Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints

Output setpoints for AHU control

Information

This package contains sequences generating setpoints for single zone VAV AHU control.

Package Content

Name	Description
CoolingCoil	Controller for cooling coil valve
FreezeProtection	Freeze protection sequence for single zone air handling unit
ModeAndSetPoints	Output zone setpoint with operation mode selection
PlantRequests	Output plant requests for single zone air handling unit
ReliefDamper	Relief damper control for AHUs using actuated dampers without fan
ReliefFan	Sequence for control of relief fan in AHU
ReliefFanGroup	Sequence for relief fans control for AHUs using actuated relief dampers with relief fan(s)
ReturnFan	Return fan control for single zone AHU
Supply	Supply air set point for single zone VAV system
Validation	Collection of validation models

Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.CoolingCoil

Controller for cooling coil valve

Information

This block outputs the cooling coil control signal if the fan is on and the zone is in cooling status (see Buildings.Controls.OBC.ASHRAE.G36.Types.ZoneStates). Otherwise, the control signal for the coil is set to 0. The implementation is according to the Section 5.18.5.3 of ASHRAE Guideline 36, May 2020.

Parameters

Connectors

Modelica definition

Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.FreezeProtection

Freeze protection sequence for single zone air handling unit

Information

Freeze protection sequence for single zone AHU system. It is developed based on Section 5.18.11 of ASHRAE Guideline 36, May 2020.

1. If the supply air temperature TAirSup drops below 4 °C (40 °F) for 5 minutes, send two (or more, as required to ensure that heating plant is active, minHotWatReq) heating hot-water plant requests, override the outdoor air damper to the minimum position, and modulate the heating coil to maintain a suppy air temperature of at least 6 °C (42 °F). Disable this function when supply air temperature rises above 7 °C (45 °F) for 5 minutes.
2. If the supply air temperature TAirSup drops below 3 °C (38 °F) for 5 minutes, fully close both the economizer damper and the minimum outdoor air damper for 1 hour and set a Level 3 alarm noting that minimum ventilation was interrupted. After 1 hour, the unit shall resume minimum outdoor air ventilation and enter the previous stage of freeze protection.
   • If it is warm enough that the supply air temperature rises above 7 °C (45 °F) with minimum ventilation, the unit will remain in Stage 1 freeze protection for 5 minutes then resume normal operation.
3. Upon signal from the freeze-stat (if installed), or if supply air temperature drops below 3 °C (38 °F) for 15 minutes or below 1 °C (34 °F) for 5 minutes, shut down supply and return (or relief) fan(s), close outdoor air damper, open the cooling-coil valve to 100%, and energize the CHW pump system. Also send two (or more, as required to ensure that heating plant is active, minHotWatReq) heating hot-water plant requests, modulate the heating coil to maintain the higher of the supply air temperature or the mixed air temperature at 27 °C (80 °F), and set a Level 2 alarm indicating the unit is shut down by freeze protection.
   • If a freeze-protection shutdown is triggered by a low air temperature sensor reading, it shall remain in effect until it is reset by a software switch from the operator's workstation. (If a freeze-stat with a physical reset switch is used instead, there shall be no software reset switch.)

Parameters

Connectors

Modelica definition

Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.ModeAndSetPoints

Output zone setpoint with operation mode selection

Information

Block that outputs the zone setpoint temperature (TCooSet, THeaSet) and system operation mode (yOpeMod).

The sequence consists of the following two subsequences.

Operation mode selector

The subsequence outputs one of seven types of system operation mode (occupied, warm-up, cooldown, setback, freeze protection setback, setup, unoccupied) according to current time, the time to next occupied hours tNexOcc and current zone temperature TZon. See Buildings.Controls.OBC.ASHRAE.G36.ZoneGroups.OperationMode.

