System Availability
Managers[LINK]
System availability managers, or AvailabilityManagers, are
one of the high-level control constructs in EnergyPlus. An
AvailabilityManager is able to access data from any of the
HVAC system nodes and use this data to set flags telling a
central air system or plant loop to turn on or off. Also, some
of the HVACZone:* components can use these same availability
managers to turn their supply air fan on or off. Each type of
availability manager encapsulates a specific high-level on-off
control strategy. For instance, the input object AvailabilityManager:NightVentilation
allows the user to specify a control strategy for pre-cooling
the building with night-time ventilation.
Availability managers are contained in the program module
SystemAvailabilityManager. The Availability managers
are executed at the start of each HVAC time step by a call to
ManageSystemAvailability, and they reside outside the
HVAC system iteration loops. Thus, the availability managers
are executed once per HVAC time step, and they use previous
time step information to calculate their control actions.
If a given instance of an AvailabilityManager is specific
to an AirLoopHVAC
or to a PlantLoop,
then in the input, each loop references its availability
managers through a AvailabilityManagerAssignmentList.
Once the data has been read in and processed, the
AvailabilityManager data for each loop is stored in array
PriAirSysAvailMgr in DataAirLoop (for
AirLoopHVAC) and in array PlantAvailMgr in
DataPlant for plant loops.
The availability status for each AirLoopHVAC
(PriAirSysAvailMgr) is also passed to a zone
equipment availability status array (ZoneEquipAvail)
for possible use by the zones served by that air loop. This
sets the availability for certain zone equipment which are
assumed to operate in conjunction with the air loop.
Specifically, the availability of zone exhaust fans (Ref.
Fan:ZoneExhaust) and terminal unit fans (Ref.
AirTerminal:SingleDuct:SeriesPIU: Reheat,
AirTerminal:SingleDuct: ParallelPIU:Reheat, and
AirTerminal:SingleDuct:VAV: Reheat:VariableSpeedFan), if
specified in the input, will be the same as the corresponding
AirLoopHVAC
availability if an AvailabilityManager is specified. Other
zone equipment are not affected by the AirLoopHVAC
system availability managers (e.g., Window
AC, PTAC and PTHP).
However, system availability managers can separately be
specified for zone components (currently only allowed for Window
AC, PTAC, PTHP, Unit Heater, Unit Ventilator, Zone
Water to Air Heat Pump, Zone
Terminal Unit (VRF), Standalone Energy Recovery Ventilator,
Outdoor Air Unit, Fan Coil Unit, and Ventilated Slab). Similar
to AirLoopHVAC
or PlantLoop,
inputs of these zone components refer to their availability
managers through a AvailabilityManagerAssignmentList.
System availability managers only operate when zone components
are available. If the Window
AC (or any other unit) is scheduled off then the system
availability manager will not operate until the Window
AC is scheduled on. The functioning of the system availability
manager for zone components is same as for AirLoopHVAC
or PlantLoop.
Except night ventilation SAM, all other SAMs can be specified
for these zone components.
The actual action of turning on or off a loop is taken by
the loop prime movers: fans for AirLoopHVACs and pumps for
plant loops. For instance when a fan is deciding whether it is
on or off, it checks its on/off schedule and whether the loop
availability status flag is CycleOn or
ForceOff. If the schedule is on and the status flag
is ForceOff, the fan will be off. If the fan schedule
says off and the status flag is CycleOn, the fan will
be on. Thus the availability managers overrule the fan on/off
schedule.
The input object AvailabilityManager:Scheduled
provides the simplest availability manager. The sole input for
this manager is a schedule name. If the current schedule value
is > 0.0, the availability status flag is set to
CycleOn; otherwise it is set to
ForceOff.
An alternative to the AvailabilityManager:Scheduled
object is the AvailabilityManager:ScheduledOn
that is used specifically to turn equipment on while other
availability managers may be used to turn the equipment off.
The sole input for this manager is a schedule name. If the
current schedule value is > 0.0, the availability status
flag is set to CycleOn; otherwise it is set to
NoAction.
Scheduled Off[LINK]
An alternative to the AvailabilityManager:Scheduled
object is the AvailabilityManager:ScheduledOff
that is used specifically to turn equipment off while other
availability managers may be used to turn the equipment on.
