Tracer gas used to evaluate HVAC equipment.

When controlling the performance of a ventilation system it is important to investigate how the system works together with the building it ventilates. It is the performance of the complete system which is of interest, not its individual components. This paper describes the use of a computer-controlled, tracer-gas measuring system for controlling ventilation systems. By means of 4 measuring probes the condition of the air at the intake, room injection, room extraction and exhaust is registered. On the basis of these results, the computer can calculate the efficiency coefficients for the heat exchange, the percentage of air being recirculated, the outdoor short-circuit from exhaust to air intake and the percentage of extracted air resulting from room injection. On the basis of field measurements with the equipment, the experience gained is discussed. In particular, it it interesting to see how large a percentage of the air blown through the ventilation system into the building is refound in the extracted air. Percentages of 60-80% are quite normal. If only, for instance, 60% of the injected air is returned, the building will have an air change which is at least 1.66 times the performance of the ventilation system.