Secondary Circuit Controller for Temperature Control of Heating or Cooling Circuits with 3 x Triac Outputs (3T version) with 2 x 0-10V DC Outputs (AOP version)
Main Features Controls a Secondary LPHW or Chilled Water Circuit - Pump and Valve Control Provides Control of Variable Temperature (VT) or Constant Temperature (CT) Circuits Weather Compensated Control (VTC Version) Temperature Control Based on Zone Demand (VTU Version) Constant Temperature Control (CTU Version) Intelligent Demand Filtering

Summary Features

General

The SeaChange Secondary Circuit Controller provides control of LPHW or Chilled Water secondary circuits. These may be VT or CT circuits which are coupled to the primary circuit by valves and pump sets or other plant, and require individual control. These circuits may feed Radiator Zones, Air Handling Units, Fan Coil Units, DHW systems or other types of load; ideally all of the associated loads will be controlled by SeaChange 'Consumer' Modules (for instance, Zone Controllers or AHU Controllers).

Configuration parameters can be set to allow operation to match the plant control requirements. A full table of configuration and monitoring parameters is detailed later in this data sheet.

A table of available product versions is shown on the last page.

Demand Control

The Secondary Circuit Controller is known as a Distributor Module ; it receives Heating or Cooling Demand signals from its Consumer Modules. It collates the demand signals and calculates a setpoint which is then passed back as a Demand to a SeaChange Provider Module controlling a primary source of energy (eg. Boilers or Chillers). In this way, the primary plant will run only when a demand for it’s services exists.

Intelligent Demand Filtering

The Secondary Circuit Controller has Intelligent Demand Filtering and can be set to produce a Demand for heating or cooling only when certain criteria are met, e.g. when at least 5 Fan Coils of the 50 on a circuit are demanding Cooling - this would prevent a large Chiller from running when only 1 Fan Coil was demanding cooling energy.

Temperature Control

The Secondary Circuit Controller provides temperature control of the Secondary Circuit allowing Primary and Secondary Circuits to run at different temperatures. The temperature setpoint used is calculated by the Secondary Circuit Controller according to its type;
1) VTC, Variable Temperature Compensated uses a combination of Zone Demands and Outside Temperature to calculate its setpoint.
2) VTU, Variable Temperature Uncompensated uses only Zone Demands to calculate its setpoint.
3) CTU, Constant Temperature Uncompensated works to a fixed setpoint.

Different Output Driver types can be used for different types of valve; Raise/Lower, Time Proportioning and Staged Drivers are available. The accompanying secondary pump can be switched using the Occupation Switch output C.

An Analogue Output variant can control a 0 - 10Vdc valve and a pump via an external relay module.

For CT Circuits where the Primary and Secondary temperatures are the same (i.e. no valve is used) then the CTU Controller can be used for pump control only. No temperature sensor is necessary in this case, but it may be fitted for monitoring purposes.

A Pump Changeover variant of the Secondary Circuit Controller is available to control a CT twin pump set directly, where no valve is required. This product is described in the separate data sheet M4.

Description of Features

Occupation State of the Secondary Circuit

The Secondary Circuit controller has no internal Occupation Time Schedules; instead it determines whether it is working in an Occupied Mode (controlling to its Occupied Setpoint) or Unoccupied Mode (pumps off, controlling to its Non-Occupied Setpoint) by 3 methods:

A) Occupancy determined by Zone energy demands

In this mode the Secondary Circuit controller determines whether it is working in an Occupied or Non-Occupied mode depending on the Heating or Cooling Demand Signals it receives from the Consumer Modules registered to it.

The occupied or non-occupied state of the controller is determined by the settings of minimum demand MIND, minimum average demand MNAV and minimum number occupied MNOC. These parameters can be used singly or together. They are particularly useful when many Consumers are being fed from one large primary plant, and it is undesirable to allow this plant to run below a certain minimum load.

MIND minimum demand

The highest Demand signal from the Consumer Modules is compared with the Minimum Demand parameter MIND and if greater the Controller is put into occupied mode. Once occupied the Demand signal from the Consumers must drop below half the MIND setting to become non-occupied.

MNAV minimum average demand

The average Demand signal from the Consumer Modules is compared with this value and if greater the Controller is put into occupied mode. Once occupied the average Demand signal from the Consumers must drop below half the MNAV setting to become non-occupied. The average value is used to prevent a small demand from a single zone activating the controller.

MNOC minimum number of occupied zones

The number of zones occupied is compared with this value and if greater the Controller is put into occupied mode. Once occupied the number of occupied zones needs to fall below half the MNOC setting to become non-occupied.

