ASHRAE Journal - September 2014 - 34
TECHNICAL FEATURE
Amplification Factor equation:
4005× A 2
F =
K
(1)
4005× A
K =
F
(2)
Flow Coefficient
K is used in an air terminal unit VAV controller to
calculate actual airflow using the following equation,
where cfm is airflow in ft3/min and ΔP is flow sensor output in in. w.g.:
Determining flow using a air terminal unit flow sensor
(3)
Q = K × ∆P
Where
Q =
ΔP =
K =
F =
A =
Airflow Rate (cfm)
Sensor Differential Pressure (in. w.g.)
K-Factor Calibration Constant (Standard Air)
Amplification Factor (Sensor Gain)
Nom. Duct Area (ft2)
Velocity sensors are not all the same. The amplification
of a sensor will vary between manufacturers Table 1 (Page
32). The range at minimum flow (0.03 in. Vp) may vary
as much as 24%. When specifying air terminal units,
a design engineer may want to consider what range of
flow is required to meet ventilation standards and make
sure the specified product and controller is designed
to operate in that range. This has become more significant, especially as engineers look to reduce flow rates
to reduce the energy usage of a system. The higher the
amplification, the lower the minimum cfm that can be
obtained and controlled.
Specifying Insulation
If the insulation specified by the designer is not specific
enough, the owner may get something other than what
the designer intended and the difference may make the
terminals unfit for the application. It may occur that the
interpretation may be within the guidelines of a specification, but not what the design engineer was actually
requiring for a project. More information on specifying
air terminal unit insulation can be
found in the September 2010 ASHRAE
Journal article, "Specifying Insulation
for Air Terminal Units."
Conclusion
Selecting and specifying air terminal units for a project is relatively simple. However, without
clearly defining what is required
for a project may cause the designer's intent to be misread, resulting
in air terminal units that met the
engineer's specified requirements,
but not what the design engineer
ultimately wanted for that project.
It is recommended that the design
engineer:
* Clearly define pressures by
choosing a pressure method to select
air terminal units.
* Use maximum allowable pressure drop to define minimum pressure that will be accepted. This method also requires the designer to state
operating pressure to allow the sound
www.info.hotims.com/49808-43
34
ASHRAE JOURNAL
ashrae.org
SEPTEM BER 2014
ASHRAE Journal - September 2014
Table of Contents for the Digital Edition of ASHRAE Journal - September 2014
Contents
ASHRAE Journal - September 2014 - Cover1
ASHRAE Journal - September 2014 - Cover2
ASHRAE Journal - September 2014 - 1
ASHRAE Journal - September 2014 - 2
ASHRAE Journal - September 2014 - Contents
ASHRAE Journal - September 2014 - 4
ASHRAE Journal - September 2014 - 5
ASHRAE Journal - September 2014 - 6
ASHRAE Journal - September 2014 - 7
ASHRAE Journal - September 2014 - 8
ASHRAE Journal - September 2014 - 9
ASHRAE Journal - September 2014 - 10
ASHRAE Journal - September 2014 - 11
ASHRAE Journal - September 2014 - 12
ASHRAE Journal - September 2014 - 13
ASHRAE Journal - September 2014 - 14
ASHRAE Journal - September 2014 - 15
ASHRAE Journal - September 2014 - 16
ASHRAE Journal - September 2014 - 17
ASHRAE Journal - September 2014 - 18
ASHRAE Journal - September 2014 - 19
ASHRAE Journal - September 2014 - 20
ASHRAE Journal - September 2014 - 21
ASHRAE Journal - September 2014 - 22
ASHRAE Journal - September 2014 - 23
ASHRAE Journal - September 2014 - 24
ASHRAE Journal - September 2014 - 25
ASHRAE Journal - September 2014 - 26
ASHRAE Journal - September 2014 - 27
ASHRAE Journal - September 2014 - 28
ASHRAE Journal - September 2014 - 29
ASHRAE Journal - September 2014 - 30
