23
ENG
Heos +0300078EN - rel. 1.6 - 23.11.2017
With reference to the Toshiba envelope shown above: the conditions
Tcond = 40°C Tevap = -10°C are inside the envelope at a speed of 30 rps,
but are outside at a speed of 15 rps.
The set point depends on the outside conditions (fl uid temperature at the
heat exchangers) and on unit operation: compressor speed, expansion
valve opening. Consequently, the set point can be shifted, increasing
or decreasing the condensing and evaporation pressures by adjusting
compressor speed and valve opening.
If operating conditions are near the limit of the envelope or outside
of it, the controller will implement corrective actions so as to keep the
set point within the limits allowed by the manufacturer. In these cases,
therefore, eff ective compressor speed may not correspond to the cooling
capacity required by the temperature controller and superheat may diff er
from the value set by the user. If operating conditions remain outside of
the envelope for a time exceeding the alarm threshold (default 180 s),
the compressor will be stopped and an alarm signal will be activated,
indicating the zone where operation was outside of the envelope.
9 5
2
8
3
4
6
1
1
7
Min Speed = 15 rps
Min Speed = 30 rps
Evaporation pressure
Condensing pressure
Fig. 6.e
The control actions are (see fi g. 6.e):
1. Inside envelope 6. Low compression ratio
2. High compression ratio 7. Low diff erential pressure
3. High condensing pressure 8. Low condensing pressure
4. High current 9. Low evaporation pressure
5. High evaporation pressure
Heos also features the following parameters for managing the compressor
ON/OFF times
Par. Description Def U.M.
Min Max
c0 Start control delay at power on 0 min 0 15
c1 Minimum time between successive compressor calls 6 min 0 15
c2 Minimum compressor off time 3 min 0 15
c3 Minimum on compressor time 3 min 0 15
c0 is used to delay the start of control when powering on This is useful in
the event of power failures, so that the controllers (in the network) don’t all
start at the same time, avoiding potential problems of electrical overload.
c1 sets the minimum time between two successive starts of the
compressor, irrespective of the request. This parameter can be used to
limit the maximum number of starts per hour;
c2 sets the minimum compressor off time. The compressor is not started
again until the minimum time set has elapsed;
c3 sets the minimum compressor running time.
c3 c2
c1
time
ON
CMP
OFF
Fig. 6.f
Key:
CMP compressor
On/off
The compressor starts whenever the request is equal to the minimum
speed in the allowed range. For example, if the compressor has a range
from 20 to 80 rps, it will be started when the request is equal to 25%.
The compressor is stopped when the request is equal to 0%.
Start-up procedure
When the compressor starts, a special startup procedure is applied. The
compressor speed value depends on the model (cIA) and is kept constant,
irrespective of the request from the controller, for a minimum time
corresponding to the minimum ON time (c3). Once this time has elapsed,
the compressor speed will refl ect the temperature control request
time
rps
Req
cIA
Req = min rps
min rps
cIE
(decrease ramp)
c3
Fig. 6.g
Acceleration/deceleration ramps (screen Dab08)
According to the model of compressor, acceleration, deceleration and
stopping ramps are defi ned. These are expressed in rps/s, and represent the
maximum speed variation allowed each second to increase or decrease
operating speed or stop the compressor. When the request varies more
quickly, the compressor speed will change according to the set ramps.
Par. Description Def U.M.
Min Max
cId Maximum speed increase (control) 1.0 rps/s 0.1 Type comp
cIE Maximum speed decrease (control) 1.0 rps/s 0.1 Type comp
CIF Maximum speed decrease (shutdown) 1.0 rps/s 0.1 Type comp
Req
Min
Speed
Strat-up
Speed
Speed ref.
time
rps
Min ON time
Acc. ramp
Very fast
Switch o ramp
Dec. ramp
Acc. ramp
Fig. 6.h
Equalising procedure (screen Daa02, Dab05)
If, when the compressor is requested to start, the diff erence between
discharge pressure and suction pressure is greater than the maximum
allowed for start-up (cI5), the equalising procedure (cE1) can be activated:
• using the expansion valve; this procedure involves opening the valve
by a set percentage (cE3) and for a set time (cE2);
• using an equalising solenoid valve;
• When the pressure diff erential is less than (cI5), the expansion valve
is positioned at the initial opening set for CP1, while if equalising by
solenoid is set, this is closed and the compressor can be started.
Par. Description Def U.M.
Min Max
cE1 Select equalising procedure mode 0 -- 0 1
cE2 Maximum EEV opening time during equalisation 90 s 0 999
cE3 EEV pre-opening percentage during equalisation 60 % 20 99.9
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