The sole input for this manager is a schedule name. If the
current schedule value is = 0.0, the availability status flag
is set to ForceOff; otherwise it is set to
NoAction.
The input object AvailabilityManager:NightCycle
is to specify when a system that has been scheduled off during
unoccupied hours should cycle on to prevent building
temperatures from becoming too hot or too cold. This manager
can not be used to force a system off. The inputs are:
A manager applicability schedule;
The name of the fan schedule this manager will
override;
The control type: Stay Off, Cycle On Any,
Cycle On Control Zone,
or Cycle On Any - Zone
Fans Only;
Thermostat on/off tolerance Ttol
(degrees C);
Cycling run time in seconds; used to calculate a stop time
(in time steps since the start of the current run period) once
the status has become Cycle On.
If the fan schedule current value is > 0 or the
applicability schedule value is 
0 or if the program is in warmup,
AvailStatus = NoAction.
Otherwise,
if current time (in time steps since the start of the run
period) is greater than the start time and less than the stop
time, AvailStatus = CycleOn (or
CycleOnZoneFansOnly if the control type is Cycle
On Any – Zone
Fans only).
If the current time equals the stop time, AvailStatus =
NoAction and the fan schedule will determine if the
system is on.
If the current time is greater than the stop time, the
manager can potentially cycle the system on.
For control types Cycle On Any and Cycle On
Any – Zone
Fans Only the manger looks at each zone served by the air
loop and detects whether the zone temperature at the
thermostat is greater than the cooling setpoint plus
½Ttol or less than the heating setpoint
minus ½Ttol. If it is,
AvailStatus is set to CycleOn (or
CycleOnZoneFansOnly). If not, AvailStatus is
set to NoAction.
For control type Cycle On Control Zone,
the manager does the same check just for the control zone.
Lastly if the new status is CycleOn the start time is reset
to the current time and the stop time is reset. When this
availability manager is specified for a zone component then
the only allowed control types are Stay Off
and Cycle On Control Zone.
Night Ventilation[LINK]
The input object AvailabilityManager:NightVentilation
is a manager that looks at indoor and outdoor conditions to
see if night ventilation might be beneficial. In addition to
being able to cycle the air system on, this manager can
specify what the ventilation air flow rate should be. The
inputs are:
A manager applicability schedule;
The name of the fan schedule this manager will
override;
A ventilation temperature schedule;
A ventilation delta T;
A ventilation low limit temperature;
The night ventilation flow fraction;
The name of the control zone.
If the fan schedule current value is > 0 or the
applicability schedule value is 
0 or if the program is in warmup,
AvailStatus = NoAction.
Otherwise, the manager performs 3 limit checks.
If for all the zones connected to the air loop the room
temperature at the thermostat of any zone is greater than the
ventilation temperature schedule value, this check is
true.
If for all the zones connected to the air loop the room
temperature at the thermostat of any zone is less than the
ventilation low limit temperature, this check is true.
If the difference between the control zone room temperature
at the thermostat and the outside temperature is greater than
the specified night venting delta T, this check is true.
If 1) and 3) are true and 2) is false, the status is set to
CycleOn; otherwise the status is NoAction.
If the status is CycleOn this manager sets some
additional values in the AirLoopControlInfo data
structure (a flag is set to indicate night ventilation is
occurring and a flag is set to indicate that the air system
flow rate has been specified by a manager) and in the
AirLoopFlow data structure (the system flow fraction
is specified). The night ventilation flag indicates to the fan
that it should use alternate performance characteristics if
they have been specified in a FanPerformance:NightVentilation
object.
Differential Thermostat[LINK]
The input object AvailabilityManager:DifferentialThermostat
is a manager that overrides fan or pump schedules depending on
the temperature difference between two nodes. A typical use
would be for one node to be an outdoor air node and the other
a zone node. The inputs are:
name of the hot node;
name of the cold node;
temperature difference for turning the system on
(DeltaTon);
temperature difference for turning the system off
(DeltaToff).
Note that there is no applicability schedule for this
manager. Also, this manager always returns a status of
CycleOn or ForceOff, never
NoAction.
