，这方面的重要参数是时间和局部流量，而不是通风工程中的传统概念，例如换气率或混合系数。 年龄或停留时间的概念适用于描述供应的空气或污染物如何在封闭空间内传播，以及污染物清除的速度。本文对这一概念在任何带有进气口和排气口的封闭空间中的应用进行了全面的讨论。建立了年龄概念、污染物暴露和平衡浓度之间的直接关系。还讨论了测量年龄分布和导出量的不同示踪气体技术。给出了基于最大浓度或平均房间浓度的通风效率的不同定义，以及“空气扩散效率”的定义。 在一个机械通风的两室试验室中进行的测量结果显示，一个试验室配备一个进气口和一个提取物，另一个试验室配备一个进气口和两个提取物。最后，在不同位置配备终端的办公室展示了测试结果。供应的空气温度低于或高于室温。正确利用浮力，几乎可以实现置换流系统。引文:研讨会，ASHRAE交易，1983年，第89卷，pt。华盛顿特区2B。

When the objective is to minimize the average room exposure to contaminants the objective of a ventilating system is the removal of contaminants from the ventilated space as quickly as possible. The shorter the resident time of a contaminant in the ventilated space, the lower the exposure to the contaminant; therefore, the sooner the contaminant reaches the extract duct, the better is the ventilation. The important parameters in this context are, therefore, time and local flow rates, and not such traditional concepts in ventilation engineering, as for example air-change rates or mixing factors. The concept of age, or residence time, is applicable to characterize both how the supplied air or a contaminant is spread within an enclosed space and how quickly a contaminant is removed. A comprehensive discussion is presented in this paper on the application of the concept to any enclosed space with air intakes and extracts. The direct relationship between the age concept, exposure to contaminants, and equilibrium concentrations is established. Different tracer-gas techniques for measuring the age distributions and the derived quantities are also treated. Different definitions of ventilation efficiency based on maximum concentration or average room concentration, and a definition of "air diffusion efficiency" are also given. Results are presented from measurements carried out in a mechanically ventilated two-room test house, equipped in one case with one intake and one extract, and in another case with one intake and two extracts.Finally, test results are presented from an office room equipped with terminals at different locations. The supplied air temperature was both lower and higher than the room air temperature. With a correct utilization of buoyancy, almost displacement flow systems may be achieved.