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 EngineeringEngsysco, Inc.
Ann Arbor, Michigan, USAwww.engsysco.com
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PurposesDirect desired flow patternsIsolate airborne cross contamination
DefinitionA technique that air pressure differences are created 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 achieveIt can be achieved by arranging the controlled volumes of supply, return, and exhaust airstreams to each room within the space.
Room Pressurization Technique
Introduction
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Air connection between 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.
Leakage FlowsDoor Closed
Room 1 Room 2
P2P1 SA1
RA1 + EA1
SA2
RA2 + EA2
P1 > P2
IntroductionBasic Rules
P1 > P2
Leakage FlowsDoor Opened
Room 1 Room 2
P2P1 SA1
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
P2P1 SA1
RA1 + EA1
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 Areaand Pressure Drop across Leakage Path
Leakage Flow
ΔP
QA
Leakage Area
Pressure Differential
Room 1 Room 2
P2P1 SA1
RA1 + EA1
SA2
RA2 + EA2
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Power Equation: (Esq.. 1)
whereQ = volumetric flow rate CFM (L/s)ΔP = pressure drop across opening in. of water (Pa)C = flow coefficient CFM/(in. of watern) (L/s/Pan)n = flow exponent dimensionless
nPCQ )(Δ⋅=
Airflow through Leakage Opening
Leakage Flow
ΔP
QA
Leakage Area
Pressure Differential
Room 1 Room 2
P2P1 SA1
RA1 + EA1
SA2
RA2 + EA2
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Orifice Equation: (Esq.. 2)
whereQ = volumetric flow rate CFM (L/s)ΔP = pressure drop across opening in. of water (Pa)A = large designated opening area's) ft2 (m2)2610 = unit conversion factor dimensionless (I-P unit)840 = unit conversion factor dimensionless (SI unit)
Leakage Flow
ΔP
QA
Leakage Area
Pressure Differential
Room 1 Room 2
P2P1 SA1
RA1 + EA1
SA2
RA2 + EA2
Airflow through Large Designated Opening
PA2610Q Δ⋅⋅=
PA840Q 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
300400
500
600
700
800
900
1,000
1,100
1,200
1,3001,400
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.)
Leak
age
Flow
rate
(cfm
)
Leakage Area(Sq. in.)
20
40
60
80
100
120
140160
180200220
240
260
280
300
320340360380
400
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Large designated openings such as doorway can be easily measured. However irregular opening such as a crack can not be measured physically, there is other means to estimate the equivalent size, or called “Effective Leakage Area” (ELA).
For Existing Rooms:
Field “Blower Door Test” (ASTM 1987, CGSB 1986) to obtain more 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 can produce a set of data of Q - ∆P, and a “power equation” curve fit with calculated constants (C, n, ELA) that defines a room’s unique 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 - ΔP data set, C and n can be calculated:
“Blower Door Test” - Multiple-Point Test Data for Power Equation Curve Fitting
n)P(CQ Δ⋅=
∑ ∑
∑∑ ∑
= =
== =
Δ⋅−Δ
Δ⋅⋅−Δ⋅
= m
1k
m
1k
2k
2k
m
1kkk
m
1k
m
1kkk
)P(lnm)Pln(
)PlnQ(lnm)PlnQln(n
⎟⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜⎜
⎝
⎛Δ⋅−
=∑∑==
m
PlnnQlnEXPC
m
1kk
m
1kk
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Opening Resistance Analysis
Q
Qi
P
PP i
PP i
Q
Leakage flow resistances connected in parallel and series
( )∑=
⎥⎦
⎤⎢⎣
⎡=
n
i i
T
ELA
ELA
12
1
1
∑=
=n
iTi
ELAELA1
ELAR 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 RoomSupply Airflow
(SA)
Total RoomExhaust and/orReturn Airflow
(EA+RA)
RoomPositively
Pressurized
+ Tota
l Roo
mSu
pply
Airf
low
(SA
)
Offset Flow ΔV
Tota
l Roo
m E
xhau
st
and/
or R
etur
n A
irflo
w
(EA
+RA
)
Total LeakageAirflows
ΣQ
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Room Pressurization Scenarios and Variable Relationship
