AAON CN-140 - Manual (Page 22)

22
Hot Gas Bypass Piping Considerations for
Evaporator Below Condensing Unit
The line must slope downward from the
HGB valve toward the evaporator.
Hot Gas Bypass Line Guidelines
Choose a small size line to ensure oil return,
and minimize refrigerant charge.
Maintain velocities below a maximum of
4,000 fpm. A general minimum velocity
guideline to use is approximately 1,000 fpm.
Hot Gas Reheat
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.
Discharge lines should be sized to ensure
adequate velocity of refrigerant to ensure oil
return, avoid excessive noise associated with
velocities that are too high, and to minimize
efficiency losses associated with friction.
Pitch the hot gas line in the direction of flow
for oil return.
When installing hot gas reheat risers, an oil
drip line must be provided at the lowest
point in the system. The oil drip line must be
vertical, its diameter should be the same as
the diameter of the riser, and it should be 1
foot long. Run a drip line, using 1/8 inch
capillary tube, 10 feet in length, from the 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.
Insulate the entire length of the hot gas line
with a minimum 1 inch thick Armaflex
insulation.
Hot Gas Reheat Guidelines
Maintain velocities below a maximum of
3,500 fpm. A general minimum velocity
guideline is 2,000 fpm.