Refrigerant Piping - Daikin WGZ030DW Installation And Maintenance Manual

Refrigerant Piping

Refrigerant Piping
Refrigerant Piping
Refrigerant piping, to and from the unit, should be sized and
installed according to the latest ASHRAE Handbook. It is
important that the unit piping be properly supported with
sound and vibration isolation between tubing and hanger, and
that the discharge lines be looped at the condenser and trapped
at the compressor to prevent refrigerant and oil from draining
into the compressors. Looping the discharge line also provides
greater line flexibility.
NOTE: Do not install any refrigerant piping underground.
The discharge gas valves, liquid line solenoids, filter-driers,
moisture indicators, and expansion valves are all factory
mounted as standard equipment with the water chiller.
For remote condenser application (WGZ-DA) such as air-
cooled or evaporative condenser, the chillers are shipped with
a nitrogen/helium holding charge. The unit is evacuated in the
factory to 500 microns before charging with the nitrogen.
The liquid line has a shutoff valve upstream from the liquid
line solenoid valve and a copper tube cap to be brazed on this
line after test to seal this line for shipment.
The discharge line has a ball valve installed between the
compressor and the discharge stub tube with a copper tube cap
brazed on the line after test to seal it for shipment.
The discharge gas valves, liquid line solenoids, filter-driers,
moisture indicators, and expansion valves are all factory-
mounted as standard equipment with the water chiller.
Do not apply heat, such as a brazing torch, to a sealed unit,
vessel, or component. Internal gases can increase the
internal pressure and cause a life-threatening explosion.
Open the system when heating. The short line between a
valve and brazed end cap can be drilled to vent it. Note that
the valve may leak and the entire unit charge may be open
to the cap.
It is important that the unit be kept tightly closed until the
remote condenser is installed, piped to the unit and the high
side evacuated.
When the field piping has been leak tested, evacuated, and is
ready to charge, the unit valves can be opened and the system
is ready to pressure test, evacuate and charge the entire system
together at one time.
After the equipment is properly installed, leak tested, and
evacuated, it can be charged with R-410A, and run at design
load conditions. Add charge until the liquid line sight glass is
clear, with no bubbles flowing to the expansion valve. Total
operating charge will depend on the air-cooled condenser used
and volume of the refrigerant piping.
10
DANGER
NOTE: On WGZ-DA units (units with remote condensers), the
installer is required to record the refrigerant charge by
stamping the total charge and the charge per circuit on the
serial plate in the appropriate blocks provided for this purpose.
Discharge lines must be designed to handle oil properly and to
protect the compressor from damage that can result from
condensing liquid refrigerant in the line during shutdown.
Total friction loss for discharge lines of 3 to 6 psi (20.7 to 41.4
kPa) is considered good design. Careful consideration must be
given for sizing each section of piping to insure that gas
velocities are sufficient at all operating conditions to carry oil.
If the velocity in a vertical discharge riser is too low,
considerable oil can collect in the riser and the horizontal
header, causing the compressor to lose its oil and result in
damage due to lack of lubrication. When the compressor load
is increased, the oil that had collected during reduced loads can
be carried as a slug through the system and back to the
compressor, where a sudden increase of oil concentration can
cause liquid slugging and damage to the compressor.
Any horizontal run of discharge piping should be pitched away
from the compressor approximately 1/8 inch (6.4 mm) per foot
(meter) or more. This is necessary to move, by gravity, any oil
lying in the header. Oil pockets must be avoided because oil
needed in the compressor would collect at such points and the
compressor crankcase can become starved.
It is recommended that any discharge lines coming into a
horizontal discharge header rise above the centerline of the
discharge header. This is necessary to prevent any oil or
condensed liquid from draining to the compressor heads when
the compressor is not running.
In designing liquid lines, it is important that the liquid reach
the expansion valve without flash gas since this gas will reduce
the capacity of the valve. Because "flashing" can be caused by
a pressure drop in the liquid line, the pressure losses due to
friction and changes in static head should be kept to a
minimum.
A check valve must be installed in the liquid line in all
applications where the ambient temperature can drop below
the equipment room temperature. This prevents liquid
migration to the condenser, helps maintain a supply of
refrigerant in the liquid line for initial start-up, and keeps
liquid line pressure high enough on "off" cycle to keep the
expansion valve closed.
On systems as described above, a relief valve or relief-type
check valve, must be used in the liquid line as shown in piping
systems (shown in and Its purpose is to relieve dangerous
hydraulic pressures that could be created as cool liquid
refrigerant trapped in the line between the check valve and the
expansion or shutoff valve warms up. Install a relief device in
the hot gas piping at the condenser coil as shown in
and Figure 8. Install a discharge check valve in the discharge
line, in a horizontal run, close to the condenser.
Figure 7
IM 1131-2