BRE has developed a new technique for measuring time-averaged ventilation rates in occupied buildings using a perfluorocarbon tracer gas. It was conceived as a way of solving the problems which arise when conventional tracer gas techniques are used in large or multi-roomed buildings. Potentially, the new technique will allow routine performance monitoring of both natural ventilation and forced air supply systems, thereby helping users to save energy and to meet the health, safety and comfort requirements of the building's occupants.
A new passive tracer gas method for ventilation measurements is described. The method utilizes passive tracer gas release from aliquid perfluorocarbon compound contained in a glass vial, equipped with a teflon membrane. Air sampling is also done passively by diffusion through a glass tube containing activated carbon. Quantitative analysis of trapped tracer compound is performed by solvent extraction and gas chromatographic separation using a liquid injection technique. Separation is done with a two-column system and quantitative analysis with an electron capture detector.
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.
One method of evaluating interzone airflow rates makes use of perfluorocarbon tracers (PFTs)(4). The PFTs are emitted at asteady rate by miniature permeation sources (the physical size is 7 mm diameter and 30 mm length) with a different PFT being