Johnson Controls YORK YCAL0043E Series, Installation Operation & Maintenance

Page: 93 / 188

JOHNSON CONTROLS
93
FORM 150.62-NM9 (709)
2
FIG. 8 – LEAVING WATER TEMPERATURE CONTROL EXAMPLE
LEAVING CHILLED LIQUID CONTROL OVERRIDE
TO REDUCE CYCLING
To avoid compressor cycling the I/O Board will adjust
the setpoint upward temporarily. The last run time of the
system will be saved. If the last run time was greater than
5 minutes, no action is to be taken. If the last run time
for the lead system was less than 5 minutes, increase the
setpoint high limit according to the chart at right, with
a maximum value allowed of 50°F.
If adding the setpoint adjust value to the setpoint high
limit causes the setpoint high limit to be greater than
50°F, the setpoint high limit will be set to 50°F, and the
difference will be added to the setpoint low limit.
Once a system runs for greater than 5 minutes, the
setpoint adjust will be set back to 0. This will occur
while the system is still running.
Leaving Water Temp. Control – Compressor Staging
Setpoint = 46.0°F (7.8°C) Range = +/- 2°F(1.1°C)
30 sec. control range 60 sec.
unloading (no compressor staging) loading
44.0°F 46.0°F 48.0°
(6.7°C) (7.8°C) (8.9°C)
Low Limit Setpoint High limit
LWT
FIG. 7 – SETPOINT ADJUST
0 1 2 3 4 5 6
LAST RUN TIME OF LEAD SYSTEM (MINUTES)
SETPOINT ADJUST (DEG.
F)
6
5
4
3
2
1
0
RETURN CHILLED LIQUID CONTROL
(Can be used on Dual System 4, 5 & 6 Comp Units
Only)
Return chilled liquid control is based on staging the com-
pressors to match the cooling load. The chiller will be
fully loaded when the return water temperature is equal
to the Cooling Setpoint plus the Range. The chiller will
be totally unloaded (all compressors off) when the re-
turn water temperature is equal to the Cooling Setpoint.
(See sample in Table 18) At return water temperatures
between the Cooling, and Cooling Setpoint plus Range,
compressor loading and unloading will be determined
by the formulas in Table 19 or Table 20.
Return Chilled Liquid Control MUST
only be used when constant chilled liq
-
uid flow is ensured.
The
range
MUST always be pro
-
grammed to equal the temperature
drop across the evaporator when the
chiller is “fully loaded”. Otherwise,
chilled liquid temperature will over or
under shoot.
Normal loading will occur at intervals of 60 seconds ac-
cording to the temperatures determined by the formulas.
Unloading will occur at a rate of 30 seconds according to
the temperatures determined in the formulas.
The return chilled liquid setpoint is programmable from
40°F to 70°F (4.4°C to 21.1°C) in water chilling mode
and from 10°F to 70°F (-12.2°C to 21.1°C) in glycol
chilling mode. In both modes, the cooling range can be
from 4°F to 20°F (2.2° to 11.1°C).
LD07617A