lecture objectives: finish with software intro –specifics for equest hvac systems –and modeling...
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Lecture Objectives:
• Finish with software intro – Specifics for eQUEST
• HVAC Systems – and modeling of HVAC Systems
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ES programs
• Large variety • http://www.eere.energy.gov/buildings/tools_directory
• DOE2• eQUEST (DOE2)• BLAST • ESPr• TRNSYS• EnergyPlus (DOE2 & BLAST)
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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
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ESPrUniversity of Strathclyde - Glasgow, Scotland, UK
• Detailed models
– Research program
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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
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Component-based simulation programs - Trnsys
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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/
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EnergyPlus
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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
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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
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HVAC systems
• Review – Psychrometrics– Air-conditioning in Air Handling Units (AHU)– Refrigeration cycles
• Building-System-Plant connection
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Psychrometrics – review
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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
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Processes in AHU presented in Psychrometric in psychrometric
OA Case forSummer in Austin
IA
MA
SA
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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?
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Building-System-Plant
Plant(boilerand/orChiller)
Building
HVAC System(AHU and distribution systems)
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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
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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
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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
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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 _)(
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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
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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:
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