1. Lecture Objectives:
• Model processes in AHU
– Use eQUEST predefined models
– Use detail modeling
• Define your topics for your final project
2. 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/
3. 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.
4. Integration of HVAC and building
physics models
Building
Heating/Cooling
System
Plant
Building
Heating/Cooling
System
Plant
Load System Plant model
Integrated models
Qbuiolding Q
including
Ventilation
and
Dehumidification
5. Schematic for model of simple air
handling unit
rmS
fans
cooler heater
mS
QC
QH
wO wS
TR
room TR
Qroom_sensibel
(1-r)mS
mS
wM
wR
Qroom_latent
TS
TO
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
6. Energy and mass balance equations for
Air handling unit model – steady state case
S
R
p
S
sensible
room T
T
c
m
Q
_
mS is the supply air mass flow rate
cp - specific capacity for air,
TR is the room temperature,
TS is the supply air temperature.
change
phase
S
R
S
latent
room i
w
w
m
Q _
_
wR and wS are room and supply humidity ratio
change
phase
i _ - 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:
R
O
M T
r
T
r
T
)
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:
R
O
M w
r
w
r
w
)
1
(
wO is the outdoor air humidity ratio and
wM is the humidity ratio after the mixing box
)
( M
S
p
S
H T
T
c
m
Q
The energy balance for the heating coil is given as:
The energy balance for the cooling coil is given as:
change
phase
M
S
S
M
S
p
S
C i
w
w
m
T
T
c
m
Q _
)
(
7. Cooling coil model
To 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:
)
(
)
(
)
(
_
_
_
_ in
ref
in
air
ref
p
air
p
in
ref
out
ref T
T
mc
E
mc
T
T
Air
Cooling
coil
mair
mref
Tr_in
Tr_out
Tair_in
wair_in
Tair_out
wair_out
8. Cooling coil model - water cooled
E =e = 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 models
based on heat transfer theory
9. Non-air system
Radiant panel heat transfer model
Room (zone 1)
Radiant Panel
c o
nv ecti on
Tsurface
Tsurounding
Tzone_air radiation
Qrad_pan
radiant panel layer (water tube)
air supply
system
m ,T = const.
s s
Qzone
Tw_out Tw_in
10. Non-air system
Radiant panel heat transfer model
)
(
)
( _
_
sup
_
sup air
room
air
ply
air
ply
p
air T
T
mc
Q
pan
rad
Q _
air
pan
rad
zone Q
Q
Q
_
)
(
)
( ,
,
_ air
panel
panel
conv
i
surface
panel
panel
i
radiation
conv
radiation
pan
rad T
T
A
h
T
T
A
h
Q
Q
Q
)
( _
_
_ in
w
out
w
pw
pan
rad T
T
mc
Q
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:
11. Integration of HVAC and building
physics models
Building
Heating/Cooling
System
Plant
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.
12. 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
