A Multi-Tracer System for Multizone Ventilation Measurements

Mass transfer due to pressure-driven air flow is one of the most important processes for determining
both environmental quality and energy requirements in buildings. Heat, moisture, and
contaminants are all transported by air movement between indoors and outdoors as well as
between different zones within a building. Measutement of these air flows are critical to understanding
the performance of buildings. Virtually all measurements of ventilation are made using
the dilution of a tracer gas. The vast majority of such measurements have been made in a single
zone, using a single tracer gas. For the past several years LBL has been developing the MultiTracer
Measurement System (MTMS) to provide full multizone air flow information in an accurate,
real-time manner. MTMS is based on a quadrupole mass spectrometer to provide highspeed
concentration analysis of multiple tracer gasses in the (low) ppm level which are injected
into multiple zones using mass flow controllers. The measurement and injection system is controlled
by a PC and can measure all concentrations in all zones (and adjust the injected tracer
flows) within two minutes and can operate unattended for weeks. The resulting injection-rate
and concentration data can be analyzed to infer the bulk air movement between zones. The system
also measures related quantities such as weather and zonal temperature to assist in the data
interpretation. Using MTMS field measurements have been made for the past two years.