Room Pressurization Control 125-2412 Rev.
Rev.2.0, June, 2004 NOTICE The information contained within this document is subject to change without notice and should not be construed as a commitment by Siemens Building Technologies, Inc. Siemens Building Technologies, Inc. assumes no responsibility for any errors that may appear in this document. All software described in this document is furnished under a license and may be used or copied only in accordance with the terms of such license.
Room Pressurization Control Application Guide Table of Contents How To Use This Application Guide ................................................................................ I How This Guide is Organzed.......................................................................................... I Getting Help .................................................................................................................... I Where To Send Comments ........................................................
Room Pressurization Control Application Guide Door Effects ............................................................................................................ 23 VAV Fume Hood Effects......................................................................................... 23 Cascaded Pressure Control ...................................................................................... 24 Dual Pressurization Laboratories..............................................................................
Room Pressurization Control Application Guide How To Use This Application Guide This section covers this how this application guide is organized, how to access help, and where to send comments regarding this document. How This Guide is Organzed This application guide contains the following chapters: • Chapter 1, Introduction, introduces the topic of room pressurization by discussing the importance of room pressurization, the objective of this application guide, and the intended audience.
Room Pressurization Control Application Guide II Siemens Building Technologies, Inc.
Chapter 1—Introduction Chapter 1 introduces the topic of room pressurization and discusses the: • Importance of Room Pressurization • Objective of this Application Guide • Intended Audience Importance of Room Pressurization Proper room pressurization is an absolute necessity to ensure occupant health and safety as well as preserve the purity and integrity of an increasing array of manufactured products.
Room Pressurization Control Application Guide Intended Audience This Application Guide has been written to serve an audience with a wide range of interests: 2 • Persons with overall administrative and management responsibilities in facilities that require room pressurization will find this guide an informative tutorial on the concept and ramifications of room pressurization.
Chapter 2—Pressurization Applications Chapter 2 defines room pressurization and discusses these topics: • Room Static Pressure • Building Pressurization • Room Pressurization Applications Room Static Pressure When referring to room pressurization, the term static pressure is usually applied to establish the fact that the pressure is not due to any air motion. Rather, the pressure exists independently of any motion of the air.
Room Pressurization Control Application Guide NOTE: In Chapter 5, Table 4. Velocity Pressure vs. Airflow Velocity shows that a differential pressure of 0.02 inches w. c. would result in an airflow velocity from the positive space to the negative space of about 566 feet per minute. Given the chance, air in a positively pressurized room (higher static pressure) will flow out of the room and into an area of lower static pressure.
Room Pressurization Applications Room Pressurization Applications In most applications, room pressurization is applied to control the direction of room transfer airflow. Transfer air is air that is not directly supplied to a room or exhausted from the room by the room’s ventilation system. Rather, transfer air is air that may enter the room or leave the room as a result of pressure differentials, through passageways other than the ventilation system ductwork.
Room Pressurization Control Application Guide Biosafety Level 1 (BL-1) Biosafety Level 1 (BL-1) is the lowest biosafety classification and applies to biological laboratories that need no special ventilation requirements apart from an adequate room ventilation rate. BL-1 laboratories present a low health risk to individuals and the community. Such laboratory rooms are only required to be separated from public areas by a closed door.
Room Pressurization Applications Biosafety Level 4 (BL-4) Biosafety Level 4 (BL-4) is the classification that applies to laboratories2 that present the highest risk to individuals in the laboratory, the facility, and to nearby communities. As such, they must be designed in accord with very strict safety requirements. BL-4 laboratories require all of the BL-3 provisions plus use of the highest classification of biological safety cabinet (Class III glove box) for all work performed.
Room Pressurization Control Application Guide Clean Rooms Nearly all pharmaceutical, biomedical, microelectronics, as well as the optical industry and many others, need to prevent contamination of their products or processes by maintaining a clean room environment.
Room Pressurization Applications Table 1 lists various room pressurization applications and the normal static pressure relationships required. Table 1. Room Static Pressurization Applications. Application Recommended Static Pressurization Level Relationship to Adjacent Area(s) Comments Inches Pascals Chemical Laboratory 0.01 to 0.02 2.5 to 5 Negative These values apply to general chemistry laboratories.
Room Pressurization Control Application Guide Table 1. Room Static Pressurization Applications. Application Recommended Static Pressurization Level Relationship to Adjacent Area(s) Comments Inches Pascals Hospital - Infectious Isolation Room 0.01 2.5 Negative inches w.c. for these rooms; however, most designs incorporate higher pressurization levels. The most effective isolation room arrangement incorporates a lower pressurized anteroom as a buffer zone between the isolation room and corridor.
