Carel Hecu CO2 - Fan Control and Management; Oil Management Solutions for BLDC Compressors

29
ENG
Hecu CO
2
+0300085EN rel. 2.2 - 07.05.2019
Cut-o
Hecu CO2 manages a cut-off control function for the fans; the function
can be enabled and the related parameters set in main menu branch
Db05. The operating principle of the cut-off function is shown in the
fi gure:
Dierential Dierential
Cut-O Set point Regulation Set point
Max capacity = 100%
Regulation
probe value
Regulation
request
Cut-O value
of request
Max
output value
Fig. 6.l
A percentage of the control request and a cut-off set point can be set.
When the control request reaches the set cut-off value, this value is kept
constant until the control value falls below the cut-off set point, after
which it falls to 0 % and remains there until the request exceeds the cut-
off value again.
Fans with compressor OFF
The fans can be stopped after a delay from when the compressor is
switched OFF. Furthermore, they can be restarted before the compressor
starts, when the request is increasing. These settings are made on screen
Db04.
Speed up
Hecu CO2 can manage the speed up function, used to overcome the
initial inertia of the fans. The function can be enabled and the related
parameters set in main menu branch Dg13.
If speed up is enabled, a start time can be set in which the fan speed is
forced to 100%. If the outside temperature sensor is used, moreover, a
threshold can be set (with reset diff erential) below which speed up is
disabled, so as to not drastically lower the condensing pressure at start-
up.
Floating condensing pressure set point
For the condenser line, the fl oating set point enabled on screen Dd05)
is based on the outside temperature. The fl oating condensing pressure
set point is achieved by adding a constant programmable value to the
outside temperature and limiting the resulting value between a settable
minimum (Db02) and the set point defi ned on screen Dd06, as shown
in the fi gure:
Setpoint
Min
oset
Floating
setpoint
external temperature
time
Fig. 6.m
6.6 Oil management
Oil injection
Oil return is a critical factor when using BLDC compressors. Hecu CO2
can manage three diff erent solutions for injecting return oil to the
compressor. The related confi gurations can be set on screen Fab15.
Capillary valve
The simplest solution is to use a capillary valve, with fi xed opening,
calibrated based on rated conditions. This solution however creates
ineffi ciencies, by injecting or less oil than required by the compressor.
1
standard
oil separator
capillary
BLDC
compressor
Fig. 6.n
Electronic expansion valve (EEV COMP SPEED)
This solution involves a CAREL expansion valve. Valve opening is
calibrated based on the BLDC compressor operating conditions, adjusted
proportionally based on compressor speed.
A standard oil separator can be installed to exploit this function. The
control algorithm is represented in the following graph, and the
parameters can be confi gured on screen Fab18.
4
standard
oil separator
EEV valve
BLDC
compressor
V
Fig. 6.o
Opening valve (%)
Compressor
Speed (lps)
Max open. valve
Min open. valve
Min Speed Max speed
Fig. 6.p