Promoting Diversity-in VAV Systems

摘要

Variable-air-volume (VAV) supply-air systems are usually designed so that the total air-handling unit (AHU) capacity (Q_(AHU)) is less than their total terminal-unit air volumes (ΣQ_(TU)). The ratio of these two numbers (Q_(AHU)/ΣQ_(TU)) is called the air-handling system diversity, often expressed as a percentage. VAV systems can be designed with diversities of less than unity because not all spaces in a building will peak—require full cooling—at the same time of a design day (see "Cooling Load: A Sample Analysis," page 36). To illustrate the concept of airflow diversity, Figure 1 shows an area of a building served by a static regain-designed supply ductwork system. The area shown is the south half of the first floor. The single AHU for the duct system, which serves the entire building, was selected for a total airflow capacity of 2 5 percent less than the sum of the building's terminal-unit peak airflow volumes. This was done because the building's cooling load diversity was calculated at 75 percent.