ASHRAE Journal - April 2013 - 48

engineer’s notebook	

100

Graphic Unavailable

Full Flow at Constant Pressure Drop (%)

90

Quick Opening

80
70
60

Linear

50
40
30
20
Equal Percentage

10
0

0	 10	20	30	 40	 50	60	 70	80	90	
100
Full Valve Stem Travel (%)

Figure 1 (left): Traditional coil pack. Figure 2 (right): Control valve flow characteristics.

Control Valves
& Coil Packs
By Mikhail Nudelman, P.E., Member ASHRAE

A

ll coil packs on the market have two devices on the return line that
regulate flow: a control valve and a manual or automatic balanc-

ing valve. This article proves that only one valve is necessary to regulate
and balance flow at the coil packs and as a result, this arrangement
will reduce material, installation, and operation costs.

A coil pack is a customizable coil solution to meet the needs of the end user
that can be provided on the jobsite as a
pre-connected unit for faster and easier
installation.
A traditional coil includes (Figure 1):
•• On supply line: combination ball
valve/strainer with pressure test plug and
blowdown/drain valve;
•• On return side: Union with manual
air vent and pressure test plug; control
48	

ASHRAE Journal	

valve; automatic flow-control (limiting)
valve or manual balance/metering valve
with pressure test plugs and union end.

Return Side
Control valve. The control valve is
used to regulate flow as demands warrant. It regulates a flowing fluid, such
as water, to compensate for the load
disturbance and keep the regulated
process variable (as close as possible to

the desired setpoint). The pressure drop
across the control valve varies between
a maximum, when it is controlling,
and a minimum, when the valve is near
full open. Typical control valve flow
characteristics are shown in ASHRAE
Handbook—HVAC Systems and Equipment, Chapter 47, Figure 16 (shown here
as Figure 2).
Selecting the correct control valve size
for a given application requires knowledge of process conditions that the valve
will actually undergo in service.
Using the principle of conservation
of energy, Daniel Bernoulli found that
when a liquid flows through an orifice,
the square of the fluid velocity is directly proportional to the specific gravity of the fluid. The greater the pressure
differential, the higher the velocity.
The greater the density, the lower the
velocity. A basic liquid sizing equation
is shown in ASHRAE Handbook—HVAC
Systems and Equipment, Chapter 47,
Equation 3:
Q = Cv ∆p

Where
Dp	= pressure drop, psi
Q	= volumetric flow, gpm
Cv	= flow coefficient, gpm at Dp = 1 psi

a s h r a e . o r g 		

April 2013



ASHRAE Journal - April 2013

Table of Contents for the Digital Edition of ASHRAE Journal - April 2013

ASHRAE Journal - April 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Ground-Coupled Heat Pump and Energy Storage
Fan Efficiency Requirements for Standard 90.1-2013
Technology Award Case Studies:
Geothermal for 5 Ecosystems
Holistic HVAC Design
Standing Columns
Engineer’s Notebook
Data Centers
Emerging Technologies
IAQ Applications
Refrigeration Applications
Special Products
People
International Column
Energy Modeling
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2013 - ASHRAE Journal - April 2013
ASHRAE Journal - April 2013 - Cover2
ASHRAE Journal - April 2013 - 1
ASHRAE Journal - April 2013 - 2
ASHRAE Journal - April 2013 - Contents
ASHRAE Journal - April 2013 - Commentary
ASHRAE Journal - April 2013 - 5
ASHRAE Journal - April 2013 - Industry News
ASHRAE Journal - April 2013 - 7
ASHRAE Journal - April 2013 - 8
ASHRAE Journal - April 2013 - Letters
ASHRAE Journal - April 2013 - Meetings and Shows
ASHRAE Journal - April 2013 - 11
ASHRAE Journal - April 2013 - 12
ASHRAE Journal - April 2013 - 13
ASHRAE Journal - April 2013 - Ground-Coupled Heat Pump and Energy Storage
ASHRAE Journal - April 2013 - 15
ASHRAE Journal - April 2013 - 16
ASHRAE Journal - April 2013 - I1
ASHRAE Journal - April 2013 - I2
ASHRAE Journal - April 2013 - I3
ASHRAE Journal - April 2013 - I4
ASHRAE Journal - April 2013 - 17
ASHRAE Journal - April 2013 - 18
ASHRAE Journal - April 2013 - 19
ASHRAE Journal - April 2013 - 20
ASHRAE Journal - April 2013 - 21
ASHRAE Journal - April 2013 - 22
ASHRAE Journal - April 2013 - 23
ASHRAE Journal - April 2013 - Fan Efficiency Requirements for Standard 90.1-2013
ASHRAE Journal - April 2013 - 25
ASHRAE Journal - April 2013 - 26
ASHRAE Journal - April 2013 - 27
ASHRAE Journal - April 2013 - 28
ASHRAE Journal - April 2013 - 29
ASHRAE Journal - April 2013 - 30
ASHRAE Journal - April 2013 - 31
ASHRAE Journal - April 2013 - Geothermal for 5 Ecosystems
ASHRAE Journal - April 2013 - 33
ASHRAE Journal - April 2013 - 34
ASHRAE Journal - April 2013 - 35
ASHRAE Journal - April 2013 - 36
ASHRAE Journal - April 2013 - 37
ASHRAE Journal - April 2013 - 38
ASHRAE Journal - April 2013 - 39
ASHRAE Journal - April 2013 - Holistic HVAC Design
ASHRAE Journal - April 2013 - 41
ASHRAE Journal - April 2013 - 42
ASHRAE Journal - April 2013 - 43
ASHRAE Journal - April 2013 - 44
ASHRAE Journal - April 2013 - 45
ASHRAE Journal - April 2013 - 46
ASHRAE Journal - April 2013 - 47
ASHRAE Journal - April 2013 - Engineer’s Notebook
ASHRAE Journal - April 2013 - 49
ASHRAE Journal - April 2013 - 50
ASHRAE Journal - April 2013 - 51
ASHRAE Journal - April 2013 - 52
ASHRAE Journal - April 2013 - 53
ASHRAE Journal - April 2013 - Data Centers
ASHRAE Journal - April 2013 - 55
ASHRAE Journal - April 2013 - 56
ASHRAE Journal - April 2013 - 57
ASHRAE Journal - April 2013 - 58
ASHRAE Journal - April 2013 - 59
ASHRAE Journal - April 2013 - Emerging Technologies
ASHRAE Journal - April 2013 - 61
ASHRAE Journal - April 2013 - 62
ASHRAE Journal - April 2013 - 63
ASHRAE Journal - April 2013 - IAQ Applications
ASHRAE Journal - April 2013 - 65
ASHRAE Journal - April 2013 - 66
ASHRAE Journal - April 2013 - Refrigeration Applications
ASHRAE Journal - April 2013 - Special Products
ASHRAE Journal - April 2013 - People
ASHRAE Journal - April 2013 - International Column
ASHRAE Journal - April 2013 - 71
ASHRAE Journal - April 2013 - Energy Modeling
ASHRAE Journal - April 2013 - 73
ASHRAE Journal - April 2013 - Products
ASHRAE Journal - April 2013 - 75
ASHRAE Journal - April 2013 - 76
ASHRAE Journal - April 2013 - 77
ASHRAE Journal - April 2013 - 78
ASHRAE Journal - April 2013 - Classified Advertising
ASHRAE Journal - April 2013 - Advertisers Index
ASHRAE Journal - April 2013 - Cover3
ASHRAE Journal - April 2013 - Cover4
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