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sections. This will however require additional
refrigerant charge.
Suction Line Accessories:
If the job requirements specify suction
accumulators, they must be separately purchased
and installed.
Hot Gas Bypass Line:
Hot Gas Bypass is available for use with DX
systems that may experience low suction pressure
during the operating cycle. This may be
due to varying load conditions associated with
VAV applications or units supplying a large
percentage of outside air. The system is designed
to divert refrigerant from the compressor
discharge to the low pressure side of the system in
order to keep the evaporator from freezing and to
maintain adequate refrigerant velocity for oil
return at minimum load.
Hot discharge gas is redirected to the evaporator
inlet via an auxiliary side connector (ASC) to false
load the evaporator when reduced suction
pressure is sensed.
Field piping between the
condensing unit and the evaporator is
required.
See Figure 10 and Figure 11 for hot gas bypass
piping configurations.
Hot Gas Bypass Piping Considerations for
Evaporator Above Condensing Unit:
Pitch the hot gas bypass line downward in the
direction of refrigerant flow, toward the
evaporator.
When installing vertical hot gas bypass lines, an
oil drip line must be provided at the lowest point
in the system. The oil drip line must be vertical,
its diameter must be the same as the diameter of
the riser, and a maximum of 10” long. Install a
sight glass in the oil drip line for observation. Run
an oil return line, using 1/8 inch capillary tube, 10
feet in length, from the hot gas bypass line oil drip
line to the suction line. Connect the oil return line
below the sight glass and 1 inch above the bottom
of the oil drip line.
Figure 9 - Oil Return Piping
HGBP valves are adjustable. Factory HGBP valve
settings will be sufficient for most applications,
but may require slight adjustments for some make
up air or other process cooling applications.
Insulate the entire length of the HGBP line with a
minimum 1 inch thick Armaflex insulation.
Refer to Figure 10 for piping diagram.
Hot Gas Bypass Piping Considerations for
Evaporator Below Condensing Unit:
The line must slope downward from the hot gas
bypass valve toward the evaporator.
Refer to Figure 11 for piping diagram
Hot Gas Bypass Line Guidelines:
Choose a small size line to ensure oil return, and
minimize refrigerant charge.
Maintain velocities below a maximum of
3500 fpm. A general minimum velocity guideline
to use is approximately 2000 fpm.
Hot Gas Reheat Line:
The AAON modulating hot gas reheat system
diverts hot discharge gas from the condenser to
the air handling unit through the hot gas line.
Field piping between the condensing unit and
the air handler is required.
The line delivers the hot discharge gas to the
reheat coil and/or the hot gas bypass valve, so it is
sized as a discharge line.
