Install Instructions

107
IM-PR 566442 1114 (Design Manual)
Once a circulator’s network is identified, the basic
theory for sizing the circulator is to size it for the
maximum flow rate seen at the circulator’s location
and at the total pressure drop that the working fluid
experiences across the circulator’s network. When
dealing with sections of parallel piping within a
network, the maximum pressure drop seen through
the parallel section is the greatest pressure drop of
any one section. When dealing with series piping
within a network, the maximum pressure drop
seen through the series section is the sum of the
pressure drop of the components in series.
To calculate the pressure drop in secondary and
panel piping within a circulator’s network, take the
following steps:
• Determine the length of each panel piping
circuit off each manifold within the circulator
network.
• Using the pressure drop tables that
correspond to the system’s glycol content
and tubing size, multiply the pressure drop
per foot (obtained from the table using
the circuit ow rate) by the circuit length.
Because a manifold’s circuits are in parallel,
identify the circuit with the largest pressure
drop at each manifold.
• To the largest circuit pressure drop at each
manifold, add the pressure drop through the
corresponding supply and return manifolds.
• For each manifold within the circulator
network, add the pressure drop of the
secondary supply and return piping located
between the primary piping and the manifold.
For series piping between the primary
piping and manifold, add the pressure drop
of adjacent sections of series piping. For
parallel piping between the primary piping
and manifold, select the maximum pressure
drop of the parallel piping sections, and
then add this to adjacent sections of series
piping. The pressure drop is determined by
using the appropriate pressure drop table
corresponding to the system’s glycol content
and ow rate seen within the relevant section
of secondary piping between the primary
piping and the manifold.
• When calculating the pressure drop of
the secondary piping, be sure to add the
pressure drop of all associated valves,
ttings, mixing devices and other piping
accessories (expansion tanks, air separators,
etc.) located within the relevant piping
sections. As much as possible, during the
design phase, select valves and accessories
with low pressure drop ratings to reduce the
system pressure drop. For balancing valves,
this means selecting units with high ow
coefcients, also known as a “Cv” rating.
For mixing valves, select a valve with a Cv
rating that is as close as possible to the
design ow rate through the valve. This will
optimize performance of the valve (good
control at reduced head). To determine the
pressure drop associated with valves based
on their Cv ratings, you may use the following
equation:
∆P =
(
D
62.4
) (
ƒ
C
v
)
•
2
where
∆P = pressure drop across the valve in psi
D = density of the fluid at operating temperature
(lb/ft
3
)
62.4 = density of water at 60ºF (lb/ft
3
)
f = flow rate of fluid (gpm)
Cv = known Cv rating of the device (gpm)
If a manufacturer provides the pressure drop of an
accessory in psi, you may convert the psi to feet of
head with the following formula:
144 • ∆P
D
H =
where
H is the “head loss,” also known as pressure drop,
of the accessory (feet of head)
∆P is the pressure drop (psi)
D is the density of the fluid at its corresponding
temperature (lbs/ft
3
). If the fluid is water, or if the
density of the fluid has already been accounted for
elsewhere, you may use D=62.4.
• The secondary piping circulator should
be sized to accommodate the secondary
piping’s maximum volumetric ow rate at the
total pressure drop for the secondary and
panel piping (calculated above).