modelPartialHVAC

Partial model of variable air volume flow system with terminal reheat that serves five thermal zones

Information

This partial model consist of an HVAC system that serves multiple thermal zones.

The HVAC system is a variable air volume (VAV) flow system with economizer and a heating and cooling coil in the air handler unit. There is also a reheat coil and an air damper in each of the zone inlet branches. The figure below shows the schematic diagram of an HVAC system that supplies 5 zones:

The control sequences for this HVAC system are added in the two models that extend this model, namely Buildings.Examples.VAVReheat.ASHRAE2006 and Buildings.Examples.VAVReheat.Guideline36.

Parameters

Type	Name	Default	Description
Integer	numZon	5	Total number of served VAV boxes
Modelica.Units.SI.Volume[numZon]	VRoo		Room volume per zone
Modelica.Units.SI.Area[numZon]	AFlo		Floor area per zone
Modelica.Units.SI.Area	ATot	sum(AFlo)	Total floor area for all zone
Real	conv	1.2/3600	Conversion factor for nominal mass flow rate
Modelica.Units.SI.HeatFlowRate	QHeaAHU_flow_nominal	mHeaAir_flow_nominalcpAir(THeaAirSup_nominal - THeaAirMix_nominal)	Nominal heating heat flow rate of air handler unit coil
Modelica.Units.SI.HeatFlowRate	QCooAHU_flow_nominal	1.3mCooAir_flow_nominalcpAir*(TCooAirSup_nominal - TCooAirMix_nominal)	Nominal total cooling heat flow rate of air handler unit coil (negative number)
Real	ratOAFlo_A	0.3e-3	Outdoor airflow rate required per unit area
Real	ratOAFlo_P	2.5e-3	Outdoor airflow rate required per person
Real	ratP_A	5e-2	Occupant density
Real	effZ	0.8	Zone air distribution effectiveness (limiting value)
Real	divP	0.7	Occupant diversity ratio
Modelica.Units.SI.VolumeFlowRate[numZon]	VZonOA_flow_nominal	(ratOAFlo_PratP_A + ratOAFlo_A)AFlo/effZ	Zone outdoor air flow rate of each VAV box
Modelica.Units.SI.VolumeFlowRate	Vou_flow_nominal	(divPratOAFlo_PratP_A + ratOAFlo_A)*sum(AFlo)	System uncorrected outdoor air flow rate
Real	effVen	if divP < 0.6 then 0.88*divP + 0.22 else 0.75	System ventilation efficiency
Modelica.Units.SI.VolumeFlowRate	Vot_flow_nominal	Vou_flow_nominal/effVen	System design outdoor air flow rate
Modelica.Units.SI.PressureDifference	dpBuiStaSet	12	Building static pressure
Real	yFanMin	0.1	Minimum fan speed
Boolean	allowFlowReversal	true	= false to simplify equations, assuming, but not enforcing, no flow reversal
Nominal mass flow rate
Modelica.Units.SI.MassFlowRate[numZon]	mCooVAV_flow_nominal		Design mass flow rate per zone for cooling
Modelica.Units.SI.MassFlowRate[numZon]	mHeaVAV_flow_nominal	0.3*mCooVAV_flow_nominal	Design mass flow rate per zone for heating
Modelica.Units.SI.MassFlowRate	mAir_flow_nominal	mCooAir_flow_nominal	Nominal mass flow rate for fan
Modelica.Units.SI.MassFlowRate	mCooAir_flow_nominal	0.7*sum(mCooVAV_flow_nominal)	Nominal mass flow rate for fan
Modelica.Units.SI.MassFlowRate	mHeaAir_flow_nominal	0.7*sum(mHeaVAV_flow_nominal)	Nominal mass flow rate for fan
Modelica.Units.SI.MassFlowRate	mHeaWat_flow_nominal	QHeaAHU_flow_nominal/cpWat/10	Nominal water mass flow rate for heating coil in AHU
Modelica.Units.SI.MassFlowRate	mCooWat_flow_nominal	QCooAHU_flow_nominal/cpWat/(-6)	Nominal water mass flow rate for cooling coil
Room temperature setpoints
Modelica.Units.SI.Temperature	THeaOn	293.15	Heating setpoint during on
Modelica.Units.SI.Temperature	THeaOff	285.15	Heating setpoint during off
Modelica.Units.SI.Temperature	TCooOn	297.15	Cooling setpoint during on
Modelica.Units.SI.Temperature	TCooOff	303.15	Cooling setpoint during off
Air handler unit nominal temperatures and humidity
Modelica.Units.SI.Temperature	TCooAirMix_nominal	303.15	Mixed air temperature during cooling nominal conditions (used to size cooling coil)
Modelica.Units.SI.Temperature	TCooAirSup_nominal	285.15	Supply air temperature during cooling nominal conditions (used to size cooling coil)
Modelica.Units.SI.MassFraction	wCooAirMix_nominal	0.017	Humidity ratio of mixed air at a nominal conditions used to size cooling coil (in kg/kg dry total)
Modelica.Units.SI.Temperature	TCooWatInl_nominal	279.15	Cooling coil nominal inlet water temperature
Modelica.Units.SI.Temperature	THeaAirMix_nominal	277.15	Mixed air temperature during heating nominal conditions (used to size heating coil)
Modelica.Units.SI.Temperature	THeaAirSup_nominal	285.15	Supply air temperature during heating nominal conditions (used to size heating coil)
Modelica.Units.SI.Temperature	THeaWatInl_nominal		Reheat coil nominal inlet water temperature

