Volume Flow Rate - Grid Measurement As Per Ashrae 111 - TESTO 400 Instruction Manual

9 Operation

At the end of a volume flow
measurement in compliance with the
standards, the average volume flows
are shown on the results display,
along with the information about
measuring accuracy, which helps to
better estimate the measurement
result.
Volume flow rate - grid measurement as per
9.4.4
ASHRAE 111
With this application, the volume flow in a ventilation system duct can be
measured as per the ASHRAE 111 standard. There are various options for this,
which differ mainly in terms of the measuring range and the required probes:
• Thermal probes (including temperature measurement and possibly humidity
measurement) for low flow velocities
• 16 mm wheel measuring head (including temperature measurement) for
average flow velocities
• Pitot tube for measurements at high velocities and in heavily contaminated
flows with a high particle content
The main prerequisite for accurate measurement is the suitability of the
measuring points. Minimum distances from points of discontinuity must be
observed:
• From points of discontinuity upstream of the flow, observe a clearance of at
least six times the hydraulic diameter Dh = 4A/U (A: duct cross-section, U:
duct circumference).
• From points of discontinuity downstream of the flow, observe a clearance of
at least twice the hydraulic diameter Dh = 4A/U (A: duct cross-section, U:
duct circumference).
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