Chapter 3—Room Pressurization Design Criteria Chapter 3 discusses the following topics: • Design Considerations • Room Pressurization Reference Data • Room Pressurization Factors • Leakage Area Design Considerations As stated previously in this guide, the positive or negative room static pressurization relationship between two spaces determines the potential for transfer airflow between them.
Room Pressurization Control Application Guide AIRFLOW TRACKING OFFSET LAB0192R1 ROOM SUPPLY AIRFLOW TOTAL ROOM EXHAUST AIRFLOW Figure 1. Negatively Pressurized Room Airflows. For a negatively pressurized room, airflow tracking ensures that the total amount of air exhausted from the room always exceeds the amount of air that is supplied to the room. This creates a slight vacuum effect in the room, which causes air from adjacent areas to flow into the room through the room’s leakage area.
Design Considerations SERVICE CORRIDOR 0.00 in. w.c. TOTAL ROOM EXHAUST AIR TRANSFER AIRFLOW INTO ROOM LAB0193R1 ROOM SUPPLY AIR LABORATORY ROOM - 0.01 in. w.c. (-2.5Pa) MAIN CORRIDOR 0.00 in. w.c. Figure 2. Laboratory Room at a Negative Static Pressure with Respect to the Adjacent Corridors. Siemens Building Technologies, Inc.
Room Pressurization Control Application Guide Room Pressurization Reference Data As indicated in Table 1, good ventilation system design for chemical laboratory rooms should ensure that the rooms are at a negative static pressure of approximately 0.01 inches w.c. with respect to adjacent non-laboratory spaces, such as a corridor3.
Room Pressurization Factors 0.020 0.019 0.1 Ft2 0.018 ROOM LEAKAGE AREA CURVES 0.017 0.2 Ft2 0.016 0.015 0.3 Ft2 0.014 0.013 DIFFERENTIAL PRESSURE 0.4 Ft2 0.012 0.011 0.5 Ft2 0.010 INCHES of WATER 0.009 0.6 Ft2 0.008 0.007 0.75 Ft2 0.006 0.005 1.0 Ft2 0.004 0.003 1.5 Ft2 LAB0194R1 0.002 0.001 0.000 0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 ROOM DIFFERENTIAL AIRFLOW - CFM Figure 3. Room Differential Airflow vs.
Room Pressurization Control Application Guide Figure 3 shows that when a room has as little as a 0.2 sq. ft. leakage area, a small change in differential airflow such as only 25 cfm causes a rather large variation in the resulting differential pressure value. Whereas, the same 25 cfm differential airflow variation for a room having a 1.0 sq. ft. leakage area would exhibit a much smaller differential pressure variation.
Chapter 4—Room Static Pressure Control Chapter 4 discusses static pressure control in rooms in the following facilities: • Laboratories • Healthcare Facilities The most appropriate method of controlling a room's static pressure is dependent upon the room application. Since the purpose for maintaining a differential pressure relationship between rooms is to prevent cross contamination, the consequences of cross contamination must be known in order to determine the most appropriate method of control.
Room Pressurization Control Application Guide SUPPLY TERMINAL ROOM GENERAL EXHAUST CFM FUME HOOD CONTROLLERS CFM CFM CFM LAB0195R1 ROOM CONTROLLER Figure 4. Airflow Tracking Control Arrangement for a Chemical Laboratory Room. The specific amount of air exhausted by a VAV fume hood depends on the extent that its respective sash is open5.
Laboratories In a VAV laboratory the Room Controller must modulate the Room General Exhaust to ensure that there is sufficient total room exhaust to meet the required minimum room ventilation rate (ACH). The ROOM CONTROLLER must also modulate the Room General Exhaust to ensure that there is sufficient total room exhaust for the amount of supply airflow necessary to maintain the desired room temperature.
Room Pressurization Control Application Guide Option 1, designing the ventilation system to maintain a specific room differential airflow, is generally recommended for applications where a lower room differential pressure (perhaps 0.01 to 0.02 inches w.c.) is sufficient. Recall that the primary purpose of room pressurization is to create the proper directional airflow to prevent or retard undesirable transfer of air.
Laboratories Direct Pressure Control The direct pressure control method uses a room pressure controller with a static pressure sensing arrangement. This enables the controller to modulate the room’s supply and total exhaust airflows as needed to maintain the room static pressure set point. Figure 5 shows the essential components of a typical chemical laboratory room ventilation system using a single duct supply terminal.
