Lecture Objectives:

• Finish with software intro – Specifics for eQUEST

• HVAC Systems – and modeling of HVAC Systems

ES programs

• Large variety • http://www.eere.energy.gov/buildings/tools_directory

• DOE2• eQUEST (DOE2)• BLAST • ESPr• TRNSYS• EnergyPlus (DOE2 & BLAST)

ESPrUniversity of Strathclyde - Glasgow, Scotland, UK

• Detailed models – Research program • Use finite difference method for conduction• Simulate actual physical systems • Enable integrated performance assessments

Includes daylight utilization, natural ventilation, airflow modeling CFD, various HVAC and control models

• Detail model – require highly educated users• Primarily for use with UNIX operating systems

ESPrUniversity of Strathclyde - Glasgow, Scotland, UK

• Detailed models

– Research program

TRNSYSSolar Energy Lab - University of Wisconsin

• Modular system approach • One of the most flexible tools available • A library of components • Various building models including HVAC • Specialized for renewable energy and emerging

technologies

• User must provide detailed information about the building and systems

• Not free

Component-based simulation programs - Trnsys

EnergyPlusU S Department of Energy

• Newest generation building energy simulation program ( BLAST + DOE-2)

• Accurate and detailed• Complex modeling capabilities• Large variety of HVAC models• Some integration wit the airflow programs Zonal models and CFD

• Detail model – require highly educated users • Till last year

• Very modest interface• Third party interface – very costly

• Recent development: open studio http://openstudio.nrel.gov/

EnergyPlus

eQUEST (DOE2)US Department of Energy & California utility customers

• eQUEST - interface for the DOE-2 solver• DOE-2 - one of the most widely used ES program - recognized as the industry standard • eQUEST very user friendly interface • Good for life-cycle cost and parametric analyses

• Not very large capabilities for modeling of different HVAC systems

• Many simplified models • Certain limitations related to research application - no capabilities for detailed modeling

eQUEST

• Download it at http://doe2.com/equest/

• Examples related to:– Defining envelope and internal loads – Selecting HVAC system– Presenting results – Finding design cooling and heating loads– Extracting simulation detail

HVAC systems

• Review – Psychrometrics– Air-conditioning in Air Handling Units (AHU)– Refrigeration cycles

• Building-System-Plant connection

Psychrometrics – review

Air-conditioning in Air Handling Unit (AHU)

Compressorand Condenser

Roof top AHU

Gas/Electric Heater

to building

Fan

air from building

fresh air

Evaporator

filtermixing

hotwatercool

water

Return fan

Supply fan

flow control dampers

AHU

Fresh air

AHU schematic

Outdoor air To room

Exhaust From room

Processes in AHU presented in Psychrometric in psychrometric

OA Case forSummer in Austin

IA

MA

SA

Refrigeration Cycle

T outdoor air

T cooled water

Cooling energy (evaporator)

Released energy (condenser)

- What is COP?- How the outdoor air temperature affects chiller performance?

Building-System-Plant

Plant(boilerand/orChiller)

Building

HVAC System(AHU and distribution systems)

Building HVAC Systems (Primary and Secondary Building Systems)

AHU

Buildingenvelope

Cooling(chiller)

(or Gas)

Electricity

Gas

Heating(boilers)

Fresh air For ventilation

Distribution systems

Air transport

Secondary systems

Primarysystems

AHU – Air Handling Unit

HVAC systems affect the energy efficiency of the building as much as the building envelope

Integration of HVAC and building physics models

BuildingHeating/Cooling

SystemPlant

BuildingHeating/Cooling

SystemPlant

Load System Plant model

Integrated models

Qbuiolding Q

including

Ventilation

and

Dehumidification

Example of System Models:Schematic of simple air handling unit (AHU)

rmSfans

cooler heater

mS

QC QH

wO wS

TR

room TR

Qroom_sensibel

(1-r)mS mS

wM

wR

Qroom_latent

TSTO

wR

TM

Tf,inTf,out

m - mass flow rate [kg/s], T – temperature [C], w [kgmoist/kgdry air], r - recirculation rate [-], Q energy/time [W]

Mixing box

Energy and mass balance equations for Air handling unit model – steady state case

SRpSsensibleroom TTcmQ _

mS is the supply air mass flow rate

cp - specific capacity for air,

TR is the room temperature,

TS is the supply air temperature.

changephaseSRSlatentroom iwwmQ __ wR and wS are room and supply humidity ratio

changephasei _ - energy for phase change of water into vapor

The energy balance for the room is given as:

The air-humidity balance for room is given as:

The energy balance for the mixing box is:

ROM TrTrT )1(‘r’ is the re-circulated air portion, TO is the outdoor air temperature, TM is the temperature of the air after the mixing box.

The air-humidity balance for the mixing box is:

ROM wrwrw )1(wO is the outdoor air humidity ratio and

wM is the humidity ratio after the mixing box

)( MSpSHeating TTcmQ

The energy balance for the heating coil is given as:

The energy balance for the cooling coil is given as:

changephaseMSSMSpSCooling iwwmTTcmQ _)(

Non-air system Radiant panel heat transfer model

Room (zone 1)

Radiant Panelc onv ecti

onTsurface

Tsurounding

Tzone_air rad iat ion

Qrad_pan

radiant panel layer (water tube)

air supplysystem

m ,T = const.s s

Qzone

Tw_out Tw_in

Non-air system Radiant panel heat transfer model

)()( __sup_sup airroomairplyairplypair TTmcQ

panradQ _

airpanradzone QQQ _

)()( ,,_ airpanelpanelconvisurfacepanelpaneliradiationconvradiationpanrad TTAhTTAhQQQ

)( ___ inwoutwpwpanrad TTmcQ

The total cooling/heating load in the room

The energy extracted/added by air system

The energy extracted/added by the radiant panel:

The radiant panel energy is:

The energy extracted/added by the radiant panel is the sum of the radiative and convective parts: