Ductwork System Calculation Input Data Sheet
System/Zone Name: XYZ system Project: UVW-123456
Designed by: Designer Date: 10/20/2009
To run this program, fill in the input below, then go to sheet 1 and run the macro "friction factor". A further
explanation of how this spreadsheet works is given on sheet 1. For guidance in selecting values for the
input, consult the ASHRAE Handbook, Fundamentals, "Duct Design". This is Chapter 21 in the 2009
Handbook, but the chapter may be different in other editions. Data generated by sheets 1 and 2 will
automatically be entered in the "Report" sheet.
Roughness e = 0.0003 [-]
Air Density rho = 0.0763 [lbm/ft3] Specific Volume = 13.106
dp/100= 0.09 [inwc/100-ft] (Target pressure drop per 100')
Kinevisc = 0.000163
Supply Air (SA) = 1,600 [CFM] Instruction:
Outdoor Air (OA) = 150 [CFM] 1) Input blue cells in Input Tab,
2) Do not make entry in gray cells
No. SA Segments = 7 these are calculated cells
No. RA Segments = 4 3) Run Macro 1: "fraction factor" in
Total Duct Segments = 11 Sheet 1 Tab,
4) Print out Report in Report tab.
fiting library
fitting type, C, and dp input by user
code Fittings Fitting C dp [inwc]
1 fan out 0.72
2 el 0.11
3 tee thru 0.04
4 tee branch 0.8 AHU
5 fan in 0.3 OA SA
6 diffuser 0.04
7 ret grille 0.03
to override automatic duct air flow reduction (see sheet 1 instructions), set override = 1
For round duct, input height = 0 override 0
segment cfm duc height segment L Fitting Codes, each segment
segment cfm in ft
1 1600 14.0 10.0 1 2 2
2 1600 14.0 5.0 2 2 0 0
3 1025 12.0 2.0 3 0
4 860 12.0 7.0 3 0
5 530 10.0 8.0 3 0
6 330 10.0 9.0 3 2 0
7 185 0.0 16.0 6 2 0
8 185 0.0 16.0 7 2 0
9 330 10.0 18.0 3 2
10 530 10.0 6.0 3 0
11 1600 14.0 20.0 3 2 2 5
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
This Excel Workbook with Visual Basic Macros is
offered for free download AS IS without warranty. The
author makes no representations or warranty, either
expressed or implied, with respect to the software
program, its accuracy, its quality, or its fitness for any
particular purpose. Anyone who uses this Excel
Workbook to size ductwork or estimate duct pressure
losses is expected to be experienced in manual
procedures for duct sizing, design, and estimating
pressure loss and is not to rely solely on the results
from this software. Therefore the Author shall have no
liability to any user with respect to any liability, loss, or
damage caused or alleged to have been caused either
directly or indirectly by its use. This includes but is not
limited to interruption of service, loss of data, loss of
consulting or anticipatory profits, or consequential
damages from the use of this software.
Duct System Pressure Drop Calculation Result
System - Zone XYZ system
Project Number UVW-123456
Designer Designer
Date 10/20/2009
System/Zone Name: XYZ system Designed by: Designer Date:
duct airflow height width dia velocity Re length duct dp dp/100' vel. dp fix'tr dp
leg Q H W D V Re L dP_duct dp/100' dP_v dP-fit
No. [cfm] [in] [in] [in] [fpm] [-] [ft] [in. w.g.] [iw/100'] [in. w.g.] [in. w.g.]
supply duct
1 1,600 14 17 17 1,034 135,889 10.0 0.010 0.097 0.07 0.06
2 1,600 14 17 17 1,034 135,889 5.0 0.005 0.097 0.07 0.01
3 1,025 12 14 14 937 103,705 2.0 0.002 0.100 0.06 0.00
4 860 12 13 14 846 90,393 7.0 0.006 0.086 0.05 0.00
5 530 10 11 11 740 66,330 8.0 0.007 0.083 0.03 0.00
6 330 10 8 10 635 48,305 9.0 0.007 0.077 0.03 0.00
7 185 0 0 8 530 36,293 16.0 0.010 0.063 0.02 0.04
return duct
8 168 0 0 8 480 32,891 16.0 0.008 0.053 0.01 0.03
9 299 10 7 9 661 46,575 18.0 0.016 0.091 0.03 0.00
10 480 10 10 11 737 63,081 6.0 0.005 0.088 0.03 0.00
11 1,450 14 16 16 994 127,097 20.0 0.019 0.093 0.06 0.04
0.095 0.20
10/20/2009
tot. dp
dP_tot
[in. w.g.]
