IOMM AGR AGR 055A through 100A 69
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 may 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 may 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.
To Next Page
Loading...
Need help?
General
