Software issue VAV Controller 3d1

VAV General

The VAV controllers are registered in exactly the same way as Fan Coil controllers. For the time being they are considered to be a special type of Fan Coil controller.

In order to talk to VAV controllers with Doorway the SLT needs to be upgraded to issue 3a5 or later. It is possible to use the [#] addressing method (last service pin pressed) if the SLT available is not 3a.

Zone controllers used with VAV's must be ZON3b1  or later running on latest large memory hardware, earlier versions will not recognise FCU controllers for registration.

VAV modes of operation

The registration procedure for all modes is the same as for registering Slave Zones to a Master Zone. Put the Master Zone Controller into config then register each VAV in turn. The zone will report SLVE 2 (for VAV 2, 3 for VAV 3 etc.) The Master Zone will be set automatically  to SPMD 3 when a Fan Coil is slaved to it, to allow the Fan Coils to receive the Setpoint and Occupation information.

The VAVs are put into the same group as the Master Zone, any number of VAVs can be linked to a single Master.

Return Air Control

The Return air sensor must be fitted and the SPTY must be set to 0 or 1.
Note the Occupation and Setpoint data is only updated every minute so be patient when commissioning, operationally this is OK because the change will normally come from the Optimum start routines which are checked every minute. If the setpoint is changed on the Master Zone (with the knob) the new setpoint is sent straightaway.

Occupancy control SPTY 0
The VAV can be left to control from it's own setpoint but Occupancy is controlled from a single Zone controller by registering the VAV to the Zone. The VAV will control to a constant Return air setpoint regardless of the heating or cooling demands from the Zone.

Setpoint supervision SPTY 1
This is the default mode of operation. The VAV(s) will control the return air (during optimum start and occupation) to the setpoint defined by the Zone Controller.
The VAV Return Air setpoints can be individually adjusted using the SPTR setpoint trim config variable to adjust for local conditions.

Slave Mode

The Return air sensor is not fitted. The mode must be set to (SPTY) 2.

Box volume slaved to Zone or master VAV heat and cool demands SPTY 2

The Heat or Cool demand from the Zone will be used to directly control the output stages, this mode is also used to 'slave a VAV' to another VAV (or FCU).

Automatic selection of Heat or Cool mode

If the controller is regulating the supply of air from a plenum with a single damper (RiverMill House) the temperature of this plenham can be reported to the controller and the damper prevented from opening if the plenham temperature is not suitable for the control mode currently required. For example if the plenham is hot but the controller is being asked to cool the room. The Plenham temperature is compared with the current space setpoint setting (SPFC+/-SPDB/2) and if the temperature is unsuitable the damper is maintained at the minimum volume (MINV fresh air) setting. This mode can be selected by setting the Re Heat REHT config variable to -1.

VAV operation with remote User switch/Trim Pot or interlock

The supply sensor can be replaced by a switch which when made will force the FCU to Occupied. On FCF or BLR boards the external connection is made to 'input a', thus retaining the use of the supply sensor.
This is achieved by adding an extra config variable input mode INMD. The following values are supported.

0 normal operation input measures Off Coil temperature
1 Occupied is External AND normal occupation (window contact)
2     Occupied is External OR normal occupation     (outside normal hours)
3 Occupation controlled by external signal only
4 Input used as an external alarm, alarm state defined by ALST

If the switch is wired in series with a 10K resistor and a 10K potentiometer Occupied/ Non occupied plus a 5 degree trim (operational only whilst occupied) is possible. The trim is slightly non linear (the applied resistance is affected by the parallel resistance on the board which helps linearise the thermistor when fitted, mechanical centre position of the pot gives -0.7C) The zero point can be adjusted to give the correct (0 trim) by backing off any error using the software trim SPTR. Suggest pot is marked Hotter/Colder or +/- !
A resistance between 0 and 20K ohm will be considered to be Occupied, non Occupied is guaranteed for resistance values above 100K. The voltage generated by the pot will be converted to a setpoint Trim  only for control modes SPTY 0 or 1

VAV Master Slave Control

This allows one 'master VAV (or FCU)' to provide the Return Air control for a large space and to send its HeatOp and CoolOp outputs to one or more 'Slave FCU's'

The Master must be operating in mode SPTY 0 or 1, i.e. must be measuring and controlling Return temperature.

The 'Slave' must be operating in mode SPTY 2. The registration process involves putting the master into config mode and then pressing the registration button on all the 'Slave FCU's'.

The Slaves are put into the same group as the Master VAV, any number of Slaves can be linked to a single Master.

