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Carrier 5H User Manual

Page 29

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It is good practice to select motors with allow­

ance for 10% voltage reduction unless there is a
certainty that this cannot occur.

Compressor

Starting

Torque

-

The

required

compressor

starting

torque

is

dependent

on

the

discharge pressure as well as the pressure dif­
ferential

occurring

during

start-up.

The

max­

imum expected torque required during the starting

period

for

5F,H

compressors,

used

as

boosters,

is shown in Table 22 at two saturated discharge
temperatures.

Selection Procedure

- The selection of a 5F,H

booster

compressor

requires

that

the

load,

sat­

urated

suction

temperature,

saturated

discharge

temperature,

type

of

system

and

refrigerant

be

known.

After

the

saturated

intermediate

temperature

is determined from Fig. 18, the booster rating on
pages 22 thru 24 can be entered and the compres­
sor selected. The low stage load is then multiplied
by the "R” factor from Table 18, 19 or 20 to ob­
tain

the

high

stage

compressor

load.

With

this

information,

the

single

stage

ratings

(Application

Ratings 5F,H-1XR) can be entered and the high

stage compressor selected.

SELECTION EXAMPLE:

Given:

Refrigeration load

= 5 . 7 tons

Saturated Suction Temperature = -60 F

Saturated Condensing Temperature = 80 F
Open Type Intercooler
Refrigerant 22

Find: Compressor size and motor size.
Solution:

1.

Figure 18 on page 27 indicates an optimum

saturated

intermediate

temperature

of

-1

F.

Allow for 1 F drop from the booster compres­
sor to the intercooler and from the intercooler
to the high stage compressor.
Booster Saturated Suction

Temperature

= - 60 F

Booster Saturated Discharge

Temperature

= OF

2.

At - 60 F suction and 0 F discharge, the 5H60

booster compressor has a capacity of 6.8 tons
with 12.1 bhp input at 1750 rpm.

The safety factor at 1750 rpm.

0^x 100

- 100 or 20%

This is satisfactory from Fig. 17 and^a 5H60

compressor is selected.

3. Indicated hp = bhp - fhp

where bhp is given in the compressor ratings,
fhp is given in Table 22.

Indicated hp = 12.1 - 3.07 = 9.03

Recommended minimum hp

= (2 X ihp) + fhp
= (2 X 9.03) + 3.07 = 21.13

Tentatively select a 25 hp motor. Assume that

the low stage will never start against a sat­
urated discharge higher than 30 F. At 30 F
discharge Table 22 indicates a starting torque
of 54 Ib-ft. Therefore, a normal starting torque
25 hp motor is selected.

4.

With - 60 F suction and OF discharge, Table 19

indicates an "R” value of 1.303. Therefore, the
high stage load is:

1.303 X 6.8 = 8.86 tons (actual load)

5.

Allowing a 1 F drop from the intercooler,

the

high

stage

saturation

suction

temperature

is - 2 F.
Allowing a 2 F drop between the compressor
and

condenser,

the

high

stage

saturated

dis­

charge temperature = 80 + 2 = 82 F.

6.

Referring

to

the

5F,H

single

stage

ratings

(5F,H-1XR) the 5F60 at 1450 rpm has a capac­
ity of 9.10 tons at - 2 F suction and 82 F dis­
charge. The 5F60 is selected and requires 13.7
bhp at 1450 rpm.

7.

Assume that the maximum load during pull­

down occurs at 50 F suction and 90 F discharge.
For

this

condition,

the

rating

tables

indicate

17.6 bhp, thus a 20-hp motor is selected.

Table 22 - Booster Compressor Starting Data

COMPR

SIZE

UNLOADING

DURING

STARTING

MAX COMPR STARTING TORQUB^LB-FT

RECOMMENDED MIN MOTOR SIZE HP

FRICTION

HP*

(FHP)

Refrigerant 12

Refrigerant 22

Refrigerant 12

Refrigerant 22

Saturated Discharge Temperature (F)

High

Torque

Normal

T orque

High

Torque

Normal

Torque

10 F

30 F

10 F

30 F

5F20

None

9

13

15

21

_

2

3

3

67

5F30

None

10

15

16

24

3

3

5

5

.91

5F40

75%

8

12

13

19

3

3

5

5

1 15

5F60

66-2/3%

10

15

16

24

3

5

5

7-1/2

1.64

5H40

75%

19

28

30

45

5

7-1/2

7-1/2

10

2.25

5H46

75%

25

36

39

59

7-1/2

10

10

15

2.79

5H60

66-2/3%

23

34

37

54

7-1/2

10

10

15

3 07

5H80

75%

26

38

41

60

10

15

15

20

3 82

5H120

66-2/3%

41

60

65

94

15

20

20

30

5 25

Based on 1750 rpm with 5FH compressors Will vary directly with rpm at other speeds

S U P E R S E D E S
SECTION

5F,H-1X

PAGES

1-42

DATE

11-63

SECTION
PAGE
DATE

5F,H-1XA

29

10-66