Southwark Air Flow Dynamics & Duct Sizing Reference Guide (Page 2 of 2) in pdf

A DJ U S T M E N T O F DU CT D E S I GN PR E S S U R E (R ATE ) F OR E Q UIVAL E NT L E NGTHS

Total Effective

.05

.06

.08

.10

.125

.14

.16

.18

.20

.25

.30

.34

.375

.40

.50

.625

.75

1.00

Length (Feet)

35 -44

.13

.15

.20

.25

.32

.35

.40

.45

.50

.63

.75

.85

.95

1.00

1.25

1.50

1.90

2.54

45- 54

.10

.12

.16

.20

.25

.28

.32

.36

.40

.50

.60

.68

.76

.80

1.00

1.26

1.52

2.02

55 - 64

.08

.10

.13

.17

.21

.23

.27

.30

.33

.42

.50

.57

.63

.67

.83

1.05

1.26

1.68

65 - 74

.07

.09

.11

.14

.18

.20

.23

.26

.29

.36

.43

.49

.54

.57

.72

.90

1.08

1.44

75 - 84

.06

.08

.10

.13

.16

.18

.20

.23

.25

.31

.38

.43

.47

.50

.63

.79

.94

1.26

85 - 94

.06

.07

.09

.11

.14

.16

.18

.20

.22

.28

.33

.38

.42

.45

.56

.70

.84

1.12

95 - 104

.05

.06

.08

.10

.13

.14

.16

.18

.20

.25

.30

.33

.38

.40

.50

.63

.75

1.01

105 - 114

.05

.07

.09

.11

.13

.15

.16

.18

.23

.28

.31

.34

.37

.47

.57

.69

.91

115 - 129

.04

.05

.07

.08

.10

.12

.13

.15

.17

.21

.25

.28

.31

.33

.46

.51

.62

.82

130 - 149

.04

.06

.07

.09

.10

.11

.13

.14

.18

.21

.24

.27

.29

.36

.45

.54

.72

150 - 169

.03

.04

.05

.06

.08

.09

.10

.11

.13

.16

.19

.21

.24

.25

.31

.39

.47

.63

170 - 189

.03

.04

.06

.07

.08

.09

.10

.11

.14

.17

.19

.21

.22

.28

.35

.42

.56

190 - 214

.03

.04

.05

.06

.07

.08

.09

.10

.13

.15

.17

.19

.20

.25

.31

.37

.50

215 - 239

.02

.03

.04

.05

.06

.07

.08

.09

.11

.13

.15

.17

.18

.22

.28

.33

.44

240 - 264

.02

.03

.04

.05

.06

.07

.08

.10

.12

.14

.15

.16

.20

.25

.30

.40

265 - 289

.02

.03

.04

.05

.06

.07

.09

.11

.12

.14

.15

.18

.23

.27

.36

290 - 324

.02

.03

.04

.05

.06

.07

.08

.10

.11

.12

.13

.17

.20

.24

.33

325 - 374

.02

.03

.04

.05

.06

.07

.09

.10

.11

.14

.18

.21

.29

375 - 424

.01

.02

.03

.03.

.04

.05

.06

.08

.09

.10

.13

.16

.19

.25

425 - 474

.01

.02

.03

.04

.05

.06

.07

.08

.09

.11

.14

.17

.22

475 - 524

.01

.02

.03

.04

.05

.06

.07

.08

.10

.13

.15

.20

525 - 574

.01

.02

.03

.04

.05

.06

.07

.09

.11

.14

.18

575 - 625

.01

.02

.03

.04

.05

.06

.07

.08

.10

.13

.17

F O R MU L AS

Sensible Heat Formula

Friction Rate

Altitude Correction

Factor (ACF)

*used in duct calculators

0 ft

1.0

5000 ft

.826

BTU/Hour = CFM x TD x 1.08

Pressure Drop x 100

500 ft

.981

6000 ft

.801

Friction Rate =

1000 ft

.962

7000 ft

.772

TEL

BTU/Hour

CFM =

2000 ft

.926

8000 ft

.749

1.08 x TD x ACF

Pressure Drop is the available static pressure

3000 ft

.891

9000 ft

.715

4000 ft

.858

10000 ft

.687

1.08 is a conversion factor

(ASP) allocated to the duct work.

TD is the Temperature Difference created by the appliance

ACF is the Altitude Correction Factor (see above table)

ASP = Blower Static Pressure - Component

Pressure Drops

Sensible Load

Sensible Heat Ratio =

Sensitive Load + Latent Load

TEL is the Total Effective Length of the longest

SHR below .80 = 21º TD

High humidity = 350 CFM/ton

supply run and the longest return run.

SHR .80 to .85 = 19º TD

Ave. humidity = 400 CFM/ton

SHR above .85 = 17º TD

Low humidity = 450 CFM/ton

CFM Calculations

Blower CFM x Room Load

CFM =

Sensible Load

Room CFM =

Equipment Sizing Load

1.08 x TD x ACF

Total Heat Equation

Blower CFM

Flow Factor =

Equipment Sizing Load

CFM =

BTU/Hr

4.5 is a conversion factor

Room CFM = Flow Factor x Room Load

4.5 x H x ACF

H is the BTU per lb. of air removed

Southwark Metal Mfg Co. • Philadelphia, PA • Piedmont, SC • Indianapolis, IN • Southaven, MS • Fremont, NE • Caldwell, ID

Corporate Headquarters: 2800 Red Lion Road, Philadelphia PA 19114 • 800-523-1052 • fax 800-722-2076 •

Southwark Air Flow Dynamics & Duct Sizing Reference Guide Page 2

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