Lecture Objectives: • Model HVAC Systems – HW3 Asignemnet • Learn about eQUEST software – How to conduct parametric analysis of building envelope
Dec 24, 2015
Lecture Objectives:
• Model HVAC Systems– HW3 Asignemnet
• Learn about eQUEST software– How to conduct parametric analysis of building envelope
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?
HW3System simulation
Simplified model (use in your HW3):
• Use the results from HW2 and calculate the sensible cooling requirement for 24 hours for ten identical rooms like the one from HW2.
• If infiltration/ventilation provides 1 ACH calculate the latent load from infiltration 24 hours for ten identical rooms like the one from HW2.
• Calculate the total cooling load for 24 hours for ten identical rooms like the one from HW2.
• Use this as Q cooling () for HW3
Note: This method:- assumes perfect process in AHU
to control RH sometimes we need to heat and cool at the same time- neglects fan power- dos not consider system properties and control Variable Air Volume or Constant Air Volume
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
Plant Models:Chiller
P electric () = COP () x Q cooling coil ()
Modeling of Chiller
CAPFT
Chiller model acronyms:
Available capacity as function of evaporator and condenser temperature
EIRFT
Full load efficiency as function of condenser and evaporator temperature
EIRFPLR
Efficiency as function of percentage of load
PLR
Part load:
EIRFPLEIRFTCAPFTPP NOMINAL
The consumed electric power [KW] under any condition of load
Part Load Ratio
Energy Input Ratio as Function of Part Load Ratio
Energy Input Ratio as Function of Temperature
CAPacity as Function of Temperature
HW3Chiller 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
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
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
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 _)(
eQUEST software