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Refrigerant 12, 22, 500, and 502 compressors – Carrier 5H User Manual

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REFRIGERANT 12, 22, 500, AND

502 COMPRESSORS

Operating Requirements

- Satisfactory operation

of a reciprocating compressor is largely depend­

ent upon the recognition of these three fundamental
requirements:

1. Prevention of excess discharge temperature

2. Adequate compressor lubrication

3. A clean and dry system

Discharge Temperature

- The temperature at the

discharge valves within the cylinders is the con­

trolling factor. Some cooling of the discharge gas
occurs before reaching the discharge stop valve,

thus when water-cooled heads are used this cooling

is greater than it is without water cooling. To pre­
vent the occurrence of excessive temperature at
the discharge valves within the compressor, the
following temperatures when measured imme­
diately following the discharge stop valve must
never be exceeded.

For nonwater-coOled heads - 275 F max

For water-cooled heads - 250 F max

The approximate discharge gas temperature

can be found by use of the following equation:

T2 =

Where:

T2 ^

Tl ^

P2 ^

Pi ^

N

Discharge temperature, F absolute

Suction temperature, F absolute

(including superheat)

Discharge pressure, psia

Suction pressure, psia

Compression exponent of the gas

(Table 4)

Table 4 - Compression Exponent ”N'

COMPRESSION

RATIO =

Discharge psia

. WITHOUT

WATER-COOLED

HEADS

WITH

WATER-COOLED

HEADS

R-22

Suction psia

R-12, :

r

-22

R-500 R-502

2

1 216 ,1 325 1 258 1 234

1 240

3

1 191 1 258

1 216 1 216

1 218

4

1 177 1.240

1 203 1 206

1 205

5

1 172 .1.234 1.196 1 197

1 3 99

6

1 166 1 232

1 191 1.190

1.196

8

1.160 1.228

1.186 1.178

1 192

10

1.155 1.225

1 182 1.169

1.187

12

1 150 1.224

1 179 1 161

1 182

The value of the compression exponent (N)

depends upon several factors such as - proper­
ties of the gas compressed, degree of cooling in
the compressor jacket, leakages, etc.

In order to simplify discharge temperature

calculations, the preceding formula maybe stated
in the following form:

T2 = [(460 + Tl) X C] - 460

Where:

T

2

= Discharge temperature, F actual

Tl = Suction gas temperature, F actual

(including superheat)

0

.

Values for C at various compression ratios are:

Table 5 - "C” Factors

COMPRESSION

RATIO =

Discharge psia

WITHOUT

WATER-COOLED

HEADS

WITH

WATER-COOLED

HEADS

Suction psia

R-12

R-22

R-500

R-502

R-22

2

1 14

1 17

1.16

1 13

1.15

3

1 19

1 25

1.22

1 22

1 22

4

1.23

1 31

1 26

1 27

1.27

5

1 26

1 36

1,30

1 30

1 31

6

1 29

1 40

T

3 3

1 33

1 34

8

1 33

1.47

1:39

1.37

1 40

10

1.36

1 53

1 43

1 40

1 44

12

1 38

1 57

1 46

1 41

1 47

SECTION

PAGE

DATE

5F,H-1XA

4

10-66

Printed in U.S.A.

Example:

Refrigerant 12

Compression Ratio — “ °

Factor C = 1.33

Suction Temperature, Tl = 0 F Saturated,

Superheated to 65 F

Solution:

'

T2 = [(460 + 65)

X

1.33] - 460

= 698 - 460
= 238 F

Although exponents are shown for high com­

pression ratios, these are for information pur­
poses only. The rating tables define the allowable

selection and operation limits.

High Compression Ratio

- Avoid compressor op­

eration at compression ratios exceeding those
covered in the rating tables. For operating condi­

tions outside the limits .shown in the tables, use
two-stage compression. Care must be taken to
prevent the compressor from pulling down to

levels outside the rating tables.

Suction Gas Superheat

- Excessive suction gas

superheat will result in abnormally high discharge
temperatures which must be avoided. When using
Refrigerants 12, 500, and 502 the actual suction gas
temperature must not exceed the values listed in
Table 6.

,

S U P E R S E D E S
SECTION

5F,H-1X

PAGES

1-42

DATE

11-63