Basic Documentation
Table Of Contents
- About this Application Guide
- Chapter 1–Introduction
- Chapter 2–Goals of the Laboratory Environment
- Chapter 3–Unique Ventilation Needs of a Laboratory Facility
- Chapter 4–Ventilation Systems Classification
- Chapter 5–Laboratory Facility Exhaust Systems
- Chapter 6–Laboratory Containment Units - Ventilation
- Chapter 7–Room Ventilation, Makeup Air, and Pressurization Control Systems
- Chapter 8–Laboratory Temperature and Humidity Control Systems
- Chapter 9–Laboratory Emergencies - Ventilation System Response
- Chapter 10–Laboratory Ventilation System - Validation
- Chapter 11–Laboratory Ventilation System - Commissioning
- Glossary
- Index
Glossary
laminar flow cabinet
Cabinet similar to a fume hood but with no sash. A laminar airflow is provided across the
work surface and is then allowed to flow outward toward the user. The laminar flow cabinet
protects the substance from airborne contamination by constantly keeping a highly pure
airflow over it that will oppose any potential source of impure airflow. Laminar flow cabinets
are used only if the substance is not hazardous and thus the airflow passing over and around
it will not entrain any hazardous gasses, vapors, or any other substances.
manometer
Instrument for measuring relatively low pressures and pressure differences commonly
associated with ventilation systems. A manometer consists of a transparent vertical or
slanted tube containing a liquid, such as oil, water, or mercury. A manometer is an accurate
and very repeatable means of pressure measurement since it is not subject to the effects of
aging or friction as are mechanical mechanism types of instruments that rely on springs, such
as gears and levers. Manometers however, are not well suited for very low pressure
measurements typically associated with room pressurization, such as 0.01 in. WC.
open loop control
Control arrangement where the controlled variable (temperature, pressure, airflow, humidity,
etc.) is not directly measured or sensed by the controller. Open loop controllers typically base
their control output on a reference to some condition rather than the specific needs of the
controlled variable and is normally applicable only to non-critical control applications where
approximate control results are acceptable. An example would be modulating an exhaust
damper in relation to the general need for more or less airflow without specifically measuring
and controlling at a specific amount of airflow.
Pitot tube
Standard configuration of an air pressure measurement probe that is often applied in
ventilation systems. A Pitot tube actually provides two pressure measurements. One
measurement samples the pressure of a moving air stream and is termed the total pressure.
The outer tube samples only the pressure component of the air stream that is perpendicular
(crosswise) to the direction of flow and is the static pressure of the air stream. By connecting
a differential pressure gauge (or a manometer) to these two measurement outputs of a Pitot
tube, the difference between them, termed the velocity pressure, is obtained. Velocity
pressure is directly related to the velocity of an air stream and is therefore a convenient way
to determine the airflow velocity in feet per minute.
plenum
Space intended to collect and temporarily confine a relatively large volume of air. In
ventilation systems, sheet metal plenums are often located close to the discharge of a supply
fans and provide a convenient point to tap off multiple supply air ducts. The space between a
room’s ceiling and the bottom of the floor above is sometimes used as a plenum to collect the
air from multiple room exhaust grills so it can then be carried off by a single exhaust duct. In
centralized exhaust systems that serve laboratory rooms and equipment, such as fume
hoods and biosafety cabinets, a plenum is often used on the roof to enable terminating
multiple exhaust risers prior to the exhaust fan inlets.
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