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Chiller Refrigeration Tons

A chiller refrigeration ton is defined as:

1 refrigeration ton = 12,000Btu/h = 3,025.9 kCalories/h

A ton is the amount of heat removed by an air conditioning system that would melt 1 tonof ice

in 24 hours.

Cooling Tower Tons

A cooling tower ton is defined as:

1 cooling tower ton = 15,000Btu/h = 3,782 kCalories/h

Heat Load and Water Flow

A water systems heat load inBtu/hcan be simplified to:

h = cp q dt

= (1 Btu/lbmoF) (8.33 lbm/gal) q (60 min/h) dt

= 500 q dt (1)

where

h = heat load (Btu/h)

cp= 1 (Btu/lbmoF) for water

= 8.33 (lbm/gal) for water

q = water volume flow rate (gal/min)

dt = temperature difference (oF)

Example - Water Chiller Cooling

Water flows with 1 gal/minand 10oFtemperature difference. The ton of cooling load can be

calculated as:

Cooling load = 500 (1 gal/min) (10oF) / 12,000

= 0.42 ton

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In a chilled-water system the air conditioner cools water down to 40 - 45oF (4 - 7

oC). The chilled

water is distributed throughout the building in a piping system and connected to air condition

cooling units wherever needed.

Total Heat Removed

The total heat removed by air condition chilled-water installation can be expressed as

h = 500 q dt (1)

where

h = total heat removed (Btu/h)

q = water flow rate (gal/min)

dt = temperature difference (o

F)

Evaporator Flow Rate

The evaporator water flow rate can be expressed as

qe= htons24 / dt (2)

where

qe= evaporator water flow rate (gal/min)

htons=air condition cooling load(tons)

Condenser Flow Rate

The condenser water flow rate can be expressed as

qc= htons30 / dt (3)

where

qc= condenser water flow rate (gal/min)

htons=air condition cooling load(tons)

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The table below can be used to compare equivalent diameters for rectangular and round circularducts. The table is based on theducts friction loss formula.

The rectangular dimensions and the air flow volume are adapted to theequal friction loss methodof sizing ventilation duct systems. An approximate friction loss of 0.8 inches water gauge per

100 ft duct (6.6 Pa/m)is used.

Air flow- q-

(Cubic Feet perMinute, cfm)

(m3/s)

Rectangular Duct

Sizes(Inches)

EquivalentDiameter

Round Duct Sizes- de -

(Inches)

Velocity

- v-

(ft/min)(m/s)

Friction Loss

(Inches water

gauge per 100 ftduct)

200

(0.09)

3 x 7

4 x 5

4.9

4.9

1527

(7.8)0.88

300

(0.14)

4 x 7

5 x 6

5.7

6.0

1635

(8.3)0.82

400(0.19)

4 x 9

5 x 7

6 x 6

6.4

6.4

6.6

1736(8.8)

0.80

500(0.24)

6 x 7 7.1 1819(9.2)

0.78

750

(0.35)

5 x 12

6 x 107 x 8

8.3

8.48.2

1996

(10.1)0.77

1000(0.47)

7 x 108 x 9

9.19.3

2166(11)

0.79

1250

(0.59)

8 x 10

9 x 9

9.8

9.8

2386

(12.1)0.88

1500

(0.71)

8 x 12

10 x 10

10.7

10.9

2358

(11.9) 0.77

1750

(0.83)

8 x 14

9 x 12

10 x 11

11.5

11.3

11.5

2469

(12.5)0.78

2000

(0.94)

8 x 15

10 x 12

11.8

12.0

2589

(13.2)0.81

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2500

(1.2)

10 x 14

12 x 12

12.9

13.1

2712

(13.8)0.8

3000(1.4)

12 x 14 14.12767(14.1)

0.75

3500(1.7) 12 x 15 14.6

3010(15.3) 0.84

4000(1.9)

10 x 2214 x 15

15.915.8

2938(14.9)

0.73

4500(2.1)

12 x 1914 x 16

16.416.4

3068(15.6)

0.76

5000

(2.4)

10 x 25

12 x 2015 x 16

16.9

16.816.9

3248

(16.5)0.82

6000

(2.8)

14 x 20

15 x 18

18.2

17.9

3358

(17.1)

0.8

7000

(3.3)

12 x 26

16 x 20

19.0

19.5

3482

(17.7)0.8

8000

(3.8)

12 x 30

14 x 25

20.2

20.2

3595

(18.3)0.8

9000

(4.3)

12 x 34

15 x 25

21.4

21.0

3671

(18.6)0.78

10000

(4.7)

12 x 36

16 x 2520 x 20

21.9

21.721.9

3858

(19.6)0.83

12500

(5.9)

12 x 4516 x 3020 x 24

24.123.723.9

4012

(20.4)0.8

15000

(7.1)

16 x 3618 x 30

23 x 25

24.725.2

26.2

4331

(22)0.87

17500(8.3)

16 x 40

20 x 32

25 x 25

27.0

27.5

27.3

4337(22)

0.79

20000

(9.4)

20 x 35

25 x 28

28.6

28.9

4483

(22.8) 0.79

25000(11.8)

16 x 55

20 x 43

25 x 38

31.0

31.5

33.5

4709(23.9)

0.78

30000

(14.2)

20 x 50

30 x 32

33.7

33.9

4815

(24.5)0.74

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35000

(16.5)

20 x 55

30 x 35

35.2

35.4

5179

(26.3)0.81

40000(18.9)

25 x 4830 x 40

37.437.8

5243(26.6)

0.77

45000(21.2) 32 x 40 39.1

5397(27.4) 0.77

50000(23.6)

32 x 4535 x 40

41.340.9

5222(26.5)

0.66

The design of the ductworks in ventilation systems are often done by using the

Velocity Method Constant Pressure Loss Method (or Equal Friction Method) Static Pressure Recovery Method

The Velocity Method

Proper air flow velocities for the application considering the environment are selected. Sizes ofducts are then given by the continuity equation like:

A = q / v (1)

where

A = duct cross sectional area (m2)

q = air flow rate (m3/s)

v= air speed (m/s)

A proper velocity will depend on the application and the environment. The table below indicatecommonly used velocity limits:

Type of Duct Comfort Systems Industrial Systems High Speed Systems

Main ducts 4 - 7 m/s 8 - 12 m/s 10 - 18 m/s

Main branch ducts 3 - 5 m/s 5 - 8 m/s 6 - 12 m/s

Branch ducts 1 - 3 m/s 3 - 5 m/s 5 - 8 m/s

Be aware that high velocities close to outlets and inlets may generate unacceptable noise.

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The Constant Pressure Loss Method (or Equal Friction Loss Method)

A proper speed is selected in the main duct close to the fan. The pressure losses in the main duct

are then used as a template for the rest of the system. The pressure (or friction) loss is kept at a

constant level throughout the system. The method gives an automatic velocity reduction throughthe system. The method may add more ducts cross sectional changes and can increase thenumber of components in the system compared to other methods.

The Static Pressure Recovery Method

With the static pressure recovery method the secondary and branch ducts are selected to achievemore or less the same static pressure in front of all outlets or inlets. The major advantages of the

method are more common conditions for outlets and inlets. Unfortunate the method is

complicated to use and therefore seldom used.

1TR = cfm/400

1TR x 2.8 gpm = (size of chilled water pumps)