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
Chapter 8–Laboratory Temperature and Humidity Control Systems
"CLEAN"
STEAM
ROOM CONTROLLER
ROOM SUPPLY TERMINAL
ROOM
GENERAL
EXHAUST
INDIVIDUAL LABORATORY ROOM
HUMIDITY
SENSOR
Figure 18. Individual Room Relative Humidity Control.
Dehumidification
Whenever excessive moisture is present in the outside air, dehumidification is
necessary. Normally this is accomplished by the condensation that occurs by the
sensible heat transfer of a primary air handling unit’s cooling coil. However, some
laboratories may require humidity levels lower than that which the conventional
cooling coil dehumidification can provide. Since 35°F
30
is the practical limit of how
low of an air temperature a conventional cooling coil may attain, this may not yield
sufficient dehumidification to attain very low humidities.
Laboratory rooms that require very low humidities should be grouped together and
served by a common primary air handling unit designed to achieve low level
dehumidification of the primary supply air. Solid desiccant dehumidification systems
are generally required for such applications.
Desiccant dehumidification systems remove moisture from the air by the moisture
adsorption process. This significantly lowers the wet bulb temperature of the air
stream thus resulting in very low humidity. However, the absorption process does not
produce much affect on the dry bulb temperature of the air stream. The dry bulb
temperature of the air will normally still require sensible cooling by a conventional
cooling coil located downstream in the primary air handling unit. Further conditioning
of the supply air then takes place at the individual laboratory supply air terminal.
Individual room control may be accomplished by locating a humidity sensor in the
laboratory room general exhaust which in turn is used as feedback for the control of
the dehumidification process in the primary HVAC unit.
30
Even with refrigeration systems that can provide temperatures lower than 32°F, condensation below freezing will result
in ice forming on the cooling coil and will block the airflow through the coil, resulting in a general ventilation system
failure.
82 Siemens Building Technologies, Inc.