.Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.TerminalUnits.Reheat.SetPoints.ActiveAirFlow

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_flow shall 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_flow shall be zero when the window is open.
If VDisSetMin_flow is non-zero and less than the lowest possible airflow setpoint allowed by the controls VDisConMin_flow, VOccDisMin_flow shall be set equal to VDisConMin_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 setpoint CO2Set - 200 ppm) and 100% at CO2Set. If ventilation outdoor airflow is controlled in accordance with ASHRAE Standard 62.1-2013, the loop output shall reset the VOccDisMin_flow from VDisSetMin_flow at 0% loop output up to VDisCooSetMax_flow at 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
Cooling maximum (`VActCooMax_flow`)	`VDisCooSetMax_flow`	`VDisCooSetMax_flow`	`VDisCooSetMax_flow`	0	0
Cooling minimum (`VActCooMin_flow`)	`VOccDisMin_flow`	0	0	0	0
Minimum (`VActMin_flow`)	`VOccDisMin_flow`	0	0	0	0
Heating minimum (`VActHeaMin_flow`)	`VOccDisMin_flow`	0	0	`VDisHeaSetMax_flow`	`VDisHeaSetMax_flow`
Heating maximum (`VActHeaMax_flow`)	max(`VDisHeaSetMax_flow,VOccDisMin_flow`)	`VDisHeaSetMax_flow`	0	`VDisCooSetMax_flow`	`VDisCooSetMax_flow`

Revisions

March 11, 2020, by Jianjun Hu:
Replaced multisum block with add blocks.
This is for #1830.
February 27, 2020, by Jianjun Hu:
Used hysteresis to check occupancy.
This is for #1788.
September 7, 2017, by Jianjun Hu:
First implementation.