Scennario 2: Room Non-PrerssurizedSA - (EA+RA) = ΔV = ΣQ = 0
Total RoomSupply Airflow
(SA)
Total RoomExhaust and/orReturn Airflow
(EA+RA)
RoomNon-Pressurized
Tota
l Roo
m E
xhau
st a
nd/o
r R
etur
n A
irflo
w (E
A+R
A)
Offset Flow
ΔV = 0
Tota
l Roo
mSu
pply
Airf
low
(SA
)
Total LeakageAirflowsΣQ = 0
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Room Pressurization Scenarios and Variable Relationship
Scennario 3: Room De-prerssurizedSA - (EA+RA) = ΔV = ΣQ < 0
Total RoomSupply Airflow
(SA)
Total RoomExhaust and/orReturn Airflow
(EA+RA)
RoomNegatively
De-pressurized-
Tota
l Roo
mSu
pply
Airf
low
(SA
)
Tota
l Roo
m E
xhau
st a
nd/o
r Ret
urn
Airf
low
(EA
+RA
)
Offset Flow ΔV
Total LeakageAirflows
ΣQ
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Central Air Handling System &Room Pressurization
SA = 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/zone
OA = Volume of outside air drawn into the AHU
FA = Volume of relief air released from return air
RA-FA = Volume of recalculated air
Q = Volume of total leakage air through space shell/zone
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Central Air Handling Unit &Room Pressurization
Two volumetric balance 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 an indicator 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 distribution arrangement.
• 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 relative pressurization 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
RSASA
1 R
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Adjacent Rooms under Various Pressures
If a room has several leakage openings with adjacent rooms, the room’s pressurization ratio is:
∑=
−= n
iiR
RR
QSA
SAR
1
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Pressure Differential and Crack Air VelocityCriterion 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)
Pressurization Criterion
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 Leakage Velocity V
fpm 109
374
587
764
920
1,064
1,198
1,444
1,670
Eq. (1), when n=0.65
Large Opening Velocity 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 entering airflow (supply airflow, SA) and leaving airflow (exhaust and/or return airflows, EA+RA), normally called “offset” value (ΔV), which equals the total 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 the appropriate 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 control techniques 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.
FumeHood
Velocity Sensor
Sash Sensor
or
Hood Valve & Controller
CHEMICAL LAB
CORRIDOR
ROOM CONTROLLER
SUPPLY AIR
Total Exhaust Air from RoomHood
ExhaustHood Exhaust
Room ExhaustValve
Room SupplyValve
DSDoor Switch
T
Leakage Air
Leakage Air
Total Supply Air to 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
FumeHood
Velocity Sensor
Sash Sensor
or
Hood Valve & Controller
CHEMICAL LAB
CORRIDOR
ROOM CONTROLLER
SUPPLY AIR
Total Exhaust Air from RoomHood
ExhaustHood Exhaust
Room ExhaustValve
Room SupplyValve
DSDoor Switch
T
Leakage Air
Leakage Air
Flow Sensor
Flow Sensor
Total Supply Air to RoomDP
DPMonitor
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
FumeHood
Velocity Sensor
Sash Sensor
or
Hood Valve & Controller
CHEMICAL LAB
CORRIDOR
ROOM CONTROLLER
SUPPLY AIR
Total Exhaust Air from RoomHood
ExhaustHood Exhaust
Room ExhaustValve
Room SupplyValve
DSDoor Switch
T
Leakage Air
Flow Sensor
Flow Sensor
Total Supply Air to Room
DPDP Sensor
Leakage Air
Thermostat
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Multiple-Room (Suite) Pressure Control Strategies
Single room control technologies often cause problems in Suite Pressure Control during air balancing, since the following phenomena are often ignored:
Adjusting one room’s offset value will impact adjacent rooms’ air pressures if they were just balanced earlier.
