Attributes (Open Loop Tower Control with Low Limit) - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 15.0

Controller Tool Help

Product name
Controller Configuration Tool
Document type
User Guide
Document number
LIT-12011147
Version
15.0
Revision date
2022-11-18

The following table describes the attributes used by the Open Loop Tower Control with Low Limit modules:

Table 1. Open Loop Tower Control with Low Limit Attributes

Name

Type 1

Description

Default Value

Absolute EWMA Effort

 

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

0.0

Display Units: %

Absolute EWMA Error

 

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

0.0

Display Units: °C, °F

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.

100 kW, 28.4 Tons

Chiller Plant Load

 

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

100 kW, 28.4 Tons

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.

0.02

Minimum: 0.01

Maximum: 0.03

Display Precision: 100ths

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.

100 kW, 134 hp

CW Temperature

 

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

29.4 °C, 85 °F

Enable

 

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

True

EWMA Error

 

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

0.0

Display Units: °C, °F

EWMA Present Value

 

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

0.0

Display Units: %

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.

VFD

Set Name: Tower Fan Type

High Control Setpoint

 

Indicates the high control (limit) temperature setpoint.

30 °C, 86 °F

Low Limit Control Status

 

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

Normal

Set Name: Control Status

Low Limit Enable

 

Enables or disables low limit control.

True

Low Limit Setpoint

 

Indicates the low limit temperature setpoint.

15.6 °C, 60 °F

Low Limit Setpoint Differential

 

Indicates the low limit temperature differential.

2.8 °C, 5 °F

Low Limit State

 

Represents the current state of the low limit control FSM.

No Low Limit

Set Name: Low Limit Control

Minimum Speed

 

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

20%

OA Humidity

 

Indicates the outdoor air humidity.

50% RH

OA Temperature

 

Indicates the outdoor air temperature.

21 °C, 70 °F

Output Overridden

 

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

False

Output Position

 

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

0%

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.

0.0%

PID Tuning Reset

 

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

Normal

Set Name: PID Tuning Reset

Process Units

 

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

°C, °FSet Name: Units

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.

3.9 °C, 7 °F

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.

5.6 °C, 10 °F

Tower Rated Power

 

Provides the name plate cooling tower power. You may enter the sum of all the cooling towers in the plant, or the Cooling Tower Selector may supply the sum of the active cooling towers.

10 kW

1 C - Configuration Mode Only, G - Default Element (Generated State, if applicable), SC - Simulation and Commissioning Modes only, V - Calculated Value (Outputs)