Room Pressurization Control Application Guide SUPPLY TERMINAL ROOM GENERAL EXHAUST CFM CFM CFM LAB0196R1 STATIC PRESSURE FUME HOOD CONTROLLERS CFM ROOM CONTROLLER ROOM STATIC PRESSURE SENSOR Figure 5. Direct Pressure Control Arrangement for a Chemical Laboratory Room. The Room Controller also monitors the room static pressure via the Room Static Pressure Sensor and controls the total room supply airflow to maintain the required room static pressure set point.
Laboratories • Maintaining the proper amount of room supply airflow to maintain the required room static pressure. • Increasing the supply airflow when needed to cool or heat the room while simultaneously increasing the room general exhaust to maintain a constant room static pressure.
Room Pressurization Control Application Guide To obtain a reliable room static pressure value from the room static pressure sensor, the room controller must sample the sensor output for several seconds to factor out the pressure variations caused by personnel movement, room air currents, and even outside air wind gusts (referred to as signal noise). This delays the room controller’s response to room static pressure variations.
Laboratories • It presents a greater design challenge and involves a more difficult startup and balancing process. In particular, the areas adjacent to the room (for example, corridors) must have the proper level of excess supply air since the laboratory room(s) airflow tracking offset will not remain at a constant value. Dual Pressurization Laboratories In some instances, it is necessary to ensure that a laboratory room does not become contaminated by airborne impurities from adjacent areas.
Room Pressurization Control Application Guide With respect to the ventilation system design, the vestibule exhaust would normally be a constant air volume (CAV) exhaust while the laboratory room could employ either a CAV or VAV ventilation arrangement. The important element is that the laboratory room controller must ensure that the total exhaust of the room combination is always greater than the room supply air.
Healthcare Facilities Healthcare Facilities Infectious Isolation Rooms Infectious isolation rooms in healthcare facilities are intended to ensure that the direction of airflow is always into the room, thus preventing the spread of disease to persons outside of the room, particularly the healthcare workers. The need for providing negatively pressurized infectious isolation rooms has become more focused because of the resurgence of the contagious disease Tuberculosis (TB).
Room Pressurization Control Application Guide Infectious Isolation Room Layout Figure 7 shows the optimum room airflow and control arrangement for an infectious isolation room. The room layout consists of the patient room and an anteroom. The anteroom provides added assurance against airflow coming out from the patient room. The airflow control arrangement maintains the patient room as the more negative of the two rooms so that airflow is always into the anteroom and then into the patient room.
Healthcare Facilities Room Pressure Monitors Room pressure monitors are provided for both the patient room and the anteroom. This ensures that proper room pressurization for both rooms can be constantly monitored and verified. It is also important that both the anteroom and the patient room controllers be located outside of the rooms so that access to these devices does not require service personnel to enter either the anteroom or patient room.
Room Pressurization Control Application Guide Isolation Room Changeover The American Institute of Architects (AIA) guidelines14 do not permit the same room to be alternately used for both Infectious and Protective Isolation. Note that Figure 7 and Figure 8 show a location of the supply diffuser and exhaust grills that is different for infectious and protective isolation rooms.
Clean Rooms • Construction Procedures—Clean rooms must be constructed using specialized techniques and practices to prevent contamination of the room materials, ventilation ductwork, and room equipment. Room components, such as ductwork, must be precleaned and sealed before installation so that no residual particulate is present. Construction personnel must be properly trained and must follow rigid guidelines for handling construction materials and equipment, and in carrying out construction procedures.
Room Pressurization Control Application Guide Table 2 provides the allowable limits for 0.1, 0.5 and 5.0 micron size airborne particles per cubic foot and cubic meter for different clean room classifications for the current versions of the FS 209E and ISO/FDIS 14644-1 standards. These standards also establish allowable limits for other size particles aside from those listed in the table, however the particle sizes listed in Table 2 provide a comparison between the two standards. Table 2.
Clean Rooms Clean Room Pressurization Applications Figure 9 shows a simplified clean room arrangement for a pharmaceutical processing application. The cleanest area is the aseptic16 filling area, which is most likely where the finished product is packaged (oral tablets, medications, etc.). FINISHED PRODUCT OUTLET ++ ++ PREPARATION AREA ASEPTIC FILLING AREA +++ AIRFLOW DIRECTION ARROWS + + LAB0200R1 PERSONNEL CORRIDOR EXIT & DE-GOWNING AIRLOCK ENTRY & GOWNING AIRLOCK Figure 9.
