Carrier AquaSnap 61WG Series - 16 Unit Operation with a Free Cooling Drycooler; Operating Principle; Communication to Control the Drycooler; Configuration of the Fans Control

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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 ow rate variation in the loop
- cooling capacity (drycooler and chiller can operate
independently or simultaneously)
- valves positions depending on operating mode.
The control denes the optimal conguration 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 ow rate of
the loop permit system operation down to -20 °C outside
temperature without any additional control.
Chiller
NO
NC
DC free cooling
LEN communication
OAT
V2V control
2
1
3
For an optimal free cooling operation, the chiller has to be
congurated:
- 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.
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 denes if free cooling mode can be activated.
16.3 - Conguration of the fans control
To set the conguration corresponding the drycooler installed
(number of fans, control type – xed 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 conguration:
- 1 to 20 fans
- xed 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 sufcient 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.