Unit Functions
www.DaikinApplied.com 61
IOM 1242-8 • PATHFINDER
®
MODEL AWV CHILLERS
same as they normally do (based on condenser pressure
control). Fans on a circuit NOT running the compressor should
all remain off in this state so that the circuit is ready to start as
needed.
Operation in Hybrid Cooling - Modulation State
When cooling state is Hybrid Cooling – Modulation:
• Waterside Economizer Valve 1 should be fully closed.
• Waterside Economizer Valve 2 should be fully opened.
• Condenser fans may be running for the purpose of
condenser pressure control on a circuit running a
compressor or for the sole purpose of WSE effect.
• One or both compressors may be running.
Operation in Mechanical Cooling State
When cooling state is Mechanical Cooling:
• Waterside Economizer Valve 1 should be fully opened.
• Waterside Economizer Valve 2 should be fully closed.
• Condenser fans may be running only for the purpose
of condenser pressure control on a circuit running a
compressor. No condenser fans should be running for the
purpose of WSE.
Capacity Control in Waterside
Economizer State
This section describes the operation of condenser fans when
the cooling state is Waterside Economizer. Fan control includes
fan staging and fan speed control. The general concept is to
stage fans to control WSE capacity and trim the capacity with
the fan variable speed drives.
During Waterside Economizer state, if a circuit is disabled then
it should not run the fans for WSE.
If transition from Hybrid Cooling to Waterside Econ occurs,
fans may start staging on during pumpdown of running
circuit(s).
During Waterside Economizer state, the Evaporator EWT will
be controlled rather than the Evaporator LWT. This is because
of the lag that occurs in the Evaporator LWT when WSE
capacity changes.
Calculated Values
WSE Delta T = WSEEWT – EEWT
LWT Error = EEWT – Active Set Point
Capacity Control In Hybrid Cooling
Modulation State
Fans on a circuit running the compressor should operate
mostly the same as they normally do (based on condenser
pressure control). The exception is that reductions in the
Saturated Condenser Temperature Target should be at a
controlled rate of 0.1°C every 30 seconds.
Fans on a circuit NOT running the compressor should all be
turned on if that circuit is enabled to run but not all at once
upon entering the Hybrid Cooling Modulation state. After the
cooling state is Hybrid Cooling Modulation for five minutes the
fans on a circuit not running the compressor can start turning
on. A minimum of 20 seconds should pass between fan stage
increases and it should only increase if LWT Error is within the
dead band calculated for unloading the running compressor
(this is to make sure the running compressor is given a chance
to unload in compensation for adding WSE capacity).
In Hybrid Cooling Modulation state, the compressor capacity
control logic should operate normally except for one change.
When the estimated full capacity delta t is calculated for the
purpose of establishing the load and unload deadbands, that
calculation should be based on the total delta t rather than just
the evaporator temperature delta.