CVGF-SVU02B-E4
71
High Lift Unloading (500 Ton
Family Only)
High Lift Unloading Valve directs
discharge gases from the
condenser through a solenoid
valve directly into the
economizer. From the
economizer, this gas then flows
to the second stage compressor
where the economizer normally
is connected. The purpose of
HLUV is to increase the gas flow
rate through the second stage
compressor. Bypass gas is
allowed to occur using an inline
normally closed solenoid valve.
The high lift unloading function
is dependent on the lift (where
lift is defined as the difference
between Condenser Saturated
Refrigerant Temperature and the
Evaporator Saturated Refrigerant
Temperature) and on chiller load.
When the high lift unloading
mode is entered, the High Lift
Unloading valve is opened and
the inlet guide vane close travel
is limited.
The HLUV valve does not
modulate the flow rate, but
rather is either open or closed.
Further, the valve was sized to
handle a mass flow sufficient to
permit operation below 35% IGV
position but not necessarily to
0%. The valve was sized to
permit substantial but
incomplete unloading and yet
was kept as small as practicable
to minimize power requirements
with HLUV operation.
Not all CVGF chillers require the
bypassing of condenser gas. In
some tonnages, the High Lift
Unloading Valve and copper
lines do not exist. The LLID (1A9)
with the High Lift Unloading
relay always exists.
Note:
There is noticeable noise,
due to gas flow, when the high
lift unloading valve is open.
Functional Description
The following equation
determines action of the high lift
unloading function:
Trigger IGV% = 0.98 * Lift + -
0.065 * CPIM + C
Where Lift is defined as
Condenser Saturated Refrigerant
Temperature minus Evaporator
Saturated Refrigerant
Temperature in °F. The CPIM is
the average impeller diameter in
inches times 100.
Machine Protection and
Adaptive
Summary of Contents for CVGF 1000
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