Operating instructions

EC3 Series
Coldroom Controllers
D A T A S H E E T
EC3-3_35041_EN_R13.docx 2 / 8 23.02.2012
Introduction
The EC3-33x series Controllers are for use in commercial
refrigeration systems, primarily to control the refrigeration circuit
of coldrooms. This includes the control of the refrigerant flow to
optimize superheat, maintain air temperature and the defrost
management. Alco Controls EX4…EX8 Electrical Control
Valves must be used in conjunction with the EC3-33x units to
modulate refrigerant flow.
Two separate control loops are coordinated in the device: one
senses evaporating pressure and temperature to maintain
optimum superheat, while the other loop controls air temperature.
Other functions include the management of defrost schedules
and sequences, data monitoring and alarm handling. Though
EC3 Controllers can operate as stand alone devices, they are
best suited to networked solutions, which take advantage of the
monitoring capabilities.
The EC3-33x Controllers are members of the range of EC2 and
EC3 devices, which can be easily assembled into complete
control systems for commercial refrigeration. They all share the
benefits of remote access and data communication. Please
refer to specific datasheets for details.
Application
The functions of the EC3-33x Controllers are described in the
functional diagram below:
With coil out temperature (1) and evaporating pressure (4) the
superheat is calculated to define the opening of the Electrical
Control Valve (11). Superheat can be set to a fixed value or an
adaptive mode may be used. Temperature sensor (2) is part of
the temperature control loop. The defrost heater (8) can be
activated locally by fixed timing intervals or remotely through the
communications port. For defrost end termination the
temperature sensor (3) can be used. Fan (10) and compressor
(7) are controlled as well. One digital input is allocated to the
compressor safety loop (5). Another digital input monitors the
door switch (6), which will activate an alarm if the door is not
closed within a specified time. The analog output (12) feeds the
evaporating pressure transmitter signal to a 2
nd
EC3-33x or
other Controller on the same suction line thus eliminating the
need for a second pressure transmitter.
In case of power loss a battery built in the EC3-33x will close
the Electrical Control Valve (11) and avoid flooding of the
compressor. Due to the positive shut-off capabilities of the EX4
… 8 valves a separate liquid line solenoid valve is not required.
Superheat Control
The EC3 Series controls evaporator superheat by varying the
mass flow through the Electrical Control Valve (ECV). The
controller automatically calculates the number of steps required
for the correct valve opening by measuring pressure and
temperature at the evaporator output. PT5-07M pressure
transmitters and ECN-Pxx pipe type temperature sensors from
EMERSON must be used.
The controller works in two operating modes: fixed superheat
and adaptive superheat. In the “fixed” mode, the superheat
set-point is fixed to a user-defined value. In the “adaptive” mode
the controller varies superheat set-points in the range between
3K and 15K depending on system conditions to maintain stable
operation. The pressure drop through a distributor or the glide
associated with certain refrigerants (e.g. R407C) can be
compensated in the controller.
Temperature Control
The ECN-Sxx air sensor is used for temperature control of the
coldroom. The dead band control function is described in the
diagram below:
The horizontal axis represents the temperature, with St the set-
point for day operation and rd the difference at day, while r6 is
the set-point for night operation and r7 the difference at night.
The vertical axis represents cooling operation (1 = cooling, 0 =
no cooling).
A control parameter allows to switch off the evaporator fan
during “no cooling”.
A more precise temperature control can be achieved by using
the modulating temperature mode as shown below:
The horizontal axis represents the temperature, the vertical axis
the superheat setting. At high temperatures, the controller
works with minimum superheat. St is the set-point for day
operation, at which the superheat is already increased. rd
specifies the proportional band in which the superheat is
modulated. Equivalent is r6, the set-point for the night operation
and r7 the width of the proportional band at night. At a
temperature of St minus ½*rd (day) or r6 minus ½*r7 (night) the
valve is closed.
In case the controller should be used in a heat pump for
heating, the function of the temperature controller can be
inversed:
When used with a standard condensing unit, the compressor
relay can be used to switch the coil of power contactor. The
compressor relay is not used in a refrigeration system with a
rack controller. In this application, the electrical control valve
closes when the thermostat set-point has been reached and the
rack will automatically pump down if there is insufficient demand
from the rest of the refrigeration system.