Dometic PGD1 User Manual

19
EN
VARC Chiller Controls Operation
6 Operation
The VARC provides many operational features to
conserve energy, improve performance, and provide
system control.
6.1 Operational Modes
The main operational modes determine whether the
VARC generates heat or cooling: Cool mode, Heat
mode, and Electric Heat mode. Pump operation is
coordinated with these modes.
The VARC also has Econo mode and a Maintenance
mode for troubleshooting.
The operational modes can also be selected using the
digital inputs if wired to the control board. These inputs
allow you to select Econo mode if enabled for either
cool or heat mode. Cool and Reverse cycle Heat mode
can be selected by using the digital input controls. This
allows the system to be switched between modes by
using a common switch or controlled through some
other automated system. These inputs do not support
Electric heat operation.
6.1.1 Cooling and Heating
The VARC supports a Cool mode and two heating
modes: Heat (reverse cycle heating) and Electric Heat.
Cool
When Cool is selected on the touch screen or the
LCD buttons, the VARC starts cooling according to the
temperature setpoint. The pumps operate as described
in “Pump Operation” on page 20.
Cool mode activity is as follows:
• If the return water/supply water temperature is
above the cooling setpoint and the staging delay has
elapsed, the board energizes the compressor relay.
• The compressor continues to run until the cooling
setpoint has been reached or an alarm condition
exists.
• A stage has a minimum run time of 60 seconds before
it can be turned off and a minimum off time of 10
seconds before it can be re-enabled. This minimum
on time is required to ensure that the system is not
cycling on and off and thereby not allowing the
compressor to properly warm-up. This ensures
proper oil lubrication of the system.
• If the system calls for a stage to be toggled on or off,
the next available stage that meets the staging criteria
is used.
• Load shedding occurs in multi-stage operation when
approaching the chilled water setpoint.
Compressor rotation is active during run mode:
• The compressor with the lowest running hours is
enabled first, and the compressor with the highest
running hours is disabled first.
• Aer chilled water and sea water flows are stable for
10 seconds (default), the first stage is enabled, and
the compressor starts.
• The first stage continues to run up to 100 percent
speed before enabling the next stage.
• If the PID loop requires demand, then the next stage
is enabled with a startup delay of three minutes
before running up to required speed.
Heat (Reverse Cycle Heating)
When Heat is selected on the touch screen or the LCD
buttons, the VARC starts heating according to the
temperature setpoint. The pumps operate as described
in “Pump Operation” on page 20.
Heat mode activity is as follows:
• There is a 45-second delay aer the compressor
ramps up before it is energized.
• The reversing valve relay is energized to operate the
VARC in Reverse Cycle Heat mode.
• If the return/supply water temperature is below the
programmed heating setpoint and the staging delay
has elapsed, the VARC energizes the compressor
relay.
• The compressor continues to run and the reversing
valve remains energized until the heating setpoint has
been reached or an alarm condition exists.

Dometic PGD1 Specifications

General

Brand	Dometic
Model	PGD1
Category	Control Unit
Language	English