Carrier 5H - Manual (Page 4)

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