The
AHU capabilities have been extended to allow multiple AHU's to feed one large
space where making individual return air measurements is impossible. Multiple
space temperature measurements are made using networked sensors, or Zone
controllers, these values are processed by a Monitoring Module (3a2) to produce
an average value which can be used as the return air temperature on the AHU.
When
using a Zone controller to perform the Space temperature control (AHU SPTY=2)
it is useful to be able to use the Zone controller temperature at the AHU as
the return air temperature, this then allows correct control of Mixing
Dampers. When registering a Zone in this mode the Zone temperature will
be networked to the AHU. A hard wired a return air sensor will take precidence
over the networked value.
The 4a version extends the AHU capabilities to include Humidity Control particularly simple De-Hum control and Close Humidity control when used with a Humidity controller. 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 AHUSM4a, this provides a real time clock and
registration of the following module types. This System Master can be used to register a
domain on a multi domain system.
| Zones ZON,ZSL,FCU,DHW | 100 |
| Supervisors SLT | 4 |
| Heat Source HSC | 5 |
| Cool source CSC | 5 |
| Alarm Monitor | 5 |
| Air Handlers AHU | 50 |
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.
SPTY 0 : Occupancy control
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.
SPTY 1 : Setpoint supervision
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.
SPTY 2 :Supply Temperature scheduled to Heat and Cool demands from
multiple Zones
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.
As
part of the registration process the Zone is setup to send it's Measured temperature,
the value being used for control which might be an average, max or min of two
sensors, to the AHU as if it were a networked sensor. The AHU uses this temperature
as a measure of Return Air temperature, this is critical if mixing dampers or
heat recovery modules are being utilised. If the AHU also has Slave AHU's which
it is supply setpoint supervising, this return air temperature is also
passed on to the Slave AHU's.
If it is practical to make a return air measurement then this should be done because this measurement will take into account heat gains through light fittings etc. A wired in sensor will take precidence over the networked value received from the zone.
SPTY 3 :Supply Temperature control, Occupancy from one or more Zones
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.
SPTY 4 :Supply Temperature control, Occupancy from one or more
Zones, setpoint supervised by a Zone Controller
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.
SPTY 5 :(SLAVE MODE) Supply Temperature control, Occupancy and
Supply setpoint from Master AHU Controller
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
master AHU can now be operating in any mode 0 through 4 and have slave AHU's
registered to it.
The Return air sensor must be fitted and the SPTY must be set to 6
or 7.
SPTY 6 :Return only Occupancy control
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.
SPTY 7: Return only Setpoint supervision
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 config variable OCDS has been added which allows the Occupancy state of one AHU to be passed to another AHU or indeed to any SeaChange module wich supports receipt of the Occupancy status (DHW for example). This might be used when a number of tempered Air plants needs to run if any zone in the building is occupied. The Occupaction status of the Zones can be collated by one AHU as normal then it's occupancy state can be passed to the next and so on. Simply set the OCDS parameter to point to the required device (AHU number plus 50) and ensure that the receiving AHU is operating in SPTY 0, 3 or 6.
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 1K resistor and a 10K
potentiometer Occupied/ Non occupied plus a 5 degree trim (operational only
whilst occupied) is possible. The lowest resistance equates to full negative
trim. 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 0.3C) 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 - 4, i.e. must be measuring
and controlling Supply 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 the master is receiving Return temperature from a networked
sensor (or Zone Controller) then the return temperature will also be available at all the
slaves.
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.
Note when operating in De-Hum mode the HCOK must be set to zero, the heating and cooling
operation is handled by the De-Hum control logic.
If Close Humidity control is being used then the AHU De-Hum features are not used and RHSP must be set to zero to disable them. In this case the Hum and De-Hum are controlled by the Humidity controller and the Cooling coil override will take place automatically when the Humidity controller is setup.
The AHU can be used as the base controller for controlling Dessicant Cooled AHU's, The following special control modules can be registered to the AHU to create a Dessicant AHU solution. The special control modules take in the Heat demand% and Cool Demand% from the AHU, and rescale it to produce either a direct output to the driver stages or a setpoint to an interposing control loop. See release notes for the other control modules as indicated for more information.