To disable a particular test set the parameter to zero. If all three parameters are zero the Controller will become occupied if any Consumer Module is occupied.

If more than one test is in action (not zero) then the occupancy state is determined by ANDing the result of each test.

For example, if the settings are: MIND = 50, MNAV = 20, MNOC = 5
The Controller will become occupied when the highest Consumer Demand is greater than 50% and the average Demand is greater than 20% and at least 5 consumers are occupied.

Note if no temperature sensor is fitted then the controller operates in driver mode, passing on the highest or average demand (depending on the setting of SPTY) to the output stages but only whilst Occupied.

Example : Heating VT Circuit with 2 subzones, weather compensation and zone influence

Occupancy state of the Secondary Circuit controller is derived from Heating demand signals from Zone controllers using MIND, MNAV, MNOC parameters.

VT flow setpoint is determined by Zone trim (and weather compensation if appropriate). CT setpoint for boilers is determined by adding LOSS parameter to VT flow setpoint.

B) Occupancy determined by Occupancy Demand signals from another controller

In this mode the Secondary Circuit controller will enter the Occupied mode if any of the controllers Interconnected to it via Occupancy Demand enters Occupancy themselves.

Example : 2 VT heating zones with weather compensation only - no zone influence

Occupancy state of both Secondary Circuit controllers is determined by occupancy status of Zone controller. Zone heating demands are ignored. VT flow setpoint is determined by weather compensation only. CT setpoint is calculated by adding LOSS parameter to VT flow setpoint.

C) Occupancy determined by external Volt-Free contact

Occupancy state of the Secondary Circuit controller can be influenced by an external VFC input.

Some secondary CT Circuits contain loads that are not controlled by SeaChange modules; because the SeaChange system is inherently demand driven, it is important that the energy requirements of all loads is accounted for, otherwise loads may not receive Hot or Chilled Water services when they need them.

To accommodate legacy systems with existing controls, the Secondary Circuit Controller can be driven into an Occupied State by applying a Volt Free Contact to terminals “3-4”. If the parameter INMD is set to 3, a contact closure will force the Controller into Occupation. INMD = 1 is an “AND” function and INMD = 2 is an “OR” function with the functions described in A) and B) above, so a mixture of SeaChange Consumer or Distributor module loads and non-SeaChange loads can be accommodated.

Demand Control

The Setpoint used by the Secondary Circuit Controller to control its own valve is also used as a Demand signal which needs to be sent to the module controlling the Primary energy feeding the Secondary Circuit. This is usually a Provider Module (e.g. Boiler or Chiller Controller) but could also be another Distributor Module (i.e. Secondary Circuit Controller) in which case the demand is sent as a % rather than a setpoint, and HTCT should be set to 0.

Example : District Heating application with CT Secondary Circuit controlling high temperature hot water primary valve to non storage calorifier. VT Secondary Circuit sends demand as % to CT controller.

The Secondary Controllers will now decode received Constant Temperature demands by converting them into a percentage demand and then prioritising this demand along with any other demands which are being received. This has been included so that the Controller still operates even if the sending controller has incorrectly been setup to send a Constant Temperature setpoint. This practise should be avoided wherever possible because the rescaling takes extra processing time and will limit the demand fan in which the controller can handle. HTCT setting in any controller should only be set if the target Controller is a Boiler and the Heat is being taken off the Primary of the Boiler.

Temperature Control

A) VTC - Variable Temperature with Weather Compensation (heating only)

The VTC version of the Secondary Circuit controller controls water temperature for the VT circuit according to a Weather Compensated setpoint; this is further modified by demand signals from the Zone Controllers to produce the Heating setpoint. The current setpoint can be monitored by parameter REQD.

Zone Trim and Adaption

Zone Controllers (or other Consumer Modules) produce demand signals varying between -100% (full cooling) and +100% (full heating). The VTC Controller adapts the Weather Compensation to “learn” the building’s characteristic by keeping the highest-demanding Zone device at a +50% demand level during occupancy.

If the demand level is above or below 50%, the Weather Compensated setpoint is modified by two effects in the Fuzzy Logic Control loop; the trim effect will rapidly raise or lower the setpoint to take care of short-term changes in load.

The adaptive effect will additionally raise or lower the setpoint if the “error” from the 50% level is sustained over a long period, which represents the control system “learning” the thermal characteristic of the building.

The effects of these adaptations can be limited; the maximum excursion from the Weather Compensated setpoint caused by their effects can be set on two Configuration Parameters: TRNG sets the maximum trim effect, and CRNG sets the maximum influence of the adaptive effect.

