Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow
Package of sequences for calculating minimum outdoor airflow rate
Information
This package contains sequences to set the minimum outdoor airflow setpoint for compliance with the ventilation rate procedure of ASHRAE 62.1-2013. The implementation is according to ASHRAE Guidline 36 (G36), PART 5.N.3.a, PART 5.B.2.b, PART3.1-D.2.a.
- Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.Zone conducts zone level calculations for specifying minimum outdoor airflow rate,
- Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.AHU conducts AHU level calculations for specifying minimum outdoor airflow rate,
- and Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.SumZone finds the sums, the maximum and the minimum of outputs from zone level calculations. They become inputs of AHU level calculation.
Package Content
Name | Description |
---|---|
AHU | Output outdoor airflow related calculations at the AHU level |
SumZone | Output the sum, maximum and minimum from the zone level calculation |
Zone | Output outdoor airflow related calculations at the zone level |
Validation | Collection of validation models |
Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.AHU
Output outdoor airflow related calculations at the AHU level
Information
This sequence outputs AHU level design minimum outdoor airflow rate
VDesOutAir_flow
and effective minimum outdoor airflow rate
VEffOutAir_flow
.
It requires following inputs which are sum, maximum or minimum of the outputs from the zone level calculation:
-
Sum of the design population of the zones in the group,
sumDesZonPop
. -
Sum of the population component design breathing zone flow rate,
VSumDesPopBreZon_flow
. -
Sum of the area component design breathing zone flow rate,
VSumDesAreBreZon_flow
. -
Minimum of all zones ventilation efficiency,
uDesSysVenEff
. -
Sum of all zones required uncorrected outdoor airflow rate,
VSumUncOutAir_flow
. -
Sum of the measured discharged flow rate of all terminal units,
VSumSysPriAir_flow
. -
Maximum of primary outdoor air fraction of all zones,
uOutAirFra_max
.
The calculation is done using the steps below.
-
Compute the occupancy diversity fraction
occDivFra
. During system operation, the system population equals the sum of the zone population, sooccDivFra=1
. It has no impact on the calculation of the uncorrected outdoor airflowsysUncOutAir
. For design purpose, compute for all zonesoccDivFra = peaSysPop/sumDesZonPop
where
peaSysPop
is the peak system population andsumDesZonPop
is the sum of the design population. -
Compute the design uncorrected outdoor airflow rate
VDesUncOutAir_flow
asVDesUncOutAir_flow = occDivFra*VSumDesPopBreZon_flow+VSumDesAreBreZon_flow.
-
Compute the uncorrected outdoor airflow rate
sysUncOutAir
assysUncOutAir = min(VDesUncOutAir_flow, VSumUncOutAir_flow)
where
VSumUncOutAir_flow
is sum of all zones required uncorrected outdoor airflow rate -
Compute the outdoor air fraction as
outAirFra = sysUncOutAir/VSumSysPriAir_flow.
For design purpose, use
aveOutAirFra = sysUncOutAir/VPriSysMax_flow.
where
VPriSysMax_flow
is the maximum expected system primary airflow at design stage. -
Compute the system ventilation efficiency
sysVenEff
. During system operation, the efficiency issysVenEff = 1 + outAirFra - uOutAirFra_max
-
Compute the minimum required AHU outdoor air intake flow rate. The minimum required system outdoor air intake flow should be the uncorrected outdoor air intake
sysUncOutAir
divided by the system ventilation efficiencysysVenEff
, but it should not be larger than the design outdoor air ratedesOutAirInt
. Hence,effMinOutAirInt = min(sysUncOutAir/sysVenEff, desOutAirInt),
where the design outdoor air rate
desOutAirInt
isdesOutAirInt = VDesUncOutAir_flow/uDesSysVenEff.
