DA-88-18-3 — Field Problems Associated with Return Fans on VAV Systems

Are return fans really needed? How do you properly control return fans? These are two of the most frequently asked questions regarding variable air volume (VAV) systems. The answer you get to these questions varies with a personÃ¢Â€Â™s personal preference and experience. Some designers almost always use a return fan, others almost never. Some people even have difficulty differentiating between return fans and relief fans. This paper will not attempt to provide specific answers to the above questions, but it will point out problems that have occurred on actual jobs and the steps that were taken to correct the problems. The control methods on these projects were not the same, and, in at least one case, the proper solution would be to eliminate the return fan. This paper will hopefully point out solutions that may help readers with projects that bare similar problems, and point out potential problem areas to be avoided in design of new projects.