These setpoint calculations remain active when the Controller is in an Occupied state (see Occupation State, earlier in this document). At all other times, it will control to its non-occupied setpoint, FRSP.

Pump Control and Demand

The Default settings of MIND, MNAV and MNOC will cause the heating to shut down when all Zones are satisfied. This is best practise for energy efficiency; however, if space temperature sensors are badly sited or not representative of the entire zone temperature, it may be necessary to disable this feature. If it is desired for the Heating pump to run at all times during any Zone’s Occupancy period, then MIND, MNAV and MNOC should all be set to zero; energy losses due to unnecessary circulation of water or overheating of parts of the zone may result, however.

Other Features

FLAV defines the unadapted Weather Compensated setpoint at 10 Deg C outside temperature
MAXF is a limit to heating flow temperature (useful for limiting the flow temperature in underfloor heating applications), and also defines the Weather Compensated setpoint at 0 Deg C Outside temperature.

SMRT defines a summer cutoff temperature; when the outside temperature exceeds this value, the Controller will be forced into non-Occupancy.

B) VTU - Variable Temperature with no Weather Compensation

The VTU Controller controls water temperature for the VT circuit according to a setpoint which is adjusted by demand signals from the Zone Controllers (or other Consumer Modules) registered to it.

Zone Trim

The maximum demand from all of the Zone Controllers registered to the Secondary Circuit Controller is used to rescale the setpoint for the VT temperature between MAXF and MINF. Thus if the maximum demand from the Zones is 100%, the VT setpoint will be set to MAXF; if the maximum demand is low, just a few percent, the setpoint will reduce to approach MINF. Cooling versions work in an inverted sense.

If the parameter SPTY is changed from its default value of 1 to 2, this will cause the average value of Zone Demands to be used instead of the maximum.

These setpoint calculations remain active when the Controller is in an Occupied state (see Occupation State, earlier in this document). At all other times, it will control to its non-occupied setpoint, FRSP (or NOSP for Cooling versions)

Pump Control and Demand

The Default settings of MIND, MNAV and MNOC will cause the Secondary Circuit to shut down when all Loads are satisfied. This is best practise for energy efficiency; however, if space temperature sensors are badly sited or not representative of the entire zone temperature, it may be necessary to disable this feature. If it is desired for the Secondary Circuit pump to run at all times during any Consumer Module’s Occupancy period, then MIND, MNAV and MNOC should all be set to zero; energy losses due to unnecessary circulation of water or overheating/cooling of the space may result, however.

C) CTU - Constant Temperature

The CTU Controller controls to a Constant Temperature Setpoint, set on parameter MAXF (MINF is not used in this application) when the Controller is in an Occupied state (see Occupation State, earlier in this document).

At all other times, it will control to its non-occupied setpoint, FRSP (or NOSP for Cooling versions).

The Default settings of MIND, MNAV and MNOC will cause the Secondary Circuit to shut down when all Loads are satisfied. This is best practise for energy efficiency; however, if space temperature sensors are badly sited or not representative of the entire zone temperature, it may be necessary to disable this feature. If it is desired for the Secondary Circuit pump to run at all times during any Consumer Module’s Occupancy period, then MIND, MNAV and MNOC should all be set to zero; energy losses due to unnecessary circulation of water or overheating/cooling of the space may result, however.

Temperature Sensors and Inputs

Depending on the application, one or more sensors can be used for temperature control. The standard flow temperature sensor is connected to input ‘temp b’ on terminals 5 and 6. The optional input ‘temp a’ on terminals 3 and 4 can either be used for a return temperature sensor or alternatively a VFC input. The behaviour of the two inputs are configured by parameters SACT and INMD.

Two Temperature Sensors

Flow Sensor and external Control Status input

Flow Sensor and external Alarm Monitor input

Sensor calibration

The resultant control sensor value (flow sensor input alone, or flow and return sensors combined as set by SACT) can be adjusted by calibration parameter SCAL.

Operation with no sensor fitted

Like many SeaChange Modules, the Secondary Circuit Controller can work with or without a Temperature Sensor; the act of connecting the sensor (or not) determines in which mode the Controller will work.

With a sensor connected, the Controller will use its internal Fuzzy Logic control loop to control its outputs according to the appropriate setpoint. This is called Closed Loop control.

If no sensor is fitted (or the sensor is disconnected) the Controller will effectively bypass its control loop, and the Zone Demands (either Maximum, or Average Demand according to the value of SPTY) will be used to drive the valve directly (thus if the Zone Demand is 70%, the valve will be driven to 70% open). This is called Open Loop control.