Parameters
Type | Name | Default | Description |
---|---|---|---|
Nominal condition | |||
Real | VPriSysMax_flow | Maximum expected system primary airflow at design stage [m3/s] | |
Real | peaSysPop | Peak system population [1] |
Connectors
Type | Name | Description |
---|---|---|
input RealInput | sumDesZonPop | Sum of the design population of the zones in the group [1] |
input RealInput | VSumDesPopBreZon_flow | Sum of the population component design breathing zone flow rate [m3/s] |
input RealInput | VSumDesAreBreZon_flow | Sum of the area component design breathing zone flow rate [m3/s] |
input RealInput | uDesSysVenEff | Design system ventilation efficiency, equals to the minimum of all zones ventilation efficiency [1] |
input RealInput | VSumUncOutAir_flow | Sum of all zones required uncorrected outdoor airflow rate [m3/s] |
input RealInput | VSumSysPriAir_flow | System primary airflow rate, equals to the sum of the measured discharged flow rate of all terminal units [m3/s] |
input RealInput | uOutAirFra_max | Maximum zone outdoor air fraction, equals to the maximum of primary outdoor air fraction of all zones [1] |
input BooleanInput | uSupFan | Supply fan status, true if on, false if off |
input IntegerInput | uOpeMod | AHU operation mode status signal |
output RealOutput | VDesUncOutAir_flow | Design uncorrected minimum outdoor airflow rate [m3/s] |
output RealOutput | yAveOutAirFraPlu | Average outdoor air flow fraction plus 1 [1] |
output RealOutput | VDesOutAir_flow | Design minimum outdoor airflow rate [m3/s] |
output RealOutput | VEffOutAir_flow | Effective minimum outdoor airflow setpoint [m3/s] |
output RealOutput | effOutAir_normalized | Effective minimum outdoor airflow setpoint, normalized by VDesOutMin_flow_nominal [1] |
output BooleanOutput | yReqOutAir | True if the AHU supply fan is on and the zone is in occupied mode |
Modelica definition
Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.SumZone
Output the sum, maximum and minimum from the zone level calculation
Information
This sequence sums up the zone level minimum outdoor airflow setpoints, finds the maximum zone outdoor air fraction and the minimum zone ventilation efficiency. It collects zone level outputs and prepares inputs for specifying AHU level minimum outdoor air setpoint.
It requires following inputs from zone level calculation,
-
Design zone peak occupancy,
uDesZonPeaOcc
, -
Population component of the breathing zone design outdoor airflow,
VDesPopBreZon_flow
, -
Area component of the breathing zone design outdoor airflow,
VDesAreBreZon_flow
, -
Design zone primary outdoor air fraction,
uDesPriOutAirFra
, -
Uncorrected outdoor airflow rate,
VUncOutAir_flow
, -
Primary outdoor air fraction,
uPriOutAirFra
, -
Primary airflow rate,
VPriAir_flow
,
and following input from AHU level calculation,
-
Average AHU level outdoor air flow fraction plus 1,
yAveOutAirFraPlu
.
The sequence gives following outputs for AHU level calculation:
-
Sum of the design population of the zones,
ySumDesZonPop
, -
Sum of the population component of the design breathing zone flow rate,
VSumDesPopBreZon_flow
, -
Sum of the area component of the design breathing zone flow rate,
VSumDesAreBreZon_flow
, -
Design system ventilation efficiency,
yDesSysVenEff
,First, compute the zone ventilation efficiency
zonVenEff
, for design purpose, aszonVenEff[i] = yAveOutAirFraPlu - uDesPriOutAirFra[i]
where the
uDesPriOutAirFra
is the design zone outdoor airflow fraction. Then the design system ventilation efficiencyyDesSysVenEff
isyDesSysVenEff = min(zonVenEff[i]).
-
Sum of the required uncorrected outdoor airflow rate,
VSumUncOutAir_flow
, -
Maximum zone outdoor air fraction,
uOutAirFra_max
, -
AHU level primary airflow rate,
VSumSysPriAir_flow
.
