lecture objectives:
DESCRIPTION
Lecture Objectives:. Solution of Exam Problems HVAC Systems Life Cycle Cost Analysis. Building-System-Plant. HVAC System (AHU and distribution systems). Plant (boiler and/or Chiller). Building. Building. Heating/Cooling System. Plant. - PowerPoint PPT PresentationTRANSCRIPT
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