BdYZa<%*)-B[\#&&$%(
"'&"
Calculating Duct Resistance
6YY^c\ YjXi ldg`! ZaWdlh! WgVcX]Zh VcY Vcn
di]ZgXdbedcZcihidVYjXia^cZ^cXgZVhZhV^g[adl
gZh^hiVcXZ hiVi^X egZhhjgZ adhh# I]^h gZh^hiVcXZ
XVcWZb^c^b^oZYWnjh^c\g^\^Yhbddi]e^eZVcY
\gVYjVa XjgkZh! Vh deedhZY id [aZm^WaZ e^eZ VcY
.%ßZaWdlh#
Id ]Zae ndj i]^c` VWdji i]^h gZh^hiVcXZ! ^bV\^cZ
g^Y^c\VW^XnXaZ^cVijccZai]Vi^hVcZmVXigZea^XV
d[ndjgYjXildg`#>[i]Z^ch^YZd[i]ZijccZa^hkZgn
Wjben[aZm^WaZe^eZVcY]VhVadid[h]Vgeijgch
.%ßZaWdlh!^il^aaiV`ZVadibdgZZ[[dgiidigVkZa
[gdbdcZZcYidi]Zdi]Zg#
I]Z ejgedhZ d[ XVaXjaVi^c\ i]Z gZh^hiVcXZ ^h id
YZiZgb^cZ^[^i^hadlZcdj\][gdbi]ZbVX]^cZid
i]ZYjhiXdaaZXidgidbZZii]Z\^kZc8;BgZfj^gZ"
bZci[dgi]ZbVX]^cZ#JhZi]ZX]Vgih^c
Figure 27
idXVaXjaViZi]ZgZh^hiVcXZd[YjXildg`#
Duct
Dia.
Approximate
Static Pressure
Loss Per Foot of
Rigid Pipe
Approximate
Static Pressure
Loss Per Foot
of Flex Pipe
BV^c
A^cZh
Vi(*%%
;EB
7gVcX]
A^cZh
Vi)%%%
;EB
BV^c
A^cZh
Vi(*%%
;EB
7gVcX]
A^cZh
Vi)%%%
;EB
'
%#%.&
%#&''
%#(*
%#)*(
'#*
%#%-
%#&%,
%#(%+
%#(.,
(
%#%,&
%#%.)
%#',&
%#(*'
)
%#%*,
%#%,*
%#'&*
%#'-
*
%#%)+
%#%*.
%#&,'
%#''*
+
%#%(,
%#%),
%#&(+
%#&-
,
%#%'.
%#%(+
%#&%+
%#&)&
-
%#%'(
%#%',
%#%-
%#&%-
.
%#%&,
%#%&.
%#%*,
%#%,.
Fitting
Dia.
90˚
Elbow
45˚
Elbow
45˚
Wye(Y)
90˚
Wye(Y)
(
%#),
%#'(*
%#'-'
%#&--
)
%#)*
%#''*
%#(,*
%#''*
*
%#*(&
%#'++
%#(*)
%#'(+
+
%#*+)
%#'-'
%#('.
%#'(*
,
%#)+-
%#'()
%#(')
%#'&+
-
%#)%*
%#'%(
%#'.,
%#&-.
Figure 27.
HiVi^XegZhhjgZadhhX]Vgih#
>cbdhihbVaa$bZY^jbh]deh^i^hdcancZXZhhVgn
idXVaXjaViZi]Za^cZl^i]i]Zadc\ZhiYjXiaZc\i]dg
i]Zbdhi[^ii^c\hdeZgVi^c\jcYZgi]ZVhhjbei^dc
i]Vi^[i]Za^cZl^i]i]Z]^\]ZhigZh^hiVcXZldg`h!
i]Zdi]Zghl^aaWZ[^cZ#
To calculate the static pressure of any given
line in the system, follow these steps:
1.
BV`ZVa^hid[ZVX]h^oZYjXi^ci]Za^cZ!^cXajY"
^c\i]ZaZc\i]!VcYbjai^eani]dhZcjbWZghWn
i]ZhiVi^XegZhhjgZkVajZ\^kZc^c
Figure 27
#
2.
A^hiZVX]ineZd[ZaWdldgWgVcX]VcYbjai^ean
i]Z fjVci^in ^[ bdgZ i]Vc dcZ Wn i]Z hiVi^X
egZhhjgZadhh\^kZc^c
Figure 27
#
3.
6YYi]ZVYY^i^dcVa[VXidgh[gdb
Figure 28
id
ndjga^hi#
Additional Factors
Static Pressure
HZVhdcZYlZaajhZY
9jhi8daaZXi^dc;^aiZg
&
:cignAdhhViAVg\Z
BVX]^cZ=ddY
'
Figure 28.
6YY^i^dcVa[VXidghV[[ZXi^c\hiVi^X
egZhhjgZ#
4.
IdiVa ndjg a^hi Vh h]dlc ^c i]Z ZmVbeaZ ^c
Figure 29
idXdbZjel^i]ndjgdkZgVaahiVi^X
egZhhjgZadhhcjbWZg[dgi]Via^cZ#
Note:
Always account for a seasoned filter,
so you don't end up with a system that only
works right when the filter is clean.
Figure 29.
IdiVa^c\hiVi^XegZhhjgZcjbWZgh#
Main Line
+G^\^YE^eZ%#%(,Vi'%
################
%#,)%
Branch Line
)G^\^YE^eZ%#%,*Vi&%
################
%#,*%
);aZmE^eZ%#'-Vi* ########################
&#)%%
Elbows/Branches
+)*ßN"7gVcX]
################################
%#('.
))*ß:aWdl
########################################
%#''*
Additional Factors
HZVhdcZY;^aiZg
################################
&#%%%
Total Static Pressure Loss ................
4.444