Danfoss 080Z2520 User guide

Brand: Danfoss

Model: 080Z2520

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

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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

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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

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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

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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.

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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.

Danfoss 080Z2520 User guide

Brand: Danfoss

Model: 080Z2520

Type: User guide

This manual is also suitable for

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