Software issue DHW Controller 3c2

General

This is the first issue of the new range of DHW Controllers. These are now quite similar to Zone Slave Controllers. The slave modes have been changed, they now support occupation time slaving , setpoint supervision from a Zone Controller or Occupancy control from one or more Zone Controllers..

The configuration variable structures have been upgraded to also store the units of the parameters. This now means that temperature parameters can be displayed in C or F on Zone Controllers ZON3c1 onwards. These changes are required for the USA market.

The major change is that this range now uses the 'universal driver' code which means versions are available to run on all the current hardware platforms, note this means that you can now run DHW code on a Boiler board with six relay outputs.

Hardware requirements

Control Modes

The control mode is selected using SPTY configuration variable.

1. Occupation times slaved from a Master Zone Controller (default). The start and stop time for the DHW controller can be modified with respect to the times from the zone controller using AJST and AJSP config variables, see later.
2. Setpoint slaved from a Zone Controller which must be software issue 3c6 or later.
3. Occupancy controlled by one or more zones registered to the DHW controller. The Zone Controllers must be software issue 3c6 or later.

For modes 0 and 1 the Master Zone Controller is put into config mode and the DHW controller is registered as a slave by pressing the registration button. The Master Zone Controller will display SLVE 2 etc to show the slave link has been made. For mode 2, register the DHW controller to the Boiler then place it in config mode. Press the registration button on all zones which need to be linked to this DHW controller.

This version makes it possible to set an Occupation link from this DHW controller to another controller which supports Occupation links, e.g. an AHU controller or another DHW controller. To link to another DHW controller, at present this must be done manually by setting the OCDS config parameter to 100+zone number of the target DHW controller. So if the target DHW controller is zone 6, set the sending DHW controller OCDS to 106. The target DHW controller must be in control mode SPTY 2 to act on the Occupation network variable.

Immersion heater Control

The second driver channel, usually used for cooling, is used to control the Electric Heater. If this option is not required set the driver type CTYP to zero.

The Immersion heater will be used when the Outside Temperature is above the Summer Temperature SUMR AND the flow temperature from the appropriate heat source is below the Low Flow temperature LOFL.

The immersion is also used to 'boost' the DHW recovery time if after 15 minutes the Boiler Flow temperature is not higher than the DHW temperature and the DHW control loop is still calling for maximum heat. Boost is disabled if the Outside temperature is above the 'summer temperature'.

Valve Mode

The heating output can be further controlled using the configuration variable VMDE valve mode which has three settings

1. DHW valve stays closed until boiler flow temperature greater than current DHW temperature.
2. boiler flow temperature ignored, default setting
3. Designed for systems where the DHW is heated from a Variable temperature circuit, if the VT temperature is higher than the DHW temperature it is used otherwise the water circuit is closed and the Electric heater used. Note set heat source to zero for this option because it is not appropriate for the DHW demand to influence the Boiler Controller.
   

Pump Control

The pump is controlled using the third driver, FTYP etc and can be made to run on or start after the heating is applied by setting HDLY. Negative values for HDLY will start the pump the defined number of minutes after the heating driver has been enabled, positive values will cause run on after the heating output shuts down. If the immersion output is used CDLY is used to set the pump characteristics to be used with the electric heater. If OCCO is set then the pump will only run during the Occupied period.

Optimum Start/Stop

These routines have been extended to cope with heating or cooling starts( DHW does not use the optimum cooling but it's there in order to standardise the code), maximum optimum start time MXOS applies for heating or cooling starts. The allowable error (droop) to terminate Optimum start can now be set on a config variable OPTE.

The Optimum off routines have been re-instated and improved. Maximum Optimum Off time MXOF applies to cooling or heating conditions. When Optimum off is invoked the control deadband is increased to the 'standby setting' see SBDB. If the control calls for heat or cool before the end of occupation then the optimum off constant is modified accordingly, otherwise the actual temperature at the end of occupation is used to adapt the optimum off constant. Optimum off can be disabled by setting MXOF to 0. During Optimum off the controller remains occupied from the point of view of any downstream plant so Air plant will normally continue to run.

