Attributes (Hx Selector) - Johnson Controls - Metasys - LIT-12011147 - Software Application - Controller Configuration Tool - 16.0

CHW Commanded Flow

Indicates the actual chilled water flow based on the pump status and pump ratings. This value is used in the percent load calculations for headered CHW systems only, and is typically available from the CHW Pump Selector. The Flow Stabilize Timer starts when the CHW Commanded Flow changes, and has a duration of 0.2 * Stabilize Time. This timer prevents the changes of the Process Variable from being recognized, and allows the system to stabilize following a change in the headered CHW flow.

CHW Headered/ Dedicated

Specifies whether operating with headered, dedicated, or no pumping on the Chilled Water side of the heat exchanger.

Control Mode

Determines how the process variable is treated:

• 0) Building Load: The process variable is the building’s chilled water heat gain calculated elsewhere in the application. This load is compared to the current requested rated device capacity to call for more or less device capacity.

• 1) Flow Differential: This mode is for use with primary constant speed pumps only. In this arrangement, the process variable provides the signed differential flow. (A positive value indicates that the flow in the primary loop is greater than the flow through the secondary loop. A negative value indicates that the flow in the primary loop is less than the flow through the secondary loop.)

  When operating in this mode, the Hx Selector module attempts to maintain the flow in the bypass close to zero, which is when the plant capacity matches the building load.

• 2) Temperature Differential: This mode is for use only with primary constant speed pumps with or without secondary pumps. The Process Variable is the Temperature drop across the heat exchangers and is used to calculate the chiller plant load.

CW Commanded Flow

CW Headered/ Dedicated

Specifies whether operating with headered, dedicated, or no pumping on the Condenser Water side of the heat exchanger.

Derate Now

Enables Derate Now, which commands the Hx Selector module to calculate a reduced capacity of the running heat exchangers and then command the module to reevaluate which heat exchangers should be operating.

Derate Reset

Resets the Derating Percent back to zero instantly.

Derating Percent

Indicates the percentage of derating internally applied to all devices. This value is calculated and used in Building Load Mode only. If devices are unable to meet the rated capacities, elsewhere in the application the Derate Now input is set to True. The Hx Selector then derates the devices by this percentage. Large values of this property should be investigated since it could indicate possible malfunction of the heat exchangers.

HX AVAILABLE CAP

Indicates the sum of the enabled derated capacities.

HX BASE LOAD

Indicates the minimum rate cooling the heat exchanger selector maintains.

HX CURRENT CAP

Indicates sum of the derated capacities of the devices currently commanded on.

HX CURRENT PCT LOAD

Indicates the percent loading of the devices currently commanded on, adjusted by the Derating Percent.

HX-MINOFFTIME (Min Off Time)

Indicates the minimum amount of off time applied to all devices.

HX-MINONTIME (Min On Time)

Indicates the minimum amount of on time applied to all devices.

HX START DELAY (System Start Delay)b

Indicates the delay applied when the System Enabled input transitions from Disabled to Enabled. The Minimum Load is maintained during this time, allowing the chilled and condenser water pumps to operate.

This time period is typically longer than the Stabilize Time to allow the system to achieve steady state after not being under control for some time.

HX1-REQUIRED DEVS (Required Devices)

Provides an integer output representing the packed bits of the desired steady state set of devices commanded On.

For example, a value of 88 means 0-1-0-1-1-0-0-0, which indicates device 2, 4, and 5 are On, and the rest are Off.

HX1-REQD INTERIM DEVS (Required Interim Devices)

Provides an integer output representing the packed bits of the intermediate devices requested to turn on while the heat exchanger selector moves toward the desired steady state.

Iso Valve Stroke Time

Indicates stroke time of the isolation valves. This input delays turning on the first headered pumps. For dedicated pumping on both CW and CHW sides, this value should equal zero.

Max CHW Flow

Indicates the sum of the Rated CHW Max Flows of all the devices currently On.

Min CHW Flow Setpoint

Indicates the minimum flow required for safe chiller operation. This output is used in headered variable speed chilled water systems.

Min CW Flow Setpoint

Indicates the minimum flow required for safe chiller operation. This output is used in headered variable speed condenser water systems.

Process Variable Units

Indicates the units used for the Process Variable depending on the Units of the application and the Mode of Operation.

Pump Delay

Indicates the longest amount of time required for the pump to stop once a stop is received, or the amount of time to speed up once the on command is received.

Pump Down Timeb

Indicates the amount of time to run the CW and CHW pumps after turning off a device. This delay allows the removal of refrigerant from the evaporator.

Required CHW Flow

Indicates the required chilled water flow associated with the currently requested (or soon to be requested) devices. This output is used in headered chilled water systems.

To ensure enough chilled water flow during taging, the CHW Required Flow is increased by 10% with a minimum value as calculated and a maximum value equal to the Rated CHW Flow.

This flow requirement value is issued with enough anticipation to allow flows to be obtained prior to devices turning on and maintains its high value while the Pump Down Timer is active, when devices are being turned off.

Required CW Flow

Indicates the required condenser water flow associated with the currently requested (or soon to be requested) devices. This output is used in headered condenser water systems.

The module calculates a minimum condenser water flow based on the individual minimum condenser water requirements and the rated condenser water flows.

To ensure enough condenser water flow during staging, the CW Required Flow is increased by 10% with a minimum value as calculated and a maximum value equal to the Rated CW Flow.

This flow requirement value is issued with enough anticipation to allow flows to be obtained prior to devices turning on and maintains its high value while the Pump Down Timer is active, when devices are being turned off.

Required Tower Flow

Indicates the required cooling tower water flow. This output is a time-shifted version of the Required CW Flow output to ensure proper sequencing of the cooling tower with the other equipment when devices are added or removed.

Rotate Now

On the rising edge of this signal, the Hx Selector calculates a new combination of devices that provides the required cooling capacity while promoting the maximum rotation of the heat exchanger.

Rotation Mode

Determines how rotation is processed:

• 0: None. The module does not attempt to equalize either runtimes or start counts of the individual devices.
• 1: Run Time. The module attempts to equalize the runtimes of the individual devices.
• 2: Start Counts. The module attempts to equalize the start counts of the individual devices.
• 3: Both. The module attempts to equalize both start counts and run times of the individual devices.

Selector Enabled

Indicates if Heat Exchanger is in operation. This input enables Heat Exchanger to determine if it can turn on pumps before opening its first isolation valves (turning on the first heat exchanger) or close its last isolation valves before turning off all the pumps (turning off the last heat exchanger). This input connects to the same source as Chiller Selector's System Enabled input, if present.

Sequence Row Control

Enables Sequence Row parameter to enable devices.

Sequence Row

Indicates the sequence table row number that the module attempts to move toward while following device timers and statuses. This input is available when the Sequence Row Control input is True. If the input value is out of range or if a sequence table is not present, Sequence Row input is ignored.

Stabilize Time

Indicates the amount of time after a device changes on or off that the must elapse before recognizing changes to the Process Variable.

System Enabled

Disables/enables the chiller plant. When System Enabled is False, the Heat Exchanger Selector downstages to zero capacity.

Tower Available Flow

Indicates the available cooling tower water flow. The Hx Selector uses this value in determining valid device combinations. The value is typically available from the Cooling Tower Selector.

Tower Commanded Flow

Indicates the actual cooling tower water flow. This value provides status feedback to the Hx Selector to ensure proper sequencing of the cooling tower with the other equipment when a device is added or removed. The value is typically available from the Cooling Tower Selector.