Application And Function Overview - Danfoss EIM 336 Manual

Manual
Applications
Regulation
The evaporator superheat is controlled by one pressure sensor Pe
(evaporator pressure) and one temperature sensor S2 (refrigerant
temperature). Alternatively the pressure and temperature signals
can be received as data via modbus. This can be useful if the
pressure and temperature sensors are mounted on a separate
controller.
Fitting the S4 (evaporator medium outlet temperature) is optional
and has no effect on regulation, it is a readout value only. S4 can
however be setup as a hardware main switch instead to provide an
external ON/OFF function for the controller.
Function overview
Minimum Stable Superheat (MSS)
The controller will search for the minimum stable superheat
between an upper and lower boundary. If the superheat has
been stable for a period of 6 minutes, the superheat reference is
decreased. If the superheat becomes unstable, the reference is
raised again. This process continues as long as the superheat is
within the bounds set by the user. The purpose of this is to search
for the lowest possible superheat that can be obtained while still
maintaining a stable system. The superheat reference can also be
fixed, in which case this function is disabled.
Maximum Operating Pressure (MOP)
In order to reduce the strain on the compressor, a maximum
operating pressure can be set. If the pressure comes above
this limit the controller will control the valve to provide a lower
pressure instead of a low superheat. The limit for this function
is usually a fixed pressure, but it is possible to offset the limit
temporarily.
Evaporator temperature (Te) control for de-humidifying
A function is provided to control on the evaporator temperature
instead of the superheat. This can be used to de-humidify the
air flowing through the evaporator. By lowering the evaporators
surface temperature, the water vapor in the air is condensed.
Superheat close
When the superheat is below a set minimum value, the valve will
close faster in order to protect the compressor from the risk of
getting liquid in the suction line.
Manual control
The valve can be controlled manually by setting the desired
opening degree via modbus.
Start/stop of regulation
The start or stop of the regulation can be controlled by setting
the software main switch, which is accessible via modbus. It is
however also possible to use a digital input from an external
hardware main switch.
© Danfoss A/S (AC-MCI / sw), 2014-11
Superheat Controller EIM 336
DKRCC.PS.RQ0.B7.02 /520H8832
Loss Of Charge indication (LOC)
A function is provided to indicate loss of refrigerant charge. This is
only indicated by setting an alarm flag which can be accessed via
modbus. No special action is performed by the controller.
External sensor values
The EIM 336 has sensor inputs for the suction pressure and
evaporator temperature (S2). It is however possible to substitute
these sensor inputs by sending external sensor values via modbus.
These external values need to be updated frequently.
Forced opening during startup
In some applications it is necessary to open the valve quickly when
the compressor turns on, to prevent too low suction pressure. This
is ensured by setting a fixed opening degree and a startup time for
the controller. Note that this will give a fixed opening degree for
the duration of the start time, regardless of the superheat value.
Forced opening during off
In some applications the valve must remain open when the
controller is off. This can be done by setting a fixed opening
degree. When normal control is switched off with the main switch,
the valve will keep this opening degree.
Defrost
The controller does not itself handle defrost of the evaporator. It is
however possible to enter a special defrost sequence, which will
overrule the normal control of the valve.
Standalone function
The EIM 336 is designed to operate in conjunction with a system
master controller, which will control the EIM 336 via modbus. It is
however possible to use it in a standalone mode with no external
control, except a digital input from the hardware main switch.
In this configuration some of the other functions will not be
available.
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