lecture objectives: specify exam time finish with hvac systems –hw3 introduce projects 1 & 2...
TRANSCRIPT
Lecture Objectives:
• Specify Exam Time
• Finish with HVAC systems – HW3
• Introduce Projects 1 & 2– eQUEST– other options
Example Available capacity as function of evaporator and condenser temperature
Equipment Selectionexample
Need 1.2 tonOf water cooling 1 ton = 12000 Btu/h
Capacity is 1.35 ton only for:
115 F air condenser temp50 F of water temperature
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 _)(
Project 1:Use eQUEST software
to model an example building
Use it in simple and detailed modes
Project 2:HVAC Topics
Heat Recovery SystemsAir to Air Heat Exchanger
Plate heat exchangers
Enthalpy wheel Effectiveness ~60%
Effectiveness ~75%
Effectiveness ~50%
Ventilation Heat Recovery Systemsfor cooling and heating
Commercial buildings Residential buildings
Saving % - depends on how much ventilation we have in the building
Water Cooled Chiller
Outside air 95°F
Inside 75°FWater 42°F
BuildingWater 52°FWater 120°F
Water 100°F
Cooling tower
Chiller
Task: analyze COP for the whole yearand different locations
Solar hot water system
Geothermal Energy Systems(in combination with a cooling machine / heat pump)
Summer Winter
In the summer, the earth acts as a cooling tower. The Cooling Machine loads the loop with heat, sending warmed water to be cooled by the earth
In the winter, the earth acts as the boiler. The Heat Pump extracts heat from the loop, sending cooled water to be warmed by the earth.