The primary purpose of this project was to determine if furnace heat exchangers were prematurely or excessively rusting due to condensation when fresh air ducts are hard connected to the return air system; In addition, occupants were to be interviewed to ascertain whether such systems were causing cool drafts. The energy impact of this type of ventilation system and the practicality of installing high inside wall supply outlets was also to be investigated.
The passive perfluorocarbon method (PFT-method) has been successfully applied in ventilation measurements in rooms. The method is, in principle, also applicable to air flow measurements in ventilation ducts. There are, however, several problems in applying a passive sampling technique in a duct. First, the concentration of the tracer may not be uniform through the cross-section of a duct. Second, the velocities in a duct are normally an order of magnitude higher than in a room.
We describe the use of constant injection and pulse injection techniques for measurement of airflow in a duct. Tracer-gas measurements were compared with measurements made using a pitot tube and a hot-wire anemometer. Tracer-gas concentration, air velocity and pressure distribution were measured at various distances from the duct wall and inlet. An empirical equation was obtained for the entrance length required to achieve fully-developed turbulent flow and this was compared with measurements made using a pitot tube and hot-wire anemometer.
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