Brochure

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Fast and Easy Sizing
and Selection of PICVs
The first steps in sizing and selecting a PICV is to determine the design flow
of your coil, then look at the flow ranges of the valves, and find the one
that falls within your design flow range.
A typical guideline is to select a valve that’s one size down from the pipe size.
You can also select a valve the same size as the line size, either one has no
effect because these are pressure independent and will control to that flow.
If there are multiple valves the design flow falls within, the recommendation is
to choose a valve where the design flow falls in the middle of the flow range.
If you choose a valve that your design flow is close to the upper range or the
lower range and the system design changes or adjustments need to be made,
then you may be limited on those adjustments.
So putting it in the middle of the range
provides the most flexibility.
Determine design flow of coil
Find PICVs with max flow range
compatible with coil design flow
Typically select a PICV one size
down or select on line size
It is possible to select a PICV
with max flow buffer for post
design adjustments
For easy sizing and selection of Siemens PICVs, use the
HVAC Integrated Tool (HIT) at usa.siemens.com/HIT
PICVS are easier to size and select in just four easy steps and no calculations
Drawbacks of traditional variable flow systems
There are a number of steps that need to be taken when selecting traditional control valves. Sizing and selecting traditional
control valves is complex and requires several calculations. To calculate the Cv and properly size a valve, the design flow
of the coil and the design pressure drop are needed. The calculated Cv will almost always be different than the actual
Cv of the valves. Typically, the closest, but higher valve Cv is selected in order to not undersize the valve. Once the valve Cv
is selected, plug that actual Cv back into the formula to derive the actual differential pressure. Calculate the valve
authority next, which is traditionally as close to 0.5 as possible.
Pressure dependent valves are more complicated to size requiring multiple calculations
In this example, valve authority is not that close.
So, sizing becomes an issue.
The formula for determining
Cv for water valves is:
Percent Authority should
be between 25% and 50%.
25-50%
Q = Flow in gallons per minute S = Specific gravity
Control Valves
Sizes
4 Cv = 1/2”
6.3 Cv = 3/4”
10 Cv = 1”
16 Cv = 1 1/4”
25 Cv = 1 1/2”
40 Cv = 2”
63 Cv = 2 1/2”
100 Cv = 3”
Valve Authority Requirement
ß = = 0.5
ß = = 0.5
10
4.3 + 0.7 + 5 + 10
10
20
95 gpm
10 psi
95
3.16
Cv = = = 30
√
∆p =
∆p = = 2.375
2
= 5.6
ß = = 0.28
Q
Cv
95
40
5.6
20
2
2
( )
( )
Authority not optimum
Recommended = 0.5