DeltaT = T~hot node~ – T~cold
node~
If DeltaT >= DeltaTon
then
AvailStatus = CycleOn
Else if *DeltaT* <= *DeltaT~off~* then
AvailStatus = ForceOff
Else
AvailStatus remains in its previous state.
High Temperature Turn
Off[LINK]
The input object AvailabilityManager:HighTemperatureTurnOff
is used to turn off a central air system or a plant loop if a
sensed node temperature exceeds a temperature limit. The
inputs are:
name of the sensed node;
limit temperature (Tu).
If T~sensed node~ >= Tu
then
AvailStatus = ForceOff
Else
AvailStatus = NoAction
High Temperature Turn
On[LINK]
The input object AvailabilityManager:HighTemperatureTurnOn
is used to turn on a central air system or a plant loop if a
sensed node temperature exceeds a temperature limit. The
inputs are:
name of the sensed node;
limit temperature (Tu).
If T~sensed node~ >= Tu
then
AvailStatus = CycleOn
Else
AvailStatus = NoAction
Low Temperature Turn
Off[LINK]
The input object AvailabilityManager:LowTemperatureTurnOff
is used to turn off a central air system or a plant loop if a
sensed node temperature is lower than a temperature limit. The
inputs are:
name of the sensed node;
limit temperature (Tl);
applicability schedule name.
If the applicability schedule exists and has a current
value of <= 0, the manager returns an availability status
of NoAction.
Otherwise,
If T~sensed node~ <= Tl
then
AvailStatus = ForceOff
Else
AvailStatus = NoAction
Low Temperature Turn On[LINK]
The input object AvailabilityManager:LowTemperatureTurnOn
is used to turn on a central air system or a plant loop if a
sensed node temperature is less than a temperature limit. The
inputs are:
name of the sensed node;
limit temperature (Tl).
If T~sensed node~ <= Tl
then
AvailStatus = CycleOn
Else
AvailStatus = NoAction
Hybrid Ventilation
Control[LINK]
The input object AvailabilityManager:HybridVentilation
serves two purposes: 1) it prevents simultaneous natural
ventilation and HVAC system operation, and 2) it allows users
to examine various strategies to maximize natural ventilation
in order to reduce heating/cooling loads. This availability
manager works with either the AirflowNetwork model or the
simple airflow objects to provide controlled natural
ventilation. The controlled natural ventilation objects
referred to here are either
AirflowNetwork:Multizone:ComponentDetailedOpening and
AirflowNetwork:Multizone:ComponentSimpleOpening objects, or
ZoneVentilation and ZoneMixing
objects. The simple airflow objects are not allowed to work
with the AirflowNetwork objects simultaneously. If there is no
air loop, this availability manager can still be applied to
controlled zone specified in the object. In order to apply
hybrid ventilation manager to the controlled zone not served
by any air loop, the HVAC air loop name input field must be
left blank. Currently, zone component objects such as unit
heater, unit ventilator, packaged terminal air conditioner,
packaged terminal heat pump, zone water source heat pump,
window air conditioner, variable refrigerant flow, energy
recovery ventilator, outdoor air unit, fan coil unit, and
ventilated slab can individually use hybrid ventilation
managers to make a decision regarding whether their fan should
be on or off. Also, hybrid ventilation manager can be applied
to zones served by the ideal load zone component to turn them
off when natural ventilation is active. Currently, hybrid
ventilation manager is restricted to one per zone. It can
either be applied through the air loop or directly to the
zone. If hybrid ventilation manager is applied to an air loop
and one of the zones served by the air loop also has hybrid
ventilation manager, then zone hybrid ventilation manager is
disabled. This availability manager performs somewhat
differently from the other availability managers:
- This availability manager is called before the program
estimates (predicts) the cooling or heating load that needs to
be met by the cooling/heating systems for the simulation time
step. On the other hand, the other availability managers are
called after the system cooling/heating load prediction. The
main reason for calling AvailabilityManager:HybridVentilation
early is that this manager determines whether natural
ventilation is allowed or not, and the loads from natural
ventilation are used to predict system loads.
- This availability manager has its own control schedule and
does not work in tandem with
AvailabilityManager:Scheduled.
