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When using the Ladder method, when the cooling
demand varies, the pulse length remains the same within
predetermined cooling demand ranges (i.e. 0%-20%). When
the cooling demand reaches the next range (i.e.20%-40%),
the pulse length then changes.
For both methods, the pulse lengths can also be influenced
by the outside temperature (OT). This allows the system to
use less water when OT is low. The user must first set a
low outside temperature (OutTempLW) and a high outside
temperature (OutTempLW + OutTempLW band). Then, the
user can set a low outside temperature pulse length (LOT)
and a high outside temperature pulse length (HOT) for each
cooling demand percentage.
LOT
= Pulse length when outside temperature is equal or
below OutTempLW.
HOT
= Pulse length when outside temperature is equal or
above OutTempLW + OutTempLW band.
PER = Period of pulsing valve open-close cycle
OutTempLW = Outside temperature when the pulse lengths
are shortest.
OutTempLW + OutTempLW band = Outside temperature
when the pulse lengths are longest.
Also, the user must choose between Proportional and
Range:
Proportional: The pulses will be shorter as OT approaches
OutTempLW and longer as OT approaches OutTempLW +
OutTempLW band.
Range: When OT is equal or below OutTempLW, the
pulses will be shorter (LOT). When OT is equal or above
OutTempLW + OutTempLW band, the pulses will be longer
(HOT). When OT is between OutTempLW and OutTempLW
+ OutTempLW band, the pulses will remain the same; this
means if OT rises and passes OutTempLW, shorter pulses
are still used, and If OT drops and passes OutTempLW +
OutTempLW band, longer pulses are still used.
SCALER
The next two screens show an example of a Scaler
configuration.
SYSTEM SPECIFICATIONS
Pulse length: Scaler
PumpON when CD is: 010%
OutTempLW:
OutTempLW band:
OutTempLW mode:
Screen A
6
Demand:
0%
020%
040%
060%
080%
100%
Screen B
In this example, the OutTempLW is set to 22
corresponds to the low outside temperature point where
the shortest pulses (LOT) will be applied, depending on
the cooling demand (left column on Screen B). Here, the
OutTempLW band is set to 5
temperature point (OutTempLW + OutTempLW band)
is equal to 27
applied, depending on the cooling demand (left column on
Screen B).
The cooling demand is expressed in % as shown in Graph 1.
For each percentage, there is an associated pulse length
range in seconds, as shown on Screen B. For example, for
a 20% cooling demand, the pulse length LOT is 6 seconds
and HOT is 10 seconds. Then the pulse length range is 6-10
seconds.
The next three graphs represent the settings shown on
Screen A and Screen B.
60
50
47
39
34
28
22
17
10
6
Graph 2 Pulse length range vs cooling demand (according to
22.0C
05.0C
Prop
SYSTEM SPECS (SCALER)
LOT HOT PER
006-010/060s
006-010/060s
0 1 7 -022/060s
028-034/060s
039-047/060s
050-060/060s
C, this means the high outside
o
C, where the longest pulses (HOT) will be
o
Cooling demand (CD) changes pulse length
Pulse length variation depending on OT
0%
20%
40%
60%
COOLING DEMAND
parameters on screen B)
C, which
o
HOT
60
50
LOT
40
30
20
10
0
80%
100%
R
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