Trane Centrifugal Water Chillers CVGF - Manual (Page 17)

Extended Operation Package
Select the extended-operation package for chillers that require external, hot water control, and/or
base-loading capabilities. This package also includes a 4-20 mA or 0-10 Vdc analog input for a
refrigerant monitor.
• External base-loading control
• External base-loading relay
• External hot-water control relay
• Refrigerant monitor input
Base-Loading Control
This feature allows an external controller to directly modulate the capacity of the chiller. It is typically
used in applications where virtually infi nite sources of evaporator load and condenser capacity are
available and it is desirable to control the loading of the chiller. Two examples are industrial process
applications and cogeneration plants. Industrial process applications might use this feature to
impose a specifi c load on the facility’s electrical system. Cogeneration plants might use this feature
to balance the system’s heating, cooling, and electrical generation.
All chiller safeties and Adaptive Control functions are in full effect when Base Loading is enabled.
If the chiller approaches full current, the evaporator temperature drops too low, or the condenser
pressure rises too high, the controller’s Adaptive Control logic limits the loading of the chiller to
prevent the chiller from shutting down on a safety limit. These limits may prevent the chiller from
reaching the load requested by the Base Loading signal.
An alternative and less radical approach to Base Loading indirectly controls chiller capacity.
Artifi cially load the chiller by setting the chilled-water setpoint lower than it is capable of achieving.
Then, modify the chiller’s load by adjusting the current-limit setpoint. This approach provides
greater safety and control stability because it leaves the chilled-water temperature-control logic in
effect. The chilled-water temperature control responds more quickly to dramatic system changes
and limits chiller loading prior to reaching an Adaptive Control limit.
Hot-Water Control
This feature allows an external controller to enable/disable and modulate the hot-water control
mode. Occasionally, centrifugal chillers are used to provide heating as a primary mission. In this
case the external controller or operator would select a hot-water temperature setpoint and the
chiller capacity would be modulated to maintain the setpoint. Heating is the primary mission and
cooling is a waste product or a secondary mission. This technique provides application fl exibility,
especially in multiple-chiller plants in conjunction with undersized heating plants.
The chiller needs only one condenser for hot-water control, whereas Heat Recovery uses a
secondary condenser.
Refrigerant Monitor
The Extended Operation package allows for a refrigerant monitor to send a 4-20 mA signal to
the Tracer AdaptiView TM control display. It can be calibrated to correspond to either 0-100 ppm
or 0-1,000 ppm concentration levels. The concentration level is displayed at Tracer AdaptiView TM
control, but the chiller will not take any action based on the input from the refrigerant monitor.
Alternatively, a refrigerant monitor can be connected to Tracer Summit, which has the ability to
increase ventilation in the equipment room in response to high refrigerant concentrations.
Optional Features
17
Controls
CTV-PRC001-E4