Delay Timer; Operation Lead-Lag/Load Balance Panel; Lead-Lag; Automatic Startup - McQuay MicroTech Unit Controller Installation And Maintenance Data

Ent Evap. Timer-This timer is an integral part of the "Enter-
ing" chilled water temperature reset feature. As the building
load changes, entering, or return, chilled water temperature
increases or decreases. At fixed time intervals, the software
compares return water temperature and leaving chilled water
temperature. If the time interval is too short, over-adjustment
and hunting may result; if it's too long, system inefficiency
may exist. The actual setting should be adjusted to suit the
job system characteristics.
Delay Timer-The "Delay Timer" applies only to dual unit
or dual compressor installations. The second, or lag com-
pressor, will not be started unless the lead compressor's
operating amps exceeds the Enable % RLA for the preset
"Delay Timer" interval. Conversely, the lag compressor or
chiller will not shut off unless the lead compressor's operating
amps is less than the Disable % RLA for the preset "Delay
Timer" interval.
In this manner, unnecessary cycling "on" and "off" of the
lag machine is avoided.
Load Delay (Waiting for Load)-Where energy efficiency dic-
tates that a chilled water pump be shut off when its chiller
is inoperative, water temperature within the piping system may
vary widely depending upon the ambient temperature condi-
tions. The "Load Delay" timer permits the chilled water pump
to circulate and mix chilled water in the piping system before
the chiller is actually started. By so doing, the temperature
imparted to the chiller's water sensors more closely resembles
the total building water temperature. The Load Delay time in-
terval should be set shorter or longer as the mass of water
in the building's system is comparatively little or great.
OPERATION OF THE LEAD-LAG/LOAD BALANCE PANEL
GENERAL (See IM 425-2 for the latest LLLB)
The LLLB controller is provided with an internal 3 amp cir-
cuit breaker switch, or a cover panel mounted "on"--"off"
switch. When power is applied, and the switch closed, an LED
status light in the front cover panel will blink.
LED's will blink also on the cover panel to confirm the opera-
tional status of controller number l's microprocessor, and that
of controller number 2. Another LED will indicate which com-
pressor or unit is the "Lead".
Lead-Lag - A three-position switch on the front cover panel
is marked
* Controller (Number) 1 Lead
Auto Lead, (and)
l
* Controller (Number) 2 Lead
If the switch is positioned to either Controller 1 or Controller
2, that unit will be the lead unit, and the other, the lag.
If the switch is positioned for Auto Lead, the computer will
read the operating hours of the two machines and select the
one with the least operating hours to be the lead. A change
from one lead unit to the other will only occur when both units
are off, or both are operating. In this manner the units are
protected against a sudden switch in the lead unit selection
as the hours of the operating machine overtake the operating
hours of the other (off) machine.
Lag Start-Stop - The lead machine increases its capacity
to satisfy an increasing cooling load. When this compressor's
maximum capacity is approached, at a pre-set value input
under the "Set-up Options" key, the signal is communicated
to the lag machine to start and run. The operating signal is
"Enable Lag" and it is set based on the percent of the Lead
MCR Is On (or Stop, Unloading)-The time interval associ-
ated with the MCR operation is intended to establish
reasonable delay for closure of the starter transition contacts.
"Stop, Unloading" provides a time period to permit the oil
pump to close the compressor vanes.
Override (HRS)-This feature permits overriding the establish-
ed clock schedule to operate a unit on an "off" day, without
changing the entire schedule. The desired number of
operating hours are entered into the program and the regular
schedule will be overridden for that number of hours.
Soft Load (Ramp Up Time)-The soft load ramp up time
establishes a period that may be as long as two hours to per-
mit a controlled increase in chiller capacity. During that con-
trolled time interval, it's possible that the sizeable cooling load
developed only by a weekend shutdown may be reduced to
a manageable partial load at less than maximum electrical
demand.
Step and Wait-Within a range of plus or minus two tenths
the compressor capacity control system will "hold," neither
loading or unloading the compressor. As the leaving chilled
water temperature drifts above or below the setpoint within
a range of two tenths (0.2) to two (2.0) degrees F, the com-
pressor will pulse control to the unload or load solenoids,
respectively, to return the water temperature to setpoint.
Should the chilled water temperature drift away from setpoint
be more than two (2.0) degrees F, as it might be following an
overnight shutdown, loading is continuous until this water
temperature returns to within 2.O"F of the CHW setpoint.
units operating amps. The Enable Lag cannot be set for less
than 8 0 % nor more than 100%. A normal recommended set-
point is 95%. Further, the lag machine will not start immediate-
ly when the % amps reaches the setpoint. A "Delay Timer"
setpoint requires that the % amps consumed equal or exceed
the setpoint % amps for the period of time programmed.
In this manner, unnecessary cycling is avoided.
A third setpoint, "Disable Lag = XX%," also requires setting.
This too is a of the lead compressor's operating amps. The
%
value may be set anywhere between 35% to 60%. A recom-
mended value is 40%. Here too the "Delay Timer" setpoint
will require that the lead compressor's operating amps be
equal or less than the setpoint value for the programmed
"Delay " time.
Because either compressor can be the "Lead" unit, the
three values must be set the same in each MicroTech chiller
panel.

AUTOMATIC STARTUP

If the lead compressor has shutdown and is inoperative
because of a fault, the LLLB controller will automatically start
the other machine. No operator changeover is required.

LOAD BALANCE

When both units, or compressors, are operating, the controller
unloads the compressor drawing the greatest % of amps un-
til the % of amps drawn by both are within 5% of each other.
At any given load, as the one compressor is unloaded, the
second is loaded to achieve the balance and satisfy the set-
point water temperature.
NOTE: Clock schedule and hex switches must be set in ac-
cordance with earlier instructions.
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