ASHRAE Journal - May 2024 - 34
TECHNICAL FEATURE
be accurate enough for the purposes of the findings
presented in this article.
Case 2, the case of condenser water pumps serving
open cooling towers, seems to be an outlier, with an
average effective exponent of 3.0. It's not clear why this
scenario would have a higher exponent than the others.
Flow-to-Power Exponents
Calculating power as a function of flow is not as
straightforward as calculating power as a function of
motor speed because the power depends on the pressure
variation in addition to the flow variation. If accurate
data is available, it's best to calculate BHP from flow and
pressure (see Equation 5 and Equation 6 for examples),
then calculate VFD input power from BHP using
Equation 7 for I-P units.
BHP =
fan
Flow cfm × in.w.g.
6,356 ×
() (
∆ P
η
fan
Equation 5: Fan BHP Calculation from Flow and Pressure
(for Standard Density Air)
)
BHPpump
=
Flow gpm P ft w.g. )
×
() (
,
∆
3 960
×
pump
Equation 6: Pump BHP Calculation from Flow and Pressure
(for Water)
Input Power kW =
()
BHP
fan_or_ pump
belt
×
×
mottor
kW/HP
ηη ηVFD
×
Equation 7: Power Draw Calculation from BHP
The efficiencies in the above equations can be
obtained from the manufacturers and online
resources. Typical ranges:
* ηfan is typically ~50% for small fans, ~75% for large
fans. For more accurate values, use fan performance
data from the manufacturer.
* ηpump is typically ~50% for small pumps, ~80%
for large pumps. For more accurate values, use pump
performance data from the manufacturer.
* ηbelt is typically ~90% for small belt-driven fans and
pumps (e.g., <5 HP [4 kW]) at full speed, ~95% for large
Check Valve for VFD Drives
Introducing the VFD Check Valve, the fi rst Center
Guided Silent Check Valve developed for VFDs.
Metrafl ex re-engineered a classic hydronic
component to improve effi ciency and cut costs.
Pressure Drop Across the 6-inch VFD Check Valve
The VFD Check Valve
* Hydrodynamic disc design increases fl ow.
* Provides superior functionality in low-fl ow
conditions, common with VFD drives.
* Same face-to-face dimension as common
globe-style center-guided check valves.
www.Metrafl ex.com/VFD
sales@metrafl ex.com
© 2024 The Metrafl ex Company
34
ASHRAE JOURNAL ashrae.org MAY 2 0 2 4
A Close-Up of the Velocity Distribution Around
the Check Valve (Inlet from Right).
http://www.Metraflex.com/VFD
http://www.ashrae.org
ASHRAE Journal - May 2024
Table of Contents for the Digital Edition of ASHRAE Journal - May 2024
Contents
ASHRAE Journal - May 2024 - Intro
ASHRAE Journal - May 2024 - Cover1
ASHRAE Journal - May 2024 - Cover2
ASHRAE Journal - May 2024 - 1
ASHRAE Journal - May 2024 - Contents
ASHRAE Journal - May 2024 - 3
ASHRAE Journal - May 2024 - 4
ASHRAE Journal - May 2024 - 5
ASHRAE Journal - May 2024 - 6
ASHRAE Journal - May 2024 - 7
ASHRAE Journal - May 2024 - 8
ASHRAE Journal - May 2024 - 9
ASHRAE Journal - May 2024 - 10
ASHRAE Journal - May 2024 - 11
ASHRAE Journal - May 2024 - 12
ASHRAE Journal - May 2024 - 13
ASHRAE Journal - May 2024 - 14
ASHRAE Journal - May 2024 - 15
ASHRAE Journal - May 2024 - 16
ASHRAE Journal - May 2024 - 17
ASHRAE Journal - May 2024 - 18
ASHRAE Journal - May 2024 - 19
ASHRAE Journal - May 2024 - 20
ASHRAE Journal - May 2024 - 21
ASHRAE Journal - May 2024 - 22
ASHRAE Journal - May 2024 - 23
ASHRAE Journal - May 2024 - 24
ASHRAE Journal - May 2024 - 25
ASHRAE Journal - May 2024 - 26
ASHRAE Journal - May 2024 - 27
ASHRAE Journal - May 2024 - 28
ASHRAE Journal - May 2024 - 29
ASHRAE Journal - May 2024 - 30
ASHRAE Journal - May 2024 - 31
ASHRAE Journal - May 2024 - 32
ASHRAE Journal - May 2024 - 33
ASHRAE Journal - May 2024 - 34
ASHRAE Journal - May 2024 - 35
ASHRAE Journal - May 2024 - 36
ASHRAE Journal - May 2024 - 37
ASHRAE Journal - May 2024 - 38
ASHRAE Journal - May 2024 - 39
ASHRAE Journal - May 2024 - 40
ASHRAE Journal - May 2024 - 41
ASHRAE Journal - May 2024 - 42
ASHRAE Journal - May 2024 - 43
ASHRAE Journal - May 2024 - 44
ASHRAE Journal - May 2024 - 45
ASHRAE Journal - May 2024 - 46
ASHRAE Journal - May 2024 - 47
ASHRAE Journal - May 2024 - 48
ASHRAE Journal - May 2024 - 49
ASHRAE Journal - May 2024 - 50
ASHRAE Journal - May 2024 - 51
ASHRAE Journal - May 2024 - 52
ASHRAE Journal - May 2024 - 53
ASHRAE Journal - May 2024 - 54
ASHRAE Journal - May 2024 - 55
ASHRAE Journal - May 2024 - 56
ASHRAE Journal - May 2024 - 57
ASHRAE Journal - May 2024 - 58
ASHRAE Journal - May 2024 - 59
ASHRAE Journal - May 2024 - 60
ASHRAE Journal - May 2024 - 61
ASHRAE Journal - May 2024 - 62
ASHRAE Journal - May 2024 - 63
ASHRAE Journal - May 2024 - 64
ASHRAE Journal - May 2024 - 65
ASHRAE Journal - May 2024 - 66
ASHRAE Journal - May 2024 - 67
ASHRAE Journal - May 2024 - 68
ASHRAE Journal - May 2024 - 69
ASHRAE Journal - May 2024 - 70
ASHRAE Journal - May 2024 - 71
ASHRAE Journal - May 2024 - 72
ASHRAE Journal - May 2024 - 73
ASHRAE Journal - May 2024 - 74
ASHRAE Journal - May 2024 - 75
ASHRAE Journal - May 2024 - 76
ASHRAE Journal - May 2024 - 77
ASHRAE Journal - May 2024 - 78
ASHRAE Journal - May 2024 - 79
ASHRAE Journal - May 2024 - 80
ASHRAE Journal - May 2024 - Cover3
ASHRAE Journal - May 2024 - Cover4
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