pressure room
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Emerging Technologies in Room (Suite) Pressure Control, Performance Modeling and Design Practices Wei Sun, P.E. ASHRAE Principal, Director of Engineering Engsysco, Inc. Ann Arbor, Michigan, USA Emerging Technologies in Room (Suite) Pressure Control, Performance Modeling and Design Practices Engsysco Presented by Wei Sun, P.E. ASHRAE “Clean Spaces”Technical Committee (TC9.11) Chairman “Healthc are Facilities” Technical Committee (TC9.6) Member “Labora tory Systems” Technical Committee (TC9.10) Member Principal, Director of Engineering Engsysco, Inc. Ann Arbor, Michigan, USA www.engsysco.com ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ Purposes Direct desired flow patterns Isolate airborne cross contamination Definition A technique th at air pressure di fferences are crea ted mechanically between rooms to introduce intentional air movement paths through room leakage openings. These openings could be either designated, such as doorways, or undesignated, such as air gaps around doorframes or other duct/piping penetration cracks. How to achieve It can be achieved by arranging the controlled volumes of supply, return, and exhaust airstreams to each room within the space. Room Pressurization Technique Introduction ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ Air connection bet ween two adjacent rooms is through connecting opening(s). If a door between two rooms is open, the doorway will be the main designated flow path. If the door is closed, then the leakage will be through undesignated paths, such as air gaps along doorframes, joints, pipe and duct penetrations and gaps around ceiling panels etc. Most of these controllable cracks (except for operable doors) in typical controlled spaces are required to be permanently sealed. LeakageFlows Door Closed Room1 Room2 P2 P1 SA1 RA1+ EA1 SA2 RA2+ EA2 P1 > P2 Introduction Basic Rules P1 > P2 LeakageFlows DoorOpened Room1 Room2 P2 P1 SA1 RA1+ EA1 SA2 RA2+ EA2 ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________ ___________________________ ________
Transcript of pressure room
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Emerging Technologies in Room (Suite) Pressure Control,Performance Modeling and Design Practices
Wei Sun, P.E.ASHRAE
Principal, Director of Engineering
Engsysco, Inc.Ann Arbor, Michigan, USA
Emerging Technologies in Room (Suite)
Pressure Control, Performance
Modeling and Design Practices
Engsysco
Presented by
Wei Sun, P.E. ASHRAE
“Clean Spaces”Technical Committee (TC9.11) Chairman
“Healthcare Facilities” Technical Committee (TC9.6) Member
“Laboratory Systems” Technical Committee (TC9.10) Member
Principal, Director of Engineering
Engsysco, Inc.
Ann Arbor, Michigan, USAwww.engsysco.com
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PurposesDirect desired flow patternsIsolate airborne cross contamination
Definition A technique that air pressure differences are createdmechanically between rooms to introduce intentional air movement paths through room leakage openings. Theseopenings could be either designated, such as doorways, or undesignated, such as air gaps around doorframes or other duct/piping penetration cracks.
How to achieve
It can be achieved by arranging the controlled volumes of supply, return, and exhaust airstreams to each room within thespace.
Room Pressurization Technique
Introduction
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Air connection bet ween two adjacent
rooms is through connecting opening(s).
If a door between two rooms is open, the
doorway will be the main designated flow
path.
If the door is closed, then the leakage will
be through undesignated paths, such as
air gaps along doorframes, joints, pipe
and duct penetrations and gaps around
ceiling panels etc. Most of these
controllable cracks (except for operable
doors) in typical controlled spaces are
required to be permanently sealed.
LeakageFlows
Door Closed
Room 1 Room 2
P2P1SA1
RA1 + EA1
SA2
RA2 + EA2
P1 > P2
Introduction
Basic Rules
P1 > P2
LeakageFlows
DoorOpened
Room 1 Room 2
P2P1SA1
RA1 + EA1
SA2
RA2 + EA2
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Introduction
Basic Rules
To Achieve P1 > P2 ,
SA1 > (RA1+EA1), andSA2 < (RA2+EA2)
SA1 = (RA1+EA1) + Q
SA2 + Q = (RA2+EA2)
Q is the leakage (transfer) air
from Room 1 to Room 2, if
both rooms are tightly sealed,
except for the opening
between rooms.
Leakage FlowQ
Leakage Opening
Room 1 Room 2
P2P1SA1
RA1 +EA 1
SA2
RA2 + EA2
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The pressure drop (differential)
across an opening (either a crack
or a doorway) is strongly related
with the leakage opening size(effective leakage area) and
leakage flow through the opening.
To quantitatively achieve a
desired room pressure(or,
pressure differential between
rooms), leakage openings and
respective leakage airflows need
to be studied together.
