McQuay AGS 225D, Руководство по эксплуатации

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OM AGSD-1 47
Stage-Up Error Step = Saturated Condenser Refrigerant temperature – ( Stage-Up
dead band)
The Stage-Up Error Step is added to Stage-Up Accumulator once every Stage-Up Error-
Delay seconds. When the Stage-Up Error Accumulator is greater than the Stage-Up Error
SetPoint another stage is added.
When a Stage-Up occurs or the saturated condenser temperature falls back within the Stage-
Up dead band, the Stage-Up Accumulator is reset to zero.
Forced Fan Stage At Start
Fans may be started simultaneously with the compressor based on outdoor ambient
temperature. When the compressor starts, a Fantrol stage is forced based on the following
table. Since this logic applies only to Fantrol fans, the VFD fan is not affected.
OAT Fantrol Stage At Start
> 75
o
F Forced Fantrol 1 SP
> 90
o
F Forced Fantrol 2 SP
> 105
o
F Forced Fantrol 3 SP
Staging Down
There are four Stage-Down dead bands. Stages one through three use their respective dead
bands. Stages four to eight share the fourth Stage-Down dead band.
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 dead band) - Saturated Condenser
Refrigerant temperature
The Stage-Down Error Step is added to Stage-Down Accumulator once every Stage-Down
Error Delay seconds. When the Stage-Down Error Accumulator is greater than the Stage-
Down Error Setpoint another stage of condenser fans turned off.
When a stage-down occurs, or the saturated temperature rises back within the Stage-Down
dead band, the Stage-Down Error Accumulator is reset to zero. The accumulator is also
held at zero after startup until either the outside ambient temperature is less than or equal to
75
°
F, or the saturated condenser temperature is greater than the condenser target less the
active stage-down deadband.
EXV Control
Pressure Control
In pressure control, the evaporator pressure is controlled by the EXV position. The
pressure target varies based on evaporator LWT and discharge superheat values. A PID
logic is used to control the pressure to the target value.
The base pressure target is calculated using the following formula:
Base target = 0.6(LWT) – 2
The base target is limited to a range from the low pressure inhibit setpoint plus 2 psi, up to
52 psi.
The pressure control target may be adjusted if the discharge superheat is not within an
acceptable range. If the superheat is less than 22 degrees F, the base pressure target will be
reduced by a value equal to the low superheat error. If the superheat is more than 40
degrees F, the base pressure target will be increased by a value equal to the high superheat