- AvailabilityManager:HybridVentilation works completely
independent of the other system availability managers, so this
manager is not a valid system availability manager type in the
AvailabilityManagerAssignmentList object.
Control logic[LINK]
The control logic for each ventilation control mode is
described below.
Temperature control[LINK]
This control mode checks whether the outdoor air dry-bulb
temperature is between the Minimum Outdoor Temperature and
Maximum Outdoor Temperature specified. If the outdoor
temperature is between the two values then natural ventilation
is allowed, else natural ventilation is not allowed.
When natural ventilation is allowed, the control then
checks the temperature difference between the zone temperature
and the temperature setpoint(s) in the controlled zone based
on the specified temperature control type (four available
temperature control types) to make a final decision:
Single Heating Setpoint:
If the zone temperature is below the setpoint, then the
initial decision is overridden and natural ventilation is not
allowed. This is intended to avoid overcooling a space, which
could result in additional heating load.
Single Cooling Setpoint:
If the zone temperature is above the setpoint, then the
initial decision is overridden and natural ventilation is not
allowed. This is intended to avoid overheating a space, which
could result in additional cooling load.
Single Heating Cooling Setpoint:
Since this temperature control type requires only a single
setpoint, natural ventilation is not allowed. A recurring
warning message is issued.
Dual Setpoint with DeadBand:
If the zone temperature is beyond the deadband, the initial
decision is overridden and natural ventilation is not allowed.
This is intended to avoid either overcooling a space, which
could result in additional heating load when the zone
temperature is below the heating setpoint, or overheating a
space, which could result in additional cooling load when the
zone temperature is above the cooling setpoint.
Enthalpy control[LINK]
This control mode checks whether the outdoor air enthalpy
is between the Minimum Outdoor Enthalpy and Maximum Outdoor
Enthalpy specified. If the outdoor enthalpy is between the two
values then natural ventilation is allowed, else natural
ventilation is not allowed.
When natural ventilation is allowed, the control then
checks the temperature difference between the zone temperature
and the temperature setpoint(s) in the controlled zone based
on the specific temperature control type to make a final
decision. This procedure is the same as defined above for the
temperature control mode.
Single Heating Setpoint:
If the zone temperature is below the setpoint, then the
initial decision is overridden and natural ventilation is not
allowed. This is intended to avoid overcooling a space, which
could result in additional heating load.
Single Cooling Setpoint:
If the zone temperature is above the setpoint, then the
initial decision is overridden and natural ventilation is not
allowed. This is intended to avoid overheating a space, which
could result in additional cooling load.
Single Heating Cooling Setpoint:
Since this temperature control type requires only a single
setpoint, natural ventilation is not allowed. A recurring
warning message is issued.
Dual Setpoint with DeadBand:
If the zone temperature is beyond the deadband, then the
initial decision is overridden and natural ventilation is not
allowed. This is intended to avoid either overcooling a space,
which could result in additional heating load when the zone
temperature is below the heating setpoint, or overheating a
space, which could result in additional cooling load when the
zone temperature is above the cooling setpoint.
Dew-Point control[LINK]
This control mode checks whether the outdoor air dewpoint
temperature is between the Minimum Outdoor Dew-Point and
Maximum Outdoor Dew-Point specified. If the outdoor dewpoint
temperature is between the two values then natural ventilation
is allowed, else national ventilation is not allowed.
When natural ventilation is allowed and a humidistat is
available in the controlled zone, the control then checks the
humidity ratio difference between the zone air humidity ratio
and humidistat setpoint in the controlled zone to make a final
decision. It should be pointed out that the humidistat object
provides the setpoint of relative humidity, the value of
relative humidity has to be converted into the setpoint of
humidity ratio using the actual zone air temperature for
comparison. Since the humidistat only provides a single value
for relative humidity, there are two possible scenarios:
If the actual zone air humidity ratio is below the humidity
ratio setpoint and the controlled zone needs humidification as
the first scenario, then the initial decision is overridden
and natural ventilation is not allowed. This is intended to
avoid dehumidifying a space, which could result in additional
humidification load.