Connectors

Type	Name	Description
Modelica.Fluid.Interfaces.FluidPort_a[numZon]	port_supAir	Supply air to thermal zones
Modelica.Fluid.Interfaces.FluidPort_a[numZon]	port_retAir	Return air from thermal zones
Modelica.Blocks.Interfaces.RealInput[numZon]	TRoo	Room temperatures
BoundaryConditions.WeatherData.Bus	weaBus	Weather data bus
Modelica.Fluid.Interfaces.FluidPort_a	portHeaCoiSup	Heating coil loop supply
Modelica.Fluid.Interfaces.FluidPort_b	portHeaCoiRet	Heating coil loop return
Modelica.Fluid.Interfaces.FluidPort_a	portHeaTerSup	Terminal heat loop supply
Modelica.Fluid.Interfaces.FluidPort_b	portHeaTerRet	Terminal heat loop return
Modelica.Fluid.Interfaces.FluidPort_a	portCooCoiSup	Cooling coil loop supply
Modelica.Fluid.Interfaces.FluidPort_b	portCooCoiRet	Coolin coil loop return

Components

Type	Name	Description
Buildings.Fluid.Sources.Outside	amb	Ambient conditions
Buildings.Fluid.HeatExchangers.DryCoilEffectivenessNTU	heaCoi	Heating coil
Fluid.HeatExchangers.WetCoilEffectivenessNTU	cooCoi	Cooling coil
Buildings.Fluid.FixedResistances.PressureDrop	dpRetDuc	Pressure drop for return duct
Buildings.Fluid.Movers.Preconfigured.SpeedControlled_y	fanSup	Supply air fan
Buildings.Fluid.Sensors.VolumeFlowRate	senSupFlo	Sensor for supply fan flow rate
Buildings.Fluid.Sensors.VolumeFlowRate	senRetFlo	Sensor for return fan flow rate
Modelica.Blocks.Routing.RealPassThrough	TOut
Buildings.Fluid.Sensors.TemperatureTwoPort	TSup
Buildings.Fluid.Sensors.RelativePressure	dpDisSupFan	Supply fan static discharge pressure
Buildings.Controls.SetPoints.OccupancySchedule	occSch	Occupancy schedule
Buildings.Fluid.Sensors.TemperatureTwoPort	TRet	Return air temperature sensor
Buildings.Fluid.Sensors.TemperatureTwoPort	TMix	Mixed air temperature sensor
Buildings.Fluid.Sensors.VolumeFlowRate	VOut1	Outside air volume flow rate
Results	res	Results of the simulation
Fluid.Actuators.Dampers.Exponential	damRet	Return air damper
Fluid.Actuators.Dampers.Exponential	damOut	Outdoor air damper
Fluid.FixedResistances.Junction	splCooSup	Flow splitter
Fluid.Actuators.Valves.TwoWayEqualPercentage	valCooCoi	Valve for cooling coil
Fluid.FixedResistances.Junction	splCooRet	Flow splitter
Fluid.Movers.Preconfigured.SpeedControlled_y	pumCooCoi	Supply air fan
Fluid.Movers.Preconfigured.SpeedControlled_y	pumHeaCoi	Pump for heating coil
Fluid.Actuators.Valves.TwoWayEqualPercentage	valHeaCoi	Valve for heating coil
Fluid.FixedResistances.Junction	splHeaRet	Flow splitter
Fluid.FixedResistances.Junction	splHeaSup	Flow splitter
Buildings.Examples.VAVReheat.BaseClasses.VAVReheatBox[numZon]	VAVBox	VAV boxes
Buildings.Fluid.FixedResistances.Junction[numZon - 1]	splRetRoo	Splitter for room return air
Buildings.Fluid.FixedResistances.Junction[numZon - 1]	splSupRoo	Splitter for room supply air
Fluid.FixedResistances.PressureDrop	dpSupDuc	Pressure drop for supply duct
Fluid.FixedResistances.Junction	splRetOut	Flow splitter