Introduction
Relationship between Leakage Flow, Leakage Area
and Pressure Dropacross Leakage Path
Leakage Flow
ΔP
QA
Leakage Area
Pressure Differential
Room 1 Room 2
P2P1SA1
RA1 +EA 1
SA2
RA2 +EA 2
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Power Equation: (Esq.. 1)
where
Q = volumetric flow rate CFM (L/s)
ΔP = pressure drop across opening in. of water (Pa)
C = flow coefficient CFM/(in. of water n) (L/s/Pan)
n = flow exponent dimensionless
nP C Q )(Δ⋅=
Airflow through Leakage Opening
LeakageFlow
ΔP
QA
LeakageArea
Pressure Differential
Room 1 Room 2
P2P1 SA1
RA1 +EA 1
SA2
RA2 + EA2
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Orifice Equation: (Esq.. 2)
where
Q = volumetric flow rate CFM (L/s)
ΔP = pressure drop across opening in. of water (Pa)
A = large designated o pening area's) ft2 (m2)
26 10 = uni t c onv ersio n f ac to r dim ens ion le ss ( I- P unit )
84 0 = un it c onv ersi on f ac tor dim ens ion le ss (SI unit )
LeakageFlow
ΔP
Q
ALeakageArea
Pressure Differential
Room 1 Room 2
P2P1 SA1
RA1 +EA 1
SA2
RA2 + EA2
Airflow through Large Designated Opening
P A2610Q Δ⋅⋅=
P A840Q Δ⋅⋅=
(I-P unit)
(SI unit)
Orifice Equation is more popularly used in design community
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Air Leakage Rate vs. Pressure Difference for
Various Leakage Areas (Based on Orifice Equation)
0
100
200
300
400
500
600
700
800
900
1,000
1,100
1,200
1,300
1,400
1,500
1,600
1,700
1,800
1,900
2,000
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 0.055 0.06 0.065 0.07 0.075 0.08
Pressure Differential Between Rooms (in.)
L e a k a g e F l o w
r a t e ( c f m )
Leakage Area
(Sq. in.)
20
40
60
80
100
120
140
160
180
200220
240
260
280
300
320
340
360
380
400
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Large designated openings such as doorway can be easilymeasured. However irregular opening such as a crack can notbe measured physically, there is other means to estimate theequivalent size, or called “Effective Leakage Area” (ELA).
For Existing Rooms:
Field “Blower Door Test” (ASTM 1987, CGSB 1986) to obtainmore precious data.
For Future Rooms during design phase:
Use ASHRAE ELA tables for building components (doors,walls, joints, etc.) as estimated values.
Leakage Area Value Determination
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ASTM “Blower Door” Test,
- Traditional “Room Air-tightness Test”
Portable Pressurization Blower Test canproduce a set of data of Q - ∆P, and a“power equation”curve fit with calculatedconstants (C, n, ELA) that defines a room’sunique and dynamic leakage characteristic.
Abnormal test ranges: ASTM (1987): 12.5 - 75 Pa
(0.05 - 0.30 in.)CGSB (1986): 5 - 50 Pa
(0.02 - 0.20 in.)
Labor intense, time consuming
Disruption to occupied spaces
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Power equation:
Once obtained Q - Δ
P data set, C and n can be calculated:
“Blower Door Test” - Multiple-Point TestData for Power Equation Curve Fitting
n )P ( C Q Δ⋅=
∑ ∑
∑∑ ∑
= =
== =
Δ⋅−Δ
Δ⋅⋅−Δ⋅
=m
1k
m
1k
2 k
2 k
m
1k
k k
m
1k
m
1k
k k
)P (lnm )P ln(
)P lnQ(lnm )P lnQln(
n
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛ Δ⋅−
=
∑∑==
m
P lnnQln
EXP C
m
1k
k
m
1k
k
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Opening Resistance Analysis
Q
Qi
P
P
P i
P
P i
Q
Leakage flow resistances connected in parallel and series
( )∑=
⎥⎦
⎤⎢⎣
⎡=
n
i i
T
ELA
ELA
12
1
1
∑=
=n
i
T i ELA ELA
1
ELA R
1=
Define:Leakage Flow Resistance R
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Room Pressurization Scenarios and
Variable Relationship
Scennario 1: Room PrerssurizedSA - (EA+RA) = ΔV = ΣQ > 0
Total Room
SupplyAirflow
(SA)
Total Room
Exhaustand/or
ReturnAirflow
(EA+RA)
Room
Positively
Pressurized + T
o t a l R o o m
S u p p l y A i r f l o w
( S A )
Offset
Flow
ΔV
T o t a l R o o m E
x h a u s t
a n d / o r R e t u r n A i r f l o w
( E A + R A )
Total Leakage
Airflows
ΣQ
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Room Pressurization Scenarios and
Variable Relationship
Scennario 2: Room Non-PrerssurizedSA - (EA+RA) = ΔV = ΣQ = 0
Total Room
SupplyAirflow
(SA)
Total Room
Exhaust and/or
ReturnAirflow
(EA+RA)
Room
Non-Pressurized
T o t a l R o o m E
x h a u s t a n d / o r
R e t u r n A i r f l o w
( E A + R A )
Offset
Flow
ΔV = 0
T o t a l R o o m
S u p p l y A i r f l o w
( S A )
Total Leakage
Airflows
ΣQ= 0
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Room Pressurization Scenarios and
