petrone chilled beams - comsol
TRANSCRIPT
A Numerical Investigation on A Numerical Investigation on Active Chilled Beams for Indoor Active Chilled Beams for Indoor Air ConditioningAir Conditioning
Cammarata G., Petrone G.Cammarata G., Petrone G.
Department of Industrial and Mechanical Engineering Department of Industrial and Mechanical Engineering University of Catania (Italy)University of Catania (Italy)
Presented at the COMSOL Conference 2008 Hannover
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OutlinesOutlines
Introduction to Active Chilled Beams in Introduction to Active Chilled Beams in the framework of the HVAC systemsthe framework of the HVAC systems
Modelling of Active Chilled Beams by Modelling of Active Chilled Beams by COMSOL MultiphysicsCOMSOL Multiphysics
Results & DiscussionResults & Discussion
ConclusionsConclusions
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OutlinesOutlines
Introduction to Active Chilled Beams in Introduction to Active Chilled Beams in the framework of the HVAC systemsthe framework of the HVAC systems
Modelling of Active Chilled Beams by Modelling of Active Chilled Beams by COMSOL MultiphysicsCOMSOL Multiphysics
Results & DiscussionResults & Discussion
ConclusionsConclusions
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IntroductionIntroduction totoActiveActive ChilledChilled BeamsBeams
In the modern society, In the modern society, people spend more than 90% of their timepeople spend more than 90% of their time in in an artificial environment, for instance an artificial environment, for instance inside buildingsinside buildings
Air quality and thermal comfortAir quality and thermal comfort for occupants inside conditioned for occupants inside conditioned environment environment are arguments of high interestare arguments of high interest
HVACHVAC (Heating, Ventilating, and Air Conditioning) systems are (Heating, Ventilating, and Air Conditioning) systems are designed in order to designed in order to supply comfort conditionssupply comfort conditions for occupants for occupants
Chilled Beams is one of the HVAC systemsChilled Beams is one of the HVAC systems
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IntroductionIntroduction totoActiveActive ChilledChilled BeamsBeams
In order to assure comfort conditions a In order to assure comfort conditions a HVAC system has to remove HVAC system has to remove both sensible (dry) and latent (wet) heatboth sensible (dry) and latent (wet) heat. Many traditional HVAC . Many traditional HVAC systems are based on the following scheme:systems are based on the following scheme:
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IntroductionIntroduction totoActiveActive ChilledChilled BeamsBeams
External External primary air is treated in a remote unitprimary air is treated in a remote unit. It assures . It assures ventilationventilationand takes care of the and takes care of the latent rate of heat latent rate of heat
In order to assure comfort conditions a In order to assure comfort conditions a HVAC system has to remove HVAC system has to remove both sensible (dry) and latent (wet) heat.both sensible (dry) and latent (wet) heat. Many traditional HVAC Many traditional HVAC systems are based on the following scheme:systems are based on the following scheme:
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IntroductionIntroduction totoActiveActive ChilledChilled BeamsBeams
Secondary airSecondary air is locally processed is locally processed for removing the sensiblefor removing the sensible rate of rate of heatheat
In order to assure comfort conditions a In order to assure comfort conditions a HVAC system has to remove HVAC system has to remove both sensible (dry) and latent (wet) heat.both sensible (dry) and latent (wet) heat. Many traditional HVAC Many traditional HVAC systems are based on the following scheme:systems are based on the following scheme:
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IntroductionIntroduction totoActiveActive ChilledChilled BeamsBeams
Active Chilled beams Active Chilled beams combine ventilating fresh air supplying with local combine ventilating fresh air supplying with local cooling or heatingcooling or heating
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IntroductionIntroduction totoActiveActive ChilledChilled BeamsBeams
The functional principle consists in The functional principle consists in aspiration of air room inside theaspiration of air room inside the ceiling ceiling conditioning conditioning component by an high velocity jetcomponent by an high velocity jet supplying external fresh air.supplying external fresh air.
Inducted air room is forced to flow through a waterInducted air room is forced to flow through a water--air heat exchangerair heat exchangerwhere it is cooled or heated. Then where it is cooled or heated. Then it is mixed with the fresh airit is mixed with the fresh air introduced introduced in the room from diffusing slots. in the room from diffusing slots.
