Operation - Hussmann RDI-27 Installation & Operation Manual

Operation

Sensors
Up to two thermostat sensors can be connected to the controller.
The relevant application determines how.
A sensor in the air before the evaporator:
This connection is primarily used when control is based on area.
A sensor in the air after the evaporator:
This connection is primarily used when refrigeration is controlled
and there is a risk of a too low temperature near the products.
A sensor before and after the evaporator:
This connection o ers you the possibility of adapting the
thermostat, the alarm thermostat and the display to the relevant
application. The signal to the thermostat, the alarm thermostat
and the display is set as a weighted value between the two
temperatures, and 50% will for example give the same value from
both sensors.
The signal to the thermostat, the alarm thermostat and the display
can be set independently of one another.
Defrost sensor
The best signal concerning the evaporator's temperature
is obtained from a defrost sensor mounted directly on the
evaporator. Here the signal may be used by the defrost function,
so that the shortest and most energy-saving defrost can take
place.
If a defrost sensor is not required, defrost can be stopped based
on time, or S4 can be selected.
Control of two compressors
This control is used for controlling two compressors of the same
size. The principle for control is that one of the compressors
connects at ½ the di erential of the thermostat, and the other at
the full di erential. When the thermostat cuts in the compressor
with the fewest operating hours is started. The other compressor
will only start after a set time delay, so that the load will be
divided between them. The time delay has a higher priority than
the temperature.
When the air temperature has dropped by half the di erential the
one compressor will stop, the other will continue working and not
stop until the required temperature is achieved.
The compressors used must be of a type that is capable of starting
up against a high pressure.
Change of temperature reference
In an impulse appliance, for example, used for various product
groups. Here the temperature reference is changed easily with
a contact signal on a digital input. The signal raises the normal
thermostat value by a prede ned amount. At the same time the
alarm limits with the same value are displaced accordingly.
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