Name	Description
MediumA
MediumW	Medium model for water
Resultsprotected	Model to store the results of the simulation

Revisions

February 7, 2023, by Jianjun Hu:
Set the value of parameter transferHeat to true for the mixed air temperature sensor.
February 6, 2023, by Jianjun Hu:
Added junction to mix the return and outdoor air.
This is for issue #3230.
August 22, 2022, by Hongxiang Fu:
Replaced fan and pump models with preconfigured mover models. This is for issue #2668.
April 26, 2022, by Michael Wetter:
Changed fan efficiency calculation to use Euler number.
This is for #2668.
November 9, 2021, by Baptiste Ravache:
Vectorized the terminal boxes to be expanded to any number of zones.
This is for issue #2735.
October 4, 2021, by Michael Wetter:
Refactored Buildings.Examples.VAVReheat and its base classes to separate building from HVAC model.
This is for issue #2652.
September 3, 2021, by Michael Wetter:
Updated documentation.
This is for issue #2600.
August 24, 2021, by Michael Wetter:
Changed model to include the hydraulic configurations of the cooling coil, heating coil and VAV terminal box.
This is for issue #2594.
June 30, 2021, by Antoine Gautier:
Changed cooling coil model. This is for issue #2549.
May 6, 2021, by David Blum:
Change to from_dp=false for all mixing box dampers.
This is for issue #2485.
April 30, 2021, by Michael Wetter:
Reformulated replaceable class and introduced floor areas in base class to avoid access of components that are not in the constraining type.
This is for issue #2471.
April 16, 2021, by Michael Wetter:
Refactored model to implement the economizer dampers directly in Buildings.Examples.VAVReheat.BaseClasses.PartialHVAC rather than through the model of a mixing box. Since the version of the Guideline 36 model has no exhaust air damper, this leads to simpler equations.
This is for issue #2454.
March 11, 2021, by Michael Wetter:
Set parameter in weather data reader to avoid computation of wet bulb temperature which is need needed for this model.
February 03, 2021, by Baptiste Ravache:
Refactored the sizing of the heating coil in the VAVBranch (renamed VAVReheatBox) class.
This is for #2024.
July 10, 2020, by Antoine Gautier:
Added design parameters for outdoor air flow.
This is for #2019
November 25, 2019, by Milica Grahovac:
Declared the floor model as replaceable.
September 26, 2017, by Michael Wetter:
Separated physical model from control to facilitate implementation of alternate control sequences.
May 19, 2016, by Michael Wetter:
Changed chilled water supply temperature to 6°C. This is for #509.
April 26, 2016, by Michael Wetter:
Changed controller for freeze protection as the old implementation closed the outdoor air damper during summer. This is for #511.
January 22, 2016, by Michael Wetter:
Corrected type declaration of pressure difference. This is for #404.
September 24, 2015 by Michael Wetter:
Set default temperature for medium to avoid conflicting start values for alias variables of the temperature of the building and the ambient air. This is for issue 426.