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IntroductionIntroduction totoActiveActive ChilledChilled BeamsBeams
The The main advantagesmain advantages are related to the are related to the absence of moving partabsence of moving part (fun) in (fun) in the local terminal for secondary air treatment. It allows:the local terminal for secondary air treatment. It allows:
Reduced overall electrical infrastructure in the buildingReduced overall electrical infrastructure in the building
No regular maintenance as there are no moving partsNo regular maintenance as there are no moving parts
Very low noise levels Very low noise levels
But also related to the But also related to the absence of the local unitabsence of the local unit::
Space savingSpace saving
Improved architectural design of the room Improved architectural design of the room
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IntroductionIntroduction totoActiveActive ChilledChilled BeamsBeams
The The purposespurposes of this study of this study are to numerically simulate those devicesare to numerically simulate those devices in in order to investigate on:order to investigate on:
Technical performancesTechnical performances (both in winter and in summer)(both in winter and in summer)
The related The related comfort conditionscomfort conditions (both from fluid(both from fluid--dynamical and dynamical and thermal point of view)thermal point of view)
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OutlinesOutlines
Introduction to Active Chilled Beams in Introduction to Active Chilled Beams in the framework of the HVAC systemsthe framework of the HVAC systems
Modelling of Active Chilled Beams by Modelling of Active Chilled Beams by COMSOL MultiphysicsCOMSOL Multiphysics
Results & DiscussionResults & Discussion
ConclusionsConclusions
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Modelling Modelling bybyCOMSOL MultiphysicsCOMSOL Multiphysics
Three typologiesThree typologies of active chilled beams have been studied:of active chilled beams have been studied:
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Modelling Modelling bybyCOMSOL MultiphysicsCOMSOL Multiphysics
Three typologies of active chilled beams have been studied:Three typologies of active chilled beams have been studied:
VerticalVertical disposition both for disposition both for nozzlesnozzles of incoming fresh air and of incoming fresh air and heat heat exchangerexchanger tubestubes
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Modelling Modelling bybyCOMSOL MultiphysicsCOMSOL Multiphysics
Three typologies of active chilled beams have been studied:Three typologies of active chilled beams have been studied:
HorizontalHorizontal disposition both for disposition both for nozzlesnozzles of incoming fresh air and of incoming fresh air and heat heat exchangerexchanger tubestubes
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Modelling Modelling bybyCOMSOL MultiphysicsCOMSOL Multiphysics
Three typologies of active chilled beams have been studied:Three typologies of active chilled beams have been studied:
InclinedInclined (45(45°°) disposition for ) disposition for nozzlesnozzles of incoming fresh air and of incoming fresh air and horizontalhorizontaldisposition for disposition for heat exchangerheat exchanger tubestubes
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Modelling Modelling bybyCOMSOL MultiphysicsCOMSOL Multiphysics
Distribution ductsDistribution ducts have been also modelled in order to evaluate have been also modelled in order to evaluate non non uniform primary air supplyinguniform primary air supplying at nozzles terminal:at nozzles terminal:
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Modelling Modelling bybyCOMSOL MultiphysicsCOMSOL Multiphysics
TerminalsTerminals have been have been integrated in a integrated in a standardstandard room geometryroom geometry::
Air physical properties Density, ρ 1.19 [kg/m3] Dynamic viscosity, η 1.75 e-5 [Pa s] Specific heat, Cp 1100 [J/(kg K)] Thermal conductivity, λ 0.026 [W/(m K)]
Properties of solid materials Material ρ [kg/m3] Cp [J/(kg K)] λ [W/(m K)]
Brick 900 830 0.50 Marble 2700 800 2.80 Wood 420 2700 0.12 Insulating 30 1250 0.04 Glass 2500 840 1.00
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Modelling Modelling bybyCOMSOL MultiphysicsCOMSOL Multiphysics
Turbulence (Turbulence (kk--εε) ) NavierNavier--Stokes and Energy equationsStokes and Energy equations have been solved have been solved with boundary conditions achieving both with boundary conditions achieving both transient and steadytransient and steady solutions:solutions:
( ) ( )( )ρ ρ η η∂ ⎡ ⎤+ ⋅∇ = ∇ ⋅ − + + ∇ + ∇ +⎣ ⎦∂
TT
u u u pI u u Ft
( ) 0ρ ρ∂+ ∇⋅ =
∂u
t
( )ηρ ρ η η ρεσ
⎡ ⎤⎛ ⎞∂+ ⋅∇ = ∇ + ∇ + −⎢ ⎥⎜ ⎟∂ ⎝ ⎠⎣ ⎦