Variable Relationship
Scennario 3: Room De-prerssurizedSA - (EA+RA) = ΔV = ΣQ < 0
TotalRoom
SupplyAirflow
(SA)
TotalRoom
Exhaustand/or
ReturnAirflow
(EA+RA)
Room
Negatively
De-pressurized-
T o t a l R o o m
S u p p l y A i r f l o w
( S A )
T o t a l R o o m E
x h a u s t a n d / o r R e t u r n
A i r f l o w
( E A + R A )
Offset
Flow
ΔV
TotalLeakage
Airflows
ΣQ
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Central Air Handling System &
Room PressurizationSA = Volume of total
supply air entering
the space/zone
RA = Volume of total
return air leaving the
space/zone
EA = Volume of total
exhaust air leaving
the space/zoneOA = Volume of outside air
drawn into the AHU
FA = Volume of relief air
released from return
air
RA-FA = Volume of
recalculated air
Q = Vol um e o f total
leakage air through
space shell/zone
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Central Air Handling Unit &
Room Pressurization
Two volumetricbalance equations(Mass balance equation under
assumption of same air density)
SA = RA + EA + Q(Volume balance for a space)
SA = OA + (RA – FA)(Volume balance for a typical AHU)
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Space Pressurization Ratio (R)
Define as the Ratio between SA and (RA+EA), as anindicator of pressurization scale:
By specifying SA values, R will be a function of Q. R
Value Chart is convenient for design engineers to
determine SA and (RA+EA) ratio during air distributionarrangement.
• Chart
QSASA
EARASAR −=+=
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Pressurization Ratio vs. Air Leakage Rate
for Various Supply Air Rates
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Space versus Room Pressurization Ratios
The relationship between the space pressurization ratioand its individual room pressurization ratios:
The space pressurization ratio, an indicator of relativepressurization level, can be used to adjust air gains or
losses among zones in order to arrange desired air flows within a building.
( )∑
=
= ⎥⎦
⎤⎢⎣
⎡n
1i i
i
R
SASA
1 R
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Adjacent Rooms under Various Pressures
If a room has several leakage openings with adjacentrooms, the room’s pressurization ratio is:
∑=
−= n
i
i R
R R
QSA
SAR
1
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Pressure Differential and Crack Air Velocity
Criterion 1 (Pressure Differential ΔP)For single room:
ΔP: 0.05 in. of water (12.5 Pa)
For multiple-room space with staged pressurizations:
ΔP: 0.02 in. ~ 0.03 in. (5 Pa ~ 7.5 Pa) for each pressure step
Criterion 2 (Average Crack Velocity V)100 fpm (30 M/m)
PressurizationCriterion
Unit Pressurization Criterion Comparison Basis
Pressure
Differential ΔP
In 0.0015 0.01 0.02 0.03 0.04 0.05 0.06 0.08 0.10
Crack LeakageVelocity V
fpm 109 374 587 764 920 1,064 1,198 1,444 1,670 Eq. (1),when n=0.65
Large OpeningVelocity V
fpm 100 261 369 452 522 584 639 738 825 Eq. (2a)
From comparison below, the pressure criterion of ΔP = 0.05 in. is much more
conservative than the velocity criterion of V = 100 fpm.
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Room Pressurization Variables and
Control Strategies
Airflow differential between enteringairflow (supply airflow,
SA) and leaving airflow (exhaust and/or return airflows,
EA+RA), normally called “offset” value ( Δ
V), which equals thetotal leakage airflow (ΣQ) of the room.
To maintain a specific room pressure value, the room’s offset
airflow ( ΔV) must be controlled and maintained at theappropriate value.
Room’s offset airflow can be controlled directly or indirectly.The treatment of the room “offset” value defines a
pressurization control strategy. Typical pressurization controltechniques are: Direct Pressure-Differential Control ,
Differential Flow Tracking Control , Hybrid Control and
Adaptive Control .
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Direct Pressure-Differential Control (DP)Utilizes a pressure differential sensor to measure the pressure difference
between a controlled room and an adjacent space such as a corridor. It basically
ignores the specific offset value as required, instead, it directly controls the
airflow control devices to achieve the required pressure differential.
Suitable for a tightly constructed room with limited traffics.
Door switch is recommended to trigger a reduced pressure differential set-
point if the door opens.