Zone setpoint temperature reset

It sets the zone temperature setpoint according to the globally specified setpoints, the local setpoint adjustments, the demand limits adjustment, the window status and the occupancy status. See Buildings.Controls.OBC.ASHRAE.G36.ThermalZones.Setpoints.

Usage

This version is for a single zone only to be used in the Single Zone VAV sequence.

Parameters

Connectors

Modelica definition

Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.PlantRequests

Output plant requests for single zone air handling unit

Information

This sequence outputs the system reset requests for single zone air handling unit. The implementation is according to the Section 5.18.15 of ASHRAE Guideline 36, May 2020.

chilled water reset request yChiWatResReq

1. If the supply air temperature TAirSup exceeds the cooling supply air temperature set point TSupCoo by 3 °C (5 °F) for 2 minutes, send 3 requests.
2. If the supply air temperature TAirSup exceeds the cooling supply air temperature set point TSupCoo by 2 °C (3 °F) for 2 minutes, send 2 requests.
3. Else if the chilled water valve position uCooCoi_actual is greater than 95%, send 1 request until the uCooCoi_actual is less than 85%.
4. Else if the chilled water valve position uCooCoi_actual is less than 95%, send 0 request.

Chiller plant request yChiPlaReq

Send the chiller plant that serves the system a chiller plant request as follows:

1. If the chilled water valve position uCooCoi_actual is greater than 95%, send 1 request until the uCooCoi_actual is less than 10%.
2. Else if the chilled water valve position uCooCoi_actual is less than 95%, send 0 request.

If there is a hot-water coil, hot-water reset requests yHotWatResReq

1. If the supply air temperature TAirSup is 17 °C (30 °F) less than the heating supply air temperature set point TSupHeaEco for 5 minutes, send 3 requests.
2. Else if the supply air temperature TAirSup is 8 °C (15 °F) less than the heating supply air temperature set point TSupHeaEco for 5 minutes, send 2 requests.
3. Else if the hot water valve position uHeaCoi_actual is greater than 95%, send 1 request until the uHeaCoi_actual is less than 85%.
4. Else if the hot water valve position uHeaCoi_actual is less than 95%, send 0 request.

If there is a hot-water coil and heating hot-water plant, heating hot-water plant reqeusts yHotWatPlaReq

Send the heating hot-water plant that serves the air handling unit a heating hot-water plant request as follows:

1. If the hot water valve position uHeaCoi_actual is greater than 95%, send 1 request until the hot water valve position is less than 10%.
2. If the hot water valve position uHeaCoi_actual is less than 95%, send 0 requests.

Parameters

Connectors

Modelica definition

Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.ReliefDamper

Relief damper control for AHUs using actuated dampers without fan

Information

Sequence for controlling actuated relief damper yRelDam for AHUs using actuated relief damper without a fan. It is implemented according to Section 5.18.8 of ASHRAE Guideline G36, May 2020.

In Section 3.2.2.3, find the relief damper position setpoint limits:

• relDam_min: the relief damper position that maintainx a building pressure of 12 Pa (0.05 in. of water) while the economizer is positioned to provide minimum outdoor airflow while the supply fan is at minimum speed.
• relDam_max: the relief damper position that maintainx a building pressure of 12 Pa (0.05 in. of water) while the economizer damper is fully open and the fan speed is at cooling maximum.

Relief damper shall be enabled when the associated supply fan is proven on and any outdoor air damper is open, and disabled and closed otherwise.

Relief damper position shall be reset lineary from relDam_min to relDam_max as the commanded economizer damper position goes from uOutDam_min to 100% open.

Parameters

Connectors

Modelica definition

Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.ReliefFan

Sequence for control of relief fan in AHU

Information

Sequence for controling relief fan that is part of AHU. It is developed based on Section 5.16.9 of ASHRAE Guideline 36, May 2020, with the modification to accommodate the single relief fan control.