Example - Pharmaceutical Aseptic Suite
One room’s air gain could be another room’s air loss through leakages.
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Adaptive Control (DP+DF+AD)The three traditional methods (DP, DF and DP+DF) are either 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 all rooms’ pressures all together as an optimized system, instead of controlling each room pressure independently. It actively 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 leakage values between the rooms and adjust flow offset of each room 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 dynamic leakage characterization can also be automatically achieved by digital controller, precision pressure differential sensor (±0.001 in./0.25 Pa) and airflow control devices (±5%). These devices are often permanently installed in lab and clean room environments.This automated pressurization test (Q-∆P data set) is faster and cheaper, and can be handled remotely.
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Adaptive Control (Example: Control of Multiple Rooms)
CLEANESTROOM0.08 In.
CLEANERROOM0.06 In.
AIRLOCK0.03 In.
GENERALCHEMICAL LAB- 0.02 In.
CONTAINMENTLAB- 0.06 In.
Designated Leakage Flow
Supply Air
Valve
ExhaustAir
Valve
ReturnAir
Valve
Minor LeaksThru. Cracks
CORRIDOR0.00 In.
DP
DPDPDP
DPDP
Pressure Differential
Sensor
Manifolded or Open to Corridor
DSDSDS
DS
DS
DS
Legend
SUITECONTROLLER
Door Switch
SUITECONTROLLER
Valve Position Outputs
DoorSwitchInputs
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 effectWind effectInterior zones with high temperature or humidity differences
Safety Factors(Detailed procedures will be included in the next phase of the study)
Room background leaksDuct leaksAHU 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 ProbesStatic Pressure Measuring Probes
Pressure Transmitter Pressure Transmitter
Pressure Transmitter and Monitor
Pressure Transmitter and Monitor
Control DamperControl Damper
Air Valve –Type 1Air Valve –Type 1
Air Valve –Type 2Air Valve –Type 2
Air Valve -Type 3Air Valve -Type 3
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Case Study - Airflow Resistance and Leakage Flow Simulation
- Room Numbe - Wall - Flow Direction - Induced Flow (by Pressurization) - Node (Room) - Flow Resistance @ Major Opening - Flow Resistance @ Minor Opening - Forced Flow (by Fan)
Network Flow with Major Openings Only Network Flow with Major and Minor Openings
RMX
RM1RM2
RM3
RM4 RM5
RM6
RM1RM2
RM3
RM4 RM5
RM6
Major and minor leakage openings, connection in parallel and series
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Modeling of Transient Pressurization
θ L
W
Room 1
Room 2
P1
P2
Wall
Swing Door
P
Transient Flow Through Swing Door
P1 > P2
1. Pressurization Loss Characteristic During a Swing Door Opening or Closing
⎟⎠⎞
⎜⎝⎛ ⋅
⋅⋅⋅=⋅=2
sin2)()(
tWHLHAtt
ω
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛⋅⋅=
2sin2 )(
)(t
tWL
θ
)600( o≤≤ θ
WHAt
⋅=)(
)9060( o≤< θ
where,
L=width (gap) of door opening in. (cm)W=width of door in. (cm)θ=angle of door opening degreeω=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 Differential Across When A Swing 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)
Pres
sure
Diff
eren
tial A
cros
s D
oor (
Pa)
0
10
20
30
40
50
600 10 20 30 40 50 60 70 80 90
Angle of Swing Door Opening (Degree)
Wid
th (G
ap) o
f Doo
r Ope
ning
(in.
)
Pressure Drop Across DoorW idth of Door Opening
Automatic Swing Door Opens to 90o in 3 Seconds; Door Size 4 ft. (W ) x 7 ft. (H).Rooms Across The Door/Wall Are Maintained with Constant Supply and Return Flows. Initial Pressure Differential Across Door is 68.9 Pa, it drops to 1 Pa less than 2 seconds.
1. Pressurization Loss Characteristic During a Swing Door Opening or Closing
Airlock Room Pressure Profile
-0.010-0.0050.0000.0050.0100.0150.0200.0250.0300.0350.0400.0450.0500.0550.0600.0650.0700.0750.0800.0850.0900.0950.100
Airlock Sliding Door Operation Cycle
Roo
m S
tatic
Pre
ssur
e (in
. WC
)
First Door Opening First Door Closing Both Doors Closed Second Door Opening Second Door Closing
Cleanroom
Airlock
Corridor
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Modeling of Transient Pressurization
L
WP
Transient Flow Through Sliding Door
P1 > P2
Wall
Room 1 P1
Sliding Door
Room 2 P2
2. Pressurization Loss Characteristic During a Sliding Door Opening or Closing
where,
L=width (gap) of door opening in. (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 When A Sliding Door Opens
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2 2.5 3Time of Door Opening (Second)
Pres
sure
Diff
eren
tial A
cros
s D
oor
(Pa)
0
10
20
30
40
50
60
Wid
th (G
ap) o
f Doo
r O
peni
ng (i
n.)
Pressure Drop Across DoorWidth of Door Opening
Automatic Sliding Door Opens at Speed of 16 in./sec.; Door Size 4 ft. (W) x 7 ft. (H);Rooms Across The Door/Wall Are Maintained with Constant Supply and Return Flows, Initial Pressure Differential Across Door is 68.9 Pa, it drops to 1 Pa around 2 seconds.
2. Pressurization Loss Characteristic During a Sliding Door Opening or Closing
Pressure Differentials Between Rooms
-0.010-0.0050.0000.0050.0100.0150.0200.0250.0300.0350.0400.0450.0500.0550.0600.0650.0700.0750.0800.0850.0900.0950.100
Airlock Sliding Door Operation Cycle
Pres
sure
Diff
eren
tial b
etw
een
Room
s (in
. WC)
First Door Opening First Door Closing Both Doors Closed Second Door Opening Second Door Closing
DP (Cleanroom and Corridor)
DP (Door 1) DP (Door 2)
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Door Opening Transient Impact on Pressurization Control
Any passive motor-driven or actuator-driven HVAC system (such VAV box or valve) will not have enough time 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
BUBBLE AIRLOCK
AIRFLOW
CLEANROOM
AIRLOCK
+CORRIDOR
- -
-
AIRFLOW
SINK AIRLOCK
AIRFLOW CLEANROOM
AIRLOCK
-CORRIDOR
++
-
AIRFLOW
AIRFLOW
- -AIRLOCK
DUAL COMPARTMENT AIRLOCK
Air Lock Type
CascadingBubbleSinkDual-Compartment
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Dynamic Pressurization Control Strategies- Airlock
Wait!Wait!
Corridor
Cleanroom
Airlock (Cascading)ΔPDoor 1
ΔPDoor 2
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
Airlock Physical Model Network Flow Simulation
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Result of Network Flow Simulation
Wait!
Corridor
Clean room
Airlock (Cascading)ΔPDoor 1
ΔPDoor 2
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 73 CFM
Clean Room: 10000Airlock: 10,000Corridor: 100000
(12000 CFM, 75 ACH)
(2100 CFM, 75 ACH)
(560 CFM, 10ACH)
Leakage 52 CFM
Leakage 73 CFM11948 CFM
2078 CFM
Clean Room: 10000Airlock: 10,000Corridor: 100000
Case 1 – Class 10,000 Case 2 – Class 100
(48000 CFM, 300 ACH)8400 CFM, 300 ACH)
560 (CFM, 10ACH)
Leakage 52 CFM
Leakage 73 CFM
47948 CFM8378 CFM
Clean Room: 100Airlock: 100Corridor: 100000
(48000 CFM, 300 ACH)8400 CFM, 300 ACH)
560 (CFM, 10ACH)
Leakage 52 CFM
Leakage 73 CFM
47948 CFM8378 CFM
Clean Room: 100Airlock: 100Corridor: 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 PerformanceProfile of Pressure Differential Across Door
When Door Is Opening & Closing (Initial Condition: -15 Pa = -0.06 In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time (Sec.)
Pres
sure
Diff
eren
tial A
cros
s Do
or (P
a)
Test 1Test 2Test 3Average
Door Opening Door Closing
Profile of Pressure Differential Across Door When Door Is Opening & 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 11 12 13 14 15 16
Time (Sec.)
Pres
sure
Diff
eren
tial A
cros
s D
oor (
Pa)
Test 1Test 2Test 3Average
Door Opening Door Closing
Profile of Pressure Differential Across Door
When Door Is Opening & Closing (Initial Condition: -10 Pa = -0.04 In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time (Sec.)
Pres
sure
Diff
eren
tial A
cros
s D
oor (
Pa)
Test 1Test 2Test 3Average
Door Opening Door Closing
Profile of Pressure Differential Across Door When Door Is Opening & Closing
(Initial Condition: 10 Pa = 0.04 In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time (Sec.)
Pres
sure
Diff
eren
tial A
cros
s D
oor (
Pa)
Test 1Test 2Test 3Average Door Opening Door Closing
Profile of Pressure Differential Across Door
When Door Is Opening & 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 11 12 13 14 15 16
Time (Sec.)
Pres
sure
Diff
eren
tial A
cros
s D
oor (
Pa)
Test 1Test 2Test 3Average
Door Opening Door Closing
Profile of Pressure Differential Across Door When Door Is Opening & Closing
(Initial Condition: 15 Pa = 0.06 In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time (Sec.)
Pres
sure
Diff
eren
tial A
cros
s D
oor (
Pa)
Test 1Test 2Test 3Average
Door Opening Door Closing
Profile of Pressure Differential Across Door
When Door Is Opening & Closing (Initial Condition: 0 Pa = 0 In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time (Sec.)
Pres
sure
Diff
eren
tial A
cros
s D
oor (
Pa)
Test 1Test 2Test 3Average
Door Opening Door Closing
Profile of Pressure Differential Across Door When Door Is Opening & Closing
(Initial Condition: 20 Pa = 0.08 In.)
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Time (Sec.)
Pres
sure
Diff
eren
tial A
cros
s Do
or (P
a)
Test 1Test 2Test 3Average
Door Opening Door Closing
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 FactorPC = Number of Particles inside Protected Cleanroom Near DoorPO = 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 Differentials
Airborne Particle Contamination Risk Factor (CRF) Under Various Pressure Differentials Across Cleanroom Door
(Note: 5 Pa = 0.02 In., Particle Measured @ 0.5 µm)
0%
5%
10%
15%
20%
25%
-15 -10 -5 0 5 10 15 20
Initial Pressure Differential Across Door (Pa)
Con
tam
inat
ion
Ris
k Fa
ctor
(CR
F, %
)
Door Opening & Closing W/O People TrafficA Person Walks Through Door
Particle Concentrations Across Cleanroom Door When Door is Opening & Closing
(Initial Condition: Depressurization @ -15 Pa = -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 10 11 12 13 14 15 16 17 18 19 20 21 22
Time (Sec.)
Par
ticle
Con
cent
ratio
ns A
cros
s D
oor
(Cou
nts
/ FT3 )
Inside Cleanroom Door Average Outside Cleanroom Door Average
Door Opening
Door Clos ing
CRF= 18.9%
Particle Concentrations Across Cleanroom Door When Door 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 10 11 12 13 14 15 16 17 18 19 20 21 22
Time (Sec.)
Part
icle
Con
cent
ratio
ns A
cros
s D
oor
(Cou
nts
/ FT3 )
Inside Cleanroom Door Average Outside Cleanroom Door Average
Door Opening
Door Closing
CRF= 2.2%
Particle Concentrations Across Cleanroom Door When Door is Opening & Closing
(Initial Condition: Depressurization @ -10 Pa = -0.04 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 10 11 12 13 14 15 16 17 18 19 20 21 22
Time (Sec.)