ASHRAE Journal - September 2014 - 31
ASHRAE Journal - September 2014 - 32
ASHRAE Journal - September 2014 - 33
ASHRAE Journal - September 2014 - 34
ASHRAE Journal - September 2014 - 35
ASHRAE Journal - September 2014 - 36
ASHRAE Journal - September 2014 - 37
ASHRAE Journal - September 2014 - 38
ASHRAE Journal - September 2014 - 39
ASHRAE Journal - September 2014 - 40
ASHRAE Journal - September 2014 - 41
ASHRAE Journal - September 2014 - 42
ASHRAE Journal - September 2014 - 43
ASHRAE Journal - September 2014 - 44
ASHRAE Journal - September 2014 - 45
ASHRAE Journal - September 2014 - 46
ASHRAE Journal - September 2014 - 47
ASHRAE Journal - September 2014 - 48
ASHRAE Journal - September 2014 - 49
ASHRAE Journal - September 2014 - 50
ASHRAE Journal - September 2014 - 51
ASHRAE Journal - September 2014 - 52
ASHRAE Journal - September 2014 - 53
ASHRAE Journal - September 2014 - 54
ASHRAE Journal - September 2014 - 55
ASHRAE Journal - September 2014 - 56
ASHRAE Journal - September 2014 - 57
ASHRAE Journal - September 2014 - 58
ASHRAE Journal - September 2014 - 59
ASHRAE Journal - September 2014 - 60
ASHRAE Journal - September 2014 - 61
ASHRAE Journal - September 2014 - 62
ASHRAE Journal - September 2014 - 63
ASHRAE Journal - September 2014 - 64
ASHRAE Journal - September 2014 - 65
ASHRAE Journal - September 2014 - 66
ASHRAE Journal - September 2014 - 67
ASHRAE Journal - September 2014 - 68
ASHRAE Journal - September 2014 - 69
ASHRAE Journal - September 2014 - 70
ASHRAE Journal - September 2014 - 71
ASHRAE Journal - September 2014 - 72
ASHRAE Journal - September 2014 - SCover1
ASHRAE Journal - September 2014 - SCover2
ASHRAE Journal - September 2014 - S1
ASHRAE Journal - September 2014 - S2
ASHRAE Journal - September 2014 - S3
ASHRAE Journal - September 2014 - S4
ASHRAE Journal - September 2014 - S5
ASHRAE Journal - September 2014 - S6
ASHRAE Journal - September 2014 - S7
ASHRAE Journal - September 2014 - S8
ASHRAE Journal - September 2014 - S9
ASHRAE Journal - September 2014 - S10
ASHRAE Journal - September 2014 - S11
ASHRAE Journal - September 2014 - S12
ASHRAE Journal - September 2014 - S13
ASHRAE Journal - September 2014 - S14
ASHRAE Journal - September 2014 - S15
ASHRAE Journal - September 2014 - S16
ASHRAE Journal - September 2014 - S17
ASHRAE Journal - September 2014 - S18
ASHRAE Journal - September 2014 - S19
ASHRAE Journal - September 2014 - S20
ASHRAE Journal - September 2014 - S21
ASHRAE Journal - September 2014 - S22
ASHRAE Journal - September 2014 - 73
ASHRAE Journal - September 2014 - 74
ASHRAE Journal - September 2014 - 75
ASHRAE Journal - September 2014 - 76
ASHRAE Journal - September 2014 - 77
ASHRAE Journal - September 2014 - 78
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ASHRAE Journal - September 2014 - 81
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ASHRAE Journal - September 2014 - 83
ASHRAE Journal - September 2014 - 84
ASHRAE Journal - September 2014 - 85
ASHRAE Journal - September 2014 - 86
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ASHRAE Journal - September 2014 - 88
ASHRAE Journal - September 2014 - 89
ASHRAE Journal - September 2014 - 90
ASHRAE Journal - September 2014 - 91
ASHRAE Journal - September 2014 - 92
ASHRAE Journal - September 2014 - 93
ASHRAE Journal - September 2014 - 94
ASHRAE Journal - September 2014 - 95
ASHRAE Journal - September 2014 - 96
ASHRAE Journal - September 2014 - 97
ASHRAE Journal - September 2014 - 98
ASHRAE Journal - September 2014 - 99
ASHRAE Journal - September 2014 - 100
ASHRAE Journal - September 2014 - 101
ASHRAE Journal - September 2014 - 102
ASHRAE Journal - September 2014 - 103
ASHRAE Journal - September 2014 - 104
ASHRAE Journal - September 2014 - Cover3
ASHRAE Journal - September 2014 - Cover4
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