Decouple Loop Flow (CPO) - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 15.0

Controller Tool Help

Brand
Johnson Controls
Metasys
Product name
Controller Configuration Tool
Document type
User Guide
Document number
LIT-12011147
Version
15.0
Revision date
2022-11-18
Language
English

The Flow Differential method is used only with the primary/secondary chilled water pumping configuration.

Several different methods can determine the difference between primary and secondary chilled water flow.

Bi-directional Flow Sensor measures the Decouple flow directly.

Bi-directional Flow Sensor with BI input measures the Decouple flow directly, and the binary input gives indication of either normal or reverse direction.
Note: A reverse flow occurs when the secondary flow is greater than the primary flow.

Calculate Decouple Flow receives its input from the Diff Flow Calc, which calculates the difference between the Primary and Secondary Chilled Water Supply flows.

You can estimate the cooling load based on the measured flow differential, which is also the flow in the crossover decoupler pipe. The Percent Load is the percentage of the current building load to the total chiller plant available.

This control mode is much less expensive to implement than either Building Load or Chiller Load, but the disadvantage is that the Flow Differential uses half the information required to do the calculation. For example, to calculate the energy flow, the chilled water flow and the temperature difference are required. This method assumes that the chillers produce a constant temperature drop, which is not the case most of the time.