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Additional R410A refrigerant charge for a linear meter of pipe
Diameter (mm)
Gas (Kg/m)
Liquid (Kg/m)
6
0.0014
0.0133
10
0.005
0.051
12
0.008
0.079
16
0.014
0.139
18
0.019
0.182
22
0.029
0.285
28
0.045
0.445
35
0.074
0.729
42
0.111
1.082
54
0.182
1.779
64
0.281
2.721
67
0.289
2.825
76
0.377
3.689
7.2
LENGTH
The length of the suction line produces pressure losses higher than those ones found in the circuit of a machine with a single section.
Obviously consequently there is a lower pressure in the intake to the compressor. This may cause, as already mentioned, a decrease
of the output power and increase of that absorbed, with consequent reduction of the COP. A similar phenomenon occurs in the
discharge line: loss of load force the compressor to work at a pressure that is higher than the actual condensation, with effects equal
to those previously analyzed. In the following table the pressure drops effects on the cooling capacity are shown, expressed in terms
of temperature drops [°C] on the suction and discharge lines:
Losses of load (°C)
Power output (%)
Power input (%)
0
100
100
1°C suction
95.7
103.5
1°C discharge
98.4
103.5
2°C suction
92.2
106.6
2°C discharge
96.8
106.6
High pressure drops, caused by considerable lengths, create another type of problem on the liquid line: known as "gas flashing".
It consists in the evaporation of part of the refrigerant, due to the heat developed by friction along the line and due to the pressure
drops. This may cause a malfunction of the thermostatic valve. A proper sizing of the refrigerant lines will avoid these problems. A
simple and rather accurate method has been suggested by ASHRAE (American Society of Heating, Refrigerating and Air-
Conditioning Engineers
)
and will be explained below.
7.3
CALCULATION OF THE EQUIVALENT PRESSURE DROP
For a correct and quick dimensioning of refrigerant lines please refer to the following table, developed for the R410a refrigerant.
Table 1:
Cooling capacity corresponding to different tubes diameter referred to different pressure drops or speed values.
This table refers to the pressure drop values or speed values (for the liquid line) indicated in the column heading.
