Subtract - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 16.0

Controller Tool Help

Brand
Johnson Controls
Metasys
Product name
Controller Configuration Tool
Document type
User Guide
Document number
LIT-12011147
Version
16.0
Revision date
2023-10-02
Language
English

The Subtract module subtracts two inputs. This module accepts as inputs Input 1 and Input 2, and has one output. This module subtracts Input 2 from Input 1, and the differential is the output. If Input 2 resides outside of an acceptable range, the module supplies a default differential value to the output.

If Input 1 is less than 35.0, and Input 2 is less than 99.0 AND greater than 13.0, the assumption is that the module is measuring chilled water differential temperature in °C and a chiller is not running. A default value of 7.0 is provided as the output.

If Input 1 is greater than 35.0, and Input 2 is less than 99.0 AND greater than 53.0, the assumption is that the module is measuring chilled water differential temperature in °F and a chiller is not running. A default value of 14.0 is provided as the output.

For example, the Supply Return Water Differential module, a Subtract module, determines the cooling load based on the measured chilled water supply and return temperature differential. This module is designed to ensure chiller startup by providing a fixed temperature differential output of 14°F (7°C) under startup conditions when the chilled water supply and return temperature differential is typically zero. After startup, once the chilled water supply temperature falls to 46°F (or below 10°C for a metric application), the module begins to output the true chilled water supply-return temperature differential. This building load is compared to the maximum rated temperature drop across the devices, as defined in the details of the Chiller Selector Module as Max Delta CHWT. This method only uses temperature sensors.

You can view and modify the modules in this group’s logic.

Figure 1. Subtract Module's Logic