Fume
Hood
Velocity
Sensor
Sash
Sensor
or
Hood
Valve&
Controller
CHEMICAL
LAB
CORRIDOR
ROOM
CONTROLLER
SUPPLY
AIR
Total Exhaust
AirfromRoomHood
Exhaust
Hood
Exhaust
Room
Exhaust
Valve
Room
Supply
Valve
DS
Door
Switch
T
Leakage
Air
Leakage
Air
Total Supply
Airto Room
DPDP
Sensor
Thermostat
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Differential Flow Tracking Control (DF)
Intuitively assumes an offset value which is used as a flow difference
between the entering and leaving airflows to control their respective
airflow devices. Maintain the same offset value throughout the operation
to keep pressurization constant, or maintain a constant percentage offset
value which creates a weaker pressurization at lower flow.
Suitable for open-style rooms or rooms with frequent traffics
Fume
Hood
Velocity
Sensor
Sash
Sensor
or
Hood
Valve &
Controller
CHEMICAL
LAB
CORRIDOR
ROOM
CONTROLLER
SUPPLY
AIR
Total Exhaust
AirfromRoomHood
Exhaust
Hood
Exhaust
RoomExhaust
Valve
Room
Supply
Valve
DS
Door
Switch
T
Leakage
Air
Leakage
Air
Flow
Sensor Flow
Sensor
Total Supply
Airto RoomDPDP
Monitor
Thermostat
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Hybrid Control (DP+DF)
Combines the pressure accuracy of the direct pressure differential control
and the stability of the flow tracking control. The offset value is reset-able
based on pressure differential reading. The offset value reset schedule is
pre-determined and controller’s parameters are fixed manually in field.
This method is also called “cascaded”control.
Suitable for open-style rooms or rooms with frequent traffics
Fume
Hood
Velocity
Sensor
Sash
Sensor
or
Hood
Valve &
Controller
CHEMICAL
LAB
CORRIDOR
ROOM
CONTROLLER
SUPPLYAIR
Total ExhaustAirfromRoomHood
Exhaust
Hood
Exhaust
Room
Exhaust
Valve
RoomSupply
Valve
DS
Door
Switch
T
Leakage
Air
Flow
Sensor Flow
Sensor
Total Supply
Airto Room
DPDP
Sensor
Leakage
Air
Thermostat
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Multiple-Room (Suite)
Pressure Control Strategies
Single room control technologiesoften cause problems in Suite
Pressure Control during air balancing, since the followingphenomena are often ignored:
Adjusting one room’s offsetvalue will impact adjacentrooms’ air pressures if theywere just balanced earlier.
Example -Pharmaceutical Aseptic Suite
One room’s air gain could beanother room’s air lossthrough leakages.
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Adaptive Control (DP+DF+AD)
The three traditional methods (DP, DF and DP+DF) areeither to “ignore”, “assume” or “manually fix in field” the
offset value respectively.
The adaptive (DP+DF+AD) approach directly accounts for leakage flows between the rooms in a suite. It controls allrooms’ pressures all together as an optimized system,
instead of controlling each room pressure independently. Itactively adjusts the flow offset of each room according to an
on-line pressurization model. The model uses flow and
pressure differential measurements to estimate the leakagevalues between the rooms and adjust flow offset of eachroom automatically.
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Automated Room Air-tightness Test –
Pre-condition for Truly Adaptive Control
Similarly as “Blower Door Test”, but fully automated.
A room’s unique d ynamicleakage characterization canalso be automatically achievedby digital controller, precision
pressure differential sensor (±0.001 in./0.25 Pa) andairflow control devices (±5%).
These devices are oftenpermanently installed in laband clean room environments.
This automated pressurizationtest (Q-∆P data set)is faster and cheaper, and can behandled remotely.
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Adaptive Control (Example: Control of Multiple Rooms)
CLEANESTROOM
0.08In.
CLEANER
ROOM
0.06 In.
AIRLOCK
0.03In.GENERAL
CHEMICAL LAB
-0.02 In.
CONTAINMENT
LAB
- 0.06In.
Designated
LeakageFlow
Supply
Air Valve
Exhaust
Air Valve
Return
Air Valve
MinorLeaks
Thru. Cracks
CORRIDOR
0.00In.
