为什么近年来人们对最低限度的外部空气控制感到担忧，而这从来都不是一个问题？自1973年以来，各版本的ASHRAE标准62（以及1973年之前的ASHRAE指南和数据手册）已确立了确定达到可接受室内空气量所需的室外空气通风量的标准。这是“最小室外空气量”。在定容系统中，一旦适当确定了该量，并且系统设置为吸收最小外部空气量，则始终有足够的外部空气通风来稀释建筑物产生的污染物，除非发生某种机械故障或有人改变控制。这是因为物理定律规定，流体总是从高压流向低压，对于固定的几何形状，流体总是与压差的平方根成比例。 但是，变风量（VAV）系统的日益普及，给方程式引入了新的因素，也给设计师带来了新的挑战。仅考虑用于通风的最小外部空气量，不考虑外部空气经济器循环期间的系统运行。当系统安装在外部节能器上时，外部空气量基于冷却需求，通常大于通风所需的最小值。如果在非常寒冷的天气下，满足温度要求意味着室外空气少于最小通风量，则选择的任何最小室外空气控制策略都将发挥作用。为了简单明了，讨论完全忽略了节约型循环，因为问题是保持最低通风量。同样，讨论的是带有回风机的系统。可以使用向室外提供动力排气的卸压风机代替回风机，或者可能有一个既没有回风机也没有卸压风机的单一送风机。 通常，稳定测量和控制的问题与回风机讨论的问题相同。关键词:1995年，最小值，室外空气，控制，变风量空调，通风，风扇，空气流量，节能器，空气质量，室内制冷:研讨会，ASHRAE Trans。1995年，第101卷，第2部分

Why the concern in recent years about minimum outside air control when it never used to be an issue? Since 1973, various editions of ASHRAE Standard 62 (and before 1973, ASHRAE Guide and Data Books) have established criteria for determining the amount of outside air ventilation necessary to achieve acceptable indoor air quantity. That amount is the "minimum outside air quantity". In a constant-volume system, once that quantity has been properly determined and the system has been set up to take in that minimum outside air quantity, there was always enough outside air ventilation to dilute contaminants generated with the building - unless some sort of mechanical failure occurred or someone changed the controls. That is because the laws of physics dictate that flow always goes from a high pressure to a low pressure and that, for a fixed geometry, the flow will always be proportional to the square root of the pressure difference. But the growing popularity of variable-air-volume (VAV) systems has introduced new factors into the equation and new challenges for designers. Considers only the minimum outside air quantity for ventilation and does not address system operation during the outside air economiser cycle. When the system is on an outside economiser, the outside air quantity is based on the need for cooling and is generally greater than the minimum required for ventilation. If, during very cold weather, satisfying the temperature requirement would mean less outside air than the minimum ventilation quantity, then whatever minimum outside air control strategy is selected would come into play. For simplicity and clarity, the discussion completely ignores the economiser cycle since the concern is with maintaining minimum ventilation. Similarly, the discussion is in terms of systems with return fans. A relief fan that provides power exhaust to outdoors may be used instead of a return fan, or there may be a single supply fan with neither a return fan nor a relief fan. Generally, the issues of stable measurement and control are the same as those discussed with a return fan.KEYWORDS: year 1995, minimum, outdoor air, controls, variable volume air conditioning, ventilation, fans, air flow, economisers, air quality, indoor