工业排气通风，无论是局部通风还是一般通风，长期以来一直是保护工人免受空气污染物危险浓度影响的最重要手段之一。显然，从工作场所或建筑物排出的任何空气都将被等量的进入空气所取代，根据工作场所的气候和所需的空气条件，必须对其进行加热、冷却、过滤或控制湿度。如果与建筑体积相比，排气系统较大，则应在受控条件下以机械方式引入置换空气，通常称为“补充空气系统”。即使没有补充空气系统，能源方面的考虑也是一样的，因为在这两种情况下，替代空气都将达到建筑的必要条件。显然，这种情况是非常昂贵的能源。充分清洁后的废气再循环将节省废气的大部分热能。 如果设备的设计能够使电机处于气流中，并且任何外部外壳或管道系统都具有良好的绝缘性，那么能效可以接近100%。过去几年，官方工业卫生机构的政策是，如果污染物是一种可能影响工人健康的物质，则建议不要再循环排气，而不管所用空气净化装置的效率等级如何。即使“用于再循环的空气滤清器具有足够的效率，但不正确的操作或糟糕的维护（这两种情况过去都太频繁）都会导致过度污染的空气返回给工人。在过去，由于低成本能源供应充足，这一官方立场无疑是正确的。随着能源供应变得越来越稀缺、越来越昂贵，如果能够设计出方法，允许充分清洁的再循环空气安全返回工作场所，那么在技术努力、资本、运营和维护上投入更多资金，既是良好的经济意义，也是良好的国家政策。 考虑到这种情况，三年前，美国政府工业卫生学家会议的通风委员会提出了一种方法，至少在原则上允许以安全的方式进行这种再循环。ACGIH通风委员会提出了本文讨论的四个主要但书。引文:研讨会，ASHRAE交易，第83卷，第一部分，伊利诺伊州芝加哥

Industrial exhuast ventilation, either local or general, has long been one of the most important means of providing protection of the worker from hazardous concentrations of airborne contaminants. Obviously any air exhausted from the workplace or building will be replaced with an equivalent volume of incoming air which, depending upon the climate and the required air condition of the workplace, must be heated, cooled, filtered, or of controlled humidity. If the exhaust system is large in comparison to the building volume, this replacement air should be introduced mechanically and under controlled conditions, and is commonly called a "make-up air system". Even when there is no make-up air system, the energy considerations are the same because the replacement air will be brought to the necessary condition for the building under either circumstance. Obviously this situation is very energy-expensive.Recirculation of the exhaust air after it has been adequately cleaned would conserve most of the thermal energy of the exhausted air. If the equipment can be designed so that motors are in the air stream and any external housings or ductwork are well insulated, the energy efficiency can approach 100%.In past years it has been the policy of official industrial health agencies to recommend against recirculation of exhaust air if the contaminant is a material which may have an effect on the health of the workers, regardless of the efficiency rating of the air cleaning devices used. Even'though the air cleaner used for recirculation is of adequate efficiency, either incorrect operation or poor maintenance, both all too frequent occurrences in'the past, would result in return of excessively contaminated air to the workers. In the past, with abundant supplies of low cost energy, that official position was undoubtedly correct.As energy supplies get more scarce and more expensive, it is both good economic sense and good national policy to spend more on technological effort, capital, operation and maintenance, if ways can be devised to permit safe return of adequately cleaned recirculated air to the workplace. With this situation in mind, three years ago the Ventilation Committee of the American Conference of Governmental Industrial Hygienists proposed a methodology for permitting such recirculation in a safe manner, at least in principle.Four major provisos which are discussed in this paper were suggested by the ACGIH Ventilation Committee.