Hot Gas Bypass - Daikin R-22 Refrigerant Piping Design Manual

Hot Gas Bypass

Hot gas bypass is a method of maintaining compressor
suction pressure (creating a false load) during lightloads. This
has the affect of modulating compressor capacity below the
minimum unloading point without cycling the compressor. It is
accomplished by returning hot (discharge) gas from the leaving
side of the compressor back to a point on the low-pressure
side of the refrigeration circuit.
Figure 18 shows the preferred method for piping hot gas bypass
for fin tube condensers only. If Micro-channel condensers
are used then refer to IM 914. Hot gas is introduced into the
inlet of the evaporator and is given ample time to distribute
its energy into the main flow of refrigerant prior to returning
it to the compressor. A special fitting called an Auxiliary Side
Connector (ASC) should be used to introduce the hot gas into
the distributor. In addition, the distributor may need a different
nozzle. On DX coils that have a venturi, a standard copper tee
fitting may be used to introduce the hot gas.
Figure 18: Typical Hot Gas By-Pass Piping Arrangement — Fin Tube Condensers Only*
Liquid
Line
Solenoid
Filter-
Drier
* Refer to Daikin IM 914 for Micro-channel condensers.
www.DaikinApplied.com
Sight
Glass
Valve
TX
Valve
Auxiliary side
connector (ASC)
introduces hot gas
into distributor
Hot gas bypass lines include a solenoid valve and a hot gas
bypass valve. Some manufacturers provide a single device that
provides the functions of both a solenoid and control valve. The
solenoid valve is energized when hot gas bypass is required.
The hot gas bypass valve modulates the refrigerant flow
through the line to maintain the suction pressure.
Tip: Daikin Applied DX coils use distributors that
require an ASC and the nozzle in the distributor
needs to be changed. DX coils that use a venturi
introduce hot gas bypass using a standard tee fitting.
Hot gas
bypass routed
above evaporator
Hot gas
bypass valve
installed close
to suction line
Evaporator
29 AG 31-011 • REFRIGERANT PIPING DESIGN
Hot gas bypass
solenoid valve
installed close
to discharge line
Discharge
Suction
Line
Line