TT
k
k u k k P ut
( ) 21 2ε ε
ε
εη ρεηερ ρ ε η εσ
⎡ ⎤⎛ ⎞∂+ ⋅∇ = ∇ + ∇ + −⎢ ⎥⎜ ⎟∂ ⎝ ⎠⎣ ⎦
TT C P u Cut k k
( )ρ ρ∂+ ∇ ⋅ − ∇ = − ⋅∇
∂p PTC k T Q C u Tt
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OutlinesOutlines
Introduction to Active Chilled Beams in Introduction to Active Chilled Beams in the framework of the HVAC systemsthe framework of the HVAC systems
Modelling of Active Chilled Beams by Modelling of Active Chilled Beams by COMSOL MultiphysicsCOMSOL Multiphysics
Results & DiscussionResults & Discussion
ConclusionsConclusions
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ResultsResults
Results refer to Results refer to parametric analysisparametric analysis of the studied systems (all of the studied systems (all geometrical configurations) both in geometrical configurations) both in winter and summerwinter and summer climatic climatic conditions. conditions.
Parameter winter summer
Text [°C] -5 35
hext [W/(m2 K)] 25 25
Tint [°C] 8 28
hint [W/(m2 K)] 8 8
Tbatt [°C] 40-45 16-21
uin [m/s] 8-20 8-20
Tair [°C] 18-22 16-20
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ResultsResults
The active chilled beam The active chilled beam functional principle has been verifiedfunctional principle has been verified: :
The The inlet high velocity jetinlet high velocity jet of fresh air of fresh air produces a low pressure zoneproduces a low pressure zonesurrounding the nozzle, surrounding the nozzle, inducing indoor fluid to flow through the heat inducing indoor fluid to flow through the heat exchangeexchange battery. battery.
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ResultsResults
Induction RatioInduction Ratio ( IR = m2/m1 ) between primary and secondary mass ( IR = m2/m1 ) between primary and secondary mass flow rate flow rate is evaluatedis evaluated in order to quantify the induction effect in order to quantify the induction effect
m1
m2
Primary air
Secondary air
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ResultsResults
The The IRIR values values showshow a a low low sensitivity withsensitivity with respect to the respect to the inlet inlet velocityvelocity of fresh airof fresh air
The The range of variationrange of variation (24(24--32%) 32%) well fits with technical datawell fits with technical dataproposed by the leading proposed by the leading constructors of those components.constructors of those components.
22%
24%
26%
28%
30%
32%
34%
6 11 16 21u_in [m/s]
IR
Vertical nozzles
Inclined nozzles
Horizontal nozzles
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ResultsResults
Pressure dropsPressure drops generated by heating/cooling generated by heating/cooling batteries crossing has been also batteries crossing has been also evaluated. evaluated.
26,4331,86
42,57
54,29
74,43
0
50
100
5 m/s 6 m/s 8 m/s 10 m/s 13.5 m/s
u_in
Pre
ssur
e dr
op [P
a]
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ResultsResults
From an applicative point of view, From an applicative point of view, heating/cooling capacityheating/cooling capacity represents represents the most the most important parameterimportant parameter. Heating/cooling capacity is . Heating/cooling capacity is computed computed from simulationsfrom simulations by using the following expressions for the primary and by using the following expressions for the primary and secondary flows:secondary flows:
( )ρ= −nozzle in p air ambq S u C T T
SSnozzlenozzle is the total inlet surface of fresh air for 1 [m] of length (6is the total inlet surface of fresh air for 1 [m] of length (60 nozzle per meter) and 0 nozzle per meter) and SScrosscross is the crossing section for fluid is the crossing section for fluid flowing through the battery (flowing through the battery (WWbattbatt represents the battery width and ambient temperature represents the battery width and ambient temperature TTambamb is chosen 20 [is chosen 20 [°°C])C])
1 ( )ρ⎛ ⎞
= −⎜ ⎟⎜ ⎟⎝ ⎠
∫batt
cross p batt ambbatt W
Q S u dx C T TW
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ResultsResults
Values refer to the Values refer to the 4545°° inclined nozzlesinclined nozzles chilled beam that chilled beam that offers the offers the lower thermal performancelower thermal performance
0
200
400
600
800
1000
40 41 42 43 44 45
T_batt [°C]
Hea
ting
capa
city
[W/m
]
0
100
200
300
400
500
10 14 15 16 17 18 19 20
T_batt [°C]
Coo
iling
cap
acity
[W/m
]
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ResultsResults
Transient investigationTransient investigation allows to estimate allows to estimate thermal inertiathermal inertia of the system, of the system, due to the combination of walls (room structure) properties and due to the combination of walls (room structure) properties and air air conditioning system. conditioning system.
