York YCAQ10 - RWT CONTROL LOADING; UNLOADING; TYPICAL EXAMPLE (4 STAGES); OPTIONAL 6, 7, OR 8 STAGES LOADING;UNLOADING

YORK INTERNATIONAL 29
FORM 150.40-NM25
STANDARD RETURN WATER TEMPERATURE (RWT) CONTROL LOADING / UNLOADING
SINGLE CIRCUIT UNITS
LWT COOLING RANGES (4 STAGE)
The user may use LWT control with a single circuit (4
stage) chiller. The disadvantage of 4 stages is that we
are cycling large tonnages each time we turn a stage on
or off. This could cause continuous cycling with the pos-
sibility of undesirable fluctuating leaving water tempera-
tures. The variation in LWT is primarily due to the com-
pressors cycling off and water temperature rising be-
fore the anti-recycle timer times out to allow the com-
pressor to restart. The factory does not recommend that
single circuit units be used in this manner.
Loading/Unloading of cylinders is accomplished in re-
sponse to return chilled water temperature as sensed
by the Micro Logic Board and Cooling Range selection.
A typical example is illustrated below (4 stages).
RWT Setpoint = 55°F (12.8°C)
Cooling Range = 10°F (5.6°C)
System Switch = ON
Sw. 3 on Micro = OFF (RWT Control)
Return Water
Temp. °F (°C)
55 (12.8) ----------- --------- Loader ON Stage 4------------------------ -------------------------------------
Cooling 52.5 (11.4) --------- --------- Loader ON Stage 3 ------------------------ – Loader OFF Stage 4
Range 50.0 (10.00) ------- --------- Loader ON Stage 2------------------------ – Loader OFF Stage 3
*10°F(5.6°C) 47.5 (8.6)----------- --------- Compressor ON (Unloaded) Stage 1 - – Loader OFF Stage 2
45 (7.2) ------------- --------- Compressor OFF -------------------------- – Compressor OFF Stage 1
*10°F (5.6°C) ¸ 4 stages = 2.5°F (1.4°C) between stages of loading.
Temperature
Fall
Temperature
Rise
COOLING RANGE
SWITCH = 0
COOLING RANGE
OF
+1.0°F ( +.55°C)
STAGE ON OFF
Loader Stage 4 Setpoint plus 1.0°F (.55°C) Setpoint plus 0.5°F (.27°C)
Loader Stage 3 Setpoint plus 0.5°F (.27°C) Setpoint
Loader Stage 2 Setpoint Setpoint minus 0.5°F (.27°C)
Compressor Stage 1 Setpoint minus 0.5°F (.27°C) Setpoint minus 1.0°F (.55°C)
STAGE ON OFF
Loader Stage 4 Setpoint plus 1.2°F (.66°C) Setpoint plus 0.6°F (.33°C)
Loader Stage 3 Setpoint plus 0.6°F (.33°C) Setpoint
Loader Stage 2 Setpoint Setpoint minus 0.6°F (.33°C)
Compressor Stage 1 Setpoint minus 0.6°F (.33°C) Setpoint minus 1.2°F (.66°C)
STAGE ON OFF
Loader Stage 4 Setpoint plus 1.4°F (.77°C) Setpoint plus 0.7°F (.38°C)
Loader Stage 3 Setpoint plus 0.7°F (.38°C) Setpoint
Loader Stage 2 Setpoint Setpoint minus 0.7°F (.38°C)
Compressor Stage 1 Setpoint minus 0.7°F (.38°C) Setpoint minus 1.4°F (.77°C)
(Continued next page)
COOLING RANGE
SWITCH = 2
COOLING RANGE
OF
+1.4°F ( +.78°C)
COOLING RANGE
SWITCH = 1
COOLING RANGE
OF
+1.2°F (+.66°C)