Parameters
Type | Name | Default | Description |
---|---|---|---|
Integer | numZon | Total number of zones that the system serves |
Connectors
Type | Name | Description |
---|---|---|
input RealInput | uDesZonPeaOcc[numZon] | Design zone peak occupancy [1] |
input RealInput | VDesPopBreZon_flow[numZon] | Population component breathing zone design outdoor airflow [m3/s] |
input RealInput | VDesAreBreZon_flow[numZon] | Area component breathing zone design outdoor airflow [m3/s] |
input RealInput | yAveOutAirFraPlu | Average system outdoor air flow fraction plus 1 [1] |
input RealInput | uDesPriOutAirFra[numZon] | Design zone primary outdoor air fraction [1] |
input RealInput | VUncOutAir_flow[numZon] | Uncorrected outdoor airflow rate [m3/s] |
input RealInput | uPriOutAirFra[numZon] | Primary outdoor air fraction [1] |
input RealInput | VPriAir_flow[numZon] | Primary airflow rate [m3/s] |
output RealOutput | ySumDesZonPop | Sum of the design population of the zones in the group [1] |
output RealOutput | VSumDesPopBreZon_flow | Sum of the population component design breathing zone flow rate [m3/s] |
output RealOutput | VSumDesAreBreZon_flow | Sum of the area component design breathing zone flow rate [m3/s] |
output RealOutput | yDesSysVenEff | Design system ventilation efficiency, equals to the minimum of all zones ventilation efficiency [1] |
output RealOutput | VSumUncOutAir_flow | Sum of the required uncorrected outdoor airflow rate [m3/s] |
output RealOutput | uOutAirFra_max | Maximum zone outdoor air fraction, equals to the maximum of primary outdoor air fraction of all zones [1] |
output RealOutput | VSumSysPriAir_flow | AHU level primary airflow rate, equals to the sum of the measured discharged flow rate of all terminal units [m3/s] |
Modelica definition
Buildings.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.Zone
Output outdoor airflow related calculations at the zone level
Information
This sequence conducts calculations of the minimum outdoor airflow rate at the zone level. It gives outputs below.
-
The population component of the breathing zone outdoor airflow,
VDesPopBreZon_flow
. -
The area component of the breathing zone outdoor airflow,
VDesAreBreZon_flow
. -
Design zone primary outdoor air fraction,
yDesPriOutAirFra
. -
Uncorrected outdoor airflow rate,
VUncOutAir_flow
. This flow rate is calculated based on: occupancy (if there is occupancy sensor) or design occupancy (if there is no occupancy sensor), and air distribution effectiveness (warm or cool air). -
Primary outdoor air fraction,
yPriOutAirFra
. -
Primary airflow rate,
VPriAir_flow
.
The calculation is done using the steps below.
-
Compute the required breathing zone outdoor airflow using the following components.
- The area component of the breathing zone outdoor airflow,
VDesAreBreZon_flow
. - The population component of the breathing zone outdoor airflow,
VDesPopBreZon_flow
.
The number of occupant in the zone can be retrieved directly from occupancy sensor (
nOcc
) if the sensor exists, or using the default occupant density (occDen
) and multiplying it with zone area (AFlo
). The occupant density can be found from Table 6.2.2.1 in ASHRAE Standard 62.1-2013. For design purpose, use the design zone population (desZonPop
) to determine the minimum requirement at the ventilation-design condition. - The area component of the breathing zone outdoor airflow,
-
Compute the zone air-distribution effectiveness. Table 6.2.2.2 in ASHRAE 62.1-2013 lists some typical values for setting the effectiveness. Depending on difference between zone space temperature
TZon
and discharge air temperature (after the reheat coil)TDis
, Warm-air effectivenesszonDisEffHea
or Cool-air effectivenesszonDisEffCoo
should be applied. -
Compute the required zone outdoor airflow
zonOutAirRate
. If the zone is in any mode other than occupied mode (uReqOutAir=false
) or if the zone has window switches and the window is open (uWin=true
), setzonOutAirRate = 0
. Otherwise, the required zone outdoor airflowzonOutAirRate
shall be calculated as follows:-
If the zone is populated (
nOcc
> 0), or if there is no occupancy sensor (have_occSen = false
):-
If the discharge air temperature at the terminal unit is less than or equal to
the zone space temperature, set
zonOutAirRate = (breZonAre+breZonPop)/disEffCoo
. -
If the discharge air temperature at the terminal unit is greater than zone space
temperature, set
zonOutAirRate = (breZonAre+breZonPop)/disEffHea
.