DP
DPDPDP
DPDP
Pressure
Differential
Sensor
Manifolded or
OpentoCorridor
DS
DSDS
DS
DS
DS
Legend
SUITE
CONTROLLER
DoorSwitch
SUITE
CONTROLLER
ValvePosition
Outputs
Door
Switch
Inputs
Valve
Flowrate
Inputs
Room Pressure
Inputs
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Air Flows between Rooms
Airflow Between Rooms
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Personnel Flows between Rooms
Personnel Flow Between Rooms
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More Considerations
Correction Factors
(Refer to ASHRAE Handbooks 1999 &
2001, detailed procedures will be included in
the next phase of the study)
Stack effect
Wind effect
Interior zones with hightemperature or humiditydifferences
Safety Factors
(Detailed procedures will be included in thenext phase of the study)
Room background leaks
Duct leaks
AHU unit leak
Correction and Safety Factors – Add as required
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Samples of Pressurization Control Devices
Flow Control & Measure Pressure Measure
Static Pressure
Measuring Probes
Static Pressure
Measuring Probes
Pressure
Transmitter
PressureTransmitter
Pressure
Transmitter
and Monitor
Pressure
Transmitter
and Monitor
Control
Damper
Control
Damper Air Valve –Type 1
Air Valve –Type 1
Air Valve –
Type 2
Air Valve –Type 2
Air Valve -
Type 3
Air Valve -
Type 3
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Case Study - Airflow Resistance and
Leakage Flow Simulation
- Room Numbe - Wall - Flow Direction - Induced Flow (by Pressurization)
- N o de ( R oo m) - F low R es ist a nc e @ Majo r Op en ing - F lo w R e sist a nc e @ Mino r Op en in g - F or c ed Flow ( by F an )
N et wo rk Fl o w w it h M aj or Op en in gs O nl y N et wo rk Fl ow wi th Ma jo r a nd M i no r O pe ni ng s
RMX
RM1RM2
RM3
RM4 RM5
RM6
RM1RM2
RM3
RM4 RM5
RM6
Major and minor leakage openings, connection in paralleland series
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Modeling of Transient Pressurization
L
W
Room 1
Room 2
P1
P2
Wall
SwingDoor
P
Transient Flow ThroughSwingDoor
P1 > P2
1. Pressurization Loss Characteristic During a SwingDoor Opening or Closing
⎟ ⎠
⎞⎜⎝
⎛ ⋅⋅⋅⋅=⋅=
2sin2
)()(
t W H L H A
t t
ω
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛ ⋅⋅=
2sin2
)(
)(
t
t W L
θ
)600( o≤≤ θ
W H At
⋅=)(
)9060( o≤< θ
where,
L=width (gap) of door openingin. (cm)
W=width of door in. (cm)
θ =angle of door opening degree
ω =speed of door turning degree/sec.t=time sec.
H=door height in. (cm)
A=effective door opening width (gap) in2 (cm2 )
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Modeling of Transient Pressurization
Transient Pressure DifferentialAcros s When ASwing Door Opens
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2 2.5 3
Time of Door Opening(Second)
P r e s s u r e D i f f e r e n t i a l A c r o s s D o o r ( P a )
0
10
20
30
40
50
60
0 1 0 20 30 40 50 60 70 80 9 0
Angle of S wing Door Opening (D egree)
W i d t h ( G a p ) o f D o o r O p e n i n g ( i n . )
PressureDropAcross Door
Widthof Door Opening Automatic SwingDoor Opens to 90o in 3Seconds;Door Size4 ft. (W) x7ft.(H).
Rooms Across The Door/WallAreMaintained withConstantSupplyandReturn Flows.InitialPressureDifferentialAcross Door is 68.9Pa,it drops to1 Pa less than 2seconds.
1. Pressurization Loss Characteristic During a SwingDoor Opening or Closing
Airlock Room Pressure Profile
-0.010
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
0.050
0.055
0.060
0.065
0.070
0.075
0.080
0.085
0.090
0.095
0.100
Airlock Sliding Door Operation Cycle
R o o m S t a t i c P r e s s u r e ( i n . W C )
Firs t DoorOpening First DoorClos ing Bot h Doors Clos ed S e condDoor Ope ning S e c ond Door Clos ing
Cleanroom
Airlock
Corridor
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Modeling of Transient Pressurization
L
W
P
Transient Flow Through SlidingDoor
P1 > P2
Wall
Room 1P1
Sliding Door
Room 2P2
2. Pressurization Loss Characteristic During a SlidingDoor Opening or Closing
where,
L=width (gap) of door openingin. (cm)
W=width of door in. (cm)
t=time sec.
s=speed of door opening in./sec. (cm/sec.)
H=door height in. (cm)
A=effective door opening width (gap) in2(cm2)
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Modeling of Transient Pressurization
Transient Pressure Differential Across WhenA SlidingDoor Opens
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2 2.5 3
Timeof DoorOpening (Second)
P r e s s u r e D i f f e r e n t i a l A c r o s s D o o r ( P a )
0
10
20
30
40
50
60
W i d t h ( G a p ) o f D o o r O p e n i n g ( i n . )
Pressure Drop Across Door
Width of Door Opening
Automatic SlidingDoor Opens atSpeedof 16in./sec.; Door Size4 ft.(W) x 7 ft. (H);
Rooms AcrossThe Door/WallAreMaintainedwithConstantSupply and ReturnFlows,
InitialPressure DifferentialAcross Door is68.9Pa, itdrops to1Paaround2 seconds.
