Table of Contents
Advertisement
(21) Purge System
Figure 37. Horizon Purifier Purge
Horizon
Condenser
Purge Theory and Operation
An absorption chiller operates with all portions of the
system below atmospheric pressure. This can result in air
leakage into the system. The presence of air or other non-
condensables degrades the performance of the system and
must be removed. Excessive heat can also liberate
hydrogen from the water in the system. The removal of air,
hydrogen and other non-condensables is the function of
the Purifier Purge. See Figure 37.
88
Pump out
compressor
Tank Valve
Pump
Discharge
Purge Refrigerant
Compressor
Purge Refrigerant Compressor
Suction Temperature
Liquid
Return
The primary purge tank is connected to the
Horizon condenser by supply and return lines
through which refrigerant may freely flow. The
purge refrigeration system has its evaporator
located inside this tank. The purge evaporator coil
is capable of presenting a 28°F condensing surface
to the chiller refrigerant contained in the tank. The
temperature of the refrigerant in the Horizon
condenser range is 50°F with low cooling water
temperature to 180 F when the chiller is in heating
only operation. When the purge is running, the
Horizon condenser refrigerant is attracted to the
cold surface of the purge evaporator. When the
refrigerant vapor touches the surface of the purge
evaporator it condenses into a liquid, leaving a
partial vacuum behind. More condenser
refrigerant vapor migrates to fill this vacuum. As
the refrigerant condenses into a liquid, any non-
condensables present in the chiller are left behind
to fill more and more of the space in the tank. The
liquid refrigerant returns to the chiller condenser
via the liquid return line.
The temperature of the purge refrigerant system is
monitored. At the start of a purge cycle, when
there is little or no air in the tank, the purge return
refrigerant temperature is approximately the same
as the chiller condenser refrigerant temperature.
The air that accumulates in the tank is not an
efficient heat transfer medium. As air fills the tank,
the purge return refrigerant temperature begins to
fall. Low refrigerant temperature indicates air, or
other non-condensables, in the purge tank. At this
point, a pumpout cycle is initiated to remove the
non-condensables from the collection tank. With
non-condensables removed from the tank, the refrigerant
temperature will rise and the pumpout cycle will be
terminated until another tank of non-condensables is
collected. The temperatures at which the purge pumpout
cycle is initiated and terminated have been determined to
be a function of condenser saturation temperature.
Advertisement
Table of Contents
