Tracer gas tests provide a measure of how the air within a building moves under normal operating conditions. A small quantity of a harmless tracer gas is released into the building, and its concentration at a series of points is charted. In this way the rate of introduction of fresh air can be deduced, or the transfer of contaminants or odours around the building determined. The technique also gives useful information on the proportion of building working heat loss which is due to infiltration and ventilation.
The gas detection system used by EMC consists of a highly sensitive chromatograph which detects Sulphur Hexaflouride, a common choice of tracer gas. This allows us to work at tracer concentrations below 50 parts per billion, minimising the amount of gas which has to be released even in large buildings.
Tracer gas tests are conventionally carried out using one of three methods:
Recently the Energy Monitoring Company has been involved in the development of a fourth technique, in which gas is released in a carefully randomised sequence. This provides significant advantages over conventional measurements:
The basis of the method and some preliminary assessments using numerical modelling have recently been published:
A new tracer-gas testing technique: Theory and numerical simulations
J D Balcomb, C J Martin and J Littler
Building Services Engineering Research and Technology 1996 Vol 17 Number 3
At the moment the technique is still under development, but preliminary results look very encouraging.
In any building which has infiltration the results of a tracer gas test will depend on the climatic conditions at the time of the test. The test thus gives a measure of the working conditions in the building, not a measure of how well sealed it is. For that purpose a leakage test, which gives a result independent of climate, is more appropriate.
The advent of COSHH legislation meant that a large research company had to ensure that their staff were not at risk from the combustion products produced in tests at their London laboratory complex. A complex series of over 40 tracer gas tests established the ventilation rate in each laboratory, and the transfer of contaminants between adjacent laboratories. This information allowed the company to be confident that they were complying with their statutory obligations.
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