Measurement of low air flow rates using a simple pressure compensating meter.

These problems can be overcome by compensating for the pressure drop over the flow meter in such a way that the pressure on the duct side of the grille remains the same before and after the positioning of the flow meter. This is a very well known technique. However in the field of air conditioning, devices using this principle are rare. The compensation of the pressure drop is performed by a fan and regulator which blows just enoughair through the flow meter to meet the pressure compensation before the grille. At first we used a large controllable fan, a set of DII measuring tubes with orifice plates, and a box with apressure meter to be placed over the grille. All connections were made with flexible tubing. The whole set up was accurate but very large and not easy to move from position to position.