2. Pressurization Loss Characteristic During a SlidingDoor Opening or Closing
PressureDifferentialsBetweenRooms
-0.010
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
0.050
0.055
0.060
0.065
0.070
0.075
0.080
0.085
0.090
0.095
0.100
AirlockSliding DoorOperationCycle
P r e s s u r e D i f f e r e n t i a l b e t w e e n R o o m s ( i n . W C )
Firs t DoorOpe ning Firs t DoorClos ing Bot hDoors Clos ed S e c ondDoorOpe ning S e c ondDoorClosing
DP
(Cleanroom andCorridor)
DP (Door1) DP (Door2)
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Door Opening Transient Impact onPressurization Control
Any passive motor-driven or actuator-driven HVAC
system (such VAV box or valve) will not have enoughtime to react effectively to prevent possible cross
contamination.
A single barrier door could cause a short duration of backflow contamination until the motor or actuator
completes the modulation cycle of re-balancing,additional means to prevent possible backflow
contamination, such as double-door airlock is necessary.
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Dynamic Pressurization Control Strategies
- Airlock
CLEANROOM
AIRLOCK
+CORRIDOR
++
+++
AIRFLOW
CASCADING AIRLOCK
AIRFLOW CLEANROOM
AIRLOCK
+CORRIDOR
++
-
AIRFLOW
BUBBLEAIRLOCK
AIRFLOW
CLEANROOM
AIRLOCK
+CORRIDOR
- -
-
AIRFLOW
SINK AIRLOCK
AIRFLOWCLEANROOM
AIRLOCK
-CORRIDOR
++
-
AIRFLOW
AIRFLOW
- -AIRLOCK
DUAL COMPARTMENT AIRLOCK
Air Lock Type
Cascading
Bubble
SinkDual-
Compartment
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Dynamic Pressurization Control Strategies- Airlock
Wait!Wait!
Corridor
Cleanroom
Airlock (Cascading)
ΔPDo o r1
ΔPDoor 2
ΔPRooms
0.06 in.
0.03 in.
0.00 in.
-6 -3 0 3 6
-6 -3 0 3 6
-6
-3036
Airlock Physical Model Network Flow Simulation
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Result of Network Flow Simulation
Wait!
Corridor
Clean room
Airlock (Cascading)
ΔPDoor1
ΔPDoor2
ΔPRooms
0.06 in.
0.03 in.
0.00 in.
-6-3 0 3 6
- 6 - 3 0 3 6
-6-3
0
3
6
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CFD Model to Study Airlock Transient
Performance - Physical Conditions
(12000 CFM, 75 ACH)
(2100 CFM, 75 ACH)
(560 CFM, 10ACH)
11948 CFM
2078 CFM
Leakage 52 CFM
Leakage 73CFM
Clean Room: 10000
Airlock:10,000
Corridor: 100000
(12000 CFM, 75 ACH)
(2100 CFM, 75 ACH)
(560 CFM, 10ACH)
Leakage 52 CFM
Leakage 73CFM11948 CFM
2078 CFM
Clean Room: 10000
Airlock:10,000
Corridor: 100000
Case 1 –Class 10,000 Case 2 –Class 100
(48000CFM,300ACH)8400 CFM, 300ACH)
560(CFM,10ACH)
Leakage 52CFM
Leakage 73CFM
47948CFM8378CFM
CleanRoom:100Airlock:100
Corridor:100000
(48000CFM,300ACH)8400 CFM, 300ACH)
560(CFM,10ACH)
Leakage 52CFM
Leakage 73CFM
47948CFM8378CFM
CleanRoom:100Airlock:100
Corridor:100000
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Steady State Airflow Distribution
Case 1 –Class 10,000 Case 2 –Class 100
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Steady State Cleanroom Particle
Concentration
Case 1 –Class 10,000 Case 2 –Class 100
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Corridor Particles Enter Airlock Room
Case 1 –Class 10,000 Case 2 –Class 100
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Airlock Particles Enter Clean Room and
Corridor
Case 1 –Class 10,000 Case 2 –Class 100
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Airlock Particles Enter Clean Room and
Corridor
Case 1 –Class 10,000 Case 2 –Class 100
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Variation of Corridor Particle Concentration
Case 1 –Class 10,000 Case 2 –Class 100
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Airlock Door Transient Performance
Profileof PressureDifferentialAcrossDoor
When Door IsOpening & Closing(Initial Condition:-15 Pa= -0.06In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 1 0 11 1 2 13 1 4 15 1 6
Time (Sec.)
P r e s s u r e D i f f e r e n t i a l A c r o s s D o o r ( P a )
Test 1
Test 2
Test 3
Average
D o o r O p e n in g D o o r C l o s in g
Profileof Pressure DifferentialAcrossDoor
WhenDoorIsOpening& Closing(Initial Condition: 5Pa= 0.02 In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 1 0 11 1 2 13 1 4 15 1 6
Time (Sec.)
P r e s s u r e D i f f e r e n t i a l A c r o s s D o o r ( P a )
Test 1
Test 2
Test 3
Average
Door Openin g D o or C l os i ng
Profileof PressureDifferentialAcrossDoor
WhenDoor IsOpening& Closing(Initial Condition:-10 Pa= -0.04In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 1 0 11 1 2 13 1 4 15 1 6
Time (Sec.)
