This version extends the AHU capabilities to include Humidity Control particularly
De-Hum control. The control outputs to the internal driver can also be rescaled to allow
some of the heating or cooling duty to be done internally and some to be achieved
externally with extra Actutator style modules. This has been included to allow Dessicant
Cooling AHUs to be supported but could also be useful in some multi stage AHU situations,
e.g. Heat Pump plus electric boost.
The AHU controllers are registered to a Boiler Controller, this must be at least BLRxx3a5
Zone controllers used with AHU's must be ZON3a or later running on latest large memory
hardware.
A System Master version of code is available AHUSM3d, this provides a real time clock and
registration of Zone Controllers(ZON , ZSL and FCU), DHW controllers (total100), SLTs (8),
Air Handlers (50).
Note Heat and cool sources are NOT included because if you need these then you will need a
Boiler Controller or a Floor Controller. All other features described below apply equally
to the AHUSM version. If a System Master version is used it is always AHU 1.
The Fan Fail alarm will be raised if the Alarm Mode (ALRM) config variable is set to 2
or 3. If in mode 3 the AHU will be shut down and the AHU will not run again until the
alarm has been cleared manually by pressing the override button. The same action will take
place if Fan Changeover modules are registered to the AHU and a valid signal is not
received from the Air Flow switch.
This AHU failure mode can be reset by setting switch 3 to OFF. The state of switch 3
reflects the current state of AHU failure mode.
The Return air sensor must be fitted and the SPTY must be set to 0 or 1.
Occupancy control SPTY 0
The AHU can be left to control from it's own setpoint but Occupancy control from one
or more Zone controllers can be achieved by putting the AHU into config and pressing the
registration button on all appropriate zones. The zones will report OCDS 51 (for AHU 1, 52
for AHU 2 etc.) The AHU will control to a constant Return air setpoint regardless of the
heating or cooling demands from the Zones.
Setpoint supervision SPTY 1
One Zone controller controlling many AHU's. For this mode put the Zone controller into
config, then register all the AHU's for this zone. Zone will report SAHU number as slave
link is setup. This is the default mode of operation. The AHU(s) will control the return
air (during optimum start and occupation) to the setpoint defined by the Zone Controller.
The AHU Return Air setpoints can be individually adjusted using the SPTR setpoint trim
config variable to adjust for local conditions.
The Return air sensor is optional except if required for other functions e.g. night
purge or free cooling using the additional Mixing Box Controller. The mode must be set to
(SPTY) 2,3 or 4.
Supply Temperature scheduled to Heat and Cool demands from multiple Zones SPTY 2
Designed to be used when a central Tempered Air plant supplies fresh air to a
multi-zone building.
The registration procedure is to put AHU into config then register all subservient zones ,
ZON LCD, ZSL LCD, ZSL RLY, are currently supported, the ZSL version of the Fan Coil will
also be able to be registered in this way. ZON LCD's will report HSCS 51,CLSC 51 for AHU 1
etc. as the zone is registered. Pre issue 3a zones only support Heat/Cool sources up to 20
so cannot be used.
The setpoint for the Supply Air control is calculated from the MAXS, MINS config limits
using the heating and cooling demands. The combined demand (heating-cooling) is used to
calculate the supply setpoint in the range -100% to +100% for MINS to MAXS. In this way
the tempered air supply can be made to assist the warm up or cool down of the building.
Supply Temperature control, Occupancy from one or more Zones SPTY 3
This mode allows the AHU to supply fixed temperature air when any of the registered
Zones are occupied. The Zones provide this information using an additional network
variable thus allowing the Heat/Cool demands from each zone to be passed to the relevant
main plant for the primary Space temperature control. The AHU is put into config and the
zones are registered to it, the Zone will confirm the connection by displaying OCDS
(occupancy destination) 51 (for AHU1)
The Supply air setpoint is set on Knob 1 (or config C1) and is the midpoint setpoint. The
deadband between heating and cooling setpoints is set on config C2 SPDB.
Supply Temperature control, Occupancy from one or more Zones, setpoint supervised by a
Zone Controller SPTY 4
This mode operates as for the above mode SPTY 3 with the additional feature that the
supply setpoint can be made to track the setpoint of a particular Zone Controller. To
achieve this the zones are registered to the AHU as above, then the designated Zone is put
into config and the AHU registration button pressed to make the Setpoint supervision link,
the Zone will report SAHU 1 etc.
The AHU setpoint can be 'modified' with the SPTR setpoint trim config variable, this will
be useful if the AHU air needs to be say 1 degree too low so that the zone makes up the
correct space temperature with say perimeter heating, or where one Zone is used to set all
the AHU's in the building and they need to be individually trimmed to compensate for local
conditions.
