Carrier Aquasnap 30RB 100R - Unit operation with a free cooling drycooler; Operating principle

12.2.6 - Unit operation with a free cooling drycooler
12.2.6.1 - Operating principle
The units have been designed to optimise the operation of the
systems, using drycoolers as a free cooling system (method using
low outdoor air temperatures to chill the water in the air conditioning
system).
This system enables substantial energy and cost savings, and is
at its most e󰀨ective when the outdoor air temperature is low.
The unit's SmartVu
TM
control system includes algorithms which
enables the following to be constantly automatically optimised:
- the operation of the drycooler fans,
- the variation of the ow rate in the water loop,
- the cooling capacity (the drycooler and chiller can operate
independently or simultaneously),
- the positions of the valves, depending on the operating mode.
The control denes the optimal conguration, taking the water
setpoint value, outdoor air temperature, and water loop
temperature into account (the control will give priority to the
drycooler).
Parallel control of the fans and of the variable ow rate in the water
loop enable the system to operate at outdoor temperatures of
down to -20 °C without any additional control.
Warning: the drycooler and chiller both need to be equipped
with the Free cooling management option.
Chiller
LEN communication bus
3
2
1
Drycooler free cooling
2-way valve control
No
NC
OAT
For an optimal free cooling operation, the chiller has to be
congurated:
- using the water inlet temperature control,
- using the temperature delta control for the variable-speed
pump option.
12.2.6.2 - Communication to control the drycooler
When the option is selected, a specific electronic board is
integrated in the control box of the drycooler. A communication
LEN bus connected between the drycooler (board AUX1) and the
chiller is needed for the overall system control.
This cable must be a 3-point Wago type cable (5 mm spacing or
equivalent) and must be shielded.
The board integrated in the drycooler electrics box has analogue
inputs for the outside air temperature (mark 1), water loop return
temperature sensor (mark 3) and drycooler leaving water
temperature sensor (mark 2), as well as digital outputs permitting
the control of the fans.
The option works as if the system was split in two parts:
The chiller (with free cooling option)
• Dedicated control algorithms with LEN connector to
communicate and control the drycooler.
The drycooler (with free cooling option):
• AUX board with the I/O,
• room air temperature sensor to be placed outdoors,
• drycooler water outlet temperature sensor (factory-tted),
• water loop temperature sensor (to be tted on the common
pipe upstream of the valve),
• Control & 230V power supply for 2 two ways valve or one
three ways valve
The di󰀨erence between the drycooler outdoor air temperature and
the water loop sensor temperature determines whether or not it
is possible to activate free cooling mode.
12.2.6.3 - Conguration of the fan control
To set the conguration corresponding to the drycooler installed
(number of fans, control type – xed or variable speed), please
refer to the instructions in the SmartVu
TM
control manual. Using
these parameters, the SmartVu
TM
control will activate the correct
number of outputs to control the fans.
SmartVu
TM
controls the automatic switching of all fans, based on
operating time and number of start-ups, to ensure the fan motors
provide a long service life.
Compatible fans conguration:
- 1 to 20 fans,
- xed speed or variable speed,
- 1 or 2 rows of fans.
Refer to the drycooler wiring diagram to see the arrangement of
the fan stages.
12.2.6.4 - Valves on the water loop
The free cooling system requires 2 two-way valves (one normally
open, one normally closed) or a three-way valve, not supplied with
the unit or the drycooler.
A two-way valve kit is available in the list of accessories for the
drycooler.
The drycooler electrics box has a 230 V power supply for 2 two-
way valves.
Recommended motor valve (per default): 230V 3 points
See the drycooler wiring diagram for cabling the valves to the
customer terminal strip.
12.2.6.5 - Guidelines for system installation
For physical characteristics, dimensions, performances: refer to
the drycooler documentation.
For the electrical connections, see the electrical wiring diagram
supplied with the drycooler.
For software configuration information, refer to the control
documentation of the chiller.
For a proper drycooler installation, follow the professional
guidelines for the following topics:
- sizing of the water piping;
- pressure drops (verify that the operating pressure of the unit
pump is su󰀩cient compared to the pipe and valve pressure
drops; check for all operating modes);
- maximum height for the drycooler (in relation to the unit safety
valve);
- Good positioning for temperature sensors: outside air
temperature and water loop temperature .
12 - OPTIONS
44