If the actual zone air humidity ratio is above the humidity
ratio setpoint and the controlled zone needs dehumidification
as the second scenario, then the initial decision is
overridden and natural ventilation is not allowed. This is
intended to avoid humidifying a space, which could result in
additional dehumidification load.
Outdoor ventilation
air control[LINK]
This control mode does not require any additional checks.
The control only works with Airflow Network opening objects
only, and is not allowed to work with ZoneVentilation and ZoneMixing
objects.
Availability Status[LINK]
After the hybrid ventilation control determines whether
natural ventilation is allowed or not, the availability status
flag is set as follows:
If Natural Ventilation then
AvailStatus = CycleOn
Else
AvailStatus = ForceOn
System Availability Managers[LINK]
Overview[LINK]
System availability managers, or AvailabilityManagers, are one of the high-level control constructs in EnergyPlus. An AvailabilityManager is able to access data from any of the HVAC system nodes and use this data to set flags telling a central air system or plant loop to turn on or off. Also, some of the HVACZone:* components can use these same availability managers to turn their supply air fan on or off. Each type of availability manager encapsulates a specific high-level on-off control strategy. For instance, the input object AvailabilityManager:NightVentilation allows the user to specify a control strategy for pre-cooling the building with night-time ventilation.
Availability managers are contained in the program module SystemAvailabilityManager. The Availability managers are executed at the start of each HVAC time step by a call to ManageSystemAvailability, and they reside outside the HVAC system iteration loops. Thus, the availability managers are executed once per HVAC time step, and they use previous time step information to calculate their control actions.
If a given instance of an AvailabilityManager is specific to an AirLoopHVAC or to a PlantLoop, then in the input, each loop references its availability managers through a AvailabilityManagerAssignmentList. Once the data has been read in and processed, the AvailabilityManager data for each loop is stored in array PriAirSysAvailMgr in DataAirLoop (for AirLoopHVAC) and in array PlantAvailMgr in DataPlant for plant loops.
The availability status for each AirLoopHVAC (PriAirSysAvailMgr) is also passed to a zone equipment availability status array (ZoneEquipAvail) for possible use by the zones served by that air loop. This sets the availability for certain zone equipment which are assumed to operate in conjunction with the air loop. Specifically, the availability of zone exhaust fans (Ref. Fan:ZoneExhaust) and terminal unit fans (Ref. AirTerminal:SingleDuct:SeriesPIU: Reheat, AirTerminal:SingleDuct: ParallelPIU:Reheat, and AirTerminal:SingleDuct:VAV: Reheat:VariableSpeedFan), if specified in the input, will be the same as the corresponding AirLoopHVAC availability if an AvailabilityManager is specified. Other zone equipment are not affected by the AirLoopHVAC system availability managers (e.g., Window AC, PTAC and PTHP).
However, system availability managers can separately be specified for zone components (currently only allowed for Window AC, PTAC, PTHP, Unit Heater, Unit Ventilator, Zone Water to Air Heat Pump, Zone Terminal Unit (VRF), Standalone Energy Recovery Ventilator, Outdoor Air Unit, Fan Coil Unit, and Ventilated Slab). Similar to AirLoopHVAC or PlantLoop, inputs of these zone components refer to their availability managers through a AvailabilityManagerAssignmentList. System availability managers only operate when zone components are available. If the Window AC (or any other unit) is scheduled off then the system availability manager will not operate until the Window AC is scheduled on. The functioning of the system availability manager for zone components is same as for AirLoopHVAC or PlantLoop. Except night ventilation SAM, all other SAMs can be specified for these zone components.
The actual action of turning on or off a loop is taken by the loop prime movers: fans for AirLoopHVACs and pumps for plant loops. For instance when a fan is deciding whether it is on or off, it checks its on/off schedule and whether the loop availability status flag is CycleOn or ForceOff. If the schedule is on and the status flag is ForceOff, the fan will be off. If the fan schedule says off and the status flag is CycleOn, the fan will be on. Thus the availability managers overrule the fan on/off schedule.
Scheduled[LINK]
The input object AvailabilityManager:Scheduled provides the simplest availability manager. The sole input for this manager is a schedule name. If the current schedule value is > 0.0, the availability status flag is set to CycleOn; otherwise it is set to ForceOff.
