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ISO 16956:2015 pdf free

ISO 16956:2015 pdf free.Thermal performance in the built environment
For cross-section air velocity measurement, the thermal anemometer (hot-wire anemometer and semi-conductor anemometer), Pitot tube, precise manometer, vane-type anemometer, etc. are used.
The tracer gas measurement method estimates the flow rate in the duct by steadily injecting a fixed amount of tracer gas with known concentration and measuring of dilution of concentration at the downstream in the duct. The measurement items are gas concentration in the air on the upstream and downstream sides of the tracer gas injection point and the injection rate of the tracer gas. As preconditions for this measurement, the tracer gas shall be sufficiently mixed at the point where the air is collected and the concentration distribution on the inner cross-section of the duct shall be lower than the accuracy of the measuring instrument. It is also necessary to use a gas that is not adsorbed onto the inner surfaces of the duct or sampling tube.
The tracer gas normally used for this measurement method shall not be a substance whose discharge into the atmosphere is prohibited and its concentration level during measurement shall not be toxic to humans. In comparison with the amount of tracer gas, the absorption and adsorption of tracer gas on the wall surface and in the sampling tube shall be negligibly small. For selection, see Annex C.
For the tracer gas method, the following procedures are used:
a) a fixed amount of tracer gas of known concentration is continuously injected into the duct;
b)at a portion where the gas is uniformly mixed downstream from the tracer gas injection point (more than 10 times the diameter of the duct), the tracer gas concentration is measured at a minimum N+1 points (Table 2) including one point at the centre of the duct cross-section and the centre of each area when the duct cross-section is divided into N areas (see Figure 4);
c) if return air is included in the duct system, fluctuation in concentration is expected upstream from the tracer gas injection point and thus, the concentration of N areas should also be measured upstream from the injection point to confirm that the distribution is small;
d) the tracer gas injection rate is recorded;
e) either the air flow rate or mass flow rate is calculated, as required.ISO 16956 pdf download.

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