15
6.1.4 - Discharge pipe sizing
The discharge piping must be sized to achieve reasonable
pressure drops: a variation of 1.5 K of the saturated tempera-
ture is normally accepted (approx. 60 kPa variation for a
condensing temperature of 50°C).
For most applications the refrigerant gas velocity is sufficient
to entrain the liquid refrigerant/oil mixture. Nevertheless, Table
2 shows the minimum required cooling capacities for different
pipe diameters and different saturated discharge temperatures.
This table is based on 8 K superheat, a saturated suction
temperature of 4°C and 8 K subcooling. Table 3 shows the
correction factors to be applied to the values from Table 2, if
the operating conditions are different from those previously
stated.
6.1.5 - Liquid line sizing
The 30SZV compressors are supplied with an oil that is fully
miscible with refrigerant R407C in the liquid phase.
Consequently low refrigerant velocities in the liquid lines are
not a problem.
The admissible pressure drops in the liquid lines depend
mainly on the subcooling level of the liquid refrigerant at the
condenser outlet. Pressure drops corresponding to 1.5°C
saturated temperature must not be exceeded.
Special attention must be paid to the liquid line sizing when the
expansion device ist positioned higher than the condenser. It
may now be necessary to increase the pipe diameter to
compensate for the additional pressure of the liquid refrigerant
column. If the liquid refrigerant head ist very high, it may even
be necessary to increase the subcooling to prevent an phase
change in the liquid line. This can be done e.g. by a liquid-
vapour heat exchanger or an additional coil.
At 45°C the volume mass of refrigerant R407C in the liquid
phase is approximately 1050 kg/m
3
. A pressure of 1 bar
corresponds to a liquid head of: 100 000/(1050 x 9.81) = 9.7 m.
Table 1 - R-407C correction factors for copper tube
30SZV
Saturated suction temperature, °C
Cond. temp. -18
-12
-7
-1
4
10
°C
S
HG
L
S
HG
L
S
HG
L
S
HG
L
S
HG
L
S
HG
L
27
2.01 1.36 1.09
1.61 1.34
1.07
1.31 1.30
1.06
1.07 1.26 1.04
0.89 1.23 1.03
0.74 1.19 1.01
32
2.11
1.27 1.08
1.69 1.23
1.06
1.37 1.19
1.04
1.12 1.16 1.03
0.93 1.12 1.01
0.77 1.09 1.00
38
2.22 1.17 1.08
1.78 1.13
1.06
1.44 1.10
1.04
1.18 1.06 1.02
0.97 1.03 1.01
0.81 1.00 0.99
43
2.34 1.09 1.08
1.88 1.06
1.06
1.52 1.02
1.04
1.24 0.99 1.02
1.03 0.96 1.00
0.85 0.93 0.99
49
2.49 1.03 1.09
1.99 0.99
1.07
1.61 0.96
1.05
1.32 0.93 1.03
1.09 0.90 1.01
0.90 0.87 0.99
54
2.66 0.97 1.12
2.13 0.94
1.10
1.72 0.90
1.07
1.40 0.87 1.05
1.16 0.85 1.03
0.96 0.82 1.01
60
2.87 0.93 1.16
2.29 0.90
1.13
1.85 0.86
1.11
1.50 0.83 1.08
1.24 0.81 1.06
1.03 0.78 1.04
66
3.13 0.91 1.21
2.49 0.87
1.18
2.01 0.84
1.15
1.63 0.81 1.12
1.34 0.78 1.10
1.11
0.75 1.08
71
3.46 0.89 1.29
2.74 0.85
1.26
2.21 0.82
1.22
1.79 0.78 1.19
1.47 0.76 1.16
1.21 0.73 1.13
Legend
S
Suction
HG Hot gas
L
Liquid
Table 2 - Minimum capacity for oil entrainment in the discharge piping (kW) for R407C copper tube
30SZV
Outside pipe diameter
1/2”
5/8”
3/4”
7/8”
1-1/8”
1-3/8”
1-5/8”
2-1/8”
2-5/8”
3-1/8”
3-5/8”
4-1/8”
Saturated condensing temperature, °C
27
0.81
1.48
2.39
3.66
7.14
12.06
18.64
37.21
63.94
99.81
145.60
201.98
32
0.84
1.51
2.46
3.76
7.28
12.34
19.06
38.09
65.42
102.13
148.94
206.66
38
0.84
1.51
2.50
3.80
7.42
12.56
19.41
38.76
66.61
103.96
151.62
210.35
43
0.88
1.55
2.53
3.87
7.53
12.73
19.66
39.25
67.42
105.23
153.48
212.92
49
0.88
1.55
2.53
3.87
7.56
12.80
19.77
39.50
67.84
105.90
154.43
214.26
54
0.88
1.55
2.53
3.87
7.56
12.80
19.77
39.46
67.81
105.86
154.40
214.19
60
0.84
1.55
2.53
3.87
7.49
12.70
19.62
39.18
67.32
105.05
153.24
212.60
66
0.84
1.51
2.46
3.80
7.39
12.45
19.27
38.44
66.08
103.12
150.42
208.66
71
0.81
1.48
2.43
3.69
7.17
12.17
18.78
37.49
64.43
100.55
146.69
203.49
Table 3 - R407C correction factors
for oil entrainment in the discharge piping
Saturated suction temperature, °C
-23
-18
-12
-7
-1
4
10
0.86
0.89
0.92
0.94
0.97
1.00
1.03
See chapter "Discharge pipe sizing"