Scheduled On[LINK]
An alternative to the AvailabilityManager:Scheduled object is the AvailabilityManager:ScheduledOn that is used specifically to turn equipment on while other availability managers may be used to turn the equipment off. The sole input for this manager is a schedule name. If the current schedule value is > 0.0, the availability status flag is set to CycleOn; otherwise it is set to NoAction.
Scheduled Off[LINK]
An alternative to the AvailabilityManager:Scheduled object is the AvailabilityManager:ScheduledOff that is used specifically to turn equipment off while other availability managers may be used to turn the equipment on. The sole input for this manager is a schedule name. If the current schedule value is = 0.0, the availability status flag is set to ForceOff; otherwise it is set to NoAction.
Night Cycle[LINK]
The input object AvailabilityManager:NightCycle is to specify when a system that has been scheduled off during unoccupied hours should cycle on to prevent building temperatures from becoming too hot or too cold. This manager can not be used to force a system off. The inputs are:
A manager applicability schedule;
The name of the fan schedule this manager will override;
The control type: Stay Off, Cycle On Any, Cycle On Control Zone, or Cycle On Any - Zone Fans Only;
Thermostat on/off tolerance Ttol (degrees C);
Cycling run time in seconds; used to calculate a stop time (in time steps since the start of the current run period) once the status has become Cycle On.
If the fan schedule current value is > 0 or the applicability schedule value is
0 or if the program is in warmup,
AvailStatus = NoAction.
Otherwise,
if current time (in time steps since the start of the run period) is greater than the start time and less than the stop time, AvailStatus = CycleOn (or CycleOnZoneFansOnly if the control type is Cycle On Any – Zone Fans only).
If the current time equals the stop time, AvailStatus = NoAction and the fan schedule will determine if the system is on.
If the current time is greater than the stop time, the manager can potentially cycle the system on.
For control types Cycle On Any and Cycle On Any – Zone Fans Only the manger looks at each zone served by the air loop and detects whether the zone temperature at the thermostat is greater than the cooling setpoint plus ½Ttol or less than the heating setpoint minus ½Ttol. If it is, AvailStatus is set to CycleOn (or CycleOnZoneFansOnly). If not, AvailStatus is set to NoAction.
For control type Cycle On Control Zone, the manager does the same check just for the control zone.
Lastly if the new status is CycleOn the start time is reset to the current time and the stop time is reset. When this availability manager is specified for a zone component then the only allowed control types are Stay Off and Cycle On Control Zone.
Night Ventilation[LINK]
The input object AvailabilityManager:NightVentilation is a manager that looks at indoor and outdoor conditions to see if night ventilation might be beneficial. In addition to being able to cycle the air system on, this manager can specify what the ventilation air flow rate should be. The inputs are:
A manager applicability schedule;
The name of the fan schedule this manager will override;
A ventilation temperature schedule;
A ventilation delta T;
A ventilation low limit temperature;
The night ventilation flow fraction;
The name of the control zone.
If the fan schedule current value is > 0 or the applicability schedule value is
0 or if the program is in warmup,
AvailStatus = NoAction.
Otherwise, the manager performs 3 limit checks.
If for all the zones connected to the air loop the room temperature at the thermostat of any zone is greater than the ventilation temperature schedule value, this check is true.
If for all the zones connected to the air loop the room temperature at the thermostat of any zone is less than the ventilation low limit temperature, this check is true.
If the difference between the control zone room temperature at the thermostat and the outside temperature is greater than the specified night venting delta T, this check is true.
If 1) and 3) are true and 2) is false, the status is set to CycleOn; otherwise the status is NoAction. If the status is CycleOn this manager sets some additional values in the AirLoopControlInfo data structure (a flag is set to indicate night ventilation is occurring and a flag is set to indicate that the air system flow rate has been specified by a manager) and in the AirLoopFlow data structure (the system flow fraction is specified). The night ventilation flag indicates to the fan that it should use alternate performance characteristics if they have been specified in a FanPerformance:NightVentilation object.
