Lecture Objectives:

• Solution of Exam Problems

• HVAC Systems

• Life Cycle Cost Analysis

Building-System-Plant

Plant(boilerand/orChiller)

Building

HVAC System(AHU and distribution systems)

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

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?

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:

TOA

water

Building users (cooling coil in AHU)

TCWR=11oCTCWS=5oC

Evaporation at 1oC

T Condensation = TOA+ ΔT

What is COP for this air cooled chiller ?

COP is changing with the change of TOA

Example of Plant Models:Chiller

P electric () = COP () x Q cooling coil ()

Chiller model: COP= f(TOA , Qcooling , chiller properties)

OACWSOAOACWSCWS TTfTeTdTcTbaCAPTF 12

112

111

CAPFTQ

QPLR

NOMINAL

)(

Chiller data: QNOMINAL nominal cooling power, PNOMINAL electric consumption for QNOMINAL

Cooling water supply Outdoor air

OACWSOAOACWSCWS TTfTeTdTcTbaEIRFT 22

222

222

Full load efficiency as function of condenser and evaporator temperature

PLRcPLRbaEIRFPLR 333

Efficiency as function of percentage of load

Percentage of load:

The coefficient of performance under any condition:

EIRFPLEIRFTCAPFTPP NOMINAL

The consumed electric power [KW] under any condition

)(

)()(

P

QCOP

Available capacity as function of evaporator and condenser temperature

Example of HVAC system in

eQUEST

Life Cycle Cost Analysis

• Engineering economics

Life Cycle Cost Analysis

• Engineering economics

• Compound-amount factor (f/p)• Present worth factor value (p/f) • Future worth of a uniform series of amount (f/a)• Present worth of a uniform series of amount (p/a)• Gradient present worth factor (GPWF)

Parameters in life cycle cost analysis

Beside energy benefits expressed in $,you should consider:

• First cost• Maintenance• Operation life• Change of the energy cost • Interest (inflation)• Taxes, Discounts, Rebates, other Government

measures

Example

• Using eQUEST analyze the benefits (energy saving and pay back period)

of installing

- low-e double glazed window

- variable frequency drive