Trane TCAA Series - Page 60

60
ARTC-SVX013A-EN
Economizer Control
The Economizer Control (ECO) provides cooling refrigerant
vapour to the interstage port of the Turbocor compressor.
The ECO function has the following algorithms:
Table 20. ECO function algorithms
Algorithm Display Detail
Speed – Enables the ECO function between threshold settings based on
relative compressor speed (%). Includes a capacity-based permissive.
PR (default) – Enables the ECO function between threshold settings based on
relative Compressor pressure ratio.
Capacity – Enables the ECO function between threshold settings based on
compressor capacity (%).
The ECO system has the following control options:
Table 21. ECO control options
Control
Display Detail
Solenoid valves only – source of cooling vapour is external for the control
system, very often, it is a brazed plate heat exchanger with TXV – Thermal
Expansion Valve (mechanical device).
Flash Tank – requires an additional level control (modulating device) with PI
loop. Mostly implemented on water-cooled chillers. Includes a level permissive
that with close the solenoid if level exceeds setting.
Brazed-Plate – in this case, the heat exchanger is control with EXV and PI
loop.
NoSolenoid_DX – same as above but there are no additional solenoids
between ECO and compressor. Requires a DX heat exchanger with EXV and
PI loop per compressor.
While ECO function is enabled (determined by threshold
configuration of the selected algorithm), if there is a
solenoid valve to the compressor interstage, it is open and
if the control option includes an EXV (modulating), it is
opened and controlled to specific setpoint for the option.
Economizer valves control option in the controller can be
enabled / disabled on HMI Configuration page.
This also reveals economizers control screen at Main
Menu > Devices Menu > ECO.
As shown above, there are two modulating valve control
options:
1. Brazed-plate with an EXV.
2. Flash Tank with a level control.
Brazed-Plate EXV Control
Brazed-Plate EXV control deals with an air-cooled chiller
with a complete ECO system per refrigeration circuit. If
EXV option is selected, the ECO EXV button appears for
circuit defined in the chiller.
Operating Procedures