Famco Danfoss Maneurop MT, Руководство пользователя

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Application guidelines
25
FRCC.PC.004.A9.22
System design recommendations
Horizontal suction line sections shall have a
slope of 0.5% in the direction of refrigerant
flow (5/8" per 10 ft of pipe). The cross-section of
horizontal suction lines shall be such that the
resulting gas velocity is at least 13 ft/s. In vertical
risers, a gas velocity of 26 to 40 ft/s is required
to ensure proper oil return. A U-trap is required
at the foot of each vertical riser. If the riser is
higher than 4 m, additional U-traps are required
for each additional 4 meters. The length of each
U-trap must be as short as possible to avoid the
accumulation of excessive quantities of oil (see
figure below).
For compressors mounted in parallel, the
common suction riser should be designed as
a double riser. Also refer to the News bulletin
"Mounting instructions for installation of
Maneurop® compressors in parallel " and "Parallel
application guidelines".
Gas velocities higher than 40 ft/s will not
contribute to significantly better oil return.
However they will cause higher noise levels
and result in higher suction line pressure drops
which will have a negative effect on the system
capacity.
Oil in a refrigeration circuit is required to lubricate
moving parts in the compressor. During normal
system operation small oil quantities will
continuously leave the compressor, with the
discharge gas. With good system piping design
this oil will return to the compressor. As long
as the amount of oil circulating through the
system is small it will contribute to good system
operation and improved heat transfer efficiency.
However, too large amounts of oil in the system
will have a negative effect on condenser and
evaporator efficiency. If, in a poorly designed system, the amount of oil returning to the
compressor is lower than the amount of oil
leaving the compressor, the compressor will
become starved of oil and the condenser,
evaporator and/or refrigerant lines will become
filled with oil. In such situations, additional oil
charge will only correct the compressor oil level
for a limited period of time and increase the
amount of surplus oil in the rest of the system.
Only correct piping design can ensure a good oil
balance in the system.
Suction lines
Piping design
Note that the suction rotolock valves, which
can be ordered from Danfoss as accessories, are
designed for average pipe sizes, selected for
systems running at nominal conditions. The pipe sizes selected for specific systems may
differ from these recommended sizes.
It is recommended that the suction lines are
insulated to limit suction gas superheat.
Discharge line
When the condenser is mounted above the
compressor, a loop above the condenser and a
U-trap close to the compressor are required to
prevent liquid draining from the condenser into
the discharge line during standstill.