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Depending on the installation, the suction line (gas) can
be:
1.
The outdoor unit is above the indoor unit. Suction
with ascending refrigerant flow.
2.
The outdoor unit is below the indoor unit. Suction
with descending refrigerant flow.
3.
Units on the same level. The refrigerant flow
direction does not change, the flow is towards the
compressor.
-
The liquid line is affected as explained later, depending on
the unit installation. If the head exceeds 10 m, install a
control valve (see Fig. 45).
-
In the first installation case calculate the gas pipe as
ascending.
In the second case, calculate the suction as ascending.
-
The suction line must comply with the following points:
•
Maximum admissible pressure loss for the total
length = 20 kPa (3 psi).
•
Minimum velocity in ascending sections = 6 m/s.
•
Horizontal or descending sections: the velocity can be
between 4 and 6 m/s.
•
Maximum line velocity = 15 m/s.
•
The horizontal sections must have a 2% slope towards
the compressor.
•
In the vertical sections with ascending gas flow, it is
advisable to install siphons every 8 m in height.
Install the first siphon at the base of the ascending
column.
•
Select the suction line diameter (Fig. 49).
Pressure loss/10 m equivalent length in m
Legend
1
- 38XTZ 007 + 40ABZ 007
2
- 38XTZ 008 + 40ABZ 008
- 38XTZ 016 + 40ABZ 016
3
- 38XTZ 011 + 40ALZ 011
- 38XTZ 020 + 40ABZ 020
4
- 38XTZ 014 + 40ALZ 014
- 38XTZ 024 + 40ABZ 024
Note: See Table 4, page 4 for the standard outlet connection diameters.
Fig. 49 - Suction line diameter
Selection process:
-
Enter the diagram in Fig. 49 horizontally at the model
number given in the legend.
-
The model number lines run horizontally and intersect the
various diameter curves (lines going from right to left) and
the various gas velocity curves (lines going from left to
right).
-
Select a diameter and a velocity, and record the one shown
in the specified design conditions for the suction line.
-
For the intersection point of the model number line with
the selected diameter and velocity run down vertically to
find out the pressure loss in kPa or psi for each 10 m
equivalent length (length in line metres plus accessories).
For other lengths the pressure loss is directly proportional.
Liquid line
The liquid line diameter can be selected using the table below.
Table 10 - Liquid line diameter
Total equivalent length
Models
Up to 10 m
38XTZ 007 + 40ABZ 007
5/8"
38XTZ 008 + 40ABZ 008
5/8"
38XTZ 011 + 40ALZ 011
5/8"
38XTZ 014 + 40ALZ 014
5/8"
38XTZ 016 + 40ABZ 016
5/8"
38XTZ 020 + 40ABZ 020
5/8"
38XTZ 024 + 40ABZ 024
5/8"
Calculate the equivalent lengths of the horizontal and vertical
sections and then add them to the equivalent length of the
installed accessories. Enter Table 10 for the total equivalent
length value to select the piping diameter for the right model.
Liquid line requirements:
-
Do not insulate the liquid line, except where it is exposed
to the outside.
-
If the liquid refrigerant flow is descending and the column
height exceeds 10 m, a pressure-balancing valve must be
installed in the lower part to equalise the pressures
between this point and the higher liquid column (see Fig.
45).
Normal cooling mode.
The manual control valve permits equalisation of the
pressures between the highest and lowest point of the
liquid column. Adjust the valve so that the pressure at the
expansion system inlet is the same as at the highest liquid
column point.
-
The pressure loss in the liquid line must not be higher than
34 kPa (5 psi).
-
If the refrigerant flow is ascending and the piping height
exceeds 15 m, at least 1 K of liquid subcooling is required
for each 3.6 m in excess of 15 m.
Subcooling can be contained in the liquid and suction lines
(maximum 15 m).
-
In long lines it is advisable to install expansion bends.
From 10 to 30 m
From 30 to 45 m
5/8"
5/8"
5/8"
3/4"
3/4"
3/4"
3/4"
7/8"
5/8"
3/4"
3/4"
3/4"
3/4"
7/8"
33
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