Sharp JX-9400 Informações Técnicas descarregar pdf (Página 34)

The long-term integral method, generally used with passive sources and

samplers, also gives a biased estimate of the average airﬂow rate. Since the

measurement time is larger, the bias may not be negligible. This technique,

however, provides an unbiased estimate of the average tracer concentration.

If the tracer is used to simulate a contaminant, such experiments are of great

interest for indoor air quality studies.

The constant concentration te chnique is accurate and gives an unbiased

estimate of the average airﬂow rate, but it requires the most technical

equipment.

Table 1.2 Summary of single-zone methods

Suited for

Method name Tracer injection

technique

Interpretation

method

Unbiased

average

Continuous

record

Transient methods (tracer gas concentration changes)

(Simple) decay Decay Identiﬁcation No No

Two-point decay Decay Integral Yes (Yes)

Step-up Constant rate Identiﬁcation No No

Steady-state methods (tracer gas concentration is nearly constant)

Pulse Pulse Integral No (Yes)

Constant injection Constant rate Direct solution Yes

†

Long-term integral Any Integral No No

Constant

concentration

Constant

concentration Integral Yes Yes

Note: y Under condition.

Source: Sherman, 1990.

Table 1.3 Summary of multi-zone methods

Tracer injection strategy Unbiased average of

time-varying ﬂow

Well suited for

continuous record

Single tracer (repeated measurements)

Pulse injection No No

Decay No No

Constant injection rate No No

Constant concentration Yes No

Multi-tracer

Pulse injection No No

Decay Yes* No

Constant injection rate No Yes

Constant concentration Yes Yes

Note:



Only for a two-point estimate.

Airﬂow Rates in Buildings 13

1 2 ... 29 30 31 32 33 34 35 36 37 38 39 ... 210 211

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