Application Note

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Application Note

HVAC pressure

applications with

the Fluke 922

F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y

For contractors troubleshooting pressure,

a lot depends on system peculiarities. Are

the installation instructions with the equip-

ment? Is the start-up performance report

with them? Is the TAB (test and balance)

report available? Do you understand the

Atmospheric Pressure 1 psi 1” hg 1” wc

14.696 psia 1 psi 0.019 psi 0.0361 psi

29.921 “ hg 2.036” hg 1” hg 0.0736” hg

406.8” wc 27.68” wc 13.595” wc 1” wc

Pressure measurement

Pressure is measured in sev-

eral different scales. Pounds

per square inch (psi), inches of

water column (in. wc), inches

of mercury column (in. hg), and

millionths of a meter of mercury

column (microns) are the most

typical in HVAC work.

Bourdon gauges are the tradi-

tional choice for higher pressure

readings in psi. Finer precision

measurements use mercury col-

umn scales. And for the most

precise measurements—and most

low pressure measurements in

HVAC—inches water column is

the standard.

The following chart compares

these common pressure scales

and their precision.

Using the Fluke 922 low pressure differential meter in a duct traverse.

control system? More often than not, it

seems, you can only answer yes to the

last question. You rely on your experience,

knowledge, and tools to check the funda-

mentals. And for that much, at least, Fluke

can help.

Of the many different low

pressure measuring instruments

used over the years, electronic

manometers/micromanometers

(very low pressure gauges)

now offer durability, precision,

accuracy, and the significant

time saving convenience of fully

automatic calculations as well as

minimum-maximum-average and

memory functions.

Summary of content (4 pages)

PAGE 1
HVAC pressure applications with the Fluke 922 For contractors troubleshooting pressure, a lot depends on system peculiarities. Are the installation instructions with the equipment? Is the start-up performance report with them? Is the TAB (test and balance) report available? Do you understand the Application Note control system? More often than not, it seems, you can only answer yes to the last question. You rely on your experience, knowledge, and tools to check the fundamentals.
PAGE 2
How pressure sensing works The Fluke 922 is a low pressure differential meter used in traditional manometer or micromanometer applications. It has a range of +/-16” wc, resolution of 0.001” wc, and over-pressure protection of 10 psi at each high and low pressure port. With a single tube connected to its high or low port, the meter will display positive or negative pressure relative to the ambient pressure at the meter’s open port.
PAGE 3
Combustion air blower pressure differential: Category IV direct vent gas appliances typically use a combustion air blower to ensure airflow through the vent system and appliance before ignition. In most cases, a pressure differential switch monitors pressure differential across an orifice. Greater pressure differential indicates more airflow, lower differential indicates less airflow.
PAGE 4
TSP and ESP: Total Static Pressure (TSP) and External Static Pressure (ESP) are used in conjunction with the manufacturer’s blower performance tables to ensure that the blower performance is sufficient to overcome airside device pressure drops and the pressure drop associated with duct friction and fittings losses. Manufacturer’s blower performance tables will specify whether the tables are based on TSP or ESP.