Differential Thermostat[LINK]
The input object AvailabilityManager:DifferentialThermostat is a manager that overrides fan or pump schedules depending on the temperature difference between two nodes. A typical use would be for one node to be an outdoor air node and the other a zone node. The inputs are:
name of the hot node;
name of the cold node;
temperature difference for turning the system on (DeltaTon);
temperature difference for turning the system off (DeltaToff).
Note that there is no applicability schedule for this manager. Also, this manager always returns a status of CycleOn or ForceOff, never NoAction.
DeltaT = T~hot node~ – T~cold node~
If DeltaT >= DeltaTon then
AvailStatus = CycleOn
AvailStatus = ForceOff
Else
AvailStatus remains in its previous state.
High Temperature Turn Off[LINK]
The input object AvailabilityManager:HighTemperatureTurnOff is used to turn off a central air system or a plant loop if a sensed node temperature exceeds a temperature limit. The inputs are:
name of the sensed node;
limit temperature (Tu).
If T~sensed node~ >= Tu then
AvailStatus = ForceOff
Else
AvailStatus = NoAction
High Temperature Turn On[LINK]
The input object AvailabilityManager:HighTemperatureTurnOn is used to turn on a central air system or a plant loop if a sensed node temperature exceeds a temperature limit. The inputs are:
name of the sensed node;
limit temperature (Tu).
If T~sensed node~ >= Tu then
AvailStatus = CycleOn
Else
AvailStatus = NoAction
Low Temperature Turn Off[LINK]
The input object AvailabilityManager:LowTemperatureTurnOff is used to turn off a central air system or a plant loop if a sensed node temperature is lower than a temperature limit. The inputs are:
name of the sensed node;
limit temperature (Tl);
applicability schedule name.
If the applicability schedule exists and has a current value of <= 0, the manager returns an availability status of NoAction.
Otherwise,
If T~sensed node~ <= Tl then
AvailStatus = ForceOff
Else
AvailStatus = NoAction
Low Temperature Turn On[LINK]
The input object AvailabilityManager:LowTemperatureTurnOn is used to turn on a central air system or a plant loop if a sensed node temperature is less than a temperature limit. The inputs are:
name of the sensed node;
limit temperature (Tl).
If T~sensed node~ <= Tl then
AvailStatus = CycleOn
Else
AvailStatus = NoAction
Hybrid Ventilation Control[LINK]
The input object AvailabilityManager:HybridVentilation serves two purposes: 1) it prevents simultaneous natural ventilation and HVAC system operation, and 2) it allows users to examine various strategies to maximize natural ventilation in order to reduce heating/cooling loads. This availability manager works with either the AirflowNetwork model or the simple airflow objects to provide controlled natural ventilation. The controlled natural ventilation objects referred to here are either AirflowNetwork:Multizone:ComponentDetailedOpening and AirflowNetwork:Multizone:ComponentSimpleOpening objects, or ZoneVentilation and ZoneMixing objects. The simple airflow objects are not allowed to work with the AirflowNetwork objects simultaneously. If there is no air loop, this availability manager can still be applied to controlled zone specified in the object. In order to apply hybrid ventilation manager to the controlled zone not served by any air loop, the HVAC air loop name input field must be left blank. Currently, zone component objects such as unit heater, unit ventilator, packaged terminal air conditioner, packaged terminal heat pump, zone water source heat pump, window air conditioner, variable refrigerant flow, energy recovery ventilator, outdoor air unit, fan coil unit, and ventilated slab can individually use hybrid ventilation managers to make a decision regarding whether their fan should be on or off. Also, hybrid ventilation manager can be applied to zones served by the ideal load zone component to turn them off when natural ventilation is active. Currently, hybrid ventilation manager is restricted to one per zone. It can either be applied through the air loop or directly to the zone. If hybrid ventilation manager is applied to an air loop and one of the zones served by the air loop also has hybrid ventilation manager, then zone hybrid ventilation manager is disabled. This availability manager performs somewhat differently from the other availability managers:
Control logic[LINK]
The control logic for each ventilation control mode is described below.
Temperature control[LINK]
This control mode checks whether the outdoor air dry-bulb temperature is between the Minimum Outdoor Temperature and Maximum Outdoor Temperature specified. If the outdoor temperature is between the two values then natural ventilation is allowed, else natural ventilation is not allowed.
