FORM 201.10-NM4
105
YORK INTERNATIONAL
When the chilled liquid leaving temperature is within the
Neutral Zone, load / unload pulses will only be initiated if
the leaving liquid temperature rises or falls faster than
preset rate control limits internal to the micro.
The Neutral Zone is equally spaced between the low
and high limits of the Control Range and therefore also
has the Target temperature at its midpoint. The width
of the Neutral Zone is half of the width of the Control
Range. The upper and lower limits of the Neutral Zone
can be calculated as follows:
NEUTRAL
ZONE
=
/
HLWT LLWT
LIMITS
4
For example, if the desired Target temperature is 44.0°F
and the programmed acceptable Control Range limits
are 42.0°F and 46.0°F, then the Neutral Zone limits are
as follows:
NEUTRAL
ZONE
=
44.0°F
+/
46.0°F 42.0°F
LIMITS
4
=
44.0°F
+/ 1.0°F
=
43.0°F and 45.0°F
This can be viewed pictorially as follows:
As stated above, no loading or unloading will occur in
the Neutral Zone unless the internal non-programmable
rate control limit (rate of temperature change of the leav-
ing liquid) is exceeded. Limiting loading will occur; how-
ever, is the temperature range between the top end of
the Neutral Zone and the High Limit Water Tempera-
ture. Normal loading, as dictated by internal timers, will
occur above the Control Range. Limited unloading will
also occur when temperature falls between the bottom
of the Neutral Zone and the Low Limit Water Tempera-
ture. Normal unloading, as dictated by internal timers,
will occur below the Control Range.
High Limit Water Temperature
Low Limit Water Temperature
TARGET
temp.
CONTROL
RANGE
➤
➤
NEUTRAL
ZONE
➤
➤
46.F
45°F
44°F
43°F
42°F
Compressor Starting Sequence for 2 and 3
Compressor YCAS Chillers
If no compressors are running, all safeties and run
permissives are satisfied, the anti-recycle timers have
timed out, and the leaving liquid temperature rises above
the upper limit of the Control Range, the lead compres-
sor will be started. An unload pulse of 3 seconds dura-
tion is sent to the compressor to assure it is fully un-
loaded. After an initial period of 150 seconds, the micro
will begin to load up the lead compressor to match cool-
ing demand.
If the lead compressor reaches a programmed percent-
age of full load (Lag Compressor Start Point) and de-
mand continues to rise, the (first) lag compressor will
be starter in a fully unloaded condition. The lead com-
pressor will then be maintained at a constant load and
the micro will load up the lag compressor to match the
cooling demand.
On 2 compressor chillers, if the lag compressor reaches
the same percentage of full load as the lead compres-
sor and demand continues to rise, equalized loading of
the two compressors will take place.
On 3 compressor chillers, if the first lag compressor
reaches the same percentage of full load as the lead
compressor, and demand continues to rise, the two run-
ning compressors will be maintained at constant load
and the second lag compressor will be started. The
micro will then begin loading the second lag compres-
sor. If the second lag compressor reaches the same
percentage of full load as the other two compressors
and demand still continues to rise, equalized loading of
all three compressors will take place.
NOTE: Under some conditions, lag compressor(s) may
be started before the lead compressor reaches
the required percentage of full load. This may
occur if the chilled liquid is not brought to within
2°F of the control range after 5 minutes of op-
eration time on the lead compressor. For more
details, see Section 8.2 Lag Compressor Start
Point.
Содержание Millennium YDAS 410
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