Room Pressurization Control Application Guide The clean spaces are positively pressurized according to their required level of purity or cleanliness. The most critical operations are performed in the area that has the highest level of cleanliness (aseptic area), which also has the highest level of pressurization. In Figure 9, each plus sign indicates the area's relative level of positive pressurization. The more plus signs, the higher the positive pressurization.
Clean Rooms • Potent Compound18 Airlock—Figure 13 shows a pressure bubble airlock combined with a pressure sink airlock. This two-compartment airlock arrangement allows personnel to protect themselves by putting on Personal Protective Equipment (PPE), such as outer garments and sometimes respirators, in the pressure bubble area (++) before entering the pressure sink area (– –) and clean space area in which the potent compound substances are present.
Room Pressurization Control Application Guide CLEAN SPACE FILTERED CEILING SUPPLY* SLIDING OR HINGED DOORS AIRLOCK LAB0202R1 NON CLASSIFIED CORRIDOR *CEILING SUPPLY CFM = AIRLOCK DOOR LEAKAGE CFM Figure 11. Pressure Bubble Airlock. 36 Siemens Building Technologies, Inc.
Clean Rooms CLEAN SPACE CEILING SUPPLY* SLIDING OR HINGED DOORS AIRLOCK FLOOR EXHAUST RISER* LAB0203R1 NON CLASSIFIED CORRIDOR *FLOOR EXHAUST CFM = CEILING SUPPLY + DOOR LEAKAGE CFM Figure 12. Pressure Sink Airlock. Siemens Building Technologies, Inc.
Room Pressurization Control Application Guide FLOOR EXHAUST RISER* CLEAN SPACE CEILING SUPPLY* CEILING SUPPLY* LAB0204R1 SLIDING OR HINGED DOORS NON CLASSIFIED CORRIDOR Figure 13. Potent Compound Airlock. Airlock Construction Proper airlock construction is critical to ensuring that the required pressurization levels can be attained. All surfaces should be well sealed and covered with a highly impervious finish such as epoxy paint. Airlock doors can be either hinged or sliding.
Clean Rooms Table 3. Airlock Door Clearance Areas. Door Size Total Closed Door Clearance Area Hinged Door Sliding Door (See Note 1) (See Note 2) 36 in. × 78 in. 0.229 sq. ft. 0.792 sq. ft. 36 in. × 84 in. 0.240 sq. ft. 0.833 sq. ft. 42 in. × 78 in. 0.245 sq. ft. 0.833 sq. ft. 42 in. × 84 in. 0.255 sq. ft. 0.875 sq. ft. 48 in. × 78 in. 0.875 sq. ft. 48 in. × 84 in. 0.917 sq. ft. 60 in. × 78 in. 0.958 sq. ft. 72 in. × 78 in. 1.042 sq. ft.
Room Pressurization Control Application Guide Q = 840 A (dP)1/2 (SI) where: Q is the differential airflow in Liters per Second, A is the total room leakage area in Square Meters dP is the differential pressure in Pascals 0.0600 0.0575 1.1 Ft2 0.0550 1.2 Ft2 0.0525 1.3 Ft2 0.0500 0.1 Ft2 0.0475 1.4 Ft2 0.2 Ft2 0.0450 1.5 Ft2 0.0425 0.4 Ft2 0.0400 1.7 Ft2 0.5 Ft2 0.0375 DIFFERENTIAL 0.0350 PRESSURE 1.8 Ft2 0.6 Ft2 1.9 Ft2 2.0 Ft2 0.7 Ft2 0.0325 INCHES of WATER 1.6 Ft2 0.3 Ft2 0.
LAB0206R1 Clean Rooms ROOM EXHAUST MAKEUP AIRFLOW ROOM EXHAUST AIRFLOW MEASUREMENT & CONTROL INPUTS / OUTPUTS MAKEUP AIRFLOW DOOR SWITCH INPUTS 'CLEANEST' SPACE +0.200 in. w.c. STATIC PRESSURE INPUTS DOOR SWITCH ROOM CONTROLLER DS AIRFLOW LEAKAGE ARROWS ROOM EXHAUST +0.100 in. w.c. DS +0.150 in. w.c. DS AIRLOCK +0.050 in. w.c. MAKEUP AIRFLOW EXHAUST DS PERSONNEL CORRIDOR (NEUTRAL) SUPPLY ROOM STATIC PRESSURE SENSOR Figure 15. Multi-room Pressurization Control Arrangement.
Room Pressurization Control Application Guide • The Makeup Airflow and Exhaust Airflow for each room is individually measured and controlled by the room controller. Room Pressurization Control The Room Controller continuously monitors each room's static pressure level between the respective room and the Personnel Corridor by means of the Room Static Pressure Sensor.