P r e s s u r e D i f f e r e n t i a l A c r o s s D o o r ( P a )
Test 1
Test 2
Test 3
Average
D o o r O p e n in g D o o r C l o s in g
Profileof PressureDifferentialAcross Door
When DoorIs Opening & Closing(Initial Condition: 10Pa= 0.04 In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 1 0 11 1 2 13 1 4 15 1 6
Time (Sec.)
P r e s s u r e D i f f e r e n t i a l A c r o s s D o o r ( P a )
T e s t 1
T e s t 2
T e s t 3
AverageD o o r O pe n i n g D o o r Cl o s i ng
ProfileofPressureDifferentialAcrossDoor
When Door IsOpening & Closing(Initial Condition:-5 Pa= -0.02 In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 1 1 12 1 3 14 1 5 16
Time (Sec.)
P r e s s u r e D i f f e r e n t i a l A c r o s s D o o r ( P a )
T e s t 1
T e s t 2
T e s t 3
Average
Door O p e n i ng D o o r C lo s i n g
Profileof Pressure DifferentialAcrossDoor
When DoorIsOpening & Closing(Initial Condition:15 Pa =0.06In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 1 0 11 1 2 13 1 4 15 1 6
Time(Sec.)
P r e s s u r e D i f f e r e n t i a l A c r o s s D o o r ( P a )
Test 1
Test 2
Test 3
verage
D o o r O p e n i n g D o o r C lo s i n g
ProfileofPressureDifferentialAcrossDoor
When Door IsOpening & Closing(Initial Condition:0Pa=0 In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 1 1 12 1 3 14 1 5 16
Time(Sec.)
P r e s s u r e D i f f e r e n t i a l A c r o s s D o o r ( P a )
T e s t 1
T e s t 2
T e s t 3
Average
Door O p e n i ng D o o r C lo s i n g
Profile of PressureDifferentialAcross Door
WhenDoorIsOpening& Closing(Initial Condition:20 Pa =0.08In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 1 1 12 1 3 14 1 5 16
Time (Sec.)
P r e s s u r e D i f f e r e n t i a l A c r o s s D o o r ( P a )
Test 1
Test 2
Test 3
Average
D o o r O p e ni n g D o o r C l o s in g
Pressure Differential Across Cleanroom Door During Walk-Through
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Contamination Risk Factor (CRF)
CRF is a criterion which is to quantity the effectiveness of cleanroom particle
containment in preventing the airborne particles migration into cleanroom.
CRF = PC / PO
CRF = Contamination Risk Factor
PC = Number of Particles inside Protected Cleanroom Near Door
PO = Number of Particles at Corridor Entrance Near Door
This criterion is applied for a “Barrier Device” which is to minimize particle
migration. This barrier could be single door, an airlock (two doors in series),
mini environment, or glove box.
The lower of the CRF level, the better barrier’s performance, or the better de-
contamination effectiveness. This expression can not only apply for airborne
particle, but also for airborne microorganism egress, in which the particle
counts will be replaced with Colony Forming Unit (CFU).
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Particle Concentrations & CRF Across Cleanroom
Door Under Various Pressure DifferentialsAirborne Particle ContaminationRisk Factor (CRF)
Under VariousPressure DifferentialsAcross Cleanroom Door (Note: 5 Pa=0.02In.,Particle Measured @ 0.5µm)
0%
5%
10%
15%
20%
25%
-15 -10 -5 0 5 10 15 20
Initial PressureDifferentialAcrossDoor(Pa)
C o n t a m
i n a t i o n R i s k F a c t o r ( C R F ,
% )
Door Opening& ClosingW/O People Traffic
APersonWalks Through Door
ParticleConcentrationsAcrossCleanroom Door When DoorisOpening &Closing
(Initial Condition:Depressurization @ -15 Pa= -0.06In.)
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 14 1 5 1 6 17 1 8 1 9 20 2 1 2 2
Time (Sec.)
P a r t i c l e C o n c e n t r a t i o n s A c r o s s D o o r
( C o u n t s / F T
3 )
Ins ideCleanroom DoorAverage Outs ide CleanroomDoorAverage
Door Opening
Door Closing
CRF= 18.9%
Particle Concentrations Across CleanroomDoor WhenDoor is Opening & Closing
(Initial Condition:Pressurization @ 5 Pa=0.02 In.)
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
0 1 2 3 4 5 6 7 8 9 1 0 11 1 2 1 3 14 1 5 1 6 17 1 8 1 9 20 2 1 2 2
Time (Sec.)
P a r t i c l e C o n c e n t r a t i o n s A c r o s s D o o r
( C o u n t s / F T 3 )
InsideCleanroomDoorAverage Outside Cleanroom Door Average
Door Opening
Door Closing
CRF
= 2.2%
ParticleConcentrationsAcrossCleanroomDoor When Door isOpening & Closing
(Initial Condition: Depressurization @ -10 Pa = -0.04In. )
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 14 1 5 1 6 17 1 8 1 9 20 2 1 2 2
Time (Sec.)
