The Heat Exchanger Selector primitive provides the logic for sequencing a bank of up to four heat exchangers. The primitive provides individual outputs for the equipment required by each heat exchanger, including isolation valves, pumps, and cooling towers (as necessary). The primitive works in concert with the Pump and Tower Selector primitives to provide proper sequencing and timing.
The Heat Exchanger Selector primitive is designed to help maximize the chiller plant's operating efficiency while minimizing total starts and attempting to balance run times for the devices involved. The user can control the Rotation method by reducing the devices' internally rated efficiency based on run time imbalance.
The primitive supports three modes of operation.
- Building Load - The cooling load is directly represented by the value of the Process Variable input. Typically, this is provided (by a separate module in the application) as some product of delta T, Heat Capacity, and Flow.
- Flow Differential - Only for systems with primary constant speed pumps. The cooling load can be determined based on the measured flow differential that is input on the Process Variable. For this calculation, the users also needs to know the actual chilled water flow as the CHW Commanded Flow input.
- Temperature Differential - Only for primary constant speed pumps. The cooling load can be determined based on the measured temperature differential that is input on the Process Variable. For this calculation, the users also needs to know the actual chilled water flow as the CHW Commanded Flow input and the maximum rated temperature drop across the devices.
The user can optionally designate a device type for groups of devices and indicate the desired staging or sequencing. The desired sequencing is specified as a Sequence Table. Basically, this table defines which combinations of devices can be used.
This primitive is used within a Control Sequence. The Heat Exchanger Selector primitive can only exist within a Control Sequence or Control Activity within a Control Sequence. For this release, a maximum of four devices are supported.
You cannot view and modify the modules in this group’s logic.
Once system selection is complete, the Heat Exchanger Selector module requires further configuration. Refer to the Johnson Controls Central Plant Optimization™ 10 Application Note (LIT-12011575) for information on configuring this module and for more application level information.