Carel Heos - High Discharge Temperature Control

24
ENG
Heos +0300078EN - rel. 1.6 - 23.11.2017
Req
rps
EEV
Pressure
Disch P
Suct P
time
rps
Control increase in ΔP when starting (screen Dab05)
To verify correct compressor rotation and a correct increase in pressure
diff erential, the latter is checked whenever the compressor is started. This
involves measuring the increase in ΔP after a set time (cI7). If the increase
is less than the settable threshold (cI6), the compressor is stopped and the
failed start alarm is signalled.
Par. Description Def U.M.
Min Max
cI5 Maximum pressure delta for compressor start 0.5
(7.3)
bar/
psi
0.0
(0.0)
120
(1762.8)
cI6 Minimum pressure delta for compressor start 0.2
(2.9)
bar/
psi
0.1
(1.5)
2.0
(29.4)
cI7 Pressure delta control delay to check comp.
start-up
10 s 1 99
Start failure management (screen Dab06)
If the compressor fails to start, the controller will make several attempts
to start it again.
Par.
Description
Def U.M.
Min Max
cI8
Activation delay after failed start
30 s 1 360
cI9
Number of restart attempts after failed start
5--09
Oil recovery procedure (screen Dab11, 12)
In the event of operation a low speed, with low refrigerant fl ow-rate and
speed, the risk may arise of insuffi cient oil return to the compressor. One
solution to this problem involves a momentary acceleration (at speed
cIV) of the compressor for a time cIS whenever operating speed is below
a certain threshold (cIu) for a set time (cIr).
time
rps
cIV - speed during procedure
cIu - Threshold
cIr - time below threshold cIS
time at high speed
Fig. 6.i
Par. Description Def U.M.
Min Max
cIP Enable oil recovery management 1 -- 0 1
cIr Oil recovery procedure activation time 30 min 1 480
cIS Compressor override time during procedure 2 min 1 10
cIu Min. comp. output to activate oil recovery procedure Comp % 10.0 99.9
cIV Comp. speed during oil recovery procedure 100 % 0 100
Oil recovery procedure in multi-evaporator system
If the system is confi gured as multi-evaporator, the oil recovery procedure
will be:
• cIS Compressor override time: multiplied by the number of evaporators.
• The procedure is performed as shown in the fi gure:
time
EEV
S2
EEV
S1
EEV
M
OIL
CMP
speed
cIb
cIA
cIS
close
close
PEV
close
close
PEV
close
close
PEV
cIS cIS
Fig. 6.j
• The total procedure lasts cIS x no. of evap., and is divided into equal
sections corresponding to the number of evaporators.
• In each section, the valve on that evaporator is active (PEV), while the
others are closed.
• When the valves start normal control again at the end of the procedure,
these return to the last position saved at the start.
• The compressor speed varies between StartUp (cIA) and cIb (keeping
envelope control active), based on the weight of the evaporator.
• If Treg falls below the set point minus a set delta, the procedure ends,
without a delay, for the cabinet/showcase in question.
The changeover from one section to the next occurs as follows:
• showcase 1 ends the procedure;
• the valve on showcase 2 opens;
• the valve on showcase 1 closes after a 5 second delay.
High discharge temperature control (screen Daa03, Daa04, Daa05)
Discharge temperature is an important indicator of the compressor’s
health: by continuously monitoring this value, a procedure can be
implemented to keep the temperature under control.
Envelope control involves actions to adjust compressor speed and
expansion valve opening, so as to keep discharge temperature within
the allowed limits. In addition, a liquid injection procedure can also be
confi gured:
1. by an ON/OFF liquid injection valve activated when the discharge
temperature exceeds a threshold, and deactivated when it returns
below the threshold minus a diff erential.
2. by an electronic valve (connected to connector J8 - see Fig. 2.d); in
this case there will be continuous modulation of operation with P+I
control set by parameter LII.
time
Temp.
Di
T
inj
EV
OFF
ON
Fig. 6.k
Par. Description Def U.M. Min Max
LIV
Type of liquid injection valve
0--01
LIt
Liquid injection function activation threshold
95.0
(203.0)
°C
(°F)
50.0
(122.0)
150.0
(302.0)
LIP
Liquid injection control proportional coeffi cient
5 -- 1 200
LII
Liquid injection control integral time
100 s 1 999
LId
Liquid injection diff erential
5.0
(9.0)
°C
(°F)
0.1
(0.2)
20.0
(36.0)
LIc
Duty Cycle
100 % 0 100
LIS
Duty Cycle period
30 s 0 60