P a r t i c l e C o n c e n t r a t i o n
s A c r o s s D o o r
( C o u n t s / F
T 3 )
Ins id e C l e an r o o m e r a g eD o or A v O u ts i de C leanroom DoorAverage
Door
Opening
Door
Closing
CRF
= 8.5%
ParticleConcentrationsAcrossCleanroom Door When Door isOpening & Closing
(Initial Condition:Pressurization @ 10Pa= 0.04In. )
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 14 1 5 1 6 17 1 8 1 9 20 2 1 2 2
Time (Sec.)
P a r t i c l e C o n c e n t r a t i o n
s A c r o s s D o o r
( C o u n t s / F
T 3 )
InsideCle an r ag er o om D o or A v e O u tside Cleanroom DoorAver age
Door Opening
Door Closing
CRF
= 0.7%
ParticleConcentrationsAcrossCleanroom Door
When Door isOpening & Closing(Initial Condition:Depressurization @ -5Pa =-0.02In. )
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 14 1 5 1 6 17 1 8 1 9 20 2 1 2 2
Time (Sec.)
P a r t i c l e C o n c e n t r a t i o n s A c r o s s D o o r
( C o u n t s / F T
3 )
Ins ide CleanroomDoorAverage Outs ide Cleanroom DoorAverage
Door
Opening
Door
Closing
CRF
=6.9%
ParticleConcentrationsAcrossCleanroom Door When DoorisOpening &Closing
(Initial Condition: Pressurization@ 15Pa = 0.06 In. )
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 14 1 5 1 6 17 1 8 1 9 20 2 1 2 2
Time (Sec.)
P a r t i c l e C o n c e n t r a t i o n s A c r o s s D o o r
( C o u n t s / F T
3 )
Ins ide CleanroomD o o r A ve r a g e O u ts ide CleanroomDoorAverage
Door Opening
Door Closing
CRF
= 0.8%
AirborneParticle Contamination RiskFactor(CRF)
UnderVarious PressureDifferentials Across CleanroomDoor (Note: 5 Pa= 0.02In.,[email protected]µm)
Particle Concentrations Across Cleanroom Door
When DoorisOpening &Closing(Initial Condition: Neutral @ 0Pa=0In. )
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
0 1 2 3 4 5 6 7 8 9 1 0 1 1 12 1 3 1 4 15 1 6 1 7 18 1 9 2 0 21 2 2
Time (Sec.)
P a r t i c l e C o n c e n t r a t i o n s A c r o s s D o o r
( C o u n t s / F T
3 )
Ins ideCleanroomDoorAverage Outs ide Cleanroom Door Average
Door
Opening
Door
Closing
CRF=4.2%
ParticleConcentrationsAcrossCleanroom Door When Door isOpening &Closing
(Initial Condition:Pressurization@ 20 Pa= 0.08In.)
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
0 1 2 3 4 5 6 7 8 9 1 0 1 3 1 4 15 1 6 1 7 18 1 9 2 0 21 2 2
Time (Sec.)
P a r t i c l e C o n c e n t r a t i o n s A c r o s s D o o r
( C o u n t s / F T
3 )
1112
Ins ideCleanroom Door Average Outs ideCleanroom DoorAverage
Door
Opening
Door
Closing
CRF
= 0.3%
RegressionCurve:
CRF= 0.0332e-0.1181*PD
R2
= 0.9656
(No PeopleTraffic)
RegressionCurve:
CRF= 0.0418e-0.0703*PD
R2
= 0.9129
(With PeopleTraffic)
0%
5%
10%
15%
20%
25%
-15 -10 -5 0 5 10 15 20
Initial PressureDifferential AcrossDoor(Pa)
C o n t a m i n a t i o n R i s k F a c t o r ( C R F ,
% )
DoorOpening&ClosingW/OPeopleTraffic
APerson Walks ThroughDoor
Regression(DoorOpening&Closing W/O PeopleTraffic)
Regression(APersonWalksThrough Door)
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Dynamic Pressurization Control Strategies
– Adjustable Pressure Stabilizer
A leakage regulato r,controllable pressure relief damper across a wall tomaintain a minimumrequired pressurization.
When a door is normallyclosed, this damper shouldstay open and maintainnormal pressure differential;when the door opens, thedamper shall beautomatically closed either by spring-loaded or counter-weight gravity damper, andmaintain a lower whileacceptable pressuredifferential.
Pressure
Stabilizer
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Importance
Air-handling unit control
Lab HVAC control
Prefabricated clean room
Precision environmental test chamber
Smoke management control
Air distribution system
In addition to design engineers and researchscientists, the information presented may alsobenefit manufacturers in the fields of:
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Pressurization Study
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Q & A
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