Danfoss 080Z2583 User guide

Type
User guide

This manual is also suitable for

Improved Neutral Zone
Refrigeration Control
AK-SC 255
Service Guide
ADAP-KOOL® Refrigeration Control System
Service Guide | Improved Neutral Zone Ref. Control AK-SC 255
© Danfoss | ADAP-KOOL® | 2018.08
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AKCESS © 1999 Danfoss Inc. 17 May 1999
Improved Neutral Zone Refrigeration Control
a Danfoss Functional Description
There are three more parameters we can normally
set while configuring compressors, called Neutral
Zone, Plus Zone Delay and Minus Zone Delay,
which are shown in here:
Neutral Zone control is not a new idea, but some
years ago Danfoss introduced and patented
improvements to Neutral Zone control which
make it more suited to refrigeration systems.
To begin with, we set a reference pressure (tar-
get) when we configure Suction Info.
There are also some other parameters which
should only be adjusted by trained technicians.
Not normally accessible, they are shown in the
second half of the Neutral Zone configuration
screen
Service Guide | Improved Neutral Zone Ref. Control AK-SC 255
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The additional parameters are all multipliers.
Now let’s see how these parameters are applied
to the pressure-time diagram of a hypothetical
refrigeration system
The central horizontal line (labeled “REF”)
represents the target set in configuration. The
first parameter in configuration, Neutral Zone,
which in the example screen is 2 psi, defines the
size of the Neutral Zone. Half of the Neutral
Zone lies on each side of the target. In the
example, the Neutral Zone ranges from 11 psi to
13 psi (the target is 12 psi and the Neutral Zone
is 2 psi).
a b c d e f g h i j k l m
Above the Neutral Zone is the Plus Zone. Its
pressure range is determined by applying the
Plus Zone multiplier to the range of the Neutral
Zone, so that in our example, the Plus Zone
ranges from 13 psi to 16 psi (2 x 1.5 = 3).
Below the Neutral Zone is the Minus Zone. Its
pressure range is determined by applying the
Minus Zone multiplier to the range of the Neu-
tral Zone, so that in our example the Minus Zone
ranges from 9 to 11 psi. (1 x 2 = 2).
The Plus Plus Zone contains all pressures above
the upper limit of the Plus Zone. In a like man-
ner, the Minus Minus Zone contains all pressures
below the lower limit of the Minus Zone.
Our “special parameters” list gives delay multi-
pliers for the Plus Plus Zone and the Minus
Minus Zone.
The rules of strategy are these:
1. In the Neutral, Plus, and Minus zones,
the Up Timer runs whenever the slope
of the pressure curve is positive, and is
paused whenever the slope changes to
negative. In the Neutral, Plus, and
Minus zones, the Down Timer runs
whenever the slope of the pressure
curve is negative, and is paused when-
ever the slope changes to positive..
2. In the Neutral Zone, refrigeration
capacity is never changed. The timers
run and are paused according to strategy
rule 1.
3. If the pressure rises from the Neutral
Service Guide | Improved Neutral Zone Ref. Control AK-SC 255
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AKCESS © 1999 Danfoss Inc. 17 May 1999
Zone to the Plus Zone, and if the Up
Timer has reached or reaches its delay
setting, refrigeration capacity is added
and the Up Timer is restarted at zero.
Each time the Up Timer reaches its
delay setting, a step of refrigeration
capacity is added.
4. If the pressure is in the Plus Zone and
the slope of the pressure curve changes
from positive (rising) to negative
(falling) the Up Timer is paused. Accu-
mulated time is preserved on the timer.
5. If the pressure is in the Plus Zone and
the slope of the pressure curve changes
from negative to positive, the Up Timer
is re-started.
6. If the pressure enters the Plus Plus
Zone, and if the Up Timer has reached
or reaches the Plus Plus Zone delay
time [(Plus Zone Delay) X (Plus Plus
Delay Multiplier)], refrigeration capac-
ity will be added. While the pressure is
in the Plus Plus Zone, capacity steps are
added based strictly on the Up Timer
value, regardless of the slope of the
pressure curve. Each time the Up
Timer reaches the Plus Plus Zone delay
time, a step of refrigeration capacity is
added. The Up Timer continues to run
in the Plus Plus Zone regardless of the
slope of the pressure curve.
7. When the pressure falls from the Plus
Plus Zone to the Plus Zone, no change
in refrigeration capacity occurs and the
Up Timer is paused and remains paused
as long as the slope of the pressure
curve remains negative. The Down
Timer starts.
8. If the pressure falls from the Neutral
Zone to the Minus Zone, and if the
Down Timer has reached or reaches the
Minus Zone Delay setting, refrigeration
capacity is dropped and the Down
Timer is re-started at zero. Each time
the Down Timer reaches the Minus
Zone delay setting, a step of refrigera-
tion capacity is dropped.
9. If the pressure is in the Minus Zone,
and the slope of the pressure curve is
negative, and the Down Timer timer
reaches the Minus Zone Delay setting,
refrigeration capacity is dropped and the
Down Timer is restarted at zero.
10. If the pressure is in the Minus Zone,
and the slope of the pressure curve
changes from negative (falling) to
