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| Figure 1. (Click on the image for an enlarged view.) |
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This month’s troubleshooting situation centers around a very
recently installed heating and cooling system, and a customer who has called to
complain that certain rooms in the house “just don’t seem to be getting enough
air.”
(Before we begin with the specific troubleshooting
information on this situation, we’ll establish a couple of points… First, the
problem isn’t related to the refrigeration system in any way, and second, there
are no electrical problems contributing to the complaint. In this situation,
we’re dealing with an airflow problem. Note that Figure 1 shows the design of
the supply duct system
exactly
as it appears in the attic crawl space.)
When you arrive at the customer’s home, you find that the
two rooms the customer is complaining about are closest to the air-handling
unit in this duct system that employs one central return and an extended plenum
system on the supply duct assembly. In assessing the situation, you determine
that the airflow from each supply register in these two rooms should be
approximately 120 cfm, but when you measure the airflow with a digital velocity
meter, you find the airflow to be approximately 90 cfm. As your next step, you
move on to the crawl space to check the supply ductwork and find no leakage or
crushed duct, but you do find, as we mentioned above, the supply duct system in
Figure 1.
Your troubleshooting problem: What design flaw is
responsible for the specific airflow problem we’ve described in this situation?
Compare your answer with ours by
clicking here.
Publication
date: 01/05/2009
