Buildings.Controls.OBC.ASHRAE.G36.VentilationZones.Title24
Sequences complying California Title 24
Information
This package contains sequences that specify the zone minimum outdoor air and minimum airflow set points, for compliance with the Ventilation Rate Procedure of Title 24.
Package Content
Name | Description |
---|---|
Setpoints | Specify zone minimum outdoor air and minimum airflow set points for compliance with California Title 24 |
Validation | Collection of validation models |
Buildings.Controls.OBC.ASHRAE.G36.VentilationZones.Title24.Setpoints
Specify zone minimum outdoor air and minimum airflow set points for compliance with California Title 24
Information
This sequence sets the zone minimum outdoor air and minimum airflow setpoints, for compliance with the ventilation rate procedure of California Title 24. The implementation is according to Section 5.2.1.4 of ASHRAE Guideline36, May 2020. The calculation is done following the steps below.
1. For every zone that requires mechanical ventilation, the zone minimum outdoor airflows and set points shall be calculated depending on the governing standard or code for outdoor air requirements.
2. According to section 3.1.2 of Guideline 36, the zone minimum airflow setpoint
VMin_flow
and the zone cooling maximum setpoint VCooMax_flow
should be provided by designer.
Zone ventilation set points
According to Section 3.1.1.2.b of Guideline 36,
-
The zone minimum outdoor airflow for occupants
VOccMin_flow
, per California Title 24 prescribed airflow-per-occupant requirements. -
The zone minimum outdoor airflow for building area
VAreMin_flow
, per California Title 24 prescribed airflow-per-area requirements.
Zone minimum outdoor air setpoints
The zone absolute minimum outdoor airflow setpoint VZonAbsMin_flow
is
used in terminal-unit sequences and air-handler sequences.
The zone design minimum outdoor airflow setpoint VZonDesMin_flow
is
used in air-handler sequences only.
-
VZonAbsMin_flow
shall be reset based on the following conditions in order from highest to lowest priority:- Zero if the zone has a window switch and the window is open.
-
Twenty-five percent of the
VAreMin_flow
if the zone has an occupancy sensor and is unpopulated. -
If the zone has a CO2 sensor,
VAreMin_flow
. -
Otherwise,
VZonDesMin_flow
.
-
VZonDesMin_flow
is equal to the following:- Zero if the zone has a window switch and the window is open.
-
Twenty-five percent of the
VAreMin_flow
if the zone has an occupancy sensor and is unpopulated. -
The larger of
VAreMin_flow
andVOccMin_flow
otherwise.
Occupied minimum airflow
The occupied minimum airflow shall be equal to VMin_flow
except as
noted in below section.
Occupied minimum airflow modification
-
If the zone has an occupancy sensor, the minimum airflow
VOccZonMin_flow
shall be equal to 25% of theVAreMin_flow
when the room is unpopulated. -
If the zone has a window switch, the minimum airflow
VOccZonMin_flow
shall be zero when the window is open. -
If the zone has a CO2 sensor:
-
Specify CO2 setpoint
ppmCO2Set
according to Section 3.1.1.3 of Guideline 36. - During occupied mode, a P-only loop shall maintain CO2 concentration at setpoint; reset from 0% at set point minus 200 PPM and to 100% at setpoint.
- Loop is disabled and output set to zero when the zone is not in occupied mode.
-
For cooling-only VAV terminal units, reheat VAV terminal units, constant-volume series
fan-powered terminal units, dual-duct VAV terminal units with mixing control and inlet
airflow sensors, dual-duct VAV terminal units with mixing control and a discharge
airflow sensor, or dual-duct VAV terminal units with cold-duct minimum control:
-
The CO2 control loop output shall reset the occupied minimum airflow setpoint
VOccZonMin_flow
from the zone minimum airflow setpointVMin_flow
at 0% loop output up to maximum cooling airflow setpointVCooMax_flow
at 50% loop output. The loop output from 50% to 100% will be used at the system level to reset outdoor air minimum.
-
The CO2 control loop output shall reset the occupied minimum airflow setpoint
-
For parallel fan-powered terminal units:
-
Determin the maximum flow rate for control CO2 level: when the zone state is cooling,
the maximum flow rate is equal to the maximum cooling airflow setpoint
VCooMax_flow
; when the zone state is heating or deadband, the maximum flow rate is equal toVCooMax_flow
minus the parallel fan airflowVParFan_flow
. -
The CO2 control loop ouput shall reset the occupied minimum airflow setpoint from the
zone minimum airflow setpoint
VMin_flow
at 0% loop output up to maximum cooling airflow setpoint for CO2 control at 50% loop output. The loop output from 50% to 100% will be used at the system level to reset outdoor air minimum.
-
Determin the maximum flow rate for control CO2 level: when the zone state is cooling,
the maximum flow rate is equal to the maximum cooling airflow setpoint
-
Specify CO2 setpoint
Minimum outdoor airflow for single zone VAV air handler unit
The minimum outdoor air setpoint shall be reset
based on the zone CO2 control-llop signal from VZonAbsMin_flow
at 0% signal
to VZonDesMin_flow
at 100% signal.
If there is no CO2 sensor, the minimum outdoor air setpoint should be VZonDesMin_flow
.
Parameters
Type | Name | Default | Description |
---|---|---|---|
Boolean | have_winSen | false | True: the zone has window sensor |
Boolean | have_occSen | false | True: the zone has occupancy sensor |
Boolean | have_CO2Sen | false | True: the zone has CO2 sensor |
Boolean | have_typTerUni | false | True: the zone has typical terminal units and CO2 sensor |
Boolean | have_parFanPowUni | false | True: the zone has parallel fan-powered terminal unit and CO2 sensor |
Boolean | have_SZVAV | false | True: it is single zone VAV AHU system with CO2 sensor |
Design conditions | |||
Real | VOccMin_flow | Zone minimum outdoor airflow for occupants [m3/s] | |
Real | VAreMin_flow | Zone minimum outdoor airflow for building area [m3/s] | |
Real | VMin_flow | Design zone minimum airflow setpoint [m3/s] | |
Real | VCooMax_flow | 0.025 | Design zone cooling maximum airflow rate [m3/s] |
Connectors
Type | Name | Description |
---|---|---|
input BooleanInput | u1Win | Window status, true if open, false if closed |
input BooleanInput | u1Occ | True: the zone is populated |
input IntegerInput | uOpeMod | Zone operation mode |
input RealInput | ppmCO2Set | CO2 concentration setpoint, in PPM |
input RealInput | ppmCO2 | Detected CO2 concentration |
input IntegerInput | uZonSta | Zone state |
input RealInput | VParFan_flow | Parallel fan airflow rate [m3/s] |
output RealOutput | VZonAbsMin_flow | Zone absolute minimum outdoor airflow setpoint [m3/s] |
output RealOutput | VZonDesMin_flow | Zone design minimum outdoor airflow setpoint [m3/s] |
output RealOutput | VOccZonMin_flow | Occupied zone minimum airflow setpoint [m3/s] |
output RealOutput | yCO2 | CO2 control loop signal [1] |
output RealOutput | VMinOA_flow | Zone minimum outdoor airflow setpoint [m3/s] |