Flow Control Gains in Accuracy

March/April 2002
A version of this article appears in the March/April 2002 issue of Home Energy Magazine.
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March 01, 2002
A new flow meter is easier to use than a Duct Blaster, and more accurate than the temperature rise method.
        The air flow rate through residential air handlers is an important measurement for a variety of reasons. One of the most important uses of this measurement is in assessing the adequacy of flow across a heat pump or air conditioning coil.Another is for the accurate estimation of the thermal efficiency of duct systems.Yet another use of air flow measurement is in diagnosing comfort problems in homes; such problems can be caused by too little flow for the size of the house and ducts, even if the thermal efficiency of the ducts is good and the flow over the coil is sufficient.         However, the primary method of estimating the air handler flow rate, which is the temperature change across the equipment, can be troublesome (see “Checking an Installation,”HE Jan/Feb ’02, p. 10).This is called the temperature rise method.This method combines the temperature difference between the supply and return air as measured near the air handler (for example, in the plenums) and the output capacity of the equipment to estimate air flow. For furnaces, the temperature in the supply plenum is usually extremely ...

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