0.07
0.02
0.00
0.01
0.01
0.01
0.05
0.04
0.02
0.01
0.05
0.30
DUCT SIZE CALCULATION SPREADSHEET Run macro "friction factor"
Project UVW-123456 system-zone XYZ system fitting library
<-- input data from Input tab fitting type, C, and dp input by user
formulas: code Fittings Fitting C dp [inwc]
Reynolds Number Re = 8.56*D*V fixed parameters (user input) 1 fan out 0.72 0
D=(1.3(a*b)^.625)/(a+b)^.25 Roughness e = 0.0003 [-] 2 el 0.11 0
V=Q/((Pi*D^2/4)/144) Air Density rho = 0.0763 [lbm/ft3] 3 tee thru 0.04 0
Target dp/100' = 0.090 [inwc/100-ft] 4 tee branch 0.8 0
Colbrook 1/f^.5 = -2*log(12*e/3.7/D+2.51/Re/f^.5) kinevisc = 0.000163 5 fan in 0.3 0
dp = (12*f*L*rho*(V/1097)^2)/D Zone air flow = 1600 [CFM] 6 diffuser 0 0.04
Zone outdoor air = 150 [CFM] 7 ret grille 0 0.03
Fitting Loss vdp = rho*(V/1097)^2 specific volume = 13.106
fitdp = vdp*C or fitdp = dp from fixture library
Fill out the input sheet. Enter supply segment air flows as they appear on the drawing. Return air flow will be less than supply air flow by the amount of the outdoor air
flow, proportioned to each return grille. The user should enter the return air flows based on the supply diffusers serving each grille. The program will automatically reduce
the return air for each segment by the ratio (supply - outdoor air)/supply. After the input sheet is completed and the macro "friction factor" is run, the size of each duct
segment that will give the exact desired pressure loss per 100 feet of duct length is calculated and shown on sheet 2. If a height is imput, the exact width corresponding to
the height and hydraulic diameter is also given. If height is imput as zero, round duct will be assumed. There is no need for the user to reference sheet two except to
verify results.
In the real world, there are no decimal fractions in duct diameters or the width of rectanglular ducts. Also, the objective is to calculate the external static pressure for a
fan or air handler. Therefore, the user must run the macro "friction factor" on sheet 1. This macro rounds the diameter of round ducts, or the width of rectanglular ducts to
the nearest inch. If the duct is rectangular, the macro recalculates the equivalent diamter to correspond to the new width. Velocity (V) and pressure loss per 100' (dp/100')
is then recalculated for the new hydraulic or integer duct diameter (dia D). Duct friction loss for each segment is calculated and totaled (duct dp). Fitting loss (fitdp), based
on loss coefficients or pressure losses from ASHRAE data and manufacturer's performance data, is calculated based on the fittings input from the sheet "Input". Finally,
the external static pressure (systotdp) is calculated and totaled.
Note that the duct legs below include both the supply duct segments and the return duct segments.
branch count max = 11 This macro will clear the contents of all calculated cells before running a new calculation.
duct leg airflow Q height a width b dia D V Re L duct dp dp/100' vdp fitdp systotdp fitting C or dp
cfm in in in fpm ft iw iw/100' iw iw iw coda codb codc codd
supply duct
1 1600 14 17 16.8 1034 135889 10 0.010 0.097 0.068 0.064 0.073 1 2 2
2 1600 14 17 16.8 1034 135889 5 0.005 0.097 0.068 0.015 0.020 2 2 0 0
3 1025 12 14 14.2 937 103705 2 0.002 0.100 0.056 0.002 0.004 3 0
4 860 12 13 13.7 846 90393 7 0.006 0.086 0.045 0.002 0.008 3 0
5 530 10 11 11.5 740 66330 8 0.007 0.083 0.035 0.001 0.008 3 0
6 330 10 8 9.8 635 48305 9 0.007 0.077 0.026 0.004 0.011 3 2 0
7 185 0 0 8.0 530 36293 16 0.010 0.063 0.018 0.042 0.052 6 2 0
return duct
8 168 0 0 8.0 480 32891 16 0.008 0.053 0.015 0.032 0.040 7 2 0
9 299 10 7 9.1 661 46575 18 0.016 0.091 0.028 0.004 0.021 3 2
10 480 10 10 10.9 737 63081 6 0.005 0.088 0.034 0.001 0.007 3 0
11 1450 14 16 16.4 994 127097 20 0.019 0.093 0.063 0.035 0.054 3 2 2 5
0.095 0.202 0.297
Project
System-Zone green cell: input data from Input sheet
calculation date shaded cell: calculated by UDF or formula - do not make entry
Duct Size and Rectangular/round duct conversion
supply air flow = 1600.0 cfm dp100 = 0.090
outdoor air flow = 150.0 oacfm e = 0.0003
return air flow = 1450.0 rcfm rho = 0.0763 spvol= 13.106
kinevisc = 0.000163
subcountmax = 7 supply duct segments return segments =
D=(1.3(a*b)^.625)/(a+b)^.25 Curve fit of dia for dp100=.095 (first guess): D=alog(.38352*log(cfm) + .00864
airflow height dia width dp100 L
cfm in in in iw/100' ft
1,600.0 14.0 #VALUE! #VALUE! #VALUE! 10.0
1,600.0 14.0 #VALUE! #VALUE! #VALUE! 5.0
1,025.0 12.0 #VALUE! #VALUE! #VALUE! 2.0
860.0 12.0 #VALUE! #VALUE! #VALUE! 7.0
530.0 10.0 #VALUE! #VALUE! #VALUE! 8.0
330.0 10.0 #VALUE! #VALUE! #VALUE! 9.0
185.0 0.0 #VALUE! 0.0 #VALUE! 16.0
167.7 0.0 #VALUE! 0.0 #VALUE! 16.0
299.1 10.0 #VALUE! #VALUE! #VALUE! 18.0
480.3 10.0 #VALUE! #VALUE! #VALUE! 6.0
1,450.0 14.0 #VALUE! #VALUE! #VALUE! 20.0
do not make entry
return segments = 4
D=alog(.38352*log(cfm) + .00864)
module 1 friction factor macro
module 111 fcalc UDF
module 12 AirCap UDF
module 21 Air Dia UDF
module 31 Wcalc UDF
module 51 AirPd UDF