Sometimes, Open Loop operation is required but the sensor is needed for monitoring (for instance, if the Secondary Circuit Controller was being used to enable a Chiller with its own temperature controls, then the Controller’s own control loop would need to be disabled). In these cases, setting parameter CMDE = 0 will disable the control loop, allowing Open Loop operation, whilst leaving the sensor connected for monitoring purposes.

Submodules

The Secondary Circuit controller can have up to 2 actuator or changeover submodules registered to it, and also up to 8 condensation sensors sharing a common address.

Condensation Sensor

Intelligent condensation sensors can be registered to cooling versions of the Secondary Circuit controller. The state of the condensation sensors can be monitored on input I4 and if the alarm mode is set, can be used to generate alarms. Up to 8 sensors can be registered, sharing the same cloned address.

When the sensor detects that condensation is present, the cooling demand is progressively reduced to zero. Cooling control recovers a few minutes after condensation is no longer present.

Two Pipe Systems - (Feature added from issue 4d1)

Two secondary controllers, one heating and the other cooling to be used to control a common two pipe heating and cooling system. This requirement may be found in some Natural Ventillation applications. Two new features have been included from version 4d1 to allow this (see History section for further details).

Transmission of own medium temperature

The heating secondary controller sends its measured value to all registered consumer controllers which allows them to decide whether the system is in heating or cooling mode. The consumer modules must have code which supports this feature (Zones & Fan Coils 4d1 onwards, AHU's 4c1 onwards). The associated cooling controller must have its temperature sensor connected to the same place as the heating sensor.

Interlock between Heating and Cooling to prevent both operating at the same time

The Knob ICSC Interlock Cool source (IHSC on cooling controller) where the cool source number of the other secondary controller is set. The knob IHSC must be set on the cooling controller to point to the Heating secondary controller. With these settings made the controller which has the highest demand will override the other controller off. This can be seen by looking at I3 CLOR Cooling OveRride (or HTOR Heating OveRride on cooling controller).

Frost Protection

The Heating versions of Secondary Circuit Controller have their own Frost Protection Setpoint, FRSP, which if violated, will cause the Controller to run its pump and send demand signals to its Heat provider (Cooling versions have a similar over-temperature setpoint NOSP). Additionally, if the Boiler Controller (which is responsible for global Frost Protection in a Seachange system) enters Frost Protect mode, the Secondary Circuit Controller will run its pump and open its valve to 50% to allow water circulation using FRPT.

Pump Control Interlock

Twin Pumpsets (using Changeover Submodule)

The Secondary Circuit Controller outputs can be interlocked with the status of pumps controlled by a Changeover submodule.
When the interlock pump switch ILKP = 1 the Secondary Circuit controller ensures that flow has been established by the Changeover Submodule before allowing any of its outputs to be energised. Setting ILKP = 1 will automatically set ALRM to 1 or higher.

If subsequently both pumps fail, the Secondary Circuit Controller will shut down and generate a PMPF pump failure alarm. The Secondary Circuit controller will remain disabled until the Secondary Circuit Controller Override button is pushed, or ILKP is reset.
When the established flow switch ESTF = 1, the Secondary Circuit Controller will wait for pumps to run for the minimum on time before outputs are energised.

Single Pump (using Occupation Output)

When a single pump is driven from the occupation output, INMD = 5 and ALRM = 2 or 3, the control outputs are disabled if the pump readback signal goes into alarm. The pump remains disabled until the readback signal is fixed, the Override button is pushed or the ALRM parameter is set to zero.

The pump (occupation output) can also be set to delay its start after the heating/cooling outputs have started, or to run on after they have shut down, using the configuration parameters HDLY and CDLY. A negative value will start the pump the defined number of minutes after the heating/cooling drivers have been enabled; a positive value will cause the pump to run on after the heating/cooling drivers shut down. This feature does not apply to the operation of Changeover Submodules which have their own run on feature built in.
The interlock features can be particularly useful when controlling packaged chillers.

Alarm Handling

The Secondary Circuit Controller may be set to ignore alarm conditions, report them to a SeaChange Doorway Supervisor (either locally connected to the system, or via an autodialling modem), or to both report alarms and take some control action. The ALRM parameter is used to select the desired Alarm Mode.

The Secondary Circuit Controller generates an alarm if the sensor fails and also if the external alarm input is used. The sense of the alarm input can be set by parameter ALST.

The Secondary Circuit Controller may be set to respond to the STOP System Stop Alarm which is generated by another Controller; this can be used to shut down the entire control system, or parts of it, if a particularly critical event occurs. See Boiler Controller datasheets B1 or B2 for more details about the System Stop Alarm.

