blockActiveAirFlow
Output the active airflow setpoint for VAV reheat terminal unit
Information
This atomic sequence sets the active maximum and minimum setpoints VActCooMax_flow,
VActCooMin_flow, VActMin_flow, VActHeaMin_flow,
VActHeaMax_flow for VAV reheat terminal unit according to ASHRAE
Guideline 36 (G36), PART 5.E.3-5.
1. Information provided by designer
According to G36 PART 3.1.B.2, following VAV box design information should be provided:
- Zone maximum cooling airflow setpoint
VDisCooSetMax_flow - Zone minimum airflow setpoint
VDisSetMin_flow - Zone maximum heating airflow setpoint
VDisHeaSetMax_flow
2. Occupied minimum airflow VOccDisMin_flow
The VOccDisMin_flow shall be equal to zone minimum airflow setpoint
VDisSetMin_flow except as follows:
-
If the zone has an occupancy sensor,
VOccDisMin_flowshall be equal to minimum breathing zone outdoor airflow (if ventilation is according to ASHRAE Standard 62.1-2013) or zone minimum outdoor airflow for building area (if ventilation is according to California Title 24) when the room is unpopulated. -
If the zone has a window switch,
VOccDisMin_flowshall be zero when the window is open. -
If
VDisSetMin_flowis non-zero and less than the lowest possible airflow setpoint allowed by the controlsVDisConMin_flow,VOccDisMin_flowshall be set equal toVDisConMin_flow. -
If the zone has a CO2 sensor, then following steps are applied for calculating
VOccDisMin_flow. (1) During occupied mode, a P-only loop shall maintain CO2 concentration at setpoint, reset 0% at (CO2 setpointCO2Set- 200 ppm) and 100% atCO2Set. If ventilation outdoor airflow is controlled in accordance with ASHRAE Standard 62.1-2013, the loop output shall reset theVOccDisMin_flowfromVDisSetMin_flowat 0% loop output up toVDisCooSetMax_flowat 100% loop output; (2) Loop is diabled and output set to zero when the zone is not in occupied mode.
3. Active maximum and minimum setpoints
The setpoints shall vary depending on the mode of the zone group.
| Setpoint | Occupied | Cool-down | Setup | Warmup | Setback | Unoccupied |
|---|---|---|---|---|---|---|
Cooling maximum (VActCooMax_flow) | VDisCooSetMax_flow |
VDisCooSetMax_flow | VDisCooSetMax_flow |
0 | 0 | 0 |
Cooling minimum (VActCooMin_flow) | VOccDisMin_flow |
0 | 0 | 0 | 0 | 0 |
Minimum (VActMin_flow) | VOccDisMin_flow | 0 | 0 | 0 | 0 | 0 |
Heating minimum (VActHeaMin_flow) | VOccDisMin_flow |
0 | 0 | VDisHeaSetMax_flow | VDisHeaSetMax_flow |
0 |
Heating maximum (VActHeaMax_flow) | max(VDisHeaSetMax_flow,VOccDisMin_flow) |
VDisHeaSetMax_flow | 0 | VDisCooSetMax_flow | VDisCooSetMax_flow |
0 |
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Zone sensors | |||
| Boolean | have_occSen | Set to true if the zone has occupancy sensor | |
| Boolean | have_winSen | Set to true if the zone has window status sensor | |
| Boolean | have_CO2Sen | Set to true if the zone has CO2 sensor | |
| Nominal condition | |||
| Real | VDisCooSetMax_flow | Zone maximum cooling airflow setpoint | |
| Real | VDisSetMin_flow | Zone minimum airflow setpoint | |
| Real | VDisHeaSetMax_flow | Zone maximum heating airflow setpoint | |
| Real | VDisConMin_flow | VAV box controllable minimum | |
| Real | AFlo | Area of the zone | |
| Real | VOutPerAre_flow | 3e-4 | Outdoor air rate per unit area |
| Real | VOutPerPer_flow | 2.5e-3 | Outdoor air rate per person |
| Real | CO2Set | 894 | CO2 setpoint in ppm |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | nOcc | Number of occupants | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | ppmCO2 | Detected CO2 conventration | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uWin | Window status, true if open, false if closed | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uOpeMod | Zone operation mode | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | VOccDisMin_flow | Occupied minimum airflow | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | VActCooMax_flow | Active cooling maximum | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | VActCooMin_flow | Active cooling minimum | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | VActMin_flow | Active minimum | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | VActHeaMin_flow | Active heating minimum | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | VActHeaMax_flow | Active heating maximum |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Reals.MultiplyByParameter | gai | Outdoor air per person | |
| Buildings.Controls.OBC.CDL.Reals.Add | breZon | Breathing zone airflow | |
| Buildings.Controls.OBC.CDL.Reals.Line | co2ConLoo | Maintain CO2 concentration at setpoint, reset 0% at (setpoint-200) and 100% at setpoint | |
| Buildings.Controls.OBC.CDL.Reals.Line | lin1 | Reset occupied minimum airflow setpoint from 0% at VDisSetMin_flow and 100% at VDisCooSetMax_flow | |
| Buildings.Controls.OBC.CDL.Reals.Greater | gre | Check if zone minimum airflow setpoint Vmin is less than the allowed controllable VDisConMin_flow | |
| Buildings.Controls.OBC.CDL.Reals.GreaterThreshold | greThr1 | Check if zone minimum airflow setpoint VDisSetMin_flow is non-zero | |
| Buildings.Controls.OBC.CDL.Reals.Switch | swi | Reset occupied minimum airflow according to occupancy | |
| Buildings.Controls.OBC.CDL.Reals.Switch | swi1 | Reset occupied minimum airflow according to window status | |
| Buildings.Controls.OBC.CDL.Reals.Switch | swi2 | Reset occupied minimum airflow setpoint according to minimum controllable airflow | |
| Buildings.Controls.OBC.CDL.Reals.Switch | swi3 | Switch between zero signal and CO2 control loop signal depending on the operation mode | |
| Buildings.Controls.OBC.CDL.Logical.And | and1 | Logical and | |
| Buildings.Controls.OBC.CDL.Logical.Not | not1 | Logical not | |
| Buildings.Controls.OBC.CDL.Logical.Not | not2 | Logical not | |
| Buildings.Controls.OBC.CDL.Reals.GreaterThreshold | greThr | Check if the zone becomes unpopulated |