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
Laboratory Room Pressurization
Advantages and Disadvantages of Room Pressurization Control by Airflow
Tracking
The room pressurization control by airflow tracking has many distinct advantages
over the pressure sensing method. Airflow tracking offers more stable control since
sensing duct airflow is a more robust and reliable sensing process than sensing room
differential pressure. Due to the faster response of the duct airflow sensors, airflow
tracking provides faster room control response time. Fast control response is
particularly important with regard to maintaining fume hood containment since the
room supply air must provide the fume hoods with adequate makeup air whenever a
sash is repositioned. Sensing actual room static pressure involves a much greater
time lag thus increasing overall room control response time. This can delay providing
sufficient room supply makeup air to ensure adequate fume hood containment.
Airflow tracking control is not affected by room transient conditions such as open
doors, thus it is a simpler control scenario to implement.
It must be noted that airflow tracking cannot ensure that a specific level of positive or
negative static pressure will be maintained. Rather the control scenario maintains a
differential airflow that is related to the desired room static pressure. This differential
must be established during the testing and balancing procedure since the actual
differential airflow that a given room requires cannot be determined beforehand. Also
as seasons pass and building conditions change over time, the actual static pressure
level being maintained will undoubtedly vary from what it was when initially setup.
This necessitates periodically checking (that is, annually) and perhaps readjusting
the differential tracking value.
Although there will likely be some variation in the specific static pressure level when
utilizing airflow tracking, it should be realized that the primary goal of maintaining a
room at a negative (or positive) static pressure is to ensure that an undesirable
transfer of air does not occur. Airflow tracking meets this goal by maintaining an
airflow differential that results in airflow in the desired direction thus preventing
undesired air transfer.
Cascaded Static Pressure Control
Although airflow tracking is the preferred method for preventing cross contamination
for most laboratory applications, there may be valid reasons to ensure that a specific
differential pressure level is always maintained. This may apply to certain high
toxicity laboratories or other applications where a specific minimum negative room
static pressure is required. To achieve the superior speed of response and stability of
control by airflow tracking, yet ensure that a specific static pressure is always
maintained, a combination of room pressurization control that combines both
pressure sensing and airflow tracking can be applied.
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