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