Lecture Objectives:

• Model processes in AHU– Use eQUEST predefined models– Use detail modeling

• Define your topics for your final project

Where to look for info about eQUEST simulation tool

You will find more info about eQUEST at:

• eQUEST help file• User manual http://www.doe2.com/download/equest/eQUESTv3-Overview.pdf

• Detail manual http://www.doe2.com/download/DOE-22/DOE22Vol1-Basics.pdf

• eQUEST user blog http://www.doe2.com/equest/

eQUEST HVAC Models

• Predefined configuration (no change) • Divided according to the cooling and heating sources• Details in e quest help file:

For example:

DX Coils No Heating– Packaged Single Zone DX (no heating)

• Packaged single zone air conditioner with no heating capacity, typically with ductwork.

– Split System Single Zone DX (no heating)• Central single zone air conditioner with no heating, typically with ductwork. System has indoor fan and cooling coil and remote

compressor/condensing unit.

– Packaged Terminal AC (no heating)• Packaged terminal air conditioning unit with no heating and no ductwork. Unit may be window or through-wall mounted.

– Packaged VAV (no heating)

DX Coils Furnace• Packaged direct expansion cooling system with no heating capacity. System includes a variable volume, single duct fan/distribution

system serving multiple zones each with it's own thermostatic control.

– Packaged Single Zone DX with Furnace• Central packaged single zone air conditioner with combustion furnace, typically with ductwork.

– Split System Single Zone DX with Furnace• Central single zone air conditioner with combustion furnace, typically with ductwork. System has indoor fan and cooling coil and remote

compressor/condensing unit.

– Packaged Multizone with Furnace• Packaged direct expansion cooling system with combustion furnace. System includes a constant volume fan/distribution system serving

multiple zones, each with its own thermostat. Warm and cold air are mixed for each zone to meet thermostat control requirements.

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

Schematic for model of simple air handling unit

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

)( MSpSH TTcmQ

The energy balance for the heating coil is given as:

The energy balance for the cooling coil is given as:

changephaseMSSMSpSC iwwmTTcmQ _)(

Cooling coil modelTo enable coupling of air handling unit model with the chiller model We need cooling coil model:

Models gives a relationship between the supply temperature (Tref_in) and return

temperature (Tref_out) of the circulating fluid for a given mass flow rate (mref) of this

fluid thorough the cooling coil

E = f(Tair_in ,wair_in ,Tr_in , mair ,mref)

Also, it depends on the cooling coil geometry and type of circulating fluid (water or refrigerant)

The cooling coil effectiveness (E) describes this relationship:

)()(

)(____ inrefinair

refp

airpinrefoutref TT

mc

EmcTT

Air

Cooling coil

mair

mref

Tr_inTr_out

Tair_in

wair_in

Tair_out

wair_out

Cooling coil model - water cooledE = = f(Tair_in ,wair_in ,Tr_in , mair ,mref)

mw=mref , ma=mair UA - product of heat transfer coefficient and coil area(property of coil - several page long model)

Physical based modelsbased on heat transfer theory

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:

Integration of HVAC and building physics models

BuildingHeating/Cooling

SystemPlant

Load-System-Plant model does not work in cases when HVAC components radiate to other surfaces

We have to use Integrated models:

Tw_out

mw, Tw_in

External weather parameters

T surrounding

surfaces

T surrounding

surfaces

Qrad_plant

Solve simultaneously system of equation or use iterative procedure.

Final project topics:Software based• Energy analysis of building form Integrated design course, • Envelope analysis of glass buildings• ….

Detail Modeling (your model)• Heat recovery systems, • Economizers, • Water cooled chiller,• Geothermal heat pump, • Solar hot water systems,• Mass transfer (moisture, ozone, VOCs,…) • Vented cavity walls - exam problem• ….Your ideas