positive (rising), the Down Timer is
paused. Accumulated time is preserved
on the timer.
11. If the pressure is in the Minus Zone and
the slope of the pressure curve changes
from positive to negative, the Down
Timer is re-started.
12. If the pressure enters the Minus Minus
Zone, and if the Down Timer has
reached or reaches the Minus Minus
Zone Delay time [(Minus Zone Delay)
X (Minus Minus Delay Multiplier)],
refrigeration capacity will be dropped.
While the pressure is in the Minus
Minus Zone, capacity steps are dropped
based strictly on the Down Timer,
regardless of the slope of the pressure
curve. Each time the Down Timer
reaches the Minus Minus Zone delay
time, a step of refrigeration capacity is
added. The Down Timer continues to
run in the Minus Minus Zone regardless
of the slope of the pressure curve.
Now let us look at an example, based on the
graph given above:
1. In the Neutral Zone, refrigeration
capacity is not changed; there are no
control actions. This is the situation in
our graph from its beginning to point a,
and is indicated by the level arrow on
the “Cap” line in the diagram (indicat-
ing no change in capacity). The Up
Timer is running (in our example, the
timer is set to 120 seconds.)
2. Somewhere between points a and b, the
Service Guide | Improved Neutral Zone Ref. Control AK-SC 255
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AKCESS © 1999 Danfoss Inc. 17 May 1999
Up Timer timer reached 120 seconds
and a step of refrigeration was added as
is indicated by the upward arrow on the
“Cap” line in the diagram. At the same
time, the Up Timer was restarted at
zero.
3. At point b, the slope of the curve be-
comes negative, and the Up Timer is
paused, but retains its accumulated
time. The Down Timer is started.
Capacity does not change.
4. If the pressure enters the Neutral Zone
(as at point c), Capacity does not
change. The Down Timer continues to
accumulate seconds.
5. At point d, the pressure enters the
Minus Zone (in our example, the timer
is set to 60 seconds). The Down Timer
will continue to run and accumulate
seconds as long as the slope of the
pressure curve remains negative.
6. Somewhere between point d and point
e, the Down Timer reaches its setting,
and refrigeration capacity is dropped.
The Down Timer is restarted at zero.
7. At point e, the slope of the pressure
curve changes from negative to posi-
tive. The Down Timer is paused. The
Up Timer is started.
8. At point f, pressure enters the Neutral
Zone. Capacity does not change while
pressure is in the Neutral Zone.
9. At point g, the pressure once again
enters the Plus Zone. Somewhere
between points g and h, the Up Timer
reaches its setting, and capacity is
added. The Up Timer is restarted at
zero.
10 . At point h, the pressure enters the Plus
Plus Zone. Between points h and i,
refrigeration capacity is added. The
system is reacting much quicker [the
timer setting is now {(Plus Zone Delay)
X (Plus Plus Delay Multiplier)}, or
(120 seconds X 0.4) = 48 seconds].
The Up Timer continues to run as long
as the pressure is in the Plus Plus Zone,
regardless of the slope of the pressure
curve. The Down Timer is paused.
While the pressure remains in the Plus
Plus Zone, capacity steps are added
based on the Up Timer alone, without
regard for the slope of the pressure
curve.
11. At point i, the pressure re-enters the
Plus Zone, and because the slope of the
curve is negative, the Up Timer is
paused. The Down Timer is re-started.
12. At point j, the pressure curve re-enters
the Neutral Zone. Capacity does not
change.
13. At point k, the pressure drops into the
Minus Zone. Somewhere between
points k and l, the Down Timer reaches
its setting, and refrigeration capacity is
dropped. The Down Timer is restarted
at zero.
14. At point l, the pressure goes into the
Minus Minus Zone. Between points l
and m, refrigeration capacity is
dropped. As in the Plus Plus Zone, the
system is reacting much quicker [the
timer setting is now {(Minus Zone
Delay) X (Minus Minus Delay Multi-
plier)}, or (60 seconds X 0.3) = 18
seconds]. The Down Timer continues
to run as long as the pressure is in the
Plus Plus Zone, regardless of the slope
of the pressure curve. The Up Timer is
paused.
© Danfoss | ADAP-KOOL® | 2018.08
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AKCESS © 1999 Danfoss Inc. 17 May 1999
While the pressure remains in the
Minus Minus Zone, capacity steps are
dropped based on the Down Timer
alone, without regard for the slope of
the pressure curve.
15. At point m, the pressure has risen to
enter the Minus Zone. No capacity
change occurs. The Down Timer is
paused. The Up Timer is re-started.
Danfoss can accept no responsibility for possible errors in catalogues, brochures and other printed material. Danfoss reserves the right to alter its products without notice. This also applies to products
already on order provided that such alternations can be made without subsequential changes being necessary in specifications already agreed.
All trademarks in this material are property of the respecitve companies. Danfoss and Danfoss logotype are trademarks of Danfoss A/S. All rights reserved.
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Danfoss 080Z2583 User guide

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