1
•
Horizontal sections = A
•
Vertical descending sections = B
•
Vertical ascending sections = C
The calculation of the suction or discharge line, for example,
includes sections “A”, as well as sections “B” and sections
“C” so that the total of the pressure loss is the total of the
three sections in their equivalent lengths.
Pipe diameter calculation procedure
suction and discharge line
To size the pipes:
•
Make a diagram with the actual outline of the pipes in
the system. Record the dimensions (in metres) of the
various sections and the elements to be included
(siphons, elbows, valves, etc.).
Gas pipe
Frame or roof
Beam
Beam
38UQZ
outdoor unit
38UQZ
outdoor unit
40ALZ
indoor unit
40ALZ
indoor unit
Heat pump
Heat pump
Heat pump
Heat pump
Cooling
Cooling
Cooling
Cooling
Heat
pump
Heat pump
Cooling
Cooling
Gas line
Suction (cooling)
Discharge (heat pump)
Gas line
Suction (cooling)
Discharge (heat pump)
Siphons installed
(depending on height)
Siphons installed
(depending on height)
Liquid line
Liquid line
Liquid line
Refrigerant flow
Retention valve*
Refrigerant flow
Refrigerant flow
Retention valve*
Liquid pressure
control device*
Liquid pressure
control device*
40ALZ
indoor unit
38UQZ
outdoor unit
Gas line
Suction (cooling)
Discharge (heat pump)
Cooling
Cooling
Heat pump
Heat pump
Depending on the unit installation, the piping design is as
follows:
Outdoor unit above the indoor unit (Fig. 25)
The most unfavourable gas line condition is during cooling
mode, with suction in ascending direction. In heating mode
the gas line is the discharge line and descending and does
not have problems with the oil flow. The liquid line refrige-
rant flow direction is descending in cooling mode and ascen-
ding in heat pump mode, and is calculated as explained later.
Indoor unit above the outdoor unit (Fig. 26)
For heat pump units this type of installation limits the height
difference between the units, and the discharge line speed
is approximately half of the suction line speed. The suction
line flow is descending in cooling mode, so that the oil flow
is not so problematic. The most unfavourable condition is
the discharge line that is ascending in heat pump mode.
The liquid line flow direction is ascending in cooling mode
and descending in heat pump mode, and is calculated as
explained later.
the outdoor and indoor units are on the same level (Fig. 27)
First make an actual outline diagram of the lines and an exact
calculation of the total equivalent length. If the diagram
shows any level changes to overcome (beams and other
structural elements) the resulting section (ascending and
descending) must be included in the calculations. This means
that for a gas pipe the diameter of the horizontal sections,
the vertical ascending and descending sections must be
calculated separately.
This means that in this type of installation, as in any other,
a section called horizontal can include sections that are not
all horizontal (see Fig. 8).
Fig. 28
* Install when the liquid column height exceeds 10 m.
Fig. 27 - Both units on the same level
In the 38UQZ heat pump units the gas line is always the
suction line in cooling mode. If the cycle is reversed to
heating mode it becomes the discharge line, changing the
refrigerant gas flow direction. The liquid line does not
change and always carries liquid refrigerant in one direction
or other, depending on the operating mode.
Refrigerant piping design
The design and sizing of the pipe diameters depends on
the unit location which can be:
Fig. 25 - Outdoor unit above the indoor unit
Fig. 26 - Indoor unit above the outdoor unit
