There is no simple answer. In general, it is dependent on the magnitude of the air change rate (ACR) and the room volume. We could measure without problems the Infiltration Rate in a customer service centre with 116m length, 84m width and 16m height, in total 92.000 ³, because the ACR was below 0,15h.^-1 . The purpose of the test was to measure the tightness of the facade. In such large zones you need to take of course samples at various locations and integral samples too.

Another extreme would be the measurement of the cabin tightness in a driving car (cabin volume 2-3 m³). Here we have measured ACRs of up to 20 h-1. A well-done mixing and integral sampling is advantageous here. We got reliable results with integral sampling every 2 minutes.

For special cases don't hesitate to contact us

The Combi Set allows to perform two consecutive ACR tests of a zone at two different ventilation regimes with one single injection at the beginning. The following situations are typical for combi tests:

• What is the infiltration rate (tightness of the building envelope at closed doors and windows and shut-down ventilation system) and what is the ACR if one window is tilted?
• First measure the infiltration rate, second measure the ACR with ventilation system ON.
• First measure ACR with ventilation system on stage 1, second on stage 2.

You always start to measure the situation with the lowest ACR first, after 5 samples you change the ventilation regime - without injection of new tracer - and take the next 5 samples. The only advantage of the Combi Set above two separate Standard Sets is the lower price.

There is the EN ISO 12569 for Europe and the ASTM 741 standard for the USA. The US standard was the first air change rate (ACR) standard and exists since 1983. Both standards demand to verify before the first sample is taken and after the last sample is taken that complete mixing has been achieved throughout the test period, they define the minimum number of samples (5) to be taken and in what time intervals sampling has to be done. The Standard and Combi Set comply with these requirements except the complete mixing requirement. In both sets the amount of samples was reduced for cost reasons. However, the instructions emphasize to keep the room air carefully mixed with the tracer during the complete test interval. After 30 years of applications we have seen that this assumption is almost always fulfilled in normal living rooms. In addition, the advantage of integral sampling guaranties that always a representative average concentration of the room air is taken. Incomplete mixing can be derived from the ACR plot if the data points are not on a straight line on the logarithmic y-axis.

For approval tests or legal cases TRACERTECH always recommends to use the ASTM Set.

Our very sensitive analysis equipment makes it possible to injectvery little amounts of tracer gas, usually by a factor of 1.000 and more less that ACRs using IR-Analysis. SF6 as the most often used tracer gas has the highest gobal warming potential (23.000 more than CO2). Due to the very small amounts used an ACR measurement using CO2 as a tracer harms the environment more than the use of SF6. The tracer emission (10-50ml for an ACR test) needs to be seen relative to the 180 tons of SF₆ which are annually released just only in Germany. So SF6 emissions for ACR tests can really be neglected in the climate change discussion.

We say at maximum 2 weeks, in most cases the results are transmitted within 2-5 days.

We use sulphur hexafluoride (SF₆). SF₆ is an artificial gas, which does not exist in nature. The molecules have a very high stability; there are no reactions or adsorption effects known at these low applied concentration levels. The TLV (Threshold Limit Value) for work places is 1.000 ppm. The SF₆concentrations using the Standard or Combi Sets are always below 100 ppb, this is 1/10.000 of the TLV thanks to ECD gas chromatography. According to VDI 4300 Blatt 7 our ACR test method is especially permitted also in rooms with children, elderly persons and pregnant women.

At least one year. We have had a client who used a Standard Set after 13 years of storage. From the start concentration and the amount of tracer injected one could recalculate, that the initial tracer concentration in the syringe had been diluted by roughly 50%. This was caused by diffusion. The room concentration was just half of the expected concentration. Nothingness, the sensitive Autotrac tracer gas monitor had no problems to precisely measure the concentrations.

With some syringes we have found out that a concentration reduction by 5% has taken place (maximum value). Usually a customer is interested to get the test results quickly. However, if one wants to take advantage of price reductions with 'en bloc' return of sets, we recommend not to wait longer than 6 weeks.