Unit Operation With A Free Cooling Drycooler; Operating Principle; Communication To Control The Drycooler; Configuration Of The Fans Control - Carrier AquaSnap 61WG Series Installation, Operation And Maintenance Instructions

16 - UNIT OPERATION WITH A FREE COOLING DRYCOOLER

16.1 - Operating principle

The units have been designed to optimize the operation of
systems, using drycoolers as free cooling system (method using
low outdoor air temperature to chill the water of the air conditioning
system).
This system allows substantial energy and cost savings, which is
the most effective when the outdoor air temperature is low.
The TouchPilot control of the unit includes algorithms to permit
constant automatic optimization of:
- drycooler fans operation
- water flow rate variation in the loop
- cooling capacity (drycooler and chiller can operate
independently or simultaneously)
- valves positions depending on operating mode.
The control defines the optimal configuration considering water
set point value, outdoor air temperature and water loop temperature
(the control will give priority to the drycooler).
Parallel control of the fans and of the variable water flow rate of
the loop permit system operation down to -20 °C outside
temperature without any additional control.
Chiller
LEN communication
DC free cooling
For an optimal free cooling operation, the chiller has to be
configurated:
- on entering water temperature control
- on delta temperature control in case of variable speed pump
option

16.2 - 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 should be a 3 points Wago type (5 mm spacing or
equivalent) and should be shielded.
The board integrated in the control box of the drycooler has analog
inputs for outside air temperature (mark 1) , return water loop
temperature (mark 3) and drycooler leaving water temperature
sensors (mark 2), as well as digital outputs permitting the control
of the fans.
58
3
NO
NC
2
V2V control
1
OAT
The option works as a system 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
- OAT sensor to be place in outdoor zone.
- Dry Cooler Leaving Water Temperature (factory mounted)
- Water loop Temperature (to be mounted on the common pipe
before valve)
- Control & 230V power supply for 2 two ways valve or one
three ways valve
The temperature difference between dry-cooler OAT and water
loop sensor defines if free cooling mode can be activated.

16.3 - Configuration of the fans control

To set the configuration corresponding the drycooler installed
(number of fans, control type – fixed or variable speed), please
refer to the instructions in the TouchPilot control IOM. Following
these parameters, the TouchPilot control will activate the adequate
number of digital outputs to control the fans.
TouchPilot controls the automatic switching of all fans, based on
operating time and number of start-up, to ensure a long operating
life of fan motors.
Compatible fans configuration:
- 1 to 20 fans
- fixed speed or variable speed
- fans in one l or 2 lines
- Refer to the drycooler electrical diagram to see the fan stages
arrangement.

16.4 - Water valves

The free cooling system requires 2 two-way valves (one Normally
Opened, one Normally Closed) or a three-way valve, not supplied
with the unit or the dry cooler.
A two-way valves kit is available in the list of drycooler accessories.
The drycooler electrical box includes 230V power supply for 2
two-way valves.
Recommended motor valve (per default): 230V 3 points
Refer to drycooler electrical diagram for valves wiring on customer
connections.

16.5 - System installations recommandation

For physical characteristics, dimensions, performances: refer to
the drycooler documentation.
For electrical connections information, refer to the electrical wiring
delivered 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:
- Water pipe sizing
- Pressure drops (verify that the available pressure of the unit
pump is sufficient compared to the piping and valves pressure
drops - check for all running modes)
- Maximum drycooler elevation (in relation to the unit safety
valve)
- Good positioning for temperature sensors: outside air
temperature and water loop temperature.