1. The relief fan shall be enabled when the AHU supply fan is proven ON (u1SupFan=true), and shall be disabled otherwise.
2. Building static pressure (dpBui) shall be time averaged with a sliding 5-minute window and 15 second sampling rate (to dampen fluctuations). The average value shall be that displayed and used for control.
3. A P-only control loop maintains the building pressure at a set point (dpBuiSet) of 12 Pa (0.05 in. of water) with an output ranging from 0% to 100%. The loop is disabled and output set to zero when the relief fan is disabled.
4. Fan speed shall be equal to the PID signal but no less than the minimum speed.
   1. When relief system is enabled, and the control loop output is above 5%, open the motorized dampers to the relief fans; close the dampers when the loop output drops to 0% for 5 minutes.
   2. When the control loop output is above minimum speed (relFanSpe_min) plus 15% by 7 minutes, start the relief fan.
   3. When the control loop output is below minimum speed (relFanSpe_min) by 5 minutes, shut off the relief fan.

Parameters

Connectors

Modelica definition

Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.ReliefFanGroup

Sequence for relief fans control for AHUs using actuated relief dampers with relief fan(s)

Information

Sequence for controlling relief fans and their dampers for AHUs using actuated relief dampers with relief fan(s). It is developed based on Section 5.16.9 of ASHRAE Guideline 36, May 2020.

1. All operating relief fans that serve a common or shared air volume shall be grouped and controlled as if they were one system, running at the same speed and using the same control loop, even if they are associated with different AHUs.
2. A relief fan shall be enabled when its associated supply fan is proven ON (u1SupFan=true), and shall be disabled otherwise.
3. Building static pressure (dpBui) shall be time averaged with a sliding 5-minute window and 15 second sampling rate (to dampen fluctuations). The average value shall be that displayed and used for control.
4. A P-only control loop maintains the building pressure at a set point (dpBuiSet) of 12 Pa (0.05 in. of water) with an output ranging from 0% to 100%. The loop is disabled and output set to zero when all fans in the relief system group are disabled.
5. Fan speed signal to all operating fans in the relief system group shall be the same and shall be equal to the PID signal but no less than the minimum speed. Except for Stage 0, discharge dampers of all relief fans shall be open only when fan is commanded ON.
   1. Stage 0 (barometric relief). When relief system is enabled, and the control loop output is above 5%, open the motorized dampers to all relief fans serving the relief system group that are enabled; close the dampers when the loop output drops to 0% for 5 minutes.
   2. Stage Up. When control loop is above minimum speed (relFanSpe_min) plus 15%, start stage-up timer. Each time the timer reaches 7 minutes, start the next relief fan (and open the associated damper) in the relief system group, per staging order, and reset the timer to 0. The timer is reset to 0 and frozen if control loop is below minimum speed plus 15%. Note, when staging from Stage 0 (no relief fans) to Stage 1 (one relief fan), the discharge dampers of all nonoperating relief fans must be closed.
   3. Stage Down. When PID loop is below minimum speed (relFanSpe_min), start stage-down timer. Each time the timer reaches 5 minutes, shut off lag fan per staging order and reset the timer to 0. The timer is reset to 0 and frozen if PID loop rises above minimum speed or all fans are OFF. If all fans are OFF, go to Stage 0 (all dampers open and all fans OFF).
6. For fans in a Level 2 alarm and status is OFF, discharge damper shall be closed when is above Stage 0.

Parameters

Connectors

Modelica definition

Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.ReturnFan

Return fan control for single zone AHU

Information

Sequence for controlling return fan yRetFan for single AHUs. It is implemented according to Section 5.18.10 of ASHRAE Guideline G36, May 2020.

• Exhaust damper shall open whenever associated supply fan is proven on.
• Return fan shall run whenever associated supply fan is proven on.
• Return fan speed shall be the same as supply fan speed with a user adjustable offset. See Section 3.2.1.5 for details about the offset.
• Exhaust damper shall be closed when return fan is disabled.

