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Buildings.Examples.VAVReheat

Variable air volume flow system with terminal reheat and five thermal zones

Information

This package contains variable air volume flow models for office buildings.

Note

The models Buildings.ThermalZones.EnergyPlus_9_6_0.Examples.SmallOffice.ASHRAE2006Winter and Buildings.ThermalZones.EnergyPlus_9_6_0.Examples.SmallOffice.Guideline36Winter appear to be quite similar to Buildings.Examples.VAVReheat.ASHRAE2006 and Buildings.Examples.VAVReheat.Guideline36, respectively, because they all have the same HVAC system, control sequences, and all have five thermal zones. However, the models in Buildings.ThermalZones.EnergyPlus_9_6_0.Examples.SmallOffice are from the DOE Commercial Reference Building, Small Office, new construction, ASHRAE 90.1-2004, Version 1.3_5.0, whereas the models in Buildings.Examples.VAVReheat are from the DOE Commercial Building Benchmark, Medium Office, new construction, ASHRAE 90.1-2004, version 1.2_4.0. Therefore, the dimensions of the thermal zones in Buildings.ThermalZones.EnergyPlus_9_6_0.Examples.SmallOffice are considerably smaller than in Buildings.Examples.VAVReheat. As the sizing is scaled with the volumes of the thermal zones, the model structure is the same, but the design capacities are different, as is the energy consumption.

Extends from Modelica.Icons.ExamplesPackage (Icon for packages containing runnable examples).

Package Content

Name Description
Buildings.Examples.VAVReheat.ASHRAE2006 ASHRAE2006 Variable air volume flow system with terminal reheat and five thermal zones
Buildings.Examples.VAVReheat.Guideline36 Guideline36 Variable air volume flow system with terminal reheat and five thermal zones
Buildings.Examples.VAVReheat.Validation Validation Collection of validation models
Buildings.Examples.VAVReheat.BaseClasses BaseClasses Package with base classes for Buildings.Examples.VAVReheat

Buildings.Examples.VAVReheat.ASHRAE2006 Buildings.Examples.VAVReheat.ASHRAE2006

Variable air volume flow system with terminal reheat and five thermal zones

Buildings.Examples.VAVReheat.ASHRAE2006

Information

This model consist of an HVAC system, a building envelope model and a model for air flow through building leakage and through open doors.

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 five zone inlet branches. The figure below shows the schematic diagram of the HVAC system

image

See the model Buildings.Examples.VAVReheat.BaseClasses.PartialHVAC for a description of the HVAC system, and see the model Buildings.Examples.VAVReheat.BaseClasses.Floor for a description of the building envelope.

The control is an implementation of the control sequence VAV 2A2-21232 of the Sequences of Operation for Common HVAC Systems (ASHRAE, 2006). In this control sequence, the supply fan speed is modulated based on the duct static pressure. The return fan controller tracks the supply fan air flow rate. The duct static pressure set point is adjusted so that at least one VAV damper is 90% open. The heating coil valve, outside air damper, and cooling coil valve are modulated in sequence to maintain the supply air temperature set point. The economizer control provides the following functions: freeze protection, minimum outside air requirement, and supply air cooling, see Buildings.Examples.VAVReheat.BaseClasses.Controls.Economizer. The controller of the terminal units tracks the room air temperature set point based on a "dual maximum with constant volume heating" logic, see Buildings.Examples.VAVReheat.BaseClasses.Controls.RoomVAV.

There is also a finite state machine that transitions the mode of operation of the HVAC system between the modes occupied, unoccupied off, unoccupied night set back, unoccupied warm-up and unoccupied pre-cool. In the VAV model, all air flows are computed based on the duct static pressure distribution and the performance curves of the fans. Local loop control is implemented using proportional and proportional-integral controllers, while the supervisory control is implemented using a finite state machine.

A similar model but with a different control sequence can be found in Buildings.Examples.VAVReheat.Guideline36.

References

ASHRAE. Sequences of Operation for Common HVAC Systems. ASHRAE, Atlanta, GA, 2006.

Extends from Modelica.Icons.Example (Icon for runnable examples), Buildings.Examples.VAVReheat.BaseClasses.HVACBuilding (Partial model that contains the HVAC and building model).

Parameters

TypeNameDefaultDescription
replaceable package MediumAAirMedium model for air
replaceable package MediumWWaterMedium model for water
MassFlowRatemCor_flow_nominalACHCor*VRooCor*convDesign mass flow rate core [kg/s]
MassFlowRatemSou_flow_nominalACHSou*VRooSou*convDesign mass flow rate south [kg/s]
MassFlowRatemEas_flow_nominalACHEas*VRooEas*convDesign mass flow rate east [kg/s]
MassFlowRatemNor_flow_nominalACHNor*VRooNor*convDesign mass flow rate north [kg/s]
MassFlowRatemWes_flow_nominalACHWes*VRooWes*convDesign mass flow rate west [kg/s]
TemperatureTHeaWatInl_nominal45 + 273.15Reheat coil nominal inlet water temperature [K]
RealACHCor6Design air change per hour core [1/h]
RealACHSou6Design air change per hour south [1/h]
RealACHEas9Design air change per hour east [1/h]
RealACHNor6Design air change per hour north [1/h]
RealACHWes7Design air change per hour west [1/h]

Modelica definition

model ASHRAE2006 "Variable air volume flow system with terminal reheat and five thermal zones" extends Modelica.Icons.Example; extends Buildings.Examples.VAVReheat.BaseClasses.HVACBuilding( mCor_flow_nominal=ACHCor*VRooCor*conv, mSou_flow_nominal=ACHSou*VRooSou*conv, mEas_flow_nominal=ACHEas*VRooEas*conv, mNor_flow_nominal=ACHNor*VRooNor*conv, mWes_flow_nominal=ACHWes*VRooWes*conv, redeclare Buildings.Examples.VAVReheat.BaseClasses.ASHRAE2006 hvac, redeclare replaceable Buildings.Examples.VAVReheat.BaseClasses.Floor flo( sampleModel=true)); parameter Real ACHCor(final unit="1/h")=6 "Design air change per hour core"; parameter Real ACHSou(final unit="1/h")=6 "Design air change per hour south"; parameter Real ACHEas(final unit="1/h")=9 "Design air change per hour east"; parameter Real ACHNor(final unit="1/h")=6 "Design air change per hour north"; parameter Real ACHWes(final unit="1/h")=7 "Design air change per hour west"; end ASHRAE2006;

Buildings.Examples.VAVReheat.Guideline36 Buildings.Examples.VAVReheat.Guideline36

Variable air volume flow system with terminal reheat and five thermal zones

Buildings.Examples.VAVReheat.Guideline36

Information

This model consist of an HVAC system, a building envelope model and a model for air flow through building leakage and through open doors.

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 five zone inlet branches.

See the model Buildings.Examples.VAVReheat.BaseClasses.PartialHVAC for a description of the HVAC system, and see the model Buildings.Examples.VAVReheat.BaseClasses.Floor for a description of the building envelope.

The control is based on ASHRAE Guideline 36, and implemented using the sequences from the library Buildings.Controls.OBC.ASHRAE.G36 for multi-zone VAV systems with economizer. The schematic diagram of the HVAC and control sequence is shown in the figure below.

image

A similar model but with a different control sequence can be found in Buildings.Examples.VAVReheat.ASHRAE2006. Note that this model, because of the frequent time sampling, has longer computing time than Buildings.Examples.VAVReheat.ASHRAE2006. The reason is that the time integrator cannot make large steps because it needs to set a time step each time the control samples its input.

Extends from Modelica.Icons.Example (Icon for runnable examples), Buildings.Examples.VAVReheat.BaseClasses.HVACBuilding (Partial model that contains the HVAC and building model).

Parameters

TypeNameDefaultDescription
replaceable package MediumAAirMedium model for air
replaceable package MediumWWaterMedium model for water
MassFlowRatemCor_flow_nominalACHCor*VRooCor*convDesign mass flow rate core [kg/s]
MassFlowRatemSou_flow_nominalACHSou*VRooSou*convDesign mass flow rate south [kg/s]
MassFlowRatemEas_flow_nominalACHEas*VRooEas*convDesign mass flow rate east [kg/s]
MassFlowRatemNor_flow_nominalACHNor*VRooNor*convDesign mass flow rate north [kg/s]
MassFlowRatemWes_flow_nominalACHWes*VRooWes*convDesign mass flow rate west [kg/s]
TemperatureTHeaWatInl_nominal45 + 273.15Reheat coil nominal inlet water temperature [K]
RealACHCor6Design air change per hour core [1/h]
RealACHSou6Design air change per hour south [1/h]
RealACHEas9Design air change per hour east [1/h]
RealACHNor6Design air change per hour north [1/h]
RealACHWes7Design air change per hour west [1/h]

Modelica definition

model Guideline36 "Variable air volume flow system with terminal reheat and five thermal zones" extends Modelica.Icons.Example; extends Buildings.Examples.VAVReheat.BaseClasses.HVACBuilding( mCor_flow_nominal=ACHCor*VRooCor*conv, mSou_flow_nominal=ACHSou*VRooSou*conv, mEas_flow_nominal=ACHEas*VRooEas*conv, mNor_flow_nominal=ACHNor*VRooNor*conv, mWes_flow_nominal=ACHWes*VRooWes*conv, redeclare Buildings.Examples.VAVReheat.BaseClasses.Guideline36 hvac, redeclare Buildings.Examples.VAVReheat.BaseClasses.Floor flo(sampleModel= true)); parameter Real ACHCor(final unit="1/h")=6 "Design air change per hour core"; parameter Real ACHSou(final unit="1/h")=6 "Design air change per hour south"; parameter Real ACHEas(final unit="1/h")=9 "Design air change per hour east"; parameter Real ACHNor(final unit="1/h")=6 "Design air change per hour north"; parameter Real ACHWes(final unit="1/h")=7 "Design air change per hour west"; end Guideline36;