User guide

18
When installing hot gas bypass 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. 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 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.
HGB valves are adjustable. Factory HGB
valve settings will be sufficient for most
applications, but may require slight
adjustments for some applications, including
some make up air applications.
Insulate the entire length of the HGB line
with a minimum 1 inch thick Armaflex
insulation.
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.
Predetermined Line Sizes
To aid in line sizing and selection, AAON
has predetermined line sizes for the liquid,
suction, and hot gas lines in comfort cooling
applications.
In order to generate this information, the
following cycle assumptions are made:
Saturated suction temperature = 50°F,
Saturated condensing temperature = 125°F,
Sub-cooling = 10°F, Superheat = 15°F.