Chapter 5—Air Pressurization Fundamentals Chapter 5 presents the fundamentals of air pressurization, introduces ventilation system pressure components, and summarizes important factors in relation to these components. This chapter also discusses the following topics: • Forces Exerted by Air • Total Pressure • Static Pressure • Velocity Pressure • Air Velocity • Units of Measure Forces Exerted by Air Air can exert a force in two ways.
Room Pressurization Control Application Guide AIRFLOW LAB0189R1 TOTAL PRESSURE Figure 16. Total Pressure (Force Per Unit Area) Exerted in the Direction of Airflow and the Air Movement Force. Static Pressure In contrast to the force exerted by the wind or air in motion, air at rest can exert a force within any confined or enclosed space.
Forces Exerted by Air LAB0190R1 STATIC PRESSURE Figure 17. Static Pressure is Force Per Unit Area Exerted Equally in All Directions and Not Caused by Air Movement. Now, consider what happens when air in a confined area (such as a ventilation system duct) is put in motion. In a confined area, air in motion has both a total pressure and a static pressure component, and each of these components can be individually measured.
Room Pressurization Control Application Guide In still (non-moving) air the total pressure equals the static pressure. The total pressure in a moving air stream is always greater than its static pressure. If the static pressure value of a moving air stream is subtracted from the total pressure value, the resulting difference is called the velocity pressure. This velocity pressure component bears a relationship to the speed or velocity of the moving air stream.
Air Velocity Air Velocity As illustrated in Figure 18, pressure measurement instruments can determine both the total pressure and static pressure of an airstream in a duct. Subtracting the static pressure value from the total pressure value yields the velocity pressure, which, in turn, enables the velocity of the air stream to be determined. When air is rapidly flowing through a duct, it typically has a significant total pressure as evidenced by the force exerted in the direction it is moving.
Room Pressurization Control Application Guide Differential Pressure A pressure measurement is always a measurement of the pressure difference between two points or locations. Every pressure measurement can be termed a differential pressure measurement. In most instances, a plainly visible barrier separates the two “locations.
Summary of Pressure Components Table 4 lists velocity pressures and the corresponding airflow velocities for the typical range of ventilation airflows. Table 4. Velocity Pressure vs. Airflow Velocity21 Velocity Pressure 21 Airflow Velocity Inches W. C. Pascals Feet per Minute Meters per Second 0.0050 1.2444 283 0.0100 2.4884 0.0150 Velocity Pressure Airflow Velocity Inches W. C. Pascals Feet per Minute Meters per Second 1.439 0.1300 32.3489 1444 7.336 401 2.035 0.1400 34.
Room Pressurization Control Application Guide 50 Siemens Building Technologies, Inc.
Glossary Airflow Tracking (Flow Tracking) A means of maintaining a positive or negative static pressure in a particular room with respect to an adjoining room, corridor, or building exterior. Airflow tracking consists of always maintaining a fixed amount of airflow difference between the total supply air and total exhaust air provided by the room or space ventilation system.
Room Pressurization Control Application Guide Pascals (Pa) SI unit to express relatively low air pressure values as is the case in ventilation system applications. One Pascal is much less than 1 inch w.c. (I/P unit for low pressure values) since 248.8378822 Pascals equal 1 inch w.c. In clean room pressure applications a typical room static pressure level of 0.050 inches w.c. would equate to approximately 12.4 Pascals.
Glossary Standard Air Density (Standard Atmosphere) This has been set at 0.075 lb. per cubic foot (I/P units) and is approximately the weight of one cubic foot of air at 70°F and 29.921 inches of mercury (Hg), where 29.921 inches of mercury approximately equals 14.696 psi. Static Pressure Pressure exerted by air at rest or the force of air that is exerted perpendicular to the direction of airflow when air movement is present. Static pressure is not a resultant of air movement.
Room Pressurization Control Application Guide 4-Glossary Siemens Building Technologies, Inc.
Index A G ACH........................ See Room Ventilation Rate Air Velocity .....................................................47 airflow tracking ........ 11, 12, 17, 19, 20, 21, 24, 25, 28 Airflow Tracking Control Considerations...............................19 Airlock Construction .......................................38 Airlocks...........................................................34 Animal Holding Rooms ....................................7 Glossary of Pressurization Terms .................
Room Pressurization Control Application Guide R T room differential pressure ............14, 16, 19, 20 room leakage ...................11, 14, 15, 16, 39, 40 Room Pressure Monitors ...............................29 Room Pressurization Applications ..................................................5 Control ........................................................42 Design Criteria............................................11 Factors........................................................
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