Attributes (Open Loop Tower Control with Low Limit v61) - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 13.1

Absolute EWMA Effort

Provides an EWMA based on the absolute value of (Current Present Value - Last Present Value). The PID computes this value.

Absolute EWMA Error

Provides an EWMA based on the absolute value of (Setpoint - Process Variable). The PID computes this value.

Chiller Plant Capacity

Provides the name plate chiller capacity. You may enter the sum of all the chillers in the plant, or the Chiller Selector may supply the sum of the active chillers.

Chiller Plant Load

Indicates the amount of energy added to the chilled water by the plant.

Chiller Plant Sensitivity

Indicates the incremental increase in chiller power for each degree increase in condenser water temperature as a fraction of the power. Typically, the sensitivity factor is between 0.01 and 0.03.

Chiller Rated Power

Provides the name plate chiller power. You may enter the sum of all the chillers in the plant, or the Chiller Selector may supply the sum of the active chillers.

CW Temperature

Indicates the condenser water temperature, which is the low limit process variable.

Enable

Enables or disables the module. When disabled, the Percent Cmd is 0.0%.

EWMA Error

Provides an EWMA based on the difference of (Setpoint - Process Variable). The PID computes this value.

EWMA Present Value

Provides an EWMA of the Present Value. The PID computes this value.

Fan Type

Defines the type of fans used in the cooling towers. This module supports 1-speed, 2-speed, 3-speed, and variable speed fans. It does not support vernier fans.

High Control Setpoint

Indicates the high control (limit) temperature setpoint.

Provides the current Present Value of the output that this controller drives when Limited Max is enabled.

Low Limit Control Status

Indicates the control status of the PID that controls the condenser water temperature to the condenser water low limit setpoint.

Low Limit Enable

Enables or disables low limit control.

Low Limit Setpoint

Indicates the low limit temperature setpoint.

Low Limit Setpoint Differential

Indicates the low limit temperature differential.

Low Limit State

Represents the current state of the low limit control FSM.

Minimum Speed

Sets a minimum speed for the module percent command output when controlling a VFD with such a requirement.

OA Humidity

Indicates the outdoor air humidity.

OA Temperature

Indicates the outdoor air temperature.

Output Overridden

Indicates when the actual output controlled by this output is overridden by a user.

Output Position

Provides the current Present Value of the output that this controller drives.

Percent Cmd

G,V

Indicates the control signal output sent to the cooling tower. If the Low Limit State is No Limit Control, this is the percent command output of the Near Optimal Open Loop Tower Control block. If the Low Limit State is Control Limit, this is the minimum of the output of the Near Optimal Open Loop Tower Control block and the PID controlling the condenser water temperature to the condenser water low limit setpoint.

PID Tuning Reset

Causes the PID objects to reset their tuning parameters to the default based on the appropriate Process ID.

Process Units

Specifies the units for the heating PID. For this particular module, the only two valid values are °C and °F.

Tower Approach

Indicates the designed cooling tower approach, which is the expected temperature difference between the condenser water temperature leaving the cooling tower and the outdoor air wet bulb temperature under design conditions. This value is typically 7 °F, but may be found in the cooling tower manufacturer’s literature.

Tower Range

Indicates the designed cooling tower range, which is the expected condenser water temperature drop from inlet to outlet under design conditions. This value is typically 10 °F, but may be found in the cooling tower manufacturer’s literature.