used as a stand-alone unit. When used on the pLAN Network, each unit is not required to have to
have the same software revision and date.
When the Master goes offline, all standby systems become active to standalone mode. This
reduces the chance of the controlled space temperature and humidity trailing off setpoints.
When an active unit with either Master or Slave goes into alarm, the next standby system or all
standby systems should become active. Network alarm events are programmable via the
technician menu. Communication between systems is maintained by a synchronized heartbeat.
Unit rotation can be set to achieve equal run time on. At the end of each cycle, the role of each
unit switches to its counterpart, meaning the Master becomes the Slave and the Slave becomes
the Master during the next cycle. During each cycle, the units operate according to the above
lead/lag logic.
3.4 Air Cooled DX with Chilled Water Plus
Summary of Equipment
The primary system shall be Chilled Water Cooling. Direct Expansion Cooling shall be setup as a
back up to the Chilled Water system. Both systems are designed to work independent of each
other.
The Chilled Water System comes standard with a three (3) way water modulating valve, coil, and
an optional “no water flow switch”. The DX system is equipped with a DX coil, compressor(s), and
outdoor air cooled condenser. Optional heaters and humidifiers are also available if needed.
A unique feature of Air Cooled/Chilled Water Plus units is that the chilled water coil is located at
the side of the direct expansion coil. The auxiliary chilled water coil is custom sized so that it
provides identical cooling capacity obtained during the refrigeration cycle with the compressor
operating.
Cooling-Chilled Water
Chilled Water cooling is the primary cooling system for C+ units. For optimum performance, the
controller is programmed to call chilled water cooling for the first 300 seconds regardless of the
chilled water temperature.
The C+ unit can switch over from one cooling mode to another based on sensing Chilled Water
flow or Chilled Water temperature. The standard practice is to sense the Chilled Water flow for
switching.
If “No Water flow” switch is selected, the unit senses the flow of chilled water by using a pressure
differential switch and switches over to DX cooling based on loss of water flow. When no water
flow switch is selected for switch over, the unit will only work on either DX or C.W. cooling mode.
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