Thermal Wheel/Evaporative Cooler controller registered as Mixing Damper/Heat Recovery [A1M1]
Dessicant Wheel/ReGen heater controller registered as Actuator, register first [A1C1]
Motor Speed controller, fan speed as function of Outside temperature, registered as Actuator [A1C2]
Supply Air Evaporative Cooler, Humidity controller with CMDE=0, registers as HUM [A1H1]
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.
Mixing
Damper controlA new issue Damper controller (MXDx3d7) can be setup to use the mixing dampers as the first stage of heating and cooling control. This allows modulation of the dampers without the need for a mixed air temperature sensor. The AHU needs to have a Return Air temperature values, either hard wired or networked and an Outside temperature value in order to determine the sense of operation of the dampers (heating or cooling).
If the damper is used as part of the heating/cooling sequence a configuration parameter in the Damper controller DMPC is set to the percentage of heat and cool demand which will be utilised by the damper controller. In this case the AHU driver re-scaling needs to be set up so that the AHU heating and cooling outputs do not start until the damper sequence is completed. So if DMPC (DeMand PerCent) in the Damper controller is set to 25%, then the minimum driver rescale parameters for heat and cool (HRMN,CRMN) should also be set to 25%.
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', note 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.
The AHU will accept TRH sensors for Return, Supply and Outside temperature and RH values. Register the sensors to the AHU in the normal manner. A hard wired sensor overrides the networked value.
Multiple
Space SensorsThe AHU controller can be used with the Monitor Module to enable it to control to the average, maximum, or minimum of up to 10 networked Temperature or temperature and RH sensors. In this situation a Zone controller can be used as a networked temperature sensor. The sensors are registered to the Monitor Module in the normal manner, then the Monitor Module is registered to the AHU. The AHU will consider the Monitor Module to be a Return Air (RHR) temperature and RH sensor. The values of Monitor sensor 6 (temp) and Monitor sensor 7(RH) are presented to the AHU as Return Air Temperature and RH. The monitor module can be set to deliver average (default) maximum or minimum.
In addition to the frost protection mentioned earlier and the delays associated with starting under cold conditions when the heater battery is raise lower i.e. assumed to be water heated, a further protection is that if the supply air temperature falls below the setting of CUTS (default 4) then the AHU fans will be stopped. If the AHU is not water heated, e.g. direct gas fired then this parameter should be set to zero to disable this feature. Beware of setting CUTS too high because this may lead to the AHU not being able to start when the outside temperature is very low, also do not set it too low (less than 2) beacuse it is usually only a point measurement and some areas of the heater battery may be at a significantly lower temperature.
Hardware
Test ModeThis has been included to allow hardware to be re-tested at the final booking out station and also to be easily checked at any time in the field.
The controller is put into test mode by setting config 120 to 1 or by holding the service pin down as the unit is powered up. If the later method is used then the unit will need to be re-registered after the test since this action also clears any slaving which might have been setup. The first time the controller is powered after changing the prom also initiates Test mode.
Test mode is cleared by power cycling or by setting C120 back to 0. While in test mode, TEST displays the seconds value of the real time clock.
Test mode cycles the outputs, and flashes the leds see full test specification. The values for the analogue inputs can be monitored on configs 170 onwards.
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.
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%. Actuator Controllers issue 3d1 or later and
the Dessicant control modules 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) or AHD Dessicant Wheel/ReGen Controller
or AHF Fan Speed Controller or ACT Actuators
AHP Air Handler Preheater (x1)
FCO Fan ChangeOver module (x2)
MXD Mixing Damper control (x1) MXDD or MXDA or Heat recovery HRC or AHT Thermal Wheel
controller
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 Actuators, Thermal Wheel [A1Cm] where m= 1 or 2
AHU Mixing Damper [A1M1]
AHU Preheater [A1P1]
AHU Fan Changeover [A1Fm] m=1 or 2
AHU Humidity [A1H1]
Item codes follow the normal conventions
Major new issue see complete config tables.
network variables(4a2)