McQuay AGZ 035A, Инструкция по установке, эксплуатации и обслуживанию

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58 AGZ 035A through 065A IOMM AGZ-3
Ice (for lower ice setpoint requirements, consult McQuay Marketing Support)
When in “Ice” reset mode, and adequate amount of glycol must be added to the system to protect the
evaporator from freezing. McQuay recommends a minimum of 30% solution of ethylene glycol to
protect to 7°F with the minimum leaving water temperature at unit shut down of 21°F. At 21°F shut
down, the saturated refrigerant temperature can approach 10°F.
The leaving water setpoint must be calculated according to the following formula;
LvgEvapSpt = Desired Ice Tempe 1/2 Control Band + Shut down Delta T
Lvg EvapSpt = 21°F + 1/2 (4)°F + 1.5°F
Lvg Evap Spt = 21°F + 2°F + 1.5°F
Lvg Evap Spt = 24.5°F
The remote 4-20ma input must be 4ma or less and the leaving water temperature will be controlled to
the calculated setpoint. When the remote reset input is above 4 ma, the value “MaxChwRst” is added
to the leaving water setpoint. This will be the day operating setpoint. This value cannot be reset
when in the day mode by any other reset options.
The alarm setpoints must be adjusted to allow operation of the chiller at the lower temperatures. The
following values should be adjusted and the example assumes 30% ethylene glycol solution with a
21°F shut down temperature:
1.
“FrzStat” Set to the saturated suction pressure that corresponds to a temperature several degrees
higher than the freeze point of the water / glycol solution. (10°F = 33psig.)
2. “Frz H2O” Set at least 4° F below the shut down temperature, but not lower than the freezing
point of the water / glycol solution. (21°F - 4°F = 17°F)
3. “LP cutout” Set 8 to 10 psi below the “Frz State” pressure but never below 20 psig. (33psi - 10
psi = 23 psi)
4. “LP Cutin” Set to a saturated suction pressure equal to the shut down temperature plus 1/2 the
control band. (21°F + 2°F = 23°F; 23°F = 46psig)
Network
A network refers to a McQuay MicroTech control panel (CSC or RMS) that can provide controlling
functions to several McQuay chillers. One function is to control the chiller leaving water temperature
according to some control logic in the network control panel. The network control panel will control
the leaving water setpoint when the “Network” option in the chiller is selected. The network control
panel will send a signal that reflects 0 to 100% reset of the leaving water set point according to the
value entered into the “MaxChwRst” of the unit controller.
Soft Loading
Soft loading limits the number of available stages when the unit is started to prevent excessive power
consumption and possible overshoot of the leaving water temperature set point. Soft loading is in
effect whenever the unit is started from an “off” cycle. On initial start-up, the chiller will turn on the
chilled water pump and sample the loop water temperature for a time equal to the Load Delay set
point (“LoadDelay”). If cooling is required at the end of the time-delay, a start procedure is initiated.
On entering the “Stage mode” the controller starts a countdown timer to indicate how long the unit
has been in the cool stage mode. The number of stages allowed during soft loading is determined by
the Soft Load Maximum Stages (“SoftLdMaxStg”). The duration of the soft load sequence is
determined by the Soft Load Timer. If the Soft Load Timer is set to zero, no soft loading will take
place. When the soft load option is enabled, any time remaining in the Soft Load Timer will be
displayed in the menu Soft Load Set points under item “Time Left”. The following set points can be
adjusted in SoftLoadSpts menu:
•
Soft Load: This is the amount of time soft loading will be in effect after the controller begins
staging. If set to zero, soft loading is canceled.
•
SoftLdMaxStg: Determines the maximum number of cooling stages which can be energized
while soft loading is in effect.
•
LoadDelay: The amount of time allowed for the controller to sample the loop water temperature
before initiating cooling.