Par
ticle
Con
cent
ratio
ns A
cros
s D
oor
(Cou
nts
/ FT3 )
Ins ide Cleanroom erage Door Av Outside Cleanroom Door Average
Door Opening
Door Closing
CRF= 8.5%
Particle Concentrations Across Cleanroom Door When Door is Opening & Closing
(Initial Condition: Pressurization @ 10 Pa = 0.04 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 10 11 12 13 14 15 16 17 18 19 20 21 22
Time (Sec.)
Part
icle
Con
cent
ratio
ns A
cros
s D
oor
(Cou
nts
/ FT3 )
Ins ide Clean rage room Door Ave Outside Cleanroom Door Average
Door Opening
Door Closing
CRF= 0.7%
Particle Concentrations Across Cleanroom Door When Door is Opening & Closing
(Initial Condition: Depressurization @ -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 10 11 12 13 14 15 16 17 18 19 20 21 22
Time (Sec.)
Par
ticle
Con
cent
ratio
ns A
cros
s D
oor
(Cou
nts
/ FT3 )
Inside Cleanroom Door Average Outside Cleanroom Door Average
Door Opening
Door Closing
CRF= 6.9%
Particle Concentrations Across Cleanroom Door When Door is Opening & Closing
(Initial Condition: Pressurization @ 15 Pa = 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 10 11 12 13 14 15 16 17 18 19 20 21 22
Time (Sec.)
Par
ticle
Con
cent
ratio
ns A
cros
s D
oor
(Cou
nts
/ FT3 )
Inside Cleanroom Door Average Outside Cleanroom Door Average
Door Opening
Door Clos ing
CRF= 0.8%
Airborne Particle Contamination Risk Factor (CRF) Under Various Pressure Differentials Across Cleanroom Door
(Note: 5 Pa = 0.02 In., Particle Measured @ 0.5 µm)
Particle Concentrations Across Cleanroom Door When Door is Opening & Closing
(Initial Condition: Neutral @ 0 Pa = 0 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 10 11 12 13 14 15 16 17 18 19 20 21 22
Time (Sec.)
Part
icle
Con
cent
ratio
ns A
cros
s D
oor
(Cou
nts
/ FT3 )
Ins ide Cleanroom Door Average Outside Cleanroom Door Average
Door Opening
Door Closing
CRF= 4.2%
Particle Concentrations Across Cleanroom Door When Door is Opening & Closing
(Initial Condition: Pressurization @ 20 Pa = 0.08 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 10 13 14 15 16 17 18 19 20 21 22
Time (Sec.)
Part
icle
Con
cent
ratio
ns A
cros
s D
oor
(Cou
nts
/ FT3 )
11 12
Ins ide Cleanroom Door Average Outside Cleanroom Door Average
Door Opening
Door Closing
CRF= 0.3%
Regression Curve:CRF= 0.0332e-0.1181*PD
R2 = 0.9656(No People Traffic)
Regression Curve:CRF = 0.0418e-0.0703*PD
R2 = 0.9129(With People Traffic)
0%
5%
10%
15%
20%
25%
-15 -10 -5 0 5 10 15 20
Initial Pressure Differential Across Door (Pa)
Con
tam
inat
ion
Ris
k Fa
ctor
(CR
F, %
)
Door Opening & Closing W/O People TrafficA Person Walks Through DoorRegression (Door Opening & Closing W/O People Traffic)Regression (A Person Walks Through Door)
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Dynamic Pressurization Control Strategies – Adjustable Pressure Stabilizer
A leakage regulator, controllable pressure relief damper across a wall to maintain a minimum required pressurization. When a door is normally closed, this damper should stay open and maintain normal pressure differential; when the door opens, the damper shall be automatically closed either by spring-loaded or counter-weight gravity damper, and maintain a lower while acceptable pressure differential.
PressureStabilizer
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Importance
Air-handling unit controlLab HVAC controlPrefabricated clean roomPrecision environmental test chamberSmoke management control Air distribution system
In addition to design engineers and research scientists, the information presented may also benefit manufacturers in the fields of:
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Pressurization Study
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Q & A
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