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ResultsResults
Chilled beams systems are seen to achieve Chilled beams systems are seen to achieve stationary conditionsstationary conditions for air for air temperature in the occupied region of the room temperature in the occupied region of the room in about 30 minutesin about 30 minutes since since initial time (hardest climatic conditions both in initial time (hardest climatic conditions both in winterwinter ... ...
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ResultsResults
Chilled beams systems are seen to achieve Chilled beams systems are seen to achieve stationary conditionsstationary conditions for air for air temperature in the occupied region of the room temperature in the occupied region of the room in about 30 minutesin about 30 minutes since since initial time (hardest climatic conditions both in winter and in initial time (hardest climatic conditions both in winter and in summersummer) )
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ResultsResults
Comfort conditions: fluidComfort conditions: fluid--dynamical aspectsdynamical aspects
velocity fields showvelocity fields show an an almost constant distributionalmost constant distribution in in the occupied portion of roomthe occupied portion of room
dynamical fielddynamical field is is characterized bycharacterized by velocity velocity values less then values less then 0.1 [0.1 [m/sm/s]]
Varying inlet velocity, Varying inlet velocity, vectors vectors quantitatively changesquantitatively changes closed closed to the to the inlet components onlyinlet components only
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ResultsResults
Comfort conditions: thermal aspects Comfort conditions: thermal aspects
VerticalVertical and and horizontal temperature gradienthorizontal temperature gradient, in the portion of the room , in the portion of the room where people stand, where people stand, appear slight.appear slight.
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ResultsResults
H = 1.60 [m] Tbatt
VerticalVertical and and horizontal temperature gradienthorizontal temperature gradient, in the portion of the room , in the portion of the room where people stand, where people stand, appear slight.appear slight.
Comfort conditions: thermal aspects Comfort conditions: thermal aspects
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OutlinesOutlines
Introduction to Active Chilled Beams in Introduction to Active Chilled Beams in the framework of the HVAC systemsthe framework of the HVAC systems
Modelling of Active Chilled Beams by Modelling of Active Chilled Beams by COMSOL MultiphysicsCOMSOL Multiphysics
Results & DiscussionResults & Discussion
ConclusionsConclusions
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ConclusionsConclusions
A numerical study on active chilled beams has been conduced in CA numerical study on active chilled beams has been conduced in COMSOL OMSOL Multiphysics environment:Multiphysics environment:
Models have been built for Models have been built for three typologiesthree typologies of the considered technological system. of the considered technological system. Computations were carriedComputations were carried--out for out for steady and transient analysissteady and transient analysis, simulating both , simulating both summer and wintersummer and winter functioning and functioning and varying some typical operating conditionsvarying some typical operating conditions
Two main parameters have been Two main parameters have been analysedanalysed for investigating on for investigating on dynamical and dynamical and thermal efficiencythermal efficiency: the : the Induction RateInduction Rate and the and the thermal capacitythermal capacity. . Indoor comfort Indoor comfort conditionsconditions were were also investigatedalso investigated for a chosen standard roomfor a chosen standard room
Results show a Results show a good correspondence withgood correspondence with indications supplied by indications supplied by technical sheets of technical sheets of leading constructorsleading constructors of this componentsof this components
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THANK YOU !!!THANK YOU !!!Department of Industrial and Mechanical EngineeringUniversity of Catania
Authors contactAuthors contact
Address: D.I.I.M. – University of CataniaViale Andrea Doria, 6 – 95125 CATANIA, ITALY
Phone: +39 095 738 2452Fax: +39 095 738 2496
E-mail: [email protected]@diim.unict.it
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