Fabric (Freezing) Protection

A new config variable has been added which allows a more rigorous frost protection routine to be used this is the same as the fabric protection routine used on Zone Controllers. If the DHW measured temperature falls below the non-occupied setpoint then the controller switches to 'fabric protect mode' the controller becomes 'occupied' . The controller remains in this mode until the temperature has risen by the amount specified by the new config variable FRSE fabric rise, at which point the controller reverts to non-occupied. This allows the stored water temperature to be raised to a new safe level in one operation and then the heating plant shut down again rather than have a large number of small heat inputs to maintain the non occupied setting which might result in the main plant running continuously at a low level. If FRSE is set to zero the controller will control to the non-occupied setpoint as before.

Frost Protect

The DHW Controller can now be made aware of the Frost protection status of the Boiler (or other heat source). If the Zone Controller alarms are enabled (ALRM>0) then the Controller will receive FRST alarms from the Boiler. If the Boiler is in Frost protect this is communicated to the DHW controller which will open any actuators to 50% (see also config variable FRPT) . The DHW controller remains in non-occupied so this mode can be distinguished from Fabric Protection.

Configurable Plots

The code which supports configurable plots has been included in this issue of the DHW Controller. This works the same as for the AHU controller. This has meant that the sensor order has been changed so that the first two sensors have plots

S1 HW T DHW Temperature

S2 DMND Control output 0 to +100 heating

S3 HWSP Current setpoint

Alarms

The DHW controller supports sensor fail SENF alarm, this is raised if the DHW sensor fails. The STOP alarm is also supported provided the Alarm mode is set correctly. See config variable list.

Alarm mode and Alarm State config variables have been added to the config variable list.

Additional config variables

Override extension time

A new config variable XHRS allows the 'out of hours' run time to be configured. This parameter can be set from 0.0 hours to 8.0 hours with a resolution of a tenth of an hour. The default for DHW controller is 2.0 hours.

Thermostat mode

When controlling Calorifiers which have a large thermal reservoir it might be desirable to control using ON/OFF thermostatic control, this can be selected by setting config variable STAT to 1. In this case the output will switch on if the temperature is less than setpoint-UNDH and will switch off when it reaches setpoint+OVRH.

Start/Stop adjustments

When slaving times from a master controller it is sometime useful to vary the DHW times, either earlier or later than those set on the master. In schools this is often required for cleaners or kitchen staff. The start time can be adjusted plus or minus 10 hours with a resolution of 6 minutes using AJST. Similarly the stop time can be adjusted with AJSP.

Frost Protection

This is defined with a config parameter FRPT and it defines the controllers action when it receives a 'frost alarm' from the boiler controller.

1. no action (default)
2. heating output to 50%
3. heating output 50%, run pump (fan)
   

Driver Options

The universal output driver is used for this product, the driver characteristics are setup using six driver configuration variables These have been placed in a new 'fixed block' starting at config 150. Currently supported driver types are:-

For full details on the driver options click here

The Cooling output is used to drive the immersion heater or any other type of auxiliary heat. The config labels are left the same so that the production setup software does not get confused.

The Fan type parameter FTYP is used to control a pump, the interlocks HDLY and CDLY are used to determine pump on delays or pump run on times for the heating and electric outputs. The config variable OCCO can be set to only allow pump operation during the occupied period.

Example combinations with DHW-DIN-RLY (or DHW-DIN-TOP)

Sub module registration

Will support registration of up to a total of 8 Actuators, Actuator Drivers or Pump ChangeOvers just like a regular Zone.

Doorway codes

Controllers are addressed with [Zn] where n is the Fan Coil Zone number 1-200.

Sub modules are addressed as follows

Actuators [Z1Am] m=1 to 8

Item codes follow the normal conventions