Air Flow Rate Measurements in HVAC Equipment: New Devices for Use with Tracer Gas Technique

Nowadays in order to have a good indoor air quality in buildings it is needed to rely on ventilation, either by air infiltration, natural or mechanical ventilation. They are one of the fundamentals of the sustainable energy in buildings. However, in most buildings with mechanical ventilation, it is only possible to know the nominal airflow rates of the equipment and, very often, they run far way of the set points. As a consequence, due the lack of knowledge of the real running conditions of the equipment, the indoor air quality can be very poor. This paper presents a new injection and sampling device to be used with the tracer gas technique for the measurement of airflow rates in ducts of HVAC equipment. These new devices are of an extremely importance as they enable the dispersion and mixing of the tracer gas for very short duct lengths. With the conventional tracer gas techniques, the minimum distance necessary between injection and sampling of the tracer was about seven hydraulic diameters, which means that it was necessary to have very long duct lengths in order to have feasible measurements, a situation that not occurs very often in HVAC equipment. With those new devices it is possible to go down as far as one hydraulic diameter. Experimental and simulation results of those new devices are presented in this paper, being possible to conclude that they are good enough for the measurement of duct airflows in complex situations.