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7
HOW TO SIZE REFRIGERANT LINES
In the dimensioning of refrigerant lines of air conditioning systems equipped with two sections, the designer has to take into account
that, due to the pressure loss of the refrigerant circuits, cooling capacity decrease and compressors power input increase may occur.
It is also necessary to consider that the fluid changes its state when circulating within the plant.
Another common problem is related to the oil: this, in fact, is highly miscible to the refrigerant and consequently it is easily dragged
into the circuit; obviously, it is necessary to make sure that this lubricant is able to entirely come back to the compressor. Finally, the
following basic conditions, typical of each refrigerant circuit, must be respected: cleaning of the pipes and total absence of liquid to the
compressor's inlet.
To avoid all the above-mentioned problems, the connection lines must be properly sized.
7.1
DIAMETER
The pipes diameter is one of the most critical features in sizing the refrigerant lines. The refrigerant speed inside the pipes
and the pressure drop depend on the diameter.
Although it is advisable to limit as much as possible the pressure drop (to reduce the loss of cooling capacity) is important
to ensure a velocity in the pipe to allow the oil carryover.
Generally the dimensioning of the suction line is made in order to maintain a speed higher than 4 m/s to the minimum load
(minimum step of capacity) and lower than 20 m/s at full load.
The tables below show the standard diameters. These diameters shall be considered approximate and must be verified for
each installation.
RAUS STANDARD DIAMETERS
SIZE
Suction
diameter
[mm]
Liquid
diameter
[mm]
040
22
12
050
22
12
070
22
12
080
22
12
090
22
12
100
22
12
110
22
12
130
28
16
150
28
16
RAUS connection kit includes solenoid valve, mechanical expansion valve, filter dryier with liquid sight and safety valve.
RAUX STANDARD DIAMETERS
SIZE
Suction diameter
[mm]
Liquid diameter
[mm]
Balancing
diameter
[mm]
040
22
12
12
050
22
12
12
060
22
12
12
070
22
12
12
080
22
12
12
090
22
12
12
100
22
12
12
120
28
16
16
140
28
16
16
RAUX loose connection kit includes 2 check valves, 1 mechanical expansion valve.
RAUX mounted connection kit includes: 2 safety valves on liquid line, 2 shut-off valves on liquid line and 1 shut-off valve
on suction line.
