Six types of tracer gas as listed in Table are used to measure the ventilation rate in a zone.
|Type of gas||Helium a||Carbon dioxide b||Sulfur hexafluoride c|
|Measurement method||GC-TCD||Infrared absorption & FID & GC||GC-ECD||Infrared absorption||GC|
|Example of lower limit detection||300×10-6||0.1×10-6||70×10-6||0.001×10-6|
|Relative density against air [-]||0.138||1.545||5.302|
|Global warming potential (GWP)||–||1||23,900|
|Type of gas||Perfluoro carbon d||Ethylene e||Nitrogen monoxide f|
|Measurement method||GC-ECD||Infrared absorption & FID & GC||Infrared absorption|
|Example of lower limit detection||–||0.1×10-6||0.1×10-6|
|Relative density against air [-]||Example,|
|Global warming potential (GWP)||Example,|
<NOTE 1> In addition to those gases above, nitrogen, carbon monoxide, ethane, methane, isobutene, cyclobutanoctofluoride, Bromomethanetrifluoride, dichlorodifluoridemethane, and ichlorotetrafluoridemethane can be also used as tracer gas.
<NOTE 2> The GC in the table indicates general Gas Chromatography, the GC-TCD is the gas chromatography using Thermal Conductivity Detector and GC-ECD using Electron Capture Detector.
<NOTE 3> The Global Warming Potential is defined as relative green house effect potential per weight against carbon dioxide.
<NOTE 4> Infrared gas absorption includes both TS (transmission spectroscopy) and PAS (photoacoustic spectroscopy).
[a] Helium is chemically stable.
[b] CO2 is dissolved in water and can be adsorbed with building materials or furniture, and is not suited for precise measurement. However, if the measurement does not require critical accuracy, CO2 is often used. CO2 generated by occupants or any other internal source shall be taken into account. If this CO2 emission rate is not known, this tracer cannot be used.
[c] SF6 has a large global warming potential and should not be used in a large amount. SF6 is an inactive gas. If it is heated to 500 °C it generates toxic gases. Therefore, it should not be used in a space where a fan heater is used and SF6 flows through the heat source.
[d] PFC has a large Global Warming Potential and should not be used in large amounts.
[e] Ethylene is flammable and should be handled with a great care.
[f] N2O has a large Global Warming Potential and should not be used in large amounts. N2O is dissolved in water, and reacts with aluminium. It ignites at a high temperature. Great care must be exercised not to use it over its permissible concentration as it affects health.
Reference – ISO 12569:2017
[International Organization for Standardization]