92
YORK INTERNATIONAL
(STOP LIMIT - START LIMIT)
T
ELAPSED
+ START LIMIT = % LOAD LIMIT
T
INTERVAL
LOAD LIMIT
100%
90%
80%
70%
60%
50%
40%
30%
20%
0 10 20 30 40 50 60 70 80 255
TIME (minutes)
(100 - 40) 20
+ 40 = 60
60
provides a purge pump service reminder. When the cu-
mulative purge pump operating hours since last service
equals the programmed service interval,
WARNING – PURGE PUMP SERVICE RECOMMENDED
is dis-
played on the keypad display. The service interval is pro-
grammable from 5-100 hours. The default value is 10
hours. Pressing the SETPOINT key displays the pro-
grammed service interval and accumulated pump oper-
ating hours since last service. After servicing the pump,
pressing the WARNING RESET key in SERVICE MODE
clears the warning message and resets the cumulative
operating hours to zero. Moving Micro Board program
jumper J57 from “CLKOFF” to “CLKON” position, as
would be done during unit commissioning, also resets
the cumulative operating hours to zero.
PULL DOWN DEMAND – This function is used to pro-
vide energy savings by limiting fuel or steam consump-
tion during the first 1 to 255 minutes (programmable) of
unit operation following a unit start. Instead of allowing
the load command to rapidly increase to 100%, due to
the typical high load conditions at start, the hot water
valve (hot water unit) or steam valve position (steam
units) is restricted to ramping up from a maximum al-
lowed starting load limit to a maximum allowed Stop load
limit over the pull down interval.
The programmable range is 20 to 100%. The pull down
interval is programmable from 1 to 255 minutes. Each
time the unit starts, a timer begins counting down the
pull down interval. Unit loading/unloading is controlled
by the automatic temperature control algorithm. How-
ever, during the pull down interval, it cannot load to a
value greater than the pull down demand limit will allow.
The limit ramps linearly from the programmed START
limit to the programmed STOP limit over programmed
INTERVAL (SETP). The START limit is effective when
the unit starts. The STOP limit is effective when the IN-
TERVAL timer has elapsed. The limit at any time in be-
tween these points can be determined by:
While the unit is operating and the pull down interval
has not yet expired, the present load limit and time re-
maining in the interval can be viewed by pressing the
PULL DOWN DEMAND setpoint key.
PRESENT PULL DOWN LIMIT = XX%; XXX MIN LEFT
is displayed. After the interval has elapsed, pressing this
key displays the programmed interval, start load limit
and stop load limit as follows:
SETP = XXX MIN; START = XX%; STOP = XX%
Any time the interval is in effect and the unit is being
prevented from further loading,
SYSTEM RUN – PULL DOWN LIMIT
is displayed. After
timeout, the pull down limit is no longer in effect. The
following illustrates the load limiting characteristics of a
pull down demand programmed as follows:
SETP = 60 MIN: START = 40%: STOP = 100%
Each time the unit is started, the load is linearly limited
from 40 to 100% for the first 60 minutes of unit operation
as follows:
Using the above formula, the load limit at any time dur-
ing the 60-minute interval can be determined. For ex-
ample, the load limit 20 minutes after unit has started
will be:
CLOCK – The Control Center contains an internal clock
that is an inherent part of the Micro Board. It provides
the day of the week, time of day, and calendar date. If
not programmed, the default value is
SUNDAY 12:00 AM 1/1/92
DAILY SCHEDULE – The Control Center can be pro-
grammed to automatically start and stop the chiller as
desired. This schedule will repeat on a seven-day calen-
dar basis. If the Daily Schedule is not programmed, the
default value is 00:00 AM start and stop times for all
days of the week and the holiday. (Note that the system
will not automatically start and stop on a daily basis with
these default values is 00:00 is an “Impossible” time for
the Micro Board. See “Programming System Setpoints”,
page 94). Finally one or more days in the week can be
designated as holidays (see description under HOLI-
DAY setpoint) and the Control Center can be pro-
grammed (using DAILY SCHEDULE setpoint) to auto-
matically start and stop the chiller on those days so des-
ignated. The operator can override the time clock at any
time using the UNIT switch in LOCAL mode.
Note that if only a start time is entered for a particular
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