Daikin Pathfinder AWV Installation, Operation And Maintenance Manual page 68

Staging Up
When the saturated condenser temperature is above the Target
+ the active deadband, a Stage Up error is accumulated.
Stage Up Error Step = saturated condenser temperature –
(target + Stage Up Deadband)
The Stage Up Error Step is added to Stage Up Accumulator
once every five seconds, only if the saturated condenser
temperature is not falling. When the Stage Up Error
Accumulator is greater than 11°C (19.8°F) fan stage is
increased by 1. When a stage up occurs or the saturated
condenser temperature falls back within the Stage Up
deadband the Stage Up Accumulator is reset to zero.
The first fan will turn on when condenser saturated
temperature is above the target rather than using the error
accumulator.
Staging Down
When the saturated condenser refrigerant temperature is
below the Target – the active deadband, a Stage Down error is
accumulated.
Stage Down Error Step = (target - Stage Down deadband) -
saturated condenser temperature
The Stage Down Error Step is added to Stage Down
Accumulator once every 5 seconds. When the Stage Down
Error Accumulator is greater than 3°C (5.4°F), a fan stage is
removed.
When a stage down occurs or the saturated condenser
temperature rises back within the Stage Down deadband the
Stage Down Error Accumulator is reset to zero.
Active Deadbands
Stage Up and Stage Down deadbands are determined by set
points as shown in the following table:
Table 59: Stage Deadbands
Fan Stage Up Setting
stage
0 Fan Stage Up
Deadband 0
1 Fan Stage Up
Deadband 1
2 Fan Stage Up
Deadband 2
3 Fan Stage Up
Deadband 3
4 Fan Stage Up
Deadband 4
5 to 16 Fan Stage Up
Deadband 5
IOM 1242-8 • PATHFINDER
Stage Down Setting
---
Fan Stage Down
Deadband 1
Fan Stage Down
Deadband 2
Fan Stage Down
Deadband 3
Fan Stage Down
Deadband 4
Fan Stage Down
Deadband 5
MODEL AWV CHILLERS
®
VFD on 1st Fan of Each Circuit
As an option, the first fan may be driven by a VFD. The VFD
control will vary the fan speed to drive the saturated condenser
temperature to a target value. The target value is normally the
same as the saturated condenser temperature target.
VFD Speed Control
The VFD speed should always be 0% when the fan stage is 0.
When the fan stage is greater than 0, the VFD speed will be
calculated to control the saturated condenser temperature to
the VFD target. The minimum and maximum speed are set by
the VFD Min Speed and VFD Max Speed set points.
Stage Up Compensation
In order to create a smoother transition when the fan stage
increases, the VFD compensates by slowing down initially. This
is accomplished by adding the new fan stage up deadband
to the VFD target. The higher target causes the VFD logic to
decrease fan speed. Then, every 2 seconds, 0.1°C (0.18°F) is
subtracted from the VFD target until it is equal to the saturated
condenser temperature target set point.
Speed Signal to VFD
The fan VFD is controlled using a 0-10 volt signal. When the
fan should be off, the signal will be 0 Vdc. When the fan should
be running, the signal will vary based on the percent speed
calculation.
Speed Signal = Percent Speed / 10
Fan Control In Waterside Econ State
Fan control when the cooling state is Waterside Econ includes
fan staging and fan VFD control. The general concept is to
stage fans to control WSE capacity and trim the capacity with
the fan VFD speeds. During Waterside Econ state, if a circuit is
disabled then it should not run the fans for WSE.
During Waterside Econ mode operation, the unit will change
to control the chilled fluid set point based on the evaporator
entering fluid sensor rather than the leaving sensor. Since the
evaporator is not producing any cooling effect in this mode, the
evaporator entering fluid temperature sensor is representative
of the leaving fluid temperature the system will see.
If transition from Hybrid Cooling to Waterside Econ occurs, it
is ok for fans to start staging on during pumpdown of running
circuit(s).
Fan Control In Hybrid Cooling
Modulation State
Fans on a circuit with a running compressor should operate the
same as they normally do in Mechanical Cooling Only (based
on condenser pressure control). If the compressor is not
running, fans should be staged on as requested per the unit
level capacity control logic.
During either Hybrid Cooling State, the condenser target
should be calculated as it normally would but reductions in the
value should be done at a controlled rate. Every 30 seconds
68
Circuit Functions
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