Alarm codes as they appear at Doorway Supervisor and InSite tool:

Local Indication of Alarms

Alarms are indicated by red flashing of the Temperature Indicator (Thermometer) LED, if the alarm results in a control action (e.g. shutting down the pump/valve). If ALRM is set to 0 (ignore alarms) or 1 (report alarms to supervisor only) then no control action will be taken, and the thermometer LED will not flash.

Commissioning

Setup Mode : Timing Characteristics of Output Channels

It is possible to set the stroke time (for Raise/ Lower type Actuators) and the minimum on/off time (for Time Proportion type Actuators) using pushbuttons.

Raise/Lower Types - Setting Stroke Time

1. Hold down Select until Temp lamp flashes
   Temperature indicator will flash red at one second intervals.
   Release select button; output B will energise to close valve.

2. When valve is closed press Select
   Temperature indicator will flash green and output A will energise to open valve. The controller is now measuring the stroke time.

3. When the valve is open press Select
   Flashing will stop and stroke time is now set and stored in non-volatile memory. This time will be retained until the procedure is repeated.

Note: if a Stroke Time of less than 30 secs is set using pushbuttons then the setup process is aborted. Temp indicator flashes amber rapidly for 5 secs indicating an invalid period. This allows checking of wiring without affecting Stroke Time setup. Stroke Times less than 30 secs can be entered manually via Zone Controller or InSite tool.

TP Types - Setting Minimum Time On/Off

1. Hold down Select until Temp lamp flashes
   Temperature indicator will flash green at one second intervals and relay A will energise.
   Release select button.

2. When minimum on/off time has elapsed, press select
   Flashing will stop and this time will be set and stored in non-volatile memory. This time will be retained until the procedure is repeated.
   Note that the full TP period will be 10 times this value.

The times can also be viewed and changed using parameters HPRD (heating) and CPRD (cooling).

Manual Override

Allows the outputs to be exercised during commissioning and maintenance activities. Holding the override button pressed until the Status Lamp flashes green will cause the controller to be switched from automatic control to Override Mode. Subsequent pressings of the manual override button will cycle through the available Override modes.

1. Hold down Override until Status lamp flashes
   Controller changes to Override Mode and becomes Occupied, controlling to current Occupied Setpoint.

2. Press Override again
   Controller changes to Manual Mode and output is set to 100% heating.
   Temperature lamp shows red.

3. Press Override again
   Controller changes to Manual Mode and output is set to 100% cooling.
   Temperature lamp shows amber.

4. Press Override again
   Controller cancels Manual Override and reverts to automatic control.

As this feature does not time out, care should be exercised to ensure the module is returned to the automatic mode on completion of the commissioning or maintenance activities.

Occupancy Override can also be achieved via Doorway and InSite; using AUTO and OVRD monitoring parameters. The status lamp indication shows a different sequence.

Override from Off to ON : Status lamp flashes long ON, short Off
Override from ON to Off : Status lamp flashes long Off, short ON
See our ‘Design Guide’ publication for details of the Override features.

Registration

Registration is the simple process by which logical connections are made between Controllers in a SeaChange system; it is done during commissioning and involves pressing buttons on the Controllers in a specific sequence.

For further details of the registration process, see our ‘Design Guide’ publication.

Address Allocation and System Housekeeping

Like all SeaChange Controllers, the Secondary Circuit controller must be registered with other modules in order to create a working system. During the Registration procedure, the address of each Controller is allocated by the module that contains System Housekeeping. Check that you have an appropriate System Housekeeping Module; see our ‘Design Guide’ publication.

Interconnects

The Secondary Circuit controller may receive signals from a Zone Controller or other Consumer module, either by Zone Energy Demand or Zone Occupancy Demand signals (see Occupation State section). It may also send signals to other modules (e.g. a Pump Changeover submodule when the controller’s secondary circuit has a twin pump set).

These Interconnects are put in place by Registration; again, see our ‘Design Guide’ publication.

Options and Product Codes

Secondary Circuit Controller for Temperature Control

VTC / DIN / 3T / [driver option] (heating versions only)
VTU / DIN / 3T / [driver option]
CTU / DIN / 3T / [driver option]

Driver options

VTC / DIN / AOP / [driver option] (heating versions only)
VTU / DIN / AOP / [driver option]
CTU / DIN / AOP / [driver option]

Driver options

SC Controls Ltd

PO Box313
Wadhurst
East Sussex
TN5 6JL

phone 08707 606040
fax 08707 606041
e-mail seachange@sccontrols.co.uk
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