Parameters

Connectors

Modelica definition

Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.Supply

Supply air set point for single zone VAV system

Information

Block that outputs the set points for the supply air temperature for cooling, heating and economizer control, and the fan speed for a single zone VAV system. The implementation is according to the Section 5.18.4 of ASHRAE Guideline 36, May 2020.

Fan speed setpoint

The supply fan shall run whenever the unit is in any mode other than unoccupied mode. Also, a ramp function should be applied to prevent changes in fan speed of more than 10% per minute.

Minimum, medium, and maximum fan speeds shall be as follows:

1. Minimum speed minSpe, maximum cooling speed maxCooSpe, and maximum heatng speed maxHeaSpe shall be given per Section 3.2.2.1 of ASHRAE Guideline 36.
2. Medium fan speed shall be reset linearly based on outdoor air temperature TOut from minSpe when outdoor air temperature is greater than or equal to Endpoint 1 to maxCooSpe when TOut is less than or equal to Endpoint 2.
   • Endpoint 1: the lesser of zone temperature TZon plus 0.5 °C (1 °F) and maximum supply air dew point TSupDew_max.
   • Endpoint 2: the lesser of zone temperature TZon minus 6 °C (10 °F) and maximum supply air dew point TSupDew_max minus 1 °C (2 °F).

Control mapping

1. For a heating-loop signal uHea of 100% to spePoiOne (default 50%), fan speed is reset from maxHeaSpe to minSpe.
2. For a heating-loop signal uHea of spePoiOne to 0%, fan speed set point is minSpe.
3. In deadband (uHea=0, uCoo=0), fan speed set point is minSpe.
4. For a cooling-loop signal uCoo of 0% to spePoiTwo (default 25%), fan speed is minSpe.
5. For a cooling-loop signal uCoo of spePoiTwo to spePoiThr (default 50%), fan speed is reset from minSpe to medium fan speed.
6. For a cooling-loop signal uCoo of spePoiThr to spePoiFou (default 75%), fan speed is medium.
7. For a cooling-loop signal of uCoo spePoiFou to 100%, fan speed is reset from medium to maxCooSpe.

The figure below shows the sequence.

Supply temperature setpoints

The output TSupCooSet is to be used to control the cooling coil, and the output TSupHeaEcoSet is to be used to control the heating coil and the economizer dampers.

When it is in deadband state, the output TSupCooSet and TSupHeaEcoSet shall be average of the zone heating setpoint THeaSet and the zone cooling setpoint TCooSet but shall be no lower than TSupDea_min, 21 °C (70 °F), and no higher than TSupDea_max, 24 °C (75 °F),

Control mapping

1. For a heating-loop signal uHea of 100% to temPoiOne (default 50%), TSupHeaEcoSet should be TSup_max.
2. For a heating-loop signal uHea of temPoiOne to 0%, TSupHeaEcoSet is reset from TSup_max to the deadband value.
3. In deadband (uHea=0, uCoo=0), TSupHeaEcoSet is the deadband value.
4. For a cooling-loop signal uCoo of 0% to temPoiTwo (default 25%), TSupHeaEcoSet is reset from deadband value to TSup_min minus 1 °C (2 °F), while TSupCooSet is the deadband value.
5. For a cooling-loop signal uCoo of temPoiTwo to temPoiThr (default 50%), TSupHeaEcoSet and TSupCooSet are unchanged.
6. For a cooling-loop signal uCoo of temPoiThr to temPoiFou (default 75%), TSupHeaEcoSet remains at TSup_min minus 1 °C (2 °F), while TSupCooSet is reset from the deadband value to TSup_min.
7. For a cooling-loop signal uCoo of temPoiFou to 100%, TSupHeaEcoSet and TSupCooSet are unchanged.

The figure below shows the sequence.

Note that the inputs uHea and uCoo must be computed based on the same temperature sensors and control loops.

Parameters

Connectors

Modelica definition