-
If the discharge air temperature at the terminal unit is less than or equal to
the zone space temperature, set
-
If the zone has an occupancy sensor and is unpopulated (
nOcc=0
):-
If the discharge air temperature at the terminal unit is less than or equal to
the zone space temperature, set
zonOutAirRate = breZonAre/disEffCoo
. -
If the discharge air temperature at the terminal unit is greater than zone
space temperature, set
zonOutAirRate = breZonAre/disEffHea
.
-
If the discharge air temperature at the terminal unit is less than or equal to
the zone space temperature, set
-
If the zone is populated (
-
Compute the outdoor air fraction for the zone
yPriOutAirFra
as follows. Set the zone outdoor air fraction toyPriOutAirFra = zonOutAirRate/VPriAir_flow
where,
VPriAir_flow
is the maximum between the measured discharge air flow rate from the zone VAV boxVDis_flow
and 0.1% of AHU level design uncorrected minimum outdoor airflow rateVUncOut_flow_nominal
. For design purpose, the design zone outdoor air fractionyDesPriOutAirFra
isyDesPriOutAirFra = desZonOutAirRate/minZonPriFlo
where
minZonPriFlo
is the minimum expected zone primary flow rate anddesZonOutAirRate
is the required design zone outdoor airflow rate.
References
ANSI/ASHRAE Standard 62.1-2013, Ventilation for Acceptable Indoor Air Quality.
Stanke, D., 2010. Dynamic Reset for Multiple-Zone Systems. ASHRAE Journal, March 2010.
Parameters
Type | Name | Default | Description |
---|---|---|---|
Boolean | have_occSen | true | Set to true if zones have occupancy sensor |
Boolean | have_winSen | true | Set to true if zones have window status sensor |
Real | occDen | 0.05 | Default number of person in unit area [1/m2] |
Real | zonDisEffHea | 0.8 | Zone air distribution effectiveness during heating [1] |
Real | zonDisEffCoo | 1.0 | Zone air distribution effectiveness during cooling [1] |
Nominal condition | |||
Real | VOutPerAre_flow | 3e-4 | Outdoor air rate per unit area [m3/(s.m2)] |
Real | VOutPerPer_flow | 2.5e-3 | Outdoor air rate per person [m3/s] |
Real | AFlo | Floor area of each zone [m2] | |
Real | desZonDisEff | 1.0 | Design zone air distribution effectiveness [1] |
Real | desZonPop | Design zone population during peak occupancy [1] | |
Real | minZonPriFlo | Minimum expected zone primary flow rate [m3/s] | |
Advanced | |||
Real | uLow | -0.5 | If zone space temperature minus supply air temperature is less than uLow, then it should use heating supply air distribution effectiveness [K] |
Real | uHig | 0.5 | If zone space temperature minus supply air temperature is more than uHig, then it should use cooling supply air distribution effectiveness [K] |
Connectors
Type | Name | Description |
---|---|---|
input IntegerInput | nOcc | Number of occupants |
input BooleanInput | uWin | Window status, true if open, false if closed |
input BooleanInput | uReqOutAir | True if the AHU supply fan is on and the zone is in occupied mode |
input RealInput | TZon | Measured zone air temperature [K] |
input RealInput | TDis | Measured discharge air temperature [K] |
input RealInput | VDis_flow | Primary airflow rate to the ventilation zone from the air handler, including outdoor air and recirculated air [m3/s] |
input RealInput | VUncOut_flow_nominal | AHU level design uncorrected minimum outdoor airflow rate [m3/s] |
output RealOutput | yDesZonPeaOcc | Design zone peak occupancy [1] |
output RealOutput | VDesPopBreZon_flow | Population component breathing zone design outdoor airflow [m3/s] |
output RealOutput | VDesAreBreZon_flow | Area component breathing zone outdoor airflow [m3/s] |
output RealOutput | yDesPriOutAirFra | Design zone primary outdoor air fraction [1] |
output RealOutput | VUncOutAir_flow | Uncorrected outdoor airflow rate [m3/s] |
output RealOutput | yPriOutAirFra | Primary outdoor air fraction [1] |
output RealOutput | VPriAir_flow | Primary airflow rate [m3/s] |