Principles of Operation of
the Module UCM-CLD
RLC-SVU02F-E4
14
Hot-Water Mode Control
Module - Option Model
RTWB
Scope of Supply
The following parts will be installed
in the control panel of the unit:
• One Additional Board A70 with
display
• One CDS LWT immersion
well to be installed by the customer
The sensor will be connected to
terminals B3 and GND on terminal
block J2 of the A70 module.
Sequence of Operation
• Cooling Mode
The unit will operate as a standard
chiller (i.e., the chiller controls the
leaving chilled-water temperature).
The condenser pump will be driven
by the UCM relay. The chiller uses
the cooling setpoint defined in the
A70 Module.
• Heating Mode
In the heating mode, the chiller will
control the condenser leaving-water
temperature. The temperature sensor
connected to the A70 Module should
be located in the condenser leaving-
water connection downstream from
the condenser. The control is done by
loading or unloading the chiller. To
load or unload the chiller, a chilled-
water setpoint reset is applied (i.e.,
setpoint decrease = load; setpoint
increase = unload). The condenser
pump is always in operation. The
evaporator pump is still controlled by
the UCM and is always in operation.
The chiller uses the heating setpoint
defined in the A70 Module.
The chiller will be stopped if the
condenser leaving-water
temperature is greater than the
se the “differential to stop”.
The chiller will start if the condenser
leaving-water temperature is lower
than the setpoint - the “differential
to start”.
• Sensor Failure
In the heating mode, and if the CDS
leaving-water temperature sensor
fails, the chiller is stopped and the
alarm relay of the A70 Module is
energized. The chiller can operate in
the cooling mode if the CDS
leaving-water temperature sensor
has failed.
A70 Module and UCM interaction
Chilled-Water setpoint: The A70
Module drives the chilled-water
setpoint using a linear signal from
an Analog Output of the A70
Module to the external chilled-water
setpoint input of the UCM.
Chiller Enable/Disable: The A70
Module drives the chiller (on or off)
using a dry contact from the A70
Module to the external start/stop
input of the UCM.
CDS pump relay: The A70 Module
drives the condenser pump relay.
In heating mode, the chiller controls
the condenser leaving-water
temperature. The A70 Heat Pump
Module sends an external chilled-
water setpoint to the UCM. This
analog signal (factory set at 4-
20mA) is constantly reset to match
the heating load.
• Setpoint decreases
Æ
load the
chiller
• Setpoint increases
Æ
unload the
chiller
Note that the UCM still operates as
a chilled-water controller.
On the UCM-CLD, the parameter
“External Chilled Water setpoint”
has to be enabled.