If a Slave VAV is subsequently linked to a Zone Controller the link to the Master VAV will automatically be broken.

Setpoint Supervision within a group of VAVs

Any VAV can act as a source of setpoint (and occupancy) information for a group of VAVs which are all controlling to their local Return Air sensor.
This would be useful when one VAV has a local Trim Pot (or Occupancy switch) and the same setpoint is required on other VAVs feeding the same area of the building.

Put the 'master' into config and 'slave' the other VAVs. The Slave VAVs will receive the mid point setpoint (C1 SPFC plus any external Trim) of the Master, local additional trim can be applied to each VAV using SPTR.  To maintain balance amongst the VAVs the setpoint deadband SPDB should be the same in all units within the group.

In this way a Zone Controller can provide Setpoint and/or Occupancy information to a 'master VAV' within each separate space, these VAVs can have local User Adjustments (for the cheapskates who won't buy Zone Controllers) or Occupancy overrides, these modified conditions are then sent to all VAVs within the area.
There are no limits on the number of VAVs which can be slaved to a 'master VAV'. A Slave VAV can also be a 'master' to a further group of VAVs, although this only makes sense if these VAVs are operating in mode SPTY 2;either Off Coil only control or in Driver only mode (no sensors fitted).

Fan Speed Control

The controller will automatically control fan speed, if the multi-speed fan driver is used. If either the heating or cooling demand is greater than 90% for a period longer than FPRD (seconds/10 to match other periods) then the fan speed will be incremented up to the next speed. If both the heating and cooling demand is less than 10% then the Fan Speed is reduced after the same delay time. While occupied the controller will maintain a minimum of Fan Speed 1.

Provision is made for the fan speed to be controlled from a network variable (nviFanSpeed), from a (hotel style) zone controller for example, if this network variable is non zero then this will override the automatic fan speed control.

Alarms

The FCU controller supports sensor fail SENF alarm, this is raised if the Return Air sensor fails and the FCU is in a mode which requires the Return Air temperature. The Input Mode can also be set up to generate an alarm for either a short or open circuit on terminals 'temp a', see later.

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

Alarm State determines which input state 0 or 1 is considered to be the alarm condition when using external input for the alarm as set by INMD.

Hardware

Driver Options

This controller uses the universal output driver version 3d. which allows a range of output possibilities, although the VAV controller is primariliy designed to run on an AOP board other hardware options are possible.

The controller defaults to two analogue outputs, channel one for heating  and channel two for box volume. The actual voltage levels which represent 0 and 100% can be set using  MXVA, MNVA, MXVB, MNVB.

The maximum and minimum Box volumes can be set using MAXV and MINV.

Re Heat

If the VAV needs to control a re-heater when in heating mode, this is activated by setting the config variable REHT to a value in the range 1 to 99%. The value set determines the maximum box volume when in heating, this allows the heating mode to be more energy efficient by heating a smaller volume of cold air. When using the Re Heat function the reheater is connected to the Heating output HTYP and the Box volume control is connected to the cooling output. Cooling operates by varing the air volume between minimum volume and maximum volume, heating varies the heating output from 0 to 100% and the volume output from minimum volume to the re heat volume REHT. 

Interlocks

These have been changed to a new more flexible approach. A single parameter for each driver type is provided which sets up the on delay or run on time for the fan or pump.

HDLY

• if negative sets the on delay in minutes for the fan or pump
• if positive sets run on time in minutes for fan or pump to run after heating shut down

Typically negative values will be used for wet batteries to provide start up protection against frost and positive (run on-) values would be used with electric heating batteries.

The same features are available for cooling using CDLY.

The selection of OCC or OSS is now made by setting OCCO to 1 on controllers where the control is only required when the building is in occupation. The default is for control during OSS and OCC.

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.

VAV Plots

There are three plots setup as normal on the first three 'sensors'.

Plot 1 Air Flow 0-100%
Plot 2 Return Air temperature
Plot 3 Heat/cool output -100 to +100 (negative for cooling)

The plot routine has been enhanced and the plotting period is now selectable see configurable plots for details.

VAV sub module registration

Will support registration of up to 8 Acuators, Acuator Drivers, Pump ChangeOvers just like a regular Zone. This is not supported in version 3ax 0006 issue D boards due to lake of memory.

Doorway codes

VAV Controllers are addressed with [Zn] where n is the VAV Zone number 1-200. [Fn] is also supported.

Sub modules are addressed as follows

Actuators [Z1Am]  m=1 to 8

Item codes follow the normal conventions

Configuration Variables see table.