AAON M1-011 - Manual (Page 31)

31
8. Hot Gas Bypass
The purpose of (external) hot gas bypass
(HGBP) is to prevent coil freeze-up and
compressor damage from liquid slugging
during periods of low airflow operation, or with
low entering air temperatures.
HGBP is useful when the air conditioning
system is subject to variations in load caused
by varying air volume or large proportions of
outside air. The HGBP valve meters discharge
refrigerant gas to the distributor downstream of
the expansion valve, and at the entrance to the
evaporator distributor tubes. The quantity of
gas varies to control a constant suction
pressure, allowing more gas to flow as suction
pressure decreases.
HGBP is available, factory installed, on AAON
condensing units, and for use with modular air
handlers, and all AAON split systems, in order
to meet various design conditions. A modular
air handler selected with DX cooling can be
connected to a condensing unit that has also
been prepared for HGBP to the evaporator
coil. The option requires a third piping
connection from the matching condensing unit.
This connection must observe the same length
and height restrictions as used for the liquid
and suction piping. It is advisable to insulate
the hot gas line, especially on long piping runs.
HGBP line connects to
ASC fitting between
TXV and distributor
Evaporator
Coil
TXV
Condenser Coil
HGBP
Valve
Compressor
Suction Line
HGBP Line
Isolation
Valves
Liquid Line
Factory Piping
Field Piping
Figure 8.2, External HGBP Piping
Figure 8.1, Components of Hot Gas Bypass