Sharp JX-9400 Informacje Techniczne Pobierz pdf (Strona 36)

Airﬂow Rates

in Air Handling Units

Air handling units are designed to supply new air to the ventilated zone and to

extract vitiated air from this zone. Many other airﬂows may be found in such

units, as shown in Figure 2.1.

Measurements of airﬂow rates in ventilation systems are useful in order to

check if the air follows the expected paths and thus detect potential probl ems

early so they can be corrected, also allowing the optimization of the perfor-

mance of the airﬂow system. Checks include examining if actual airﬂow rates

are close to the desired values and if leakages and short-circuits are negligible.

The checks should be performed:

when commissioning a new ventilation system in order to ensure that the

system is built according to the design speciﬁcations;

if there are indoor air quality problems to help ﬁnding their causes;

before refurbishing a ventilation system in order to accurately identify the

potential problems to be cured by the refurbishment.

Commissioning mechanical ventilation systems is paramount in order to ensure

that they function as designed. This includes not only the measurement of the

main airﬂow rates and pressure distributions, but also checks that there are no

excessive leakages or shortcuts. It should be noted that commissioning

protocols are available for most units mentioned in the Introduction that func-

tion as designed, while they are not available for units in which airﬂow rates are

not those designed or for units showing signiﬁcant leakages or shortcuts.

This chapter proposes methods for measuring most airﬂow ra tes that occur

in ventilation systems.

Measurement of the airﬂow rate in a duct

Summary of measurement methods

Common methods used to measure airﬂow rates in ducts exploit well-known

relationships between ﬂow rate and pressure drop across a restricted section

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Sharp JX-9400 Informacje Techniczne Strona 36