When natural ventilation is allowed, the control then checks the temperature difference between the zone temperature and the temperature setpoint(s) in the controlled zone based on the specified temperature control type (four available temperature control types) to make a final decision:
Single Heating Setpoint:
If the zone temperature is below the setpoint, then the initial decision is overridden and natural ventilation is not allowed. This is intended to avoid overcooling a space, which could result in additional heating load.
Single Cooling Setpoint:
If the zone temperature is above the setpoint, then the initial decision is overridden and natural ventilation is not allowed. This is intended to avoid overheating a space, which could result in additional cooling load.
Single Heating Cooling Setpoint:
Since this temperature control type requires only a single setpoint, natural ventilation is not allowed. A recurring warning message is issued.
Dual Setpoint with DeadBand:
If the zone temperature is beyond the deadband, the initial decision is overridden and natural ventilation is not allowed. This is intended to avoid either overcooling a space, which could result in additional heating load when the zone temperature is below the heating setpoint, or overheating a space, which could result in additional cooling load when the zone temperature is above the cooling setpoint.
Enthalpy control[LINK]
This control mode checks whether the outdoor air enthalpy is between the Minimum Outdoor Enthalpy and Maximum Outdoor Enthalpy specified. If the outdoor enthalpy is between the two values then natural ventilation is allowed, else natural ventilation is not allowed.
When natural ventilation is allowed, the control then checks the temperature difference between the zone temperature and the temperature setpoint(s) in the controlled zone based on the specific temperature control type to make a final decision. This procedure is the same as defined above for the temperature control mode.
Single Heating Setpoint:
If the zone temperature is below the setpoint, then the initial decision is overridden and natural ventilation is not allowed. This is intended to avoid overcooling a space, which could result in additional heating load.
Single Cooling Setpoint:
If the zone temperature is above the setpoint, then the initial decision is overridden and natural ventilation is not allowed. This is intended to avoid overheating a space, which could result in additional cooling load.
Single Heating Cooling Setpoint:
Since this temperature control type requires only a single setpoint, natural ventilation is not allowed. A recurring warning message is issued.
Dual Setpoint with DeadBand:
If the zone temperature is beyond the deadband, then the initial decision is overridden and natural ventilation is not allowed. This is intended to avoid either overcooling a space, which could result in additional heating load when the zone temperature is below the heating setpoint, or overheating a space, which could result in additional cooling load when the zone temperature is above the cooling setpoint.
Dew-Point control[LINK]
This control mode checks whether the outdoor air dewpoint temperature is between the Minimum Outdoor Dew-Point and Maximum Outdoor Dew-Point specified. If the outdoor dewpoint temperature is between the two values then natural ventilation is allowed, else national ventilation is not allowed.
When natural ventilation is allowed and a humidistat is available in the controlled zone, the control then checks the humidity ratio difference between the zone air humidity ratio and humidistat setpoint in the controlled zone to make a final decision. It should be pointed out that the humidistat object provides the setpoint of relative humidity, the value of relative humidity has to be converted into the setpoint of humidity ratio using the actual zone air temperature for comparison. Since the humidistat only provides a single value for relative humidity, there are two possible scenarios:
If the actual zone air humidity ratio is below the humidity ratio setpoint and the controlled zone needs humidification as the first scenario, then the initial decision is overridden and natural ventilation is not allowed. This is intended to avoid dehumidifying a space, which could result in additional humidification load.
If the actual zone air humidity ratio is above the humidity ratio setpoint and the controlled zone needs dehumidification as the second scenario, then the initial decision is overridden and natural ventilation is not allowed. This is intended to avoid humidifying a space, which could result in additional dehumidification load.
Outdoor ventilation air control[LINK]
This control mode does not require any additional checks. The control only works with Airflow Network opening objects only, and is not allowed to work with ZoneVentilation and ZoneMixing objects.
Availability Status[LINK]
After the hybrid ventilation control determines whether natural ventilation is allowed or not, the availability status flag is set as follows:
If Natural Ventilation then
AvailStatus = CycleOn
Else
AvailStatus = ForceOn
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This documentation is made available under the EnergyPlus Open Source License v1.0.