Supply Temperature control, Occupancy and Supply setpoint from Master AHU Controller
SPTY 5 (SLAVE MODE)
In this mode the Supply Air setpoint being used in the Master AHU is sent to the
Slave. This setpoint can be 'modified' with the SPTR setpoint trim config variable to
compensate for local conditions.
The Return air sensor must be fitted and the SPTY must be set to 6 or 7.
Return only Occupancy control SPTY 6
The AHU can be left to control from it's own setpoint but Occupancy control from one
or more Zone controllers can be achieved by putting the AHU into config and pressing the
registration button on all appropriate zones. The zones will report OCDS 51 (for AHU 1, 52
for AHU 2 etc.) The AHU will control to a constant Return air setpoint regardless of the
heating or cooling demands from the Zones. The Supply control loops are not used the
output drivers are driven directly by the Return loop demands.
Return only Setpoint supervision SPTY 7
One Zone controller controlling many AHU's. For this mode put the Zone controller into
config, then register all the AHU's for this zone. Zone will report SAHU number as slave
link is setup. The AHU(s) will control the return air (during optimum start and
occupation) to the setpoint defined by the Zone Controller. The Supply control loops are
not used the output drivers are driven directly by the Return loop demands.
The AHU Return Air setpoints can be individually adjusted using the SPTR setpoint trim
config variable to adjust for local conditions.
If using one of the Control modes based on Occupancy, it is possible to prevent the AHU
from starting for Optimum Start or Fabric Protection, this would be appropriate for Fresh
Air plants which only need to run when the building is occupied. A config variable OCCO
(Occupation only) when set to 1 provides this feature. Otherwise the AHU will start for
all Occupancy states other than non Occupied. The associated Zone Controller must be
version ZON3b or later.
The 'spare a' input can be wired with a switch which when made will force the AHU to
Occupied.
This is achieved by adding an extra config variable input mode INMD. The following values
are supported.
0 normal operation 'spare a' ignored
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
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, the mechcanical 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.
This allows one 'master AHU' to provide the Return Air control for a large space and to
send its Supply Setpoint to one or more 'Slave AHU's'
The Master must be operating in mode SPTY 0 or 1, i.e. must be measuring and controlling
Return temperature. Also to prevent too much confusion in sorting out the logical links
the Master may NOT also be a System Master for registration purposes.
The 'Slave' must be operating in mode SPTY 5. The registration process involves putting
the master into config mode and then pressing the registration button on all the 'Slave
AHU's'. The Slave will be registered again flashing it's status led green as normal, then
after 5 seconds the error led will flash green to indicate the master ahu number.
The Slaves are put into the same group as the Master AHU, any number of Slaves can be
linked to a single Master.
If a Slave AHU is subsequently linked to a Zone Controller the link to the Master AHU will
automatically be broken.
Two new config variables define the De-Hum control, RHSP setpoint and RHDB deadband. If
the Humidity setpoint RHSP is non zero and a value for SpaceRH is being received from the
network then the De-Hum control will be active. When the measured Return Air RH is above
the RH setpoint plus half the RH deadband the Supply Cooling control loop setpoint is
forced down driving the cooling to full demand. The Supply heating loop remains active and
this will endeavour to maintain the required supply temperature.
When the Return Air RH measurement falls below the RH setpoint minus half the RH deadband
then the Supply Cooling setpoint is returned to its normal value.
A new configuration variable has been introduced which allows both the heating and the
cooling supply control loops to be active at the same time. This is useful if say the
cooling is by large DX stages and one stage provides more cooling than is required under
some conditions. If the config variable HeatCoolOK (HCOK) is set to a 1, the heating will
be brought on to maintain the required supply temperature even when the cooling is still
demanding. The deadband setting can be used to control the amount of overlap.
If the Outside temperature falls below the Frost setpoint (non occupied setpoint) Knob
2 (or config variable SPFR) whilst the unit is not running. The heater battery, if raise
lower, will be opened to 50% to allow water to circulate both the coil and the bypass. The
AHU will NOT start it's fans and it will NOT make heat demands to it's heat
source. This is because without the fans running the temperatures measured by these
sensors are likely to be unrepresentative of the building temperature and we do not want
the Boiler running unnecessarily. The Boiler/Heat Source will provide protection for the
water circuit as a whole.
When the AHU starts in Frost protection mode the heating battery, if raise/lower, will be
driven to 100% until the fans are started, this is because the supply temperature may well
be reading quite a high value due to heat build up in the AHU and might otherwise close
the heating valve during the start up sequence.
The AHU has a manual override feature which is useful for testing the operation of the
unit. This mode is activated by pressing and holding the override button until the status
light fast flashes to indicate manual mode. Initially the unit will change to an occupied
state and the fans will be activated. The unit will control to the default setpoint in the
selected mode.
Pressing the override button again will select 'full heat', not this is NOT a controlled
mode the unit will run at full heat until the manual mode is changed. The 'error' LED
shows red when this mode is selected. A sequenced output will stage up in sequence but
when the mode is changed will shut down immediately.
Pressing the override button again selects 'full cool', again this is not a controlled
mode. The 'error' LED shows yellow when in this mode. A sequenced output will stage up in
sequence but when the mode is changed will shut down immediately.
Pressing the override button again exits manual mode and the status LED will revert to a
steady value or extinguish if the unit is not occupied.
There are three plots setup as normal on the first three 'sensors'.
Plot 1 Supply air temperature
Plot 2 Return Air temperature
Plot 3 Heat/cool output -100 to +100 (negative for cooling)
This controller uses Configurable
Plots like most of the other SeaChange controllers.
The plots are now automatically re-scaled within the controller to achieve the best
resolution for the data recorded. This happens at the end of every 96 readings when new
maximum and minimum settings are calculated and also if a new value is outside the current
range settings.
This is achieved by adding an extra alarm mode. Setting Alarm mode [ALRM] to 5, Alarm
state [ALST] to 0 allows a closed contact on either of the alarm inputs to force the AHU
to occupied. This will only work if the AHU is set to one of the two 'local control modes'
SPTY=0 or SPTY=3
The Fan start is delayed as a function of the node address of the AHU. This provides a
10 second delay between AHU units on the same subnet. The maximum delay is 100 seconds.
A new config variable NTCL, night cool setpoint when set to a value above 0 enables a
night purge routine. This routine will bring on just the fans, and the Pre Heater if
needed, to cool and purge the building overnight. The conditions under which this will
happen are:
Once the purge starts it will run for at least the minimum run time of the AHU or until
the Return Air temperature is below or equals the night cool setpoint. The purge routine
will not recommence for at least an hour.
As a prelude to the Dessicant Cooling AHU it is now possible to re-scale the input to
the driver on the AHU. This allows the full range of the driver output to be achieved over
a selected range of the control loop output. The selected range is set up using config
variables HRMX, HRMN for the heating driver and CRMX, CRMN for the cooling driver. An
example will clarify it's use.
If HRMN is 0, and HRMX is 50, the internal heating driver will operate from 0 to 100% as
the control output varies from 0 to 50%. A range of actuator style modules will be
developed both for the Dessicant cooling application and for general use which will also
have input re-scaling, so in this example an actuator would be able to take up the control
output for the range 50% to 100% by setting it's re-scale parameters to HRMN 50, HRMX 100.
This allows a diverse range of heating and cooling resources to be applied in a
co-ordinated manner.
Note if a Preheater module is registered to the AHU the AHU will automatically change
to the interlocks appropriate to the Pre Heater.
Frost protection interlocks
If the AHU has a heat driver type of 1 (HTYP), valve driver, it is assumed that this is
driving a water battery. In this case the following protection applies
If a valid outside temperature is being received over the network or a sensor is connected
to sensor 4 (outside air) AND if a valid flow temperature reading is being received then:
If the demand is for heating and the fan is off. The fan will not start until
If either the outside air or the flow temperature is not valid then the fan will not start until
Once running the fan will be stopped if
If the driver is type 2, electric heating is assumed in which case the interlocks are
the same as for the cooling stages.
Cooling interlocks
The cooling outputs, any driver type, will not be enabled until the fan is running and
the fan will run on for the fan minimum run time MINR, default 5 minutes after all cooling
has been shut down.
AHC Air Handler cascade (x2)
AHP Air Handler Preheater (x1)
FCO Fan ChangeOver module (x2)
MXD Mixing Damper control (x1) MXDD or MXDA or Heat recovery HRC
HUM Humidifier (x1)
TRH RH sensors (x2)
Registration of Temperature and RH (TRH) sensors types
RHR Room or Space
RHS Supply
RHO Outside
is now supported
Air Handler Controllers are addressed with [An] where n is the Air Handler number 1-50.
Sub modules are addressed as follows
AHU Mixing Damper [A1M1]
AHU Preheater [A1P1]
AHU Fan Changeover [A1Fm] m=1 or 2
AHU Humidity [A1H1]
AHU RH sensors [A1Rm] m=